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  • 1.
    Akinwekomi, Akeem
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Metallurgical and Materials Engineering, Federal University of Technology Akure, Akure 340252, Ondo State, Nigeria.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Microstructural, Mechanical, and Electrochemical Characterization of CrMoNbTiZr High-Entropy Alloy for Biomedical Application2023Ingår i: Materials, E-ISSN 1996-1944, Vol. 16, nr 15, artikel-id 5320Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-entropy alloys (HEA) with superior biocompatibility, high pitting resistance, minimal debris accumulation, and reduced release of metallic ions into surrounding tissues are potential replacements for traditional metallic bio-implants. A novel equiatomic HEA based on biocompatible metals, CrMoNbTiZr, was consolidated by spark plasma sintering (SPS). The relative sintered density of the alloy was about 97% of the theoretical density, indicating the suitability of the SPS technique to produce relatively dense material. The microstructure of the sintered HEA consisted of a BCC matrix and Laves phase, corresponding to the prediction of the thermodynamic CALPHAD simulation. The HEA exhibited a global Vickers microhardness of 531.5 ± 99.7 HV, while the individual BCC and Laves phases had hardness values of 364.6 ± 99.4 and 641.8 ± 63.0 HV, respectively. Its ultimate compressive and compressive yield strengths were 1235.7 ± 42.8 MPa and 1110.8 ± 78.6 MPa, respectively. The elasticity modulus of 34.9 ± 2.9 GPa of the HEA alloy was well within the range of cortical bone and significantly lower than the values reported for commonly used biomaterials made from Ti-based and Cr–Co-based alloys. In addition, the alloy exhibited good resistance to bio-corrosion in PBS and Hanks solutions. The CrMoNbTiZr HEA exhibited an average COF of 0.43 ± 0.06, characterized mainly by abrasive and adhesive wear mechanisms. The CrMoNbTiZr alloy’s mechanical, bio-corrosion, and wear resistance properties developed in this study showed a good propensity for application as a biomaterial.

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  • 2.
    Al-Maqdasi, Zainab
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Gong, Guan
    Rise Sicomp AB, Fibervägen 2, SE-941 26 Öjebyn, Sweden.
    Nyström, Birgitha
    Podcomp AB, Skylvägen 1, SE-943 33 Öjebyn, Sweden.
    Emami, Nazanin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Characterization of Wood and Graphene Nanoplatelets (GNPs) Reinforced Polymer Composites2020Ingår i: Materials, E-ISSN 1996-1944, Vol. 13, nr 9, artikel-id 2089Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper investigates the utilization of commercial masterbatches of graphene nanoplatelets to improve the properties of neat polymer and wood fiber composites manufactured by conventional processing methods. The effect of aspect ratio of the graphene platelets (represented by the different number of layers in the nanoplatelet) on the properties of high-density polyethylene (HDPE) is discussed. The composites were characterized for their mechanical properties (tensile, flexural, impact) and physical characteristics (morphology, crystallization, and thermal stability). The effect of the addition of nanoplatelets on the thermal conductivity and diffusivity of the reinforced polymer with different contents of reinforcement was also investigated. In general, the mechanical performance of the polymer was enhanced at the presence of either of the reinforcements (graphene or wood fiber). The improvement in mechanical properties of the nanocomposite was notable considering that no compatibilizer was used in the manufacturing. The use of a masterbatch can promote utilization of nano-modified polymer composites on an industrial scale without modification of the currently employed processing methods and facilities.

  • 3.
    Al-Maqdasi, Zainab
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ouarga, Ayoub
    High Throughput Multidisciplinary Research Laboratory, Mohammed VI Polytechnic University (UM6P), Lot 660—Hay Moulay Rachid, 43150 Benguerir, Morocco.
    Emami, Nazanin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Chouhan, Shailesh Singh
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Landström, Anton
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hajlane, Abdelghani
    Laboratory of Crystallography and Materials Sciences, National Graduate School of Engineering of Caen, 6 Boulevard Maréchal Juin, 14000 Caen, France.
    Conductive Regenerated Cellulose Fibers for Multi-Functional Composites: Mechanical and Structural Investigation2021Ingår i: Materials, E-ISSN 1996-1944, Vol. 14, nr 7, artikel-id 1746Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Regenerated cellulose fibers coated with copper via electroless plating process are investigated for their mechanical properties, molecular structure changes, and suitability for use in sensing applications. Mechanical properties are evaluated in terms of tensile stiffness and strength of fiber tows before, during and after the plating process. The effect of the treatment on the molecular structure of fibers is investigated by measuring their thermal stability with differential scanning calorimetry and obtaining Raman spectra of fibers at different stages of the treatment. Results show that the last stage in the electroless process (the plating step) is the most detrimental, causing changes in fibers’ properties. Fibers seem to lose their structural integrity and develop surface defects that result in a substantial loss in their mechanical strength. However, repeating the process more than once or elongating the residence time in the plating bath does not show a further negative effect on the strength but contributes to the increase in the copper coating thickness, and, subsequently, the final stiffness of the tows. Monitoring the changes in resistance values with applied strain on a model composite made of these conductive tows show an excellent correlation between the increase in strain and increase in electrical resistance. These results indicate that these fibers show potential when combined with conventional composites of glass or carbon fibers as structure monitoring devices without largely affecting their mechanical performance.

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  • 4.
    Asimi, Ali
    et al.
    Department of Mining and Metallurgical Engineering Yazd University, Yazd 89195-741, Iran. Bafgh Zinc Smelting Company (BZSC), Yazd 89195-741, Iran .
    Gharibi, Khodakaram
    Department of Mining and Metallurgical Engineering Yazd University, Yazd 89195-741, Iran.
    Abkhoshk, Emad
    Bafgh Zinc Smelting Company (BZSC), Yazd 89195-741, Iran.
    Moosakazemi, Farhad
    Chemical Engineering Department, Laval University, Québec, QC G1V 0A6, Canada. Beneficiation and Hydrometallurgy Research Group, Mineral Processing Research Center, Academic Center for Education, Culture and Research (ACECR) on TMU, Tehran 15119-43943, Iran.
    Chelgani, Saeed Chehreh
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Effects of Operational Parameters on the Low Contaminant Jarosite Precipitation Process-an Industrial Scale Study2020Ingår i: Materials, E-ISSN 1996-1944, Vol. 13, nr 20, artikel-id 4662Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Jarosite precipitation process (JPP) is the most frequently used procedure for iron removal in the hydrometallurgical zinc extraction process. However, there is a gap in the knowledge of the relationship between operational parameters and the low contaminant JPP on the industrial scale. This study will address these issues by investigating the behavior of zinc calcine (ZC) as a neutralizing agent, exploring the source of zinc and iron through leaching experiments, and simulating the Jarosite process of the Bafgh Zinc Smelting Company (BZSC). The results showed that the zinc dissolution efficiency was 90.3% at 90 °C, and 73% of the iron present in the calcine can be solubilized. The main outcome was the iron removal of about 85% by alkaline ions present in ZC without the addition of any precipitating agent. The second target was to evaluate the effect of operational parameters on jarosite precipitation. Results revealed that increasing the temperature to 90 °C and the stirring rate to 500 RPM as well as adjusting the ZC’s pH during the jarosite precipitation remarkably improved iron removal. Considering all these factors in the plant could improve Fe precipitation to around 80% on average.

  • 5.
    Babu, Bijish
    et al.
    Swerim AB, Heating and Metalworking, Luleå, Sweden.
    Lundbäck, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Simulation of Ti-6Al-4V Additive Manufacturing Using Coupled Physically Based Flow Stress and Metallurgical Model2019Ingår i: Materials, E-ISSN 1996-1944, Vol. 12, nr 23, artikel-id 3844Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Simulating the additive manufacturing process of Ti-6Al-4V is very complex due to the microstructural changes and allotropic transformation occurring during its thermomechanical processing. The α -phase with a hexagonal close pack structure is present in three different forms—Widmanstatten, grain boundary and Martensite. A metallurgical model that computes the formation and dissolution of each of these phases was used here. Furthermore, a physically based flow-stress model coupled with the metallurgical model was applied in the simulation of an additive manufacturing case using the directed energy-deposition method. The result from the metallurgical model explicitly affects the mechanical properties in the flow-stress model. Validation of the thermal and mechanical model was performed by comparing the simulation results with measurements available in the literature, which showed good agreement

  • 6.
    Bernaczyk, Arkadiusz
    et al.
    Jowat SE, Detmold, 32758, Germany.
    Wagenführ, André
    Institute of Natural Materials Technology, Technische Universität Dresden, Dresden, 01062, Germany.
    Terfloth, Christian
    Jowat SE, Detmold, 32758, Germany.
    Lincke, Jörg
    Jowat SE, Detmold, 32758, Germany.
    Krystofiak, Tomasz
    Department of Wood Science and Thermal Techniques, Poznań University of Life Sciences, Poznan, 60-627, Poland.
    Niemz, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik. Institute for Building Materials, ETH Zurich, 971 87 Luleå, Sweden.
    Investigations into the Influence of Temperature on the Tensile Shear Strength of Various Adhesives2023Ingår i: Materials, E-ISSN 1996-1944, Vol. 16, nr 18, artikel-id 6173Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The temperature resistance of glued timber, which is crucial for glued wood construction, represents a significant assessment criterion. To gain insights into this aspect, this study utilized methods such as a shear strength test in accordance with EN 302-1:2013-06 under thermal loading (from 20 °C to 200 °C), and Differential Scanning Calorimetry (DSC) to determine the glass transition temperature (Tg). An increase in thermal load resulted in a decrease in shear strength and an increase in wood breakage. A hierarchy of adhesive groups was established based on strength performance and wood failure percentage (WFP) at 200 °C. Thermoset adhesives (MF: Melamine Formaldehyde, PRF: Phenol Resorcinol Formaldehyde) led the ranking, followed by elastomer adhesives (1C-PUR: One-Component Polyurethane, EPI: Emulsion Polymer Isocyanate), with thermoplastic adhesive (PVAc: Polyvinyl Acetate) last. Thermoset adhesives further cured under heat. PUR adhesives exhibited higher strength performance at 150 °C and lower temperatures.

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  • 7.
    Bernaczyk, Arkadiusz
    et al.
    Jowat SE, 32758 Detmold, Germany.
    Wagenführ, André
    Institute of Natural Materials Technology, Technische Universität Dresden, 01062 Dresden, Germany.
    Zboray, Robert
    Center for X-ray Analytics, Empa—Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland.
    Flisch, Alexander
    Institute of Materials Science, Technische Universität Dresden, 01062 Dresden, Germany.
    Lüthi, Thomas
    Center for X-ray Analytics, Empa—Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland.
    Vetter, Birgit
    Institute of Materials Science, Technische Universität Dresden, 01062 Dresden, Germany.
    Rentsch, Mario
    Institute of Materials Science, Technische Universität Dresden, 01062 Dresden, Germany.
    Terfloth, Christian
    Jowat SE, 32758 Detmold, Germany.
    Lincke, Jörg
    Jowat SE, 32758 Detmold, Germany.
    Krystofiak, Tomasz
    Department of Wood Science and Thermal Techniques, Poznań University of Life Sciences, 60-627 Poznan, Poland.
    Niemz, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Investigations on the Characterization of Various Adhesive Joints by Means of Nanoindentation and Computer Tomography2022Ingår i: Materials, E-ISSN 1996-1944, Vol. 15, nr 23, s. 8604-8604Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mechanical properties of cured wood adhesive films were tested in a dry state by means of nanoindentation. These studies have found that the application of adhesives have an effect on the accuracy of the hardness and elastic modulus determination. The highest values of hardness among the tested adhesives at 20 °C have condensation resins: MF (0.64 GPa) and RPF (0.52 GPa). Then the decreasing EPI (0.43 GPa), PUR (0.23 GPa) and PVAc (0.14 GPa) adhesives. The values of the elastic modulus look a little bit different. The highest values among the tested adhesives at 20 °C have EPI (11.97 GPa), followed by MF (10.54 GPa), RPF (7.98 GPa), PVAc (4.71 GPa) and PUR (3.37 GPa). X-ray micro-computed tomography was used to evaluate the adhesive joint by the determination of the voids. It has been proven that this value depends on the type of adhesive, glue quantity and reactivity. The highest values of the void ratio achieve the PUR (17.26%) adhesives, then PVAc (13.97%), RRF (6.88%), MF (1.78%) and EPI (0.03%). The ratio of the gaps increases with the higher joint thickness. A too high proportion of voids may weaken the adhesive joint.

