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  • 1.
    Aitomäki, Yvonne
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Moreno, Sergio
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Vacuum infusion of cellulose nanofibre network composites: Influence of porosity on permeability and impregnation2016Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 95, s. 204-211Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Addressing issues around the processing of cellulose nanofibres (CNF) composites is important in establishing their use as sustainable, renewable polymer reinforcements. Here, CNF networks of different porosity were made with the aim of increasing their permeability and suitability for processing by vacuum infusion (VI). The CNF networks were infused with epoxy using two different strategies. The permeability, morphology and mechanical properties of the dry networks and the resulting nanocomposites were investigated. Calculated fill-times for CNF networks with 50% porosity were the shortest, but are only less than the gel-time of the epoxy if capillary effects are included. In experiments the CNF networks were clearly wetted. However low transparency indicated that impregnation was incomplete. The modulus and strength of the dry CNF networks increased rapidly with decreasing porosity, but their nanocomposites did not follow this trend, showing instead similar mechanical properties to each other. The results demonstrated that increasing the porosity of the CNF networks to ≈ 50% gives better impregnation resulting in a lower ultimate strength, a higher yield strength and no loss in modulus. Better use of the flow channels in the inherently layered CNF networks could potentially reduce void content in these nanocomposites and thus increase their mechanical properties.

  • 2.
    Alam, Md. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander F. H.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Tuominen, J.
    Tampere University of Technology, Department of Materials Science, FI-33101 Tampere, Finland.
    Vuoristo, P.
    Tampere University of Technology, Department of Materials Science, FI-33101 Tampere, Finland.
    Miettinen, J.
    Tampere University of Technology, Department of Mechanics and Design, FI-33101 Tampere, Finland.
    Poutala, J.
    Tampere University of Technology, Department of Mechanics and Design, FI-33101 Tampere, Finland.
    Närkki, J.
    Tampere University of Technology, Department of Materials Science, FI-33101 Tampere, Finland; Technology Centre KETEK Ltd., FI-67100 Kokkola, Finland.
    Junkala, J.
    Technology Centre KETEK Ltd., FI-67100 Kokkola, Finland.
    Peltola, T.
    Technology Centre KETEK Ltd., FI-67100 Kokkola, Finland.
    Barsoum, Z.
    Royal Institute of Technology, Department of Aeronautical and Vehicle Engineering, SE-100 44 Stockholm, Sweden.
    Analysis of the stress raising action of flaws in laser clad deposits2013Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 46, s. 328-337Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fatigue cracking of laser clad cylindrical and square section bars depends upon a variety of factors. This paper presents Finite Element Analysis (FEA) of the different macro stress fields generated as well as stress raisers created by laser cladding defects for four different fatigue load conditions. As important as the defect types are their locations and orientations, categorized into zero-, one- and two-dimensional defects. Pores and inclusions become critical close to surfaces. The performance of as-clad surfaces can be governed by the sharpness of surface notches and planar defects like hot cracks or lack-of-fusion (LOF) are most critical if oriented vertically, transverse to the bar axis. The combination of the macro stress field with the defect type and its position and orientation determines whether it is the most critical stress raiser. Based on calculated cases, quantitative and qualitative charts were developed as guidelines to visualize the trends of different combinations.

  • 3. Alam, Md. Minhaj
    et al.
    Karlsson, Jan
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Generalising fatigue stress analysis of different laser weld geometries2011Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 32, nr 4, s. 1814-1823Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two-dimensional elastic-plastic finite element analyses was carried out on a laser welded box beam in order to study the impact of the geometrical aspects of the joint type and weld root on the fatigue stress behaviour. Different experimental and hypothetical weld geometries were studied. Characteristic root shapes, measured by the plastic replica method, and critical geometrical aspects were classified and then studied by FE-analysis with respect to their impact on the maximum stress. The simulation of hypothetical transition geometries facilitated the identification of trends and the explanation of part of the phenomena. However, quantitative geometry criteria were only partially suitable to describe the relations. The results have shown that the combination of throat depth, local surface radius and its opening angle determines the peak stress value and its location. Beside extended throat depths, particularly larger toe radii and the avoidance of small opening angles and of surface ripples reduces the peak stress. The explanations were developed in a generalising manner, accompanied by illustrative and flow chart description.