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  • 8.
    Elphick, Kelvin
    et al.
    Department of Electronic Engineering, University of York, Heslington, York YO10 5DD, UK.
    Yamaguchi, Akinobu
    Laboratory of Advance Science and Technology for Industry, University of Hyogo, Hyogo 678-1205, Japan.
    Otsuki, Akira
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik. Ecole Nationale Supérieure de Géologie, GeoRessources UMR 7359 CNRS, University of Lorraine, 2 Rue du Doyen Marcel Roubault, BP 10162, 54505 Vandoeuvre-lès-Nancy, France; Neutron Science Laboratory, The Institute for Solid State Physics, The University of Tokyo, Chiba 277-8581, Japan.
    Lonio Hayagan, Neil
    Ecole Nationale Supérieure de Géologie, GeoRessources UMR 7359 CNRS, University of Lorraine, 2 Rue du Doyen Marcel Roubault, BP 10162, 54505 Vandoeuvre-lès-Nancy, France.
    Hirohata, Atsufumi
    Department of Electronic Engineering, University of York, Heslington, York YO10 5DD, UK.
    Non-Destructive Imaging on Synthesised Nanoparticles2021Ingår i: Materials, E-ISSN 1996-1944, Vol. 14, nr 3, artikel-id 613Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Our recently developed non-destructive imaging technique was applied for the characterisation of nanoparticles synthesised by X-ray radiolysis and the sol-gel method. The interfacial conditions between the nanoparticles and the substrates were observed by subtracting images taken by scanning electron microscopy at controlled electron acceleration voltages to allow backscattered electrons to be generated predominantly below and above the interfaces. The interfacial adhesion was found to be dependent on the solution pH used for the particle synthesis or particle suspension preparation, proving the change in the particle formation/deposition processes with pH as anticipated and agreed with the prediction based on the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. We found that our imaging technique was useful for the characterisation of interfaces hidden by nanoparticles to reveal the formation/deposition mechanism and can be extended to the other types of interfaces.

  • 9.
    Eppanapelli, Lavan Kumar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Forsberg, Fredrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Casselgren, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lycksam, Henrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    3D analysis of deformation and porosity of dry natural snow during compaction2019Ingår i: Materials, E-ISSN 1996-1944, Vol. 12, nr 6, artikel-id 850Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present study focuses on three-dimensional (3D) microstructure analysis of dry natural snow during compaction. An X-ray computed microtomography (micro-CT) system was used to record a total of 1601 projections of a snow volume. Experiments were performed in-situ at four load states as 0 MPa, 0.3 MPa, 0.6 MPa and 0.8 MPa, to investigate the effect of compaction on structural features of snow grains. The micro-CT system produces high resolution images (4.3 μm voxel) in 6 hours of scanning time. The micro-CT images of the investigated snow volume illustrate that grain shapes are mostly dominated by needles, capped columns and dendrites. It was found that a significant number of grains appeared to have a deep hollow core irrespective of the grain shape. Digital volume correlation (DVC) was applied to investigate displacement and strain fields in the snow volume due to the compaction. Results from the DVC analysis show that grains close to the moving punch experience most of the displacement. The reconstructed snow volume is segmented into several cylinders via horizontal cross-sectioning, to evaluate the vertical heterogeneity of porosity distribution of the snow volume. It was observed that the porosity (for the whole volume) in principle decreases as the level of compaction increases. A distinct vertical heterogeneity is observed in porosity distribution in response to compaction. The observations from this initial study may be useful to understand the snow microstructure under applied stress.

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  • 10.
    Fatahi, R.
    et al.
    School of Mining Engineering, College of Engineering, University of Tehran, Tehran, 16846-13114, Iran.
    Khosravi, R.
    Department of mining, Faculty of Engineering, Lorestan University, Khorramabad, 68151-44316, Iran.
    Siavoshi, H.
    Department of Mining and Geological Engineering, University of Arizona, Tucson, 85721, AZ, United States.
    Yazdani, S.
    Department of Electrical and Computer Engineering, North Tehran Branch, Islamic Azad University, Tehran, 1651153311, Iran.
    Hadavandi, E.
    Department of Industrial Engineering, Birjand University of Technology, Birjand, 66981, Iran.
    Chelgani, Saeed Chehreh
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Ventilation Prediction for an Industrial Cement Raw Ball Mill by BNN—A “Conscious Lab” Approach2021Ingår i: Materials, E-ISSN 1996-1944, Vol. 14, nr 12, artikel-id 3220Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In cement mills, ventilation is a critical key for maintaining temperature and material transportation. However, relationships between operational variables and ventilation factors for an industrial cement ball mill were not addressed until today. This investigation is going to fill this gap based on a newly developed concept named “conscious laboratory (CL)”. For constructing the CL, a boosted neural network (BNN), as a recently developed comprehensive artificial intelligence model, was applied through over 35 different variables, with more than 2000 records monitored for an industrial cement ball mill. BNN could assess multivariable nonlinear relationships among this vast dataset, and indicated mill outlet pressure and the ampere of the separator fan had the highest rank for the ventilation prediction. BNN could accurately model ventilation factors based on the operational variables with a root mean square error (RMSE) of 0.6. BNN showed a lower error than other traditional machine learning models (RMSE: random forest 0.71, support vector regression: 0.76). Since improving the milling efficiency has an essential role in machine development and energy utilization, these results can open a new window to the optimal designing of comminution units for the material technologies.

  • 11.
    Feng, Yan
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi. School of Resource and Safety Engineering, Central South University, Changsha 410083, China.
    Kero, Jakob
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Yang, Qixing
    Energy School, Xi'an University of Science and Technology, Xi'an 710054, China.
    Chen, Qisong
    School of Resource and Safety Engineering, Central South University, Changsha 410083, China.
    Engström, Fredrik
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Samuelsson, Caisa
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Qi, Chongchong
    School of Resource and Safety Engineering, Central South University, Changsha 410083, China.
    Mechanical Activation of Granulated Copper Slag and Its Influence on Hydration Heat and Compressive Strength of Blended Cement2019Ingår i: Materials, E-ISSN 1996-1944, Vol. 12, nr 5, artikel-id 772Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mechanical activation of granulated copper slag (GCS) is carried out in the present study for the purposes of enhancing pozzolanic activity for the GCS. A vibration mill mills the GCS for 1, 2, and 3 h to produce samples with specific surface area of 0.67, 1.03 and 1.37 m²/g, respectively. The samples are used to replace 30% cement (PC) to get 3 PC-GCS binders. The hydration heat and compressive strength are measured for the binders and derivative thermogravimetric /thermogravimetric analysis (DTG/TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) are used to characterize the paste samples. It is shown that cumulative heat and compressive strength at different ages of hydration and curing, respectively, are higher for the binders blending the GCS milled for a longer time. The compressive strength after 90 d of curing for the binder with the longest milling time reaches 35.7 MPa, which is higher than the strength of other binders and close to the strength value of 39.3 MPa obtained by the PC pastes. The percentage of fixed lime by the binder pastes at 28 days is correlated with the degree of pozzolanic reaction and strength development. The percentage is higher for the binder blending the GCS with longer milling time and higher specific surface area. The pastes with binders blending the GCS of specific surface area of 0.67 and 1.37 m²/g fix lime of 15.20 and 21.15%, respectively. These results together with results from X-ray diffraction (XRD), FTIR, and SEM investigations demonstrate that the mechanical activation via vibratory milling is an effective method to enhance the pozzolanic activity and the extent for cement substitution by the GCS as a suitable supplementary cementitious material (SCM).

  • 12.
    Forouzan, Farnoosh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Surki Aliabad, Roohallah
    Materials and Mechanical Engineering, University of Oulu, Oulu, 90014, Finland.
    Hedayati, Ali
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Hosseini, Nazanin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Maawad, Emad
    Helmholtz-Zentrum Hereon, Institute of Materials Physics, Max-Planck-Straße 1, Geesthacht, 21502, Germany.
    Blasco, Nuria
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Vuorinen, Esa
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Kinetics of Carbon Enrichment in Austenite during Partitioning Stage Studied via In-Situ Synchrotron XRD2023Ingår i: Materials, E-ISSN 1996-1944, Vol. 16, nr 4, artikel-id 1557Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present study reveals the microstructural evolution and corresponding mechanisms occurring during different stages of quenching and partitioning (Q&P) conducted on 0.6C-1.5Si steel using in-situ High Energy X-Ray Diffraction (HEXRD) and high-resolution dilatometry methods. The results support that the symmetry of ferrite is not cubic when first formed since it is fully supersaturated with carbon at the early stages of partitioning. Moreover, by increasing partitioning temperature, the dominant carbon source for austenite enrichment changes from ongoing bainitic ferrite transformation during the partitioning stage to initial martensite formed in the quenching stage. At low partitioning temperatures, a bimodal distribution of low- and high-carbon austenite, 0.6 and 1.9 wt.% carbon, is detected. At higher temperatures, a better distribution of carbon occurs, approaching full homogenization. An initial martensite content of around 11.5 wt.% after partitioning at 280 °C via bainitic ferrite transformation results in higher carbon enrichment of austenite and increased retained austenite amount by approximately 4% in comparison with partitioning at 500 °C. In comparison with austempering heat treatment with no prior martensite, the presence of initial martensite in the Q&P microstructure accelerates the subsequent low-temperature bainitic transformation.

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  • 13.
    Fukushima, Kyosuke
    et al.
    Graduate School of Engineering Science, Akita University, 1-1 Tegata Gakuen Machi, Akita 010-8502, Japan.
    Kabir, Mahmudul
    Graduate School of Engineering Science, Akita University, 1-1 Tegata Gakuen Machi, Akita 010-8502, Japan.
    Kanda, Kensuke
    Graduate School of Engineering Science, Akita University, 1-1 Tegata Gakuen Machi, Akita 010-8502, Japan.
    Obara, Naoko
    Graduate School of Engineering Science, Akita University, 1-1 Tegata Gakuen Machi, Akita 010-8502, Japan.
    Fukuyama, Mayuko
    Graduate School of Engineering Science, Cooperative Major in Life Cycle Design Engineering, Tegata Campus, Akita University, 1-1 Tegata Gakuen Machi, Akita 010-8502, Japan.
    Otsuki, Akira
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik. Ecole Nationale Supérieure de Géologie, GeoRessources, UMR 7359 CNRS, University of Lorraine, 2 Rue du Doyen, Marcel Roubault, BP 10162, 54505 Vandoeuvre-lès-Nancy, France; Facultad de Ingeniería y Ciencias, Universidad Adolfo Ibáñez, Diagonal Las Torres 2640, Peñalolén, Santiago 7941169, Chile.
    Equivalent Circuit Models: An Effective Tool to Simulate Electric/Dielectric Properties of Ores—An Example Using Granite2022Ingår i: Materials, E-ISSN 1996-1944, Vol. 15, nr 13, artikel-id 4549Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The equivalent circuit model is widely used in high-voltage (HV) engineering to simulate the behavior of HV applications for insulation/dielectric materials. In this study, equivalent circuit models were prepared in order to represent the electric and dielectric properties of minerals and voids in a granite rock sample. The HV electric-pulse application shows a good possibility of achieving a high energy efficiency with the size reduction and selective liberation of minerals from rocks. The electric and dielectric properties were first measured, and the mineral compositions were also determined by using a micro-X-ray fluorescence spectrometer. Ten patterns of equivalent circuit models were then prepared after considering the mineral distribution in granite. Hard rocks, as well as minerals, are dielectric materials that can be represented as resistors and capacitors in parallel connections. The values of the electric circuit parameters were determined from the known electric and dielectric parameters of the minerals in granite. The average calculated data of the electric properties of granite agreed with the measured data. The conductivity values were 53.5 pS/m (measurement) and 36.2 pS/m (simulation) in this work. Although there were some differences between the measured and calculated data of dielectric loss (tanδ), their trend as a function of frequency agreed. Even though our study specifically dealt with granite, the developed equivalent circuit model can be applied to any other rock.

  • 14.
    Fukushima, Kyosuke
    et al.
    Graduate School of Engineering Science, Department of Mathematical Science and Electrical-Electronic-Computer Engineering, Tegata Campus, Akita University, 1-1 Tegata Gakuen Machi, Akita 010-8502, Japan.
    Kabir, Mahmudul
    Graduate School of Engineering Science, Department of Mathematical Science and Electrical-Electronic-Computer Engineering, Tegata Campus, Akita University, 1-1 Tegata Gakuen Machi, Akita 010-8502, Japan.
    Kanda, Kensuke
    Graduate School of Engineering Science, Department of Mathematical Science and Electrical-Electronic-Computer Engineering, Tegata Campus, Akita University, 1-1 Tegata Gakuen Machi, Akita 010-8502, Japan.
    Obara, Naoko
    Graduate School of Engineering Science, Department of Mathematical Science and Electrical-Electronic-Computer Engineering, Tegata Campus, Akita University, 1-1 Tegata Gakuen Machi, Akita 010-8502, Japan.
    Fukuyama, Mayuko
    Graduate School of Engineering Science, Cooperative Major in Life Cycle Design Engineering, Tegata Campus, Akita University, 1-1 Tegata Gakuen Machi, Akita 010-8502, Japan.
    Otsuki, Akira
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik. Ecole Nationale Supérieure de Géologie, GeoRessources, UMR 7359 CNRS, University of Lorraine, 2 Rue du Doyen, Marcel Roubault, BP 10162, 54505 Vandoeuvre-lès-Nancy, France.
    Simulation of Electrical and Thermal Properties of Granite under the Application of Electrical Pulses Using Equivalent Circuit Models2022Ingår i: Materials, E-ISSN 1996-1944, Vol. 15, nr 3, artikel-id 1039Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Since energy efficiency in comminution of ores is as small as 1% using a mechanical crushing process, it is highly demanded to improve its efficiency. Using electrical impulses to selectively liberate valuable minerals from ores can be a solution of this problem. In this work, we developed a simulation method using equivalent circuits of granite to better understand the crushing process with high-voltage (HV) electrical pulses. From our simulation works, we calculated the electric field distributions in granite when an electrical pulse was applied. We also calculated other associated electrical phenomena such as produced heat and temperature changes from the simulation results. A decrease in the electric field was observed in the plagioclase with high electrical conductivity and void space. This suggests that the void volume in each mineral is important in calculating the electrical properties. Our equivalent circuit models considering both the electrical conductivity and dielectric constant of a granite can more accurately represent the electrical properties of granite under HV electric pulse application. These results will help us better understand the liberation of minerals from granite by electric pulse application.

  • 15.
    Gamil, Yaser
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Cwirzen, Andrzej
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Nilimaa, Jonny
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Emborg, Mats
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    The Impact of Different Parameters on the Formwork Pressure Exerted by Self-Compacting Concrete2023Ingår i: Materials, E-ISSN 1996-1944, Vol. 16, nr 2, artikel-id 759Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Despite the advantageous benefits offered by self-compacting concrete, its uses are still limited due to the high pressure exerted on the formwork. Different parameters, such as those related to concrete mix design, the properties of newly poured concrete, and placement method, have an impact on form pressure. The question remains unanswered on the degree of the impact for each parameter. Therefore, this study aims to study the level of impact of these parameters, including slump flow, T500 time, fresh concrete density, air content, static yield stress, concrete setting time, and concrete temperature. To mimic the casting scenario, 2 m columns were cast at various casting rates and a laboratory setup was developed. A pressure system that can wirelessly and continuously record pressure was used to monitor the pressure. Each parameter’s impact on the level of pressure was examined separately. Casting rate and slump flow were shown to have a greater influence on pressure. The results also demonstrated that, while higher thixotropy causes form pressure to rapidly decrease, a high casting rate and high slump flow lead to high pressure. This study suggests that more thorough analysis should be conducted of additional factors that may have an impact, such as the placement method, which was not included in this publication.

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  • 16.
    Gamil, Yaser
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Nilimaa, Jonny
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Emborg, Mats
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Cwirzen, Andrzej
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Lateral Formwork Pressure for Self-Compacting Concrete—A Review of Prediction Models and Monitoring Technologies2021Ingår i: Materials, E-ISSN 1996-1944, Vol. 14, nr 16, artikel-id 4767Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    The maximum amount of lateral formwork pressure exerted by self-compacting concrete is essential to design a technically correct, cost-effective, safe, and robust formwork. A common practice of designing formwork is primarily based on using the hydrostatic pressure. However, several studies have proven that the maximum pressure is lower, thus potentially enabling a reduction in the cost of formwork by, for example, optimizing the casting rate. This article reviews the current knowledge regarding formwork pressure, parameters affecting the maximum pressure, prediction models, monitoring technologies and test setups. The currently used pressure predicting models require further improvement to consider several pressures influencing parameters, including parameters related to fresh and mature material properties, mix design and casting methods. This study found that the maximum pressure is significantly affected by the concretes’ structural build-up at rest, which depends on concrete rheology, temperature, hydration rate and setting time. The review indicates a need for more in-depth studies.

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  • 17.
    Girardin, Bertrand
    et al.
    Unité Matériaux et Transformations (UMET)-CNRS UMR 8207-Group Reaction and Resistance to Fire (R2Fire), École Nationale Supérieure de Chimie de Lille, University of Lille, Avenue Mendeleiev, CS 90108, 59652 Villeneuve d'Ascq Cedex, France.
    Fontaine, Geêlle
    Unité Matériaux et Transformations (UMET)-CNRS UMR 8207-Group Reaction and Resistance to Fire (R2Fire), École Nationale Supérieure de Chimie de Lille, University of Lille, Avenue Mendeleiev, CS 90108, 59652 Villeneuve d'Ascq Cedex, France.
    Duquesne, Sophie
    Unité Matériaux et Transformations (UMET)-CNRS UMR 8207-Group Reaction and Resistance to Fire (R2Fire), École Nationale Supérieure de Chimie de Lille, University of Lille, Avenue Mendeleiev, CS 90108, 59652 Villeneuve d'Ascq Cedex, France.
    Försth, Michael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. SP Fire Research, SP Technical Research Institute of Sweden, P.O. Box 857, SE-501 15 Borås, Sweden.
    Bourbignot, Serge
    Unité Matériaux et Transformations (UMET)-CNRS UMR 8207-Group Reaction and Resistance to Fire (R2Fire), École Nationale Supérieure de Chimie de Lille, University of Lille, Avenue Mendeleiev, CS 90108, 59652 Villeneuve d'Ascq Cedex, France.
    Characterization of Thermo-Physical Properties of EVA/ATH: Application to Gasification Experiments and Pyrolysis Modeling2015Ingår i: Materials, E-ISSN 1996-1944, Vol. 8, nr 11, s. 7837-7863Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The pyrolysis of solid polymeric materials is a complex process that involves both chemical and physical phenomena such as phase transitions, chemical reactions, heat transfer, and mass transport of gaseous components. For modeling purposes, it is important to characterize and to quantify the properties driving those phenomena, especially in the case of flame-retarded materials. In this study, protocols have been developed to characterize the thermal conductivity and the heat capacity of an ethylene-vinyl acetate copolymer (EVA) flame retarded with aluminum tri-hydroxide (ATH). These properties were measured for the various species identified across the decomposition of the material. Namely, the thermal conductivity was found to decrease as a function of temperature before decomposition whereas the ceramic residue obtained after the decomposition at the steady state exhibits a thermal conductivity as low as 0.2 W/m/K. The heat capacity of the material was also investigated using both isothermal modulated Differential Scanning Calorimetry (DSC) and the standard method (ASTM E1269). It was shown that the final residue exhibits a similar behavior to alumina, which is consistent with the decomposition pathway of EVA/ATH. Besides, the two experimental approaches give similar results over the whole range of temperatures. Moreover, the optical properties before decomposition and the heat capacity of the decomposition gases were also analyzed. Those properties were then used as input data for a pyrolysis model in order to predict gasification experiments. Mass losses of gasification experiments were well predicted, thus validating the characterization of the thermo-physical properties of the material

  • 18.
    Greifzu, Moritz
    et al.
    Additive Manufacturing and Printing, Fraunhofer-Institut für Werkstoff- und Strahltechnik, Dresden, Germany.
    Tkachov, Roman
    Additive Manufacturing and Printing, Fraunhofer-Institut für Werkstoff- und Strahltechnik, Dresden, Germany; Institute of Materials Science, Technische Universität Dresden, Dresden, Germany.
    Stepien, Lukas
    Additive Manufacturing and Printing, Fraunhofer-Institut für Werkstoff- und Strahltechnik, Dresden, Germany.
    López, Elena
    Additive Manufacturing and Printing, Fraunhofer-Institut für Werkstoff- und Strahltechnik, Dresden, Germany.
    Brückner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Leyens, Christoph
    Additive Manufacturing and Printing, Fraunhofer-Institut für Werkstoff- und Strahltechnik, Dresden, Germany; Institute of Materials Science, Technische Universität Dresden, Dresden, Germany.
    Laser Treatment as Sintering Process for Dispenser Printed Bismuth Telluride Based Paste2019Ingår i: Materials, E-ISSN 1996-1944, Vol. 12, nr 20, artikel-id 3453Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Laser sintering as a thermal post treatment method for dispenser printed p- and n-type bismuth telluride based thermoelectric paste materials was investigated. A high-power fiber laser (600 W, 1064 nm) was used in combination with a scanning system to achieve high processing speed. A Design of Experiment (DoE) approach was used to identify the most relevant processing parameters. Printed layers were laser treated with different process parameters and the achieved sheet resistance, electrical conductivity, and Seebeck coefficient are compared to tube furnace processed reference specimen. For p-type material, electrical conductivity of 22 S/cm was achieved, compared to 15 S/cm in tube furnace process. For n-type material, conductivity achieved by laser process was much lower (7 S/cm) compared to 88 S/cm in furnace process. Also, Seebeck coefficient decreases during laser processing (40–70 µV/K and −110 µV/K) compared to the oven process (251 µV/K and −142 µV/K) for p- and n-type material. DoE did not yet deliver a set of optimum processing parameters, but supports doubts about the applicability of area specific laser energy density as a single parameter to optimize laser sintering process.