  • 4.
    Brandau, Benedikt
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. JENOPTIK Optical Systems GmbH, System Development Advanced Manufacturing, Göschwitzerstraße 25, 07745 Jena, Germany.
    Da Silva, Adrien
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Wilsnack, Christoph
    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.
    Kaplan, Alexander F.H.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Absorbance study of powder conditions for laser additive manufacturing2022Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 216, artikkel-id 110591Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Absorbance is often used for simulations or validation of process parameters for powder-based laser materials processing. In this work, the absorbance of 39 metal powders for additive manufacturing is determined at 20 laser wavelengths. Different grain sizes and aging states for: steels, aluminum alloys, titanium alloys, Nitinol, high entropy alloy, chromium, copper, brass and iron ore were analyzed. For this purpose, the absorbance spectrum of the powders was determined via a dual-beam spectrometer in the range of λ = 330 - 1560 nm. At the laser wavelengths of λ = 450 nm, 633 nm and 650 nm, the absorbance averaged over all materials was found to increase by a factor of 2.4 up to 3.3 compared to the usual wavelength of λ = 1070 nm, with minimal variations in absorbance between materials. In the investigation of the aged or used powders, a loss of absorbance was detectable. Almost no changes from the point of view of processing aged and new AlSi10Mg powders, is expected for laser sources with λ = 450 nm. The resulting measurements provide a good basis for process parameters for a variety of laser wavelengths and materials, as well as a data set for improved absorbance simulations.

    Fulltekst (pdf)
    fulltext
  • 5.
    Buck, Dietrich
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Wallentén, Petter
    Division of Building Physics, Department of Building and Environmental Technology, Lund University, Lund, Sweden.
    Sehlstedt-Persson, Margot
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Moisture- and mould-resistance: multi-modal modelling leveraging X-ray tomography in edge-sealed cross-laminated timber2023Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 230, artikkel-id 111967Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Edge-sealing, which involves treating the edges of wood products, improves water resistance. This study investigated the feasibility of edge-sealed cross-laminated timber (CLT) panels to reduce capillary water uptake, thereby resisting mould formation. The water and vapour permeabilities of ten characteristically different single-layer sealant coating systems were systematically determined. Multi-modal assessment leveraged by computed tomography (CT) scanning methodology was used to enhance detection of material characteristics beyond the standard coating permeability assessment. Moisture content was observed to change during the specimens’ absorption and desorption depending on the sealant system applied. The results revealed different characteristics of coatings during the water absorption and desorption stages. Findings from this study were used to develop recommendations regarding the water resistance of coating systems, curing time, susceptibility to mould formation, and industrial applicability. Results suggest that edge-sealed CLT could minimise the risk of mould formation, which can occur at worksites with minimal weather protection. The method developed in this study provides a basis to evaluate new coating systems and determine which use case is the best for a particular coating type. This study also incorporates insights from industry to identify future research orientations, which may pave the way for new designs and assessment techniques.

    Fulltekst (pdf)
    fulltext
  • 6.
    Da Silva, Adrien
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Belelli, Filippo
    Department of Mechanical Engineering, Politecnico di Milano, 1 Via Privata Giuseppe La Masa, 20156 Milano, Italy.
    Lupi, Giorgia
    Department of Mechanical Engineering, Politecnico di Milano, 1 Via Privata Giuseppe La Masa, 20156 Milano, Italy.
    Bruzzo, Francesco
    Fraunhofer, Institut für Werkstoff und Strahltechnik, Winterbergstraße 28, 01277 Dresden, Germany.
    Brandau, Benedikt
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. System Development Advanced Manufacturing, JENOPTIK Optical Systems GmbH, Göschwitzerstraße 25, 07745 Jena, Germany.
    Maier, Lukas
    IMR – Metal Powder Technologies GmbH, Jessenigstraße 4, 9220 Lind ob Velden, Austria.
    Pesl, Alexander
    IMR – Metal Powder Technologies GmbH, Jessenigstraße 4, 9220 Lind ob Velden, Austria.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Casati, Riccardo
    Department of Mechanical Engineering, Politecnico di Milano, 1 Via Privata Giuseppe La Masa, 20156 Milano, Italy.
    Lopez, Elena
    Fraunhofer, Institut für Werkstoff und Strahltechnik, Winterbergstraße 28, 01277 Dresden, Germany.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Influence of aluminium powder aging on Directed Energy deposition2022Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 218, artikkel-id 110677Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The use of aluminium alloys for Additive Manufacturing is of high interest for advanced geometries and lightweight applications. In Directed Energy Deposition, a powder stock is processed with a laser beam, which offers a high process flexibility. However, aging of the powder feedstock during storage or after recycling remains fundamentally challenging for aluminium alloys because of their sensitivity to oxida-tion and porosity. In order to investigate these effects, AlSi10Mg powder batches were aged in different conditions and processed by Directed Energy Deposition. The results showed that powder aging does not significantly change the particle size or morphology, but it introduces more oxygen and hydrogen in the powder. The oxidation of the particles reduces the laser beam absorbance of the powder and increases wetting of the melt pool, which affects the track geometry. A 3.5 to 4.2 times higher porosity was observed in the material deposited from aged powder, which are most likely hydrogen pores causedby the increased hydrogen content in the aged powder. The tensile properties of the parts built with aged powder showed 19.0% lower yield strength, 14.2% lower ultimate strength and 99.2% higher elongation, which are most likely the results of the coarser microstructure and increased porosity.