  • 19.
    Gruber, Samira
    et al.
    Fraunhofer Institute for Material and Beam Technology, IWS, Winterbergstraße 28, 01277 Dresden, Germany.
    Stepien, Lukas
    Fraunhofer Institute for Material and Beam Technology, IWS, Winterbergstraße 28, 01277 Dresden, Germany.
    López, Elena
    Fraunhofer Institute for Material and Beam Technology, IWS, Winterbergstraße 28, 01277 Dresden, Germany.
    Brueckner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology, IWS, Winterbergstraße 28, 01277 Dresden, Germany.
    Leyens, Christoph
    Fraunhofer Institute for Material and Beam Technology, IWS, Winterbergstraße 28, 01277 Dresden, Germany; Institute of Materials Science, Technische Universität Dresden, Helmholtzstr. 7, 01069 Dresden, Germany.
    Physical and Geometrical Properties of Additively Manufactured Pure Copper Samples Using a Green Laser Source2021Ingår i: Materials, E-ISSN 1996-1944, Vol. 14, nr 13, artikel-id 3642Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    So far, copper has been difficult to process via laser powder bed fusion due to low absorption with the frequently used laser systems in the infrared wavelength range. However, green laser systems have emerged recently and offer new opportunities in processing highly reflective materials like pure copper through higher absorptivity. In this study, pure copper powders from two suppliers were tested using the same machine parameter sets to investigate the influence of the powder properties on the material properties such as density, microstructure, and electrical conductivity. Samples of different wall thicknesses were investigated with the eddy-current method to analyze the influence of the sample thickness and surface quality on the measured electrical conductivity. The mechanical properties in three building directions were investigated and the geometrical accuracy of selected geometrical features was analyzed using a benchmark geometry. It could be shown that the generated parts have a relative density of above 99.95% and an electrical conductivity as high as 100% International Annealed Copper Standard (IACS) for both powders could be achieved. Furthermore, the negative influence of a rough surface on the measured eddy-current method was confirmed.

  • 20.
    Gyhlesten Back, Jessica
    et al.
    Materials Science Division, Dalarna University, 791 88 Falun, Sweden; Research and Development, SSAB Europe, 781 84 Borlänge, Sweden.
    Engberg, Göran
    Materials Science Division, Dalarna University, 791 88 Falun, Sweden.
    Investigation of Parent Austenite Grains from Martensite Structure using EBSD in a Wear Resistant Steel2017Ingår i: Materials, E-ISSN 1996-1944, Vol. 10, artikel-id 453Artikel i tidskrift (Refereegranskat)
  • 21.
    Hammarberg, Samuel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Hållfasthetslära.
    Kajberg, Jörgen
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Hållfasthetslära.
    Larsson, Simon
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Hållfasthetslära.
    Moshfegh, Ramin
    Lamera AB, A Odhners Gata 17, 421 30 Västra Frölunda, Sweden.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Hållfasthetslära.
    Novel Methodology for Experimental Characterization of Micro-Sandwich Materials2021Ingår i: Materials, E-ISSN 1996-1944, Vol. 14, nr 16, artikel-id 4396Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lightweight components are in demand from the automotive industry, due to legislation regulating greenhouse gas emissions, e.g., CO2. Traditionally, lightweighting has been done by replacing mild steels with ultra-high strength steel. The development of micro-sandwich materials has received increasing attention due to their formability and potential for replacing steel sheets in automotive bodies. A fundamental requirement for micro-sandwich materials to gain significant market share within the automotive industry is the possibility to simulate manufacturing of components, e.g., cold forming. Thus, reliable methods for characterizing the mechanical properties of the micro-sandwich materials, and in particular their cores, are necessary. In the present work, a novel method for obtaining the out-of-plane properties of micro-sandwich cores is presented. In particular, the out-of-plane properties, i.e., transverse tension/compression and out-of-plane shear are characterized. Test tools are designed and developed for subjecting micro-sandwich specimens to the desired loading conditions and digital image correlation is used to qualitatively analyze displacement fields and fracture of the core. A variation of the response from the material tests is observed, analyzed using statistical methods, i.e., the Weibull distribution. It is found that the suggested method produces reliable and repeatable results, providing a better understanding of micro-sandwich materials. The results produced in the present work may be used as input data for constitutive models, but also for validation of numerical models.

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  • 22.
    Hassan, Mohammad
    et al.
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre, Giza, Egypt; Egypt Nanotechnology Centre, Cairo University, 6th October City, Egypt.
    Berglund, Linn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Abou-Zeid, Ragab
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre, Giza , Egypt.
    Hassan, Enas
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre, Giza , Egypt.
    Abou-Elseoud, Wafaa
    Cellulose and Paper Department & Centre of Excellence for Advanced Sciences, National Research Centre, Giza , Egypt.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Fibre and Particle Engineering, University of Oulu, Oulu, Finland.
    Nanocomposite Film Based on Cellulose Acetate and Lignin-Rich Rice Straw Nanofibers2019Ingår i: Materials, E-ISSN 1996-1944, Vol. 12, nr 4, artikel-id 595Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nanofibers isolated from unbleached neutral sulfite rice straw pulp were used to prepare transparent films without the need to modify the isolated rice straw nanofibers (RSNF). RSNF with loading from 1.25 to 10 wt.% were mixed with cellulose acetate (CA) solution in acetone and films were formed by casting. The films were characterized regarding their transparency and light transmittance, microstructure, mechanical properties, crystallinity, water contact angle, porosity, water vapor permeability, and thermal properties. The results showed good dispersion of RSNF in CA matrix and films with good transparency and homogeneity could be prepared at RSNF loadings of less than 5%. As shown from contact angle and atomic force microscopy (AFM) measurements, the RSNF resulted in increased hydrophilic nature and roughness of the films. No significant improvement in tensile strength and Young’s modulus was recorded as a result of adding RSNF to CA. Addition of the RSNF did not significantly affect the porosity, crystallinity and melting temperature of CA, but slightly increased its glass transition temperature

  • 23.
    He, Hanbing
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Forouzan, Farnoosh
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Volpp, Joerg
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Robertson, Stephanie M.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Vuorinen, Esa
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Microstructure and Mechanical Properties of Laser-Welded DP Steels Used in the Automotive Industry2021Ingår i: Materials, E-ISSN 1996-1944, Vol. 14, nr 2, artikel-id 456Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of this work was to investigate the microstructure and the mechanical properties of laser-welded joints combined of Dual Phase DP800 and DP1000 high strength thin steel sheets. Microstructural and hardness measurements as well as tensile and fatigue tests have been carried out. The welded joints (WJ) comprised of similar/dissimilar steels with similar/dissimilar thickness were consisted of different zones and exhibited similar microstructural characteristics. The trend of microhardness for all WJs was consistent, characterized by the highest value at hardening zone (HZ) and lowest at softening zone (SZ). The degree of softening was 20 and 8% for the DP1000 and DP800 WJ, respectively, and the size of SZ was wider in the WJ combinations of DP1000 than DP800. The tensile test fractures were located at the base material (BM) for all DP800 weldments, while the fractures occurred at the fusion zone (FZ) for the weldments with DP1000 and those with dissimilar sheet thicknesses. The DP800-DP1000 weldment presented similar yield strength (YS, 747 MPa) and ultimate tensile strength (UTS, 858 MPa) values but lower elongation (EI, 5.1%) in comparison with the DP800-DP800 weldment (YS 701 MPa, UTS 868 MPa, EI 7.9%), which showed similar strength properties as the BM of DP800. However, the EI of DP1000-DP1000 weldment was 1.9%, much lower in comparison with the BM of DP1000. The DP800-DP1000 weldment with dissimilar thicknesses showed the highest YS (955 MPa) and UTS (1075 MPa) values compared with the other weldments, but with the lowest EI (1.2%). The fatigue fractures occurred at the WJ for all types of weldments. The DP800-DP800 weldment had the highest fatigue limit (348 MPa) and DP800-DP1000 with dissimilar thicknesses had the lowest fatigue limit (<200 MPa). The fatigue crack initiated from the weld surface.

  • 24.
    Humad, Abeer
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand. Civil Engineering Department, University of Babylon, Babylon, Iraq.
    Habermehl-Cwirzen, Karin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Cwirzen, Andrzej
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Effects of fineness and chemical composition of blast furnace slag on properties of alkali-activated binder2019Ingår i: Materials, E-ISSN 1996-1944, Vol. 12, nr 20, artikel-id 3447Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effects of fines and chemical composition of three types of ground granulated blast furnace slag (GGBFS) on various concrete properties were studied. Those studied were alkali activated by liquid sodium silicate (SS) and sodium carbonate (SC). Flowability, setting times, compressive strength, efflorescence, and carbonation resistance and shrinkage were tested. The chemical composition and microstructure of the solidified matrixes were studied by X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) coupled with EDX analyser. The results showed that the particle size distribution of the slags and the activator type had significantly stronger effects on all measured properties than their chemical composition. The highest compressive strength values were obtained for the finest slag, which having also the lowest MgO content. SC-activated mortar produced nearly the same compressive strength values independently of the used slag. The most intensive efflorescence and the lowest carbonation resistance developed on mortars based on slag containing 12% of MgO and the lowest fineness. The slag with the highest specific surface area and the lowest MgO content developed a homogenous microstructure, highest reaction temperature and lowest drying shrinkage. Thermogravimetric analysis indicated the presence of C-(A)-S-H, hydrotalcite HT, and carbonate like-phases in all studied mortars.

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  • 25.
    Khalili, Pooria
    et al.
    Material and Computational Mechanics, Department of Industrial and Materials Science, Chalmers University of Technology, Gothenburg, Sweden.
    Blinzler, Brina
    Material and Computational Mechanics, Department of Industrial and Materials Science, Chalmers University of Technology, Gothenburg, Sweden.
    Kádár, Roland
    Division of Engineering Materials, Department of Industrial and Materials Science, Chalmers University of Technology, Gothenburg, Sweden.
    Bisschop, Roeland
    Division Safety and Transport/Safety/Fire Research, RISE Research Institutes of Sweden, Borås, Sweden.
    Försth, Michael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand. Division Safety and Transport/Safety/Fire Research, RISE Research Institutes of Sweden, Borås, Sweden.
    Blomqvist, Per
    Division Safety and Transport/Safety/Fire Research, RISE Research Institutes of Sweden, Borås, Sweden.
    Flammability, Smoke, Mechanical Behaviours and Morphology of Flame Retarded Natural Fibre/Elium®Composite2019Ingår i: Materials, E-ISSN 1996-1944, Vol. 12, nr 17, artikel-id 2648Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The work involves fabrication of natural fibre/Elium® composites using resin infusion technique. The jute fabrics were treated using phosphorus-carbon based flame retardant (FR) agent, a phosphonate solution and graphene nano-platelet (GnP), followed by resin infusion, to produce FR and graphene-based composites. The properties of these composites were compared with those of the Control (jute fabric/Elium®). As obtained from the cone calorimeter and Fourier transform infrared spectroscopy, the peak heat release rate reduced significantly after the FR and GnP treatments of fabrics whereas total smoke release and quantity of carbon monoxide increased with the incorporation of FR. The addition of GnP had almost no effect on carbon monoxide and carbon dioxide yield. Dynamic mechanical analysis demonstrated that coating jute fabrics with GnP particles led to an enhanced glass transition temperature by 14%. Scanning electron microscopy showed fibre pull-out locations in the tensile fracture surface of the laminates after incorporation of both fillers, which resulted in reduced tensile properties.

  • 26.
    Kledwig, Christian
    et al.
    Development Department, Sauer GmbH LASERTEC, DMG MORI AG, Pfronten, Germany.
    Perfahl, Holger
    Development Department, Sauer GmbH LASERTEC, DMG MORI AG, Pfronten, Germany.
    Reisacher, Martin
    Development Department, Sauer GmbH LASERTEC, DMG MORI AG, Pfronten, Germany.
    Brueckner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Additive Manufacturing and Printing, Fraunhofer Institute for Material and Beam Technology IWS, Dresden, Germany.
    Bliedtner, Jens
    SciTec Department, Ernst-Abbe-Hochschule Jena, Jena, Germany.
    Leyens, Christoph
    Additive Manufacturing and Printing, Fraunhofer Institute for Material and Beam Technology IWS, Dresden, Germany; Institute of Materials Science, Technische Universität Dresden, Dresden, Germany.
    Analysis of Melt Pool Characteristics and Process Parameters Using a Coaxial Monitoring System during Directed Energy Deposition in Additive Manufacturing2019Ingår i: Materials, E-ISSN 1996-1944, Vol. 12, nr 2, artikel-id 308Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The growing number of commercially available machines for laser deposition welding show the growing acceptance and importance of this technology for industrial applications. Their increasing usage in research and production requires process stability and user-friendly handling. A commercially available DMG MORI LT 65 3D hybrid machine used in combination with a CCD-based coaxial temperature measurement system was utilized in this work to investigate what information relating to the intensity distribution of melt pool surfaces could be appropriate to draw conclusions about process conditions. In this study it is shown how the minimal required specific energy for a stable process can be determined, and it is indicated that the evolution of a plasma plume depends on thermal energy within the base material. An estimated melt pool area—calculated by the number of pixels (NOP) with intensities larger than a fixed, predefined threshold—builds the main measure in analysing images from the process camera. The melt pool area and its temporal variance can also serve as an indicator for an increased working distance

  • 27.
    Kocot, Agnieszka
    et al.
    Department of Building Materials and Processes Engineering, Silesian University of Technology, 44-100 Gliwice, Poland.
    Cwirzen, Andrzej
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Ponikiewski, Tomasz
    Department of Building Materials and Processes Engineering, Silesian University of Technology, 44-100 Gliwice, Poland.
    Katzer, Jacek
    Institute of Geodesy and Civil Engineering, Faculty of Geoengineering, University of Warmia and Mazury in Olsztyn, 10-719 Olsztyn, Poland.
    Strength Characteristics of Alkali-Activated Slag Mortars with the Addition of PET Flakes2021Ingår i: Materials, E-ISSN 1996-1944, Vol. 14, nr 21, artikel-id 6274Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The production of ordinary Portland cement is associated with significant CO2 emissions. To limit these emissions, new binders are needed that can be efficiently substituted for cement. Alkali-activated slag composites are one such possible binder solution. The research programme presented herein focused on the creation of alkali-activated slag composites with the addition of PET flakes as a partial substitute (5%) for natural aggregate. Such composites have a significantly lower impact in terms of CO2 emissions in comparison to ordinary concrete. The created composites were differentiated by the amount of activator (10 and 20 wt.%) and curing temperature (from 20 to 80 °C). Their mechanical properties were tested, and a scanning electron microscope analysis was conducted. Compressive and flexural strengths ranging from 29.3 to 68.4 MPa and from 3.5 to 6.1 MPa, respectively, were achieved. The mechanical test results confirmed that a higher amount of activator improved the mechanical properties. However, the influence of the PET particles on the mechanical properties and microstructure varied with the curing temperature and amount of activator. Areas that require further research were identified.

  • 28.
    Kothari, Ankit
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Habermehl-Cwirzen, Karin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Hedlund, Hans
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand. Skanska Teknik AB, Skanska Sverige AB, 40518 Göteborg, Sweden.
    Cwirzen, Andrzej
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    A Review of the Mechanical Properties and Durability of Ecological Concretes in a Cold Climate in Comparison to Standard Ordinary Portland Cement-Based Concrete2020Ingår i: Materials, E-ISSN 1996-1944, Vol. 13, nr 16, artikel-id 3467Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Most of the currently used concretes are based on ordinary Portland cement (OPC) which results in a high carbon dioxide footprint and thus has a negative environmental impact. Replacing OPCs, partially or fully by ecological binders, i.e., supplementary cementitious materials (SCMs) or alternative binders, aims to decrease the carbon dioxide footprint. Both solutions introduced a number of technological problems, including their performance, when exposed to low, subfreezing temperatures during casting operations and the hardening stage. This review indicates that the present knowledge enables the production of OPC-based concretes at temperatures as low as −10 °C, without the need of any additional measures such as, e.g., heating. Conversely, composite cements containing SCMs or alkali-activated binders (AACs) showed mixed performances, ranging from inferior to superior in comparison with OPC. Most concretes based on composite cements require pre/post heat curing or only a short exposure to sub-zero temperatures. At the same time, certain alkali-activated systems performed very well even at −20 °C without the need for additional curing. Chemical admixtures developed for OPC do not always perform well in other binder systems. This review showed that there is only a limited knowledge on how chemical admixtures work in ecological concretes at low temperatures and how to accelerate the hydration rate of composite cements containing high amounts of SCMs or AACs, when these are cured at subfreezing temperatures.

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  • 29.
    Kothari, Ankit
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Rajczakowska, Magdalena
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Buasiri, Thanyarat
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Habermehl-Cwirzen, Karin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Cwirzen, Andrzej
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Eco-UHPC as Repair Material-Bond Strength, Interfacial Transition Zone and Effects of Formwork Type2020Ingår i: Materials, E-ISSN 1996-1944, Vol. 13, nr 24, artikel-id 5778Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A reduced carbon footprint and longer service life of structures are major aspects of circular economy with respect to civil engineering. The aim of the research was to evaluate the interfacial bond properties between a deteriorated normal strength concrete structure and a thin overlay made of Eco-UHPC containing 50 wt% of limestone filler. Two types of formwork were used: untreated rough plywood and surface treated shuttering plywood. The normal strength concrete elements were surface scaled using water jets to obtain some degradation prior to casting of the UHPC overlay. Ultrasonic pulse velocity (UPV), bond test (pull-off test), and Scanning Electron Microscopy (SEM) combined with Energy Dispersive Spectrometry (EDS) were used for analysis. Elements repaired with the Eco-UHPC showed significantly improved mechanical properties compared to the non-deteriorated NSC sample which was used as a reference. The bond strength varied between 2 and 2.7 MPa regardless of the used formwork. The interfacial transition zone was very narrow with only slightly increased porosity. The untreated plywood, having a rough and water-absorbing surface, created a surface friction-based restraint which limited microcracking due to autogenous shrinkage. Shuttering plywood with a smooth surface enabled the development of higher tensile stress on the UHPC surface, which led to a more intensive autogenous shrinkage cracking. None of the formed microcracks penetrated through the entire thickness of the overlay and some were partly self-healed when a simple water treatment was applied. The project results showed that application of UHPC as repair material for concrete structures could elongate the lifespan and thus enhance the sustainability.

  • 30.
    Krzak, Anna
    et al.
    Scientific and Didactic Laboratory of Nanotechnology and Material Technologies, Silesian University of Technology, 44-100 Gliwice, Poland.
    Al-Maqdasi, Zainab
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Nowak, Agnieszka J.
    Scientific and Didactic Laboratory of Nanotechnology and Material Technologies, Silesian University of Technology, 44-100 Gliwice, Poland.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Effect of Thermomechanical Loading at Low Temperatures on Damage Development in Glass Fiber Epoxy Laminates2024Ingår i: Materials, E-ISSN 1996-1944, Vol. 17, nr 1, artikel-id 16Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Due to the high interest in the use of glass/epoxy laminates in aerospace applications, aviation, and as cryogenic tanks, it is crucial to understand the behavior of composites under challenging environmental conditions. Polymer composites are exposed to low temperatures, including cryogenic temperatures, which can lead to the initiation of microdamage. This paper investigates damage initiation/accumulation and its influence on the properties of cross-ply woven glass fiber epoxy composites at low temperatures compared to room temperature conditions. To evaluate the influence of a low-temperature environment on the mechanical performance of glass fiber reinforced epoxy composite (GFRP) laminates, three types of test campaigns were carried out: quasi-static tensile tests and stepwise increasing loading/unloading cyclic tensile tests at room temperature and in a low-temperature environment (−50 °C). We demonstrated that the initial stiffness of the laminates increased at low temperatures. On the other hand, there were no observed changes in the type or mechanism of developed damage in the two test conditions. However, the reduction in stiffness due to the accumulated damage was more significant for the laminates tested at low temperatures (~17% vs. ~11%). Exceptions were noted in a few formulations where the extent of damage at low temperatures was insignificant (<1%) compared to that at room temperature. Since some of the studied laminates exhibited a relatively minor decrease in stiffness (~2–3%), we can also conclude that the formulation of matrix material plays an important role in delaying the initiation and formation of damage.

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  • 31.
    Lindwall, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Hållfasthetslära.
    Lundbäck, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Hållfasthetslära.
    Marattukalam, Jithin James
    Department of Physics, Materials Physics, Uppsala University, P.O. Box 530, 75121 Uppsala, Sweden.
    Ericsson, Anders
    Division of Solid Mechanics, Lund University, P.O. Box 118, 22100 Lund, Sweden.
    Virtual Development of Process Parameters for Bulk Metallic Glass Formation in Laser-Based Powder Bed Fusion2022Ingår i: Materials, E-ISSN 1996-1944, Vol. 15, nr 2, artikel-id 450Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The development of process parameters and scanning strategies for bulk metallic glass formation during additive manufacturing is time-consuming and costly. It typically involves trials with varying settings and destructive testing to evaluate the final phase structure of the experimental samples. In this study, we present an alternative method by modelling to predict the influence of the process parameters on the crystalline phase evolution during laser-based powder bed fusion (PBF-LB). The methodology is demonstrated by performing simulations, varying the following parameters: laser power, hatch spacing and hatch length. The results are compared in terms of crystalline volume fraction, crystal number density and mean crystal radius after scanning five consecutive layers. The result from the simulation shows an identical trend for the predicted crystalline phase fraction compared to the experimental estimates. It is shown that a low laser power, large hatch spacing and long hatch lengths are beneficial for glass formation during PBF-LB. The absolute values show an offset though, over-predicted by the numerical model. The method can indicate favourable parameter settings and be a complementary tool in the development of scanning strategies and processing parameters for additive manufacturing of bulk metallic glass.