    Fulltekst (pdf)
    fulltext
  • 7.
    Da Silva, Adrien
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Volpp, Joerg
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Additive Manufacturing by laser-assisted drop deposition from a metal wire2021Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 209, artikkel-id 109987Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The subject of Additive Manufacturing includes numerous techniques, some of which have reached very high levels of development and are now used industrially. Other techniques such as Micro Droplet Deposition Manufacture are under development and present different manufacturing possibilities, but are employed only for low melting temperature metals. In this paper, the possibility of using a laser-based drop deposition technique for stainless-steel wire is investigated. This technique is expected to be a more flexible alternative to Laser Metal Wire Deposition. Laser Droplet Generation experiments were carried out in an attempt to accurately detach steel drops towards a desired position. High-speed imaging was used to observe drop generation and measure the direction of detachment of the drops. Two drop detachment techniques were investigated and the physical phenomena leading to the drop detachment are explained, wherein the drop weight, the surface tension and the recoil pressure play a major role. Optimised parameters for accurate single drop detachment were identified and then used to build multi-drop tracks. Tracks with an even geometry were produced, where the microstructure was influenced by the numerous drop depositions. The tracks showed a considerably higher hardness than the base wire, exhibiting a relatively homogeneous macro-hardness with a localised softening effect at the interfaces between drops.

    Fulltekst (pdf)
    fulltext
  • 8.
    Davoodi, M.M.
    et al.
    Universiti Putra Malaysia 43400 UPM Serdang, Selangor.
    Sapuan, S.M.
    Universiti Putra Malaysia 43400 UPM Serdang, Selangor.
    Ahmad, D.
    Universiti Putra Malaysia 43400 UPM Serdang, Selangor.
    Aidy, A.
    Universiti Putra Malaysia 43400 UPM Serdang, Selangor.
    Khalina, A.
    Universiti Putra Malaysia 43400 UPM Serdang, Selangor.
    Jonoobi, Mehdi
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Concept selection of car bumper beam with developed hybrid bio-composite material2011Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 32, nr 10, s. 4857-4865Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Application of natural fibre composites is going to increase in different areas caused by environmental, technical and economic advantages. However, their low mechanical properties have limited their particular application in automotive structural components. Hybridizations with other reinforcements or matrices can improve mechanical properties of natural fibre composite. Moreover, geometric optimizations have a significant role in structural strength improvement. This study focused on selecting the best geometrical bumper beam concept to fulfill the safety parameters of the defined product design specification (PDS). The mechanical properties of developed hybrid composite material were considered in different bumper beam concepts with the same frontal curvature, thickness, and overall dimensions. The low-speed impact test was simulated under the same conditions in Abaqus V16R9 software. Six weighted criteria, which were deflection, strain energy, mass, cost, easy manufacturing, and the rib possibility were analyzed to form an evaluation matrix. Topsis method was employed to select the best concept. It is concluded that double hat profile (DHP) with defined material model can be used for bumper beam of a small car. In addition, selected concept can be strengthened by adding reinforced ribs or increasing the thickness of the bumper beam to comply with the defined PDS.

  • 9.
    Ericsson, A.
    et al.
    Division of Solid Mechanics, Lund University, Lund, Sweden.
    Pacheco, V.
    Department of Chemistry, Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Sahlberg, M.
    Department of Chemistry, Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Lindwall, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Hallberg, H.
    Division of Solid Mechanics, Lund University, Lund, Sweden.
    Fisk, M.
    Division of Solid Mechanics, Lund University, Lund, Sweden. Materials Science and Applied Mathematics, Malmö University, Malmö, Sweden.
    Transient nucleation in selective laser melting of Zr-based bulk metallic glass2020Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 195, artikkel-id 108958Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The crystallization rate during selective laser melting (SLM) of bulk metallic glasses (BMG) is a critical factor in maintaining the material's amorphous structure. To increase the understanding of the interplay between the SLM process and the crystallization behavior of BMGs, a numerical model based on the classical nucleation theory has been developed that accounts for the rapid temperature changes associated with SLM. The model is applied to SLM of a Zr-based BMG and it is shown that the transient effects, accounted for by the model, reduce the nucleation rate by up to 15 orders of magnitude below the steady-state nucleation rate on cooling, resulting in less nuclei during the build process. The capability of the proposed modelling approach is demonstrated by comparing the resulting crystalline volume fraction to experimental findings. The agreement between model predictions and the experimental results clearly suggests that transient nucleation effects must be accounted for when considering the crystallization rate during SLM processing of BMGs.