  • 32.
    Maimaitiyili, Tuerdi
    et al.
    Photons for Engineering and Manufacturing Group, Paul Scherrer Institute, Villigen, Switzerland;Department of Materials Science and Applied Mathematics, Malmö universitet, Malmö, Sweden.
    Woracek, Robin
    European Spallation Source ERIC, Lund, Sweden; Nuclear Physics Institute of the CAS, Husinec—Řež, Czech Republic.
    Neikter, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Boin, Mirko
    Department of Microstructure and Residual Stress Analysis, Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin, Germany.
    Wimpory, Robert C.
    Department of Microstructure and Residual Stress Analysis, Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin, Germany.
    Pederson, Robert
    Department of Engineering Science, University West, Trollhättan, Sweden.
    Strobl, Markus
    European Spallation Source ERIC, Lund, Sweden; Nuclear Physics Institute of the CAS, Husinec—Řež, Czech Republic; Neutron Imaging and Applied Materials Group, Paul Scherrer Institute, Villigen, Switzerland.
    Drakopoulos, Michael
    Imaging and Microscopy Group, Diamond Light Source Ltd., Oxfordshire , UK.
    Schäfer, Norbert
    Department of Nanoscale Structures and Microscopic Analysis, Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin, Germany.
    Bjerkén, Christina
    Department of Materials Science and Applied Mathematics, Malmö universitet, Malmö, Sweden.
    Residual Lattice Strain and Phase Distribution in Ti-6Al-4V Produced by Electron Beam Melting2019Ingår i: Materials, E-ISSN 1996-1944, Vol. 12, nr 4, artikel-id 667Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Residual stress/strain and microstructure used in additively manufactured material are strongly dependent on process parameter combination. With the aim to better understand and correlate process parameters used in electron beam melting (EBM) of Ti-6Al-4V with resulting phase distributions and residual stress/strains, extensive experimental work has been performed. A large number of polycrystalline Ti-6Al-4V specimens were produced with different optimized EBM process parameter combinations. These specimens were post-sequentially studied by using high-energy X-ray and neutron diffraction. In addition, visible light microscopy, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) studies were performed and linked to the other findings. Results show that the influence of scan speed and offset focus on resulting residual strain in a fully dense sample was not significant. In contrast to some previous literature, a uniform α- and β-Ti phase distribution was found in all investigated specimens. Furthermore, no strong strain variations along the build direction with respect to the deposition were found. The magnitude of strain in α and β phase show some variations both in the build plane and along the build direction, which seemed to correlate with the size of the primary β grains. However, no relation was found between measured residual strains in α and β phase. Large primary β grains and texture appear to have a strong effect on X-ray based stress results with relatively small beam size, therefore it is suggested to use a large beam for representative bulk measurements and also to consider the prior β grain size in experimental planning, as well as for mathematical modelling.

  • 33.
    Makarava, Iryna
    et al.
    Department of Separation Science, School of Engineering Science, LUT University, Yliopistonkatu 34, FI-53850 Lappeenranta, Finland; Helmholtz-Zentrum Dresden-Rossendorf, Helmholtz Institute Freiberg for Resource Technology, 09599 Freiberg, Germany.
    Esmaeili, Mohammadamin
    Department of Separation Science, School of Engineering Science, LUT University, Yliopistonkatu 34, FI-53850 Lappeenranta, Finland.
    Kharytonau, Dzmitry S.
    Soft Matter Nanostructures Group, Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, PL-30239 Krakow, Poland.
    Pelcastre, Leonardo
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Ryl, Jacek
    Institute of Nanotechnology and Materials Engineering, Faculty of Applied Physics and Mathematics, Gdansk University of Technology, Narutowicza St. 11/12 Gdansk, PL-80233 Gdansk, Poland.
    Bilesan, Mohammad Reza
    Department of Separation Science, School of Engineering Science, LUT University, Yliopistonkatu 34, FI-53850 Lappeenranta, Finland.
    Vuorinen, Esa
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Repo, Eveliina
    Department of Separation Science, School of Engineering Science, LUT University, Yliopistonkatu 34, FI-53850 Lappeenranta, Finland.
    Influence of CeO2 and TiO2 Particles on Physicochemical Properties of Composite Nickel Coatings Electrodeposited at Ambient Temperature2022Ingår i: Materials, E-ISSN 1996-1944, Vol. 15, nr 16, artikel-id 5550Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Ni-TiO2 and Ni-CeO2 composite coatings with varying hydrophilic/hydrophobic characteristics were fabricated by the electrodeposition method from a tartrate electrolyte at ambient temperature. To meet the requirements of tight regulation by the European Chemicals Agency classifying H3BO3 as a substance of very high concern, Rochelle salt was utilized as a buffer solution instead. The novelty of this study was to implement a simple one-step galvanostatic electrodeposition from the low-temperature electrolyte based on a greener buffer compared to traditionally used, aiming to obtain new types of soft-matrix Ni, Ni-CeO2, and Ni-TiO2 coatings onto steel or copper substrates. The surface characteristics of electrodeposited nickel composites were evaluated by SEM, EDS, surface contact angle measurements, and XPS. Physiochemical properties of pure Ni, Ni-CeO2, and Ni-TiO2 composites, namely, wear resistance, microhardness, microroughness, and photocatalytic activity, were studied. Potentiodynamic polarization, EIS, and ICP-MS analyses were employed to study the long-term corrosion behavior of coatings in a 0.5 M NaCl solution. Superior photocatalytic degradation of methylene blue, 96.2% after 6 h of illumination, was achieved in the case of Ni-TiO2 composite, while no substantial change in the photocatalytic behavior of the Ni-CeO2 compared to pure Ni was observed. Both composites demonstrated higher hardness and wear resistance than pure Ni. This study investigates the feasibility of utilizing TiO2 as a photocatalytic hydrophilicity promoter in the fabrication of composite coatings for various applications.

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  • 34.
    Malmelöv, Andreas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Fisk, Martin
    Department of Materials Science and Applied Mathematics, Malmö University, SE-205 06 Malmö, Sweden. Division of Solid Mechanics, Lund University, P.O. Box 118, SE-221 00 Lund, Sweden.
    Lundbäck, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Mechanism based flow stress model for Alloy 625 and Alloy 7182020Ingår i: Materials, E-ISSN 1996-1944, Vol. 13, nr 24, artikel-id 5620Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To predict the final geometry in thermo-mechanical processes, the use of modeling tools is of great importance. One important part of the modeling process is to describe the response correctly. A previously published mechanism-based flow stress model has been further developed and adapted for the nickel-based superalloys, alloy 625, and alloy 718. The updates include the implementation of a solid solution strengthening model and a model for high temperature plasticity. This type of material model is appropriate in simulations of manufacturing processes where the material undergoes large variations in strain rates and temperatures. The model also inherently captures stress relaxation. The flow stress model has been calibrated using compression strain rate data ranging from 0.01 to 1 s−1 with a temperature span from room temperature up to near the melting temperature. Deformation mechanism maps are also constructed which shows when the different mechanisms are dominating. After the model has been calibrated, it is validated using stress relaxation tests. From the parameter optimization, it is seen that many of the parameters are very similar for alloy 625 and alloy 718, although it is two different materials. The modeled and measured stress relaxation are in good agreement.

  • 35.
    Manu, Karthik
    et al.
    Department of Material Science and Engineering, KTH Royal Institute of Technology, 100 44 Stockholm, Sweden; SWERIM AB, Aronstorpsvägen 1, 974 37 Luleå, Sweden.
    Mousa, Elsayed
    SWERIM AB, Aronstorpsvägen 1, 974 37 Luleå, Sweden; Central Metallurgical Research and Development Institute (CMRDI), Cairo 12422, Egypt.
    Ahmed, Hesham
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi. Central Metallurgical Research and Development Institute (CMRDI), Cairo 12422, Egypt.
    Elsadek, Mohamed
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi. Central Metallurgical Research and Development Institute (CMRDI), Cairo 12422, Egypt.
    Yang, Weihong
    Department of Material Science and Engineering, KTH Royal Institute of Technology, 100 44 Stockholm, Sweden.
    Maximizing the Recycling of Iron Ore Pellets Fines Using Innovative Organic Binders2023Ingår i: Materials, E-ISSN 1996-1944, Vol. 16, nr 10, artikel-id 3888Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This research work focuses on the practicality of using organic binders for the briquetting of pellet fines. The developed briquettes were evaluated in terms of mechanical strength and reduction behavior with hydrogen. A hydraulic compression testing machine and thermogravimetric analysis were incorporated into this work to investigate the mechanical strength and reduction behavior of the produced briquettes. Six organic binders, namely Kempel, lignin, starch, lignosulfonate, Alcotac CB6, and Alcotac FE14, in addition to sodium silicate, were tested for the briquetting of pellet fines. The highest mechanical strength was achieved using sodium silicate, Kempel, CB6, and lignosulfonate. The best combination of binder to attain the required mechanical strength even after 100% reduction was found to be a combination of 1.5 wt.% of organic binder (either CB6 or Kempel) with 0.5 wt.% of inorganic binder (sodium silicate). Upscaling using an extruder gave propitious results in the reduction behavior, as the produced briquettes were highly porous and attained pre-requisite mechanical strength.

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  • 36.
    Memarian, Nafiseh
    et al.
    Faculty of Physics, Semnan University, Semnan, 35131-19111, Iran.
    Rozati, Seyed Mohammad
    Department of Physics, University of Guilan, Rasht 41335, Iran.
    Concina, Isabella
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Vomiero, Alberto
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Deposition of Nanostructured CdS Thin Films by Thermal Evaporation Method: Effect of Substrate Temperature2017Ingår i: Materials, E-ISSN 1996-1944, Vol. 10, nr 7, artikel-id 773Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nanocrystalline CdS thin films were grown on glass substrates by a thermal evaporation method in a vacuum of about 2 × 10-5 Torr at substrate temperatures ranging between 25 °C and 250 °C. The physical properties of the layers were analyzed by transmittance spectra, XRD, SEM, and four-point probe measurements, and exhibited strong dependence on substrate temperature. The XRD patterns of the films indicated the presence of single-phase hexagonal CdS with (002) orientation. The structural parameters of CdS thin films (namely crystallite size, number of grains per unit area, dislocation density and the strain of the deposited films) were also calculated. The resistivity of the as-deposited films were found to vary in the range 3.11-2.2 × 104 Ω·cm, depending on the substrate temperature. The low resistivity with reasonable transmittance suggest that this is a reliable way to fine-tune the functional properties of CdS films according to the specific application.

  • 37.
    Mishra, Pragya
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Åkerfeldt, Pia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Forouzan, Farnoosh
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Svahn, Fredrik
    GKN Aerospace, 46130 Trollhättan, Sweden.
    Zhong, Yuan
    Department of Materials and Environmental Chemistry, Stockholm University, 10691 Stockholm, Sweden.
    Shen, Zhijian
    Department of Materials and Environmental Chemistry, Stockholm University, 10691 Stockholm, Sweden.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Microstructural Characterization and Mechanical Properties of L-PBF Processed 316 L at Cryogenic Temperature2021Ingår i: Materials, E-ISSN 1996-1944, Vol. 14, nr 19, artikel-id 5856Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Laser powder bed fusion (L-PBF) has attracted great interest in the aerospace and medical sectors because it can produce complex and lightweight parts with high accuracy. Austenitic stainless steel alloy 316 L is widely used in many applications due to its good mechanical properties and high corrosion resistance over a wide temperature range. In this study, L-PBF-processed 316 L was investigated for its suitability in aerospace applications at cryogenic service temperatures and the behavior at cryogenic temperature was compared with room temperature to understand the properties and microstructural changes within this temperature range. Tensile tests were performed at room temperature and at −196 °C to study the mechanical performance and phase changes. The microstructure and fracture surfaces were characterized using scanning electron microscopy, and the phases were analyzed by X-ray diffraction. The results showed a significant increase in the strength of 316 L at −196 °C, while its ductility remained at an acceptable level. The results indicated the formation of ε and α martensite during cryogenic testing, which explained the increase in strength. Nanoindentation revealed different hardness values, indicating the different mechanical properties of austenite (γ), strained austenite, body-centered cubic martensite (α), and hexagonal close-packed martensite (ε) formed during the tensile tests due to mechanical deformation.

  • 38.
    Mohammadi, Rafat
    et al.
    Department of Mechanical Engineering, Faculty of Engineering, Arak University, Arak 38156-88349, Iran.
    Ghaderi, Mohammad Reza
    Department of Mechanical Engineering, Faculty of Engineering, Arak University, Arak 38156-88349, Iran.
    Hajiyan, Ebrahim
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    A Molecular Dynamics Simulation Study of In- and Cross-Plane Thermal Conductivity of Bilayer Graphene2023Ingår i: Materials, E-ISSN 1996-1944, Vol. 16, nr 20, artikel-id 6714Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Efficient thermal management of modern electronics requires the use of thin films with highly anisotropic thermal conductivity. Such films enable the effective dissipation of excess heat along one direction while simultaneously providing thermal insulation along the perpendicular direction. This study employs non-equilibrium molecular dynamics to investigate the thermal conductivity of bilayer graphene (BLG) sheets, examining both in-plane and cross-plane thermal conductivities. The in-plane thermal conductivity of 10 nm × 10 nm BLG with zigzag and armchair edges at room temperature is found to be around 204 W/m·K and 124 W/m·K, respectively. The in-plane thermal conductivity of BLG increases with sheet length. BLG with zigzag edges consistently exhibits 30–40% higher thermal conductivity than BLG with armchair edges. In addition, increasing temperature from 300 K to 600 K decreases the in-plane thermal conductivity of a 10 nm × 10 nm zigzag BLG by about 34%. Similarly, the application of a 12.5% tensile strain induces a 51% reduction in its thermal conductivity compared to the strain-free values. Armchair configurations exhibit similar responses to variations in temperature and strain, but with less sensitivity. Furthermore, the cross-plane thermal conductivity of BLG at 300 K is estimated to be 0.05 W/m·K, significantly lower than the in-plane results. The cross-plane thermal conductance of BLG decreases with increasing temperatures, specifically, at 600 K, its value is almost 16% of that observed at 300 K.

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  • 39.
    Murgau, Corinne Charles
    et al.
    Department of Engineering Science, University West, Trollhättan, Sweden.
    Lundbäck, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Åkerfeldt, Pia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, Robert
    Department of Engineering Science, University West, Trollhättan, Sweden. GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Temperature and Microstructure Evolution in Gas Tungsten Arc Welding Wire Feed Additive Manufacturing of Ti-6Al-4V2019Ingår i: Materials, E-ISSN 1996-1944, Vol. 12, nr 21, artikel-id 3534Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present study, the gas tungsten arc welding wire feed additive manufacturing process is simulated and its final microstructure predicted by microstructural modelling, which is validated by microstructural characterization. The Finite Element Method is used to solve the temperature field and microstructural evolution during a gas tungsten arc welding wire feed additive manufacturing process. The microstructure of titanium alloy Ti-6Al-4V is computed based on the temperature evolution in a density-based approach and coupled to a model that predicts the thickness of the α lath morphology. The work presented herein includes the first coupling of the process simulation and microstructural modelling, which have been studied separately in previous work by the authors. In addition, the results from simulations are presented and validated with qualitative and quantitative microstructural analyses. The coupling of the process simulation and microstructural modeling indicate promising results, since the microstructural analysis shows good agreement with the predicted alpha lath size.

  • 40.
    Müller, Michael
    et al.
    Department of Additive Manufacturing and Printing, Fraunhofer Institute for Material and Beam Technology, Winterbergstraβe 28, 01277 Dresden, Germany; Faculty of Mechanical Science and Engineering, Institute of Materials Science, Dresden University of Technology, Helmholtzstr. 7, 01069 Dresden, Germany .
    Heinen, Bastian
    Department of Additive Manufacturing and Printing, Fraunhofer Institute for Material and Beam Technology, Winterbergstraβe 28, 01277 Dresden, Germany.
    Riede, Mirko
    Department of Additive Manufacturing and Printing, Fraunhofer Institute for Material and Beam Technology, Winterbergstraβe 28, 01277 Dresden, Germany.
    López, Elena
    Department of Additive Manufacturing and Printing, Fraunhofer Institute for Material and Beam Technology, Winterbergstraβe 28, 01277 Dresden, Germany.
    Brückner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Department of Additive Manufacturing and Printing, Fraunhofer Institute for Material and Beam Technology, Winterbergstraβe 28, 01277 Dresden, Germany.
    Leyens, Christoph
    Department of Additive Manufacturing and Printing, Fraunhofer Institute for Material and Beam Technology, Winterbergstraβe 28, 01277 Dresden, Germany; Faculty of Mechanical Science and Engineering, Institute of Materials Science, Dresden University of Technology, Helmholtzstr. 7, 01069 Dresden, Germany.
    Additive Manufacturing of β-NiAl by Means of Laser Metal Deposition of Pre-Alloyed and Elemental Powders2021Ingår i: Materials, E-ISSN 1996-1944, Vol. 14, nr 9, artikel-id 2246Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The additive manufacturing (AM) technique, laser metal deposition (LMD), combines the advantages of near net shape manufacturing, tailored thermal process conditions and in situ alloy modification. This makes LMD a promising approach for the processing of advanced materials, such as intermetallics. Additionally, LMD allows the composition of a powder blend to be modified in situ. Hence, alloying and material build-up can be achieved simultaneously. Within this contribution, AM processing of the promising high-temperature material β-NiAl, by means of LMD, with elemental powder blends, as well as with pre-alloyed powders, was presented. The investigations showed that by applying a preheating temperature of 1100 °C, β-NiAl could be processed without cracking. Additionally, by using pre-alloyed, as well as elemental powders, a single phase β-NiAl microstructure can be achieved in multi-layer build-ups. Major differences between the approaches were found within substrate near regions. For in situ alloying of Ni and Al, these regions are characterized by an inhomogeneous elemental distribution in a layerwise manner. However, due to the remelting of preceding layers during deposition, a homogenization can be observed, leading to a single-phase structure. This shows the potential of high temperature preheating and in situ alloying to push the development of new high temperature materials for AM.

  • 41.
    Naalchian, Mojtaba
    et al.
    Advanced Materials Research Center, Department of Materials Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran.
    Kasiri-Asgarani, Masoud
    Advanced Materials Research Center, Department of Materials Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran.
    Shamanian, Morteza
    Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran.
    Bakhtiari, Reza
    Department of Materials Engineering, Faculty of Engineering, Razi University, Kermanshah, Iran.
    Bakhsheshi-Rad, Hamid Reza
    Advanced Materials Research Center, Department of Materials Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran.
    Berto, Filippo
    Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway.
    Das, Oisik
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Phase Formation during Heating of Amorphous Nickel-Based BNi-3 for Joining of Dissimilar Cobalt-Based Superalloys2021Ingår i: Materials, E-ISSN 1996-1944, Vol. 14, nr 16, artikel-id 4600Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Phase transformations and the melting range of the interlayer BNi-3 were investigated by differential scanning calorimetry, which showed three stages of crystallization during heating. There were three exothermic peaks that indicated crystallization in the solid state. The cobalt-based X-45 and FSX-414 superalloys were bonded with interlayer BNi-3 at a constant holding time of 10 min with bonding temperatures of 1010, 1050, 1100, and 1150 °C using a vacuum diffusion brazing process. Examination of microstructural changes in the base metals with light microscopy and scanning electron microscopy coupled with X-ray spectroscopy based on the energy distribution showed that increasing temperature caused a solidification mode, such that the bonding centerline at 1010 °C/10 min included a γ-solid solution, Ni3B, Ni6Si2B, and Ni3Si. The athermally solidified zone of the transient liquid phase (TLP)-bonded sample at 1050 °C/10 min involved a γ-solid solution, Ni3B, CrB, Ni6Si2B, and Ni3Si. Finally, isothermal solidification was completed within 10 min at 1150 °C. The diffusion-affected zones on both sides had three distinct zones: a coarse block precipitation zone, a fine and needle-like mixed-precipitation zone, and a needle-like precipitation zone. By increasing the bonding temperature, the diffusion-affected zone became wider and led to dissolution.

  • 42.
    Neikter, Magnus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Division of Subtractive and Additive Manufacturing, University West, 46132 Trollhättan, Sweden.
    Colliander, M.
    Department of Applied Physics, Chalmers University of Technology, 41296 Göteborg, Sweden.
    de Andrade Schwerz, C.
    GKN Aerospace Engine Systems, 461 38 Trollhättan, Sweden.
    Hansson, T.
    GKN Aerospace Engine Systems, 461 38 Trollhättan, Sweden. Division of Subtractive and Additive Manufacturing, University West, 46132 Trollhättan, Sweden.
    Åkerfeldt, Pia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pederson, R.
    Division of Subtractive and Additive Manufacturing, University West, 46132 Trollhättan, Sweden.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Fatigue Crack Growth of Electron Beam Melted Ti-6Al-4V in High-Pressure Hydrogen2020Ingår i: Materials, E-ISSN 1996-1944, Vol. 13, nr 6, artikel-id 1287Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Titanium-based alloys are susceptible to hydrogen embrittlement (HE), a phenomenon that deteriorates fatigue properties. Ti-6Al-4V is the most widely used titanium alloy and the effect of hydrogen embrittlement on fatigue crack growth (FCG) was investigated by carrying out crack propagation tests in air and high-pressure H2 environment. The FCG test in hydrogen environment resulted in a drastic increase in crack growth rate at a certain Δ K, with crack propagation rates up to 13 times higher than those observed in air. Possible reasons for such behavior were discussed in this paper. The relationship between FCG results in high-pressure H2 environment and microstructure was investigated by comparison with already published results of cast and forged Ti-6Al-4V. Coarser microstructure was found to be more sensitive to HE. Moreover, the electron beam melting (EBM) materials experienced a crack growth acceleration in-between that of cast and wrought Ti-6Al-4V.

  • 43.
    Neikter, Magnus
    et al.
    Division of Subtractive and Additive Manufacturing, University West, 46132 Trollhättan, Sweden.
    Edin, Emil
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Proper, Sebastian
    Research Institutes of Sweden, 41314 Gothenburg, Sweden.
    Bhaskar, Phavan
    Division of Subtractive and Additive Manufacturing, University West, 46132 Trollhättan, Sweden.
    Nekkalapudi, Gopi Krishna
    Division of Subtractive and Additive Manufacturing, University West, 46132 Trollhättan, Sweden.
    Linde, Oscar
    GKN Aerospace Sweden AB, 46181 Trollhättan, Sweden.
    Hansson, Thomas
    Division of Subtractive and Additive Manufacturing, University West, 46132 Trollhättan, Sweden; GKN Aerospace Sweden AB, 46181 Trollhättan, Sweden.
    Pederson, Robert
    Division of Subtractive and Additive Manufacturing, University West, 46132 Trollhättan, Sweden.
    Tensile Properties of 21-6-9 Austenitic Stainless Steel Built Using Laser Powder-Bed Fusion2021Ingår i: Materials, E-ISSN 1996-1944, Vol. 14, nr 15, artikel-id 4280Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Alloy 21-6-9 is an austenitic stainless steel with high strength, thermal stability at high temperatures, and retained toughness at cryogenic temperatures. This type of steel has been used for aerospace applications for decades, using traditional manufacturing processes. However, limited research has been conducted on this alloy manufactured using laser powder-bed fusion (LPBF). Therefore, in this work, a design of experiment (DOE) was performed to obtain optimized process parameters with regard to low porosity. Once the optimized parameters were established, horizontal and vertical blanks were built to investigate the mechanical properties and potential anisotropic behavior. As this alloy is exposed to elevated temperatures in industrial applications, the effect of elevated temperatures (room temperature and 750 °C) on the tensile properties was investigated. In this work, it was shown that alloy 21-6-9 could be built successfully using LPBF, with good properties and a density of 99.7%, having an ultimate tensile strength of 825 MPa, with an elongation of 41%, and without any significant anisotropic behavior.

  • 44.
    Otsuki, Akira
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik. Facultad de Ingeniería y Ciencias, Universidad Adolfo Ibáñez, Diagonal Las Torres 2640, Peñalolén, Santiago 7941169, Chile; Neutron Beam Technology Team, RIKEN Center for Advanced Photonics, RIKEN, Wako 351-0198, Japan.
    Editorial for the Special Issue: “Characterization and Processing of Complex Materials”2023Ingår i: Materials, E-ISSN 1996-1944, Vol. 16, nr 10, artikel-id 3830Artikel i tidskrift (Övrigt vetenskapligt)
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  • 45.
    Paladugu, Sri Ram Murthy
    et al.
    VIT AP Univ, Sch Mech Engn, Amaravati 522337, India.
    Sreekanth, P. S. Rama
    VIT AP Univ, Sch Mech Engn, Amaravati 522337, India.
    Sahu, Santosh Kumar
    VIT AP Univ, Sch Mech Engn, Amaravati 522337, India.
    Naresh, K.
    Univ Southern Calif, Dept Chem Engn & Mat Sci, Los Angeles, CA 90089 USA.
    Karthick, S. Arun
    Sri Sivasubramaniya Nadar Coll Engn, Dept Biomed Engn, Feynman Nano Lab, Chennai 603110, India.
    Venkateshwaran, N.
    Rajalakshmi Engn Coll, Dept Mech Engn, Chennai 600125, India.
    Ramoni, Monsuru
    Navajo Tech Univ, Sch Engn Math & Technol, Crownpoint, NM 87313 USA.
    Mensah, Rhoda Afriyie
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Das, Oisik
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Shanmugam, Ragavanantham
    Navajo Tech Univ, Sch Engn Math & Technol, Crownpoint, NM 87313 USA.
    A Comprehensive Review of Self-Healing Polymer, Metal, and Ceramic Matrix Composites and Their Modeling Aspects for Aerospace Applications2022Ingår i: Materials, E-ISSN 1996-1944, Vol. 15, nr 23, artikel-id 8521Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Composites can be divided into three groups based on their matrix materials, namely polymer, metal and ceramic. Composite materials fail due to micro cracks. Repairing is complex and almost impossible if cracks appear on the surface and interior, which minimizes reliability and material life. In order to save the material from failure and prolong its lifetime without compromising mechanical properties, self-healing is one of the emerging and best techniques. The studies to address the advantages and challenges of self-healing properties of different matrix materials are very limited; however, this review addresses all three different groups of composites. Self-healing composites are fabricated to heal cracks, prevent any obstructed failure, and improve the lifetime of structures. They can self-diagnose their structure after being affected by external forces and repair damages and cracks to a certain degree. This review aims to provide information on the recent developments and prospects of self-healing composites and their applications in various fields such as aerospace, automobiles etc. Fabrication and characterization techniques as well as intrinsic and extrinsic self-healing techniques are discussed based on the latest achievements, including microcapsule embedment, fibers embedment, and vascular networks self-healing.

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  • 46.
    Petkov, Valeri Ivanov
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pelcastre, Leonardo
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Solano, Carlos
    Nexam Chemical AB, 234 35 Lomma, Sweden.
    Fernberg, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    The Influence of Ethynyl In-Chain Crosslinkers on the Properties of 6FDA-Based Polyimides2022Ingår i: Materials, E-ISSN 1996-1944, Vol. 16, nr 1, artikel-id 169Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two 4,4′-(hexafluoroisopropylidene)diphthalic anhydride-based thermosetting polyimide formulations with varied amounts of crosslinking sites were compared to understand the influence of crosslinking density on fracture toughness, glass transition temperature and thermal oxidative stability. The thermal and mechanical properties of both materials were investigated through a series of single-edge notched beams, differential scanning calorimetry, dilatometry, weight loss, light optical microscopy and nanoindentation experiments. It was found out that the reduced crosslinking resulted in slightly increased fracture toughness but decreased the Tg of the material. No significant difference could be observed in the thermal oxidative stability with the experimental techniques considered.

  • 47.
    Polenz, Stefan
    et al.
    Fraunhofer Institute for Material and Beam Technology (IWS), Dresden, 01277, Germany.
    Kunz, Willy
    Fraunhofer Institute for Ceramic Technologies and Systems (IKTS), Dresden, 01277, Germany.
    Braun, Benjamin
    Space Structures GmbH, Berlin, 12435, Germany.
    Franke, Andrea
    AXIAL Ingenieurgesellschaft für Maschinenbau mbH, Radebeul, 01445, Germany.
    López, Elena
    Fraunhofer Institute for Material and Beam Technology (IWS).
    Brückner, Frank
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Fraunhofer Institute for Material and Beam Technology (IWS), Dresden, 01277, Germany.
    Leyens, Cristoph
    Fraunhofer Institute for Material and Beam Technology (IWS), Dresden, 01277, Germany; Technische Universität Dresden, Dresden, 01069, Germany.
    Development of a system for additive manufacturing of ceramic matrix composite structures using laser technology2021Ingår i: Materials, E-ISSN 1996-1944, Vol. 14, nr 12, artikel-id 3248Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ceramic matrix composites (CMCs) are refractory ceramic materials with damage-tolerant behavior. Coming from the space industry, this class of materials is increasingly being used in other applications, such as automotive construction for high-performance brake discs, furnace technology, heat coatings for pipe systems and landing flaps on reusable rocket sections. In order to produce CMC faster and more cost-efficiently for the increasing demand, a new additive manufacturing process is being tested, which in the future should also be able to realize material joints and higher component wall thicknesses than conventional processes. The main features of the process are as follows. A ceramic fiber bundle is de-sized and infiltrated with ceramic suspension. The bundle infiltrated with matrix material is dried and then applied to a body form. During application, the matrix material is melted by laser radiation without damaging the fiber material. For the initial validation of the material system, samples are pressed and analyzed for their absorption properties using integrating sphere measurement. With the results, a suitable processing laser is selected, and initial melting tests of the matrix system are carried out. After the first validation of the process, a test system is set up, and the first test specimens are produced to determine the material parameters.

  • 48.
    Rajczakowska, Magdalena
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Habermehl-Cwirzen, Karin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Hedlund, Hans
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand. Skanska, Stockholm, Sweden.
    Cwirzen, Andrzej
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    The effect of exposure on the autogenous self-healing of Ordinary Portland cement mortars2019Ingår i: Materials, E-ISSN 1996-1944, Vol. 12, nr 23, artikel-id 3926Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Exposure conditions are critical for the autogenous self-healing process of Portland cement based binder matrixes. However, there is still a significant lack of fundamental knowledge related to this factor. The aim of this paper was to investigate and understand the effects of various potentially applicable curing solutions on the efficiency of the crack closure occurring both superficially and internally. Four groups of exposures were tested, including exposure with different water immersion regimes, variable temperatures, application of chemical admixtures, and use of solutions containing micro particles. The self-healing process was evaluated externally, at the surface of the crack, and internally, at different crack depths with the use of optical and scanning electron microscopes (SEM). The phase identification was done with an energy dispersive spectrometer combined with the SEM. The results showed very limited self-healing in all pure water-based exposures, despite the application of different cycles, temperatures, and water volumes. The addition of a phosphate-based retarding admixture demonstrated the highest crack closure, both internally and externally. The highest strength recovery and a very good crack closure ratio was achieved in water exposure containing micro silica particles. The main phase observed on the surface was calcium carbonate, and internally, calcium silicate hydrate, calcium carbonate, and calcium phosphate compounds. Phosphate ions were found to contribute to the filling of the crack, most likely by preventing the formation of a dense shell composed of hydration phases on the exposed areas by crack unhydrated cement grains as well as by the additional precipitation of calcium and phosphate-based compounds. The micro sized silica particles presumably served as nucleation sites for the self-healing products growth. Changes in the chemical composition of the self-healing material were observed with a distance from the surface of the specimen.

  • 49.
    Rajczakowska, Magdalena
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Nilsson, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Habermehl-Cwirzen, Karin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Hedlund, Hans
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand. Skanska, Stockholm, Sweden.
    Cwirzen, Andrzej
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Does a High Amount of Unhydrated Portland Cement Ensure an Effective Autogenous Self-Healing of Mortar?2019Ingår i: Materials, E-ISSN 1996-1944, Vol. 12, nr 20, artikel-id 3298Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is commonly accepted that the autogenous self-healing of concrete is mainly controlled by the hydration of Portland cement and its extent depends on the availability of anhydrous particles. High-performance (HPCs) and ultra-high performance concretes (UHPCs) incorporating very high amounts of cement and having a low water-to-cement ratio reach the hydration degree of only 70–50%. Consequently, the presence of a large amount of unhydrated cement should result in excellent autogenous self-healing. The main aim of this study was to examine whether this commonly accepted hypothesis was correct. The study included tests performed on UHPC and mortars with a low water-to-cement ratio and high cement content. Additionally, aging effects were verified on 12-month-old UHPC samples. Analysis was conducted on the crack surfaces and inside of the cracks. The results strongly indicated that the formation of a dense microstructure and rapidly hydrating, freshly exposed anhydrous cement particles could significantly limit or even hinder the self-healing process. The availability of anhydrous cement appeared not to guarantee development of a highly effective healing process.

  • 50.
    Rajczakowska, Magdalena
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Szeląg, Maciej
    Faculty of Civil Engineering and Architecture, Lublin University of Technology, 40 Nadbystrzycka Str., 20-618 Lublin, Poland.
    Habermehl-Cwirzen, Karin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Hedlund, Hans
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand. Skanska Sverige AB, 405 18 Göteborg, Sweden.
    Cwirzen, Andrzej
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Interpretable Machine Learning for Prediction of Post-Fire Self-Healing of Concrete2023Ingår i: Materials, E-ISSN 1996-1944, Vol. 16, nr 3, artikel-id 1273Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Developing accurate and interpretable models to forecast concrete’s self-healing behavior is of interest to material engineers, scientists, and civil engineering contractors. Machine learning (ML) and artificial intelligence are powerful tools that allow constructing high-precision predictions, yet often considered “black box” methods due to their complexity. Those approaches are commonly used for the modeling of mechanical properties of concrete with exceptional accuracy; however, there are few studies dealing with the application of ML for the self-healing of cementitious materials. This paper proposes a pioneering study on the utilization of ML for predicting post-fire self-healing of concrete. A large database is constructed based on the literature studies. Twelve input variables are analyzed: w/c, age of concrete, amount of cement, fine aggregate, coarse aggregate, peak loading temperature, duration of peak loading temperature, cooling regime, duration of cooling, curing regime, duration of curing, and specimen volume. The output of the model is the compressive strength recovery, being one of the self-healing efficiency indicators. Four ML methods are optimized and compared based on their performance error: Support Vector Machines (SVM), Regression Trees (RT), Artificial Neural Networks (ANN), and Ensemble of Regression Trees (ET). Monte Carlo analysis is conducted to verify the stability of the selected model. All ML approaches demonstrate satisfying precision, twice as good as linear regression. The ET model is found to be the most optimal with the highest prediction accuracy and sufficient robustness. Model interpretation is performed using Partial Dependence Plots and Individual Conditional Expectation Plots. Temperature, curing regime, and amounts of aggregates are identified as the most significant predictors.

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