  • 10.
    Herrera, Martha
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Sirviö, Juho A.
    Fibre and Particle Engineering Laboratory, University of Oulu.
    Mathew, Aji P.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Environmental friendly and sustainable gas barrier on porous materials: Nanocellulose coatings prepared using spin- and dip-coating2016Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 93, s. 19-25Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, environmental friendly and sustainable coatings of nanocellulose (NC) were prepared using spin- and dip-coating methods, on two different porous cellulose substrates. Microscopy studies showed that spin-coating technique was suitable for the substrate with smaller pore size, while the dip-coating was suitable for the substrate with larger pore size. The coating thickness ranged from some hundreds of nanometers for the spin-coated layers, to some micrometers for the dip-coated ones. It was also seen that the contact angle increased with the coating thickness and roughness. NC coating resulted in low oxygen permeability (between 0.12 and 24 mL ∗ μm/(m2 ∗ 24 h ∗ kPa)) at 23% RH, but at 50% RH the oxygen permeability was too high to be measured, except for the dip-coated sample with 23 μm thickness. Also, it was seen that eight month storing reduced the barrier properties of the coatings when compared with fresh materials. These results indicate that NC coatings have a great potential as sustainable alternative coating on paperboard.

  • 11.
    Herrera, Natalia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Roch, Hendrik
    Department Bio-based Plastics, Fraunhofer Institute for Environmental, Safety, and Energy Technology UMSICHT, Osterfelder Straße 3, 46047 Oberhausen.
    Salaberria, Aiser M.
    Biorefinery Processes Research Group, Department of Chemical and Environmental Engineering, Polytechnic School, University of the Basque Country.
    Pino, Maxomilano A.
    Macromolecules group, Faculty of Chemistry, Pontifical Catholic University of Chile, Avenida Libertador Bernardo O Higgins 340, Santiago.
    Labidi, Jalel
    Biorefinery Processes Research Group, Department of Chemical and Environmental Engineering, Polytechnic School, University of the Basque Country.
    Fernandes, Susana M.
    Biorefinery Processes Research Group, Department of Chemical and Environmental Engineering, Polytechnic School, University of the Basque Country.
    Radic, Deodato
    Macromolecules group, Faculty of Chemistry, Pontifical Catholic University of Chile, Avenida Libertador Bernardo O Higgins 340, Santiago.
    Lieva, Angel
    Macromolecules group, Faculty of Chemistry, Pontifical Catholic University of Chile, Avenida Libertador Bernardo O Higgins 340, Santiago.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Functionalized blown films of plasticized polylactic acid/chitin nanocomposite: Preparation and characterization2016Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 92, s. 846-852Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Bionanocomposite films prepared with melt compounding and film blowing were evaluated for packaging applications. The nanocomposite masterbatch with 75 wt% polylactic acid (PLA), 5 wt% chitin nanocrystals (ChNCs) and 20 wt% glycerol triacetate plasticizer (GTA) was melt compounded and then diluted to 1 wt% ChNCs with PLA and polybutylene adipate-co-terephthalate (PBAT) prior to film blowing. The morphological, mechanical, optical, thermal and barrier properties of the blown nanocomposite films were studied and compared with the reference material without ChNCs. The addition of 1 wt% ChNCs increased the tear strength by 175% and the puncture strength by 300%. Additionally, the small amount of chitin nanocrystals affected the glass transition temperature (Tg), which increased 4 °C compared with the reference material and slightly enhanced the films degree of crystallinity. The chitin nanocomposite also had lower fungal activity and lower electrostatic attraction between the film surfaces; leading to easy opening of the plastic bags. The barrier and optical properties as well as the thermal degradation of the films were not significantly influenced by the addition of chitin nanocrystals.

  • 12. Jomehzadeh, E.
    et al.
    Saidi, A.R.
    Atashipour, Seyed Rasoul
    An analytical approach for stress analysis of functionally graded annular sector plates2009Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 30, nr 9, s. 3679-3685Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, an exact analytical approach is used for bending analysis of functionally graded (FG) annular sector plates. The governing equilibrium equations are obtained based on the first order shear deformation plate theory. Introducing an analytical method, the coupled governing equilibrium equations are replaced by independent equations in term of transverse deflection and a new function. Using an equivalent flexural rigidity, the solutions of FG annular sector plates can be easily extracted from equation of homogeneous annular plates. Also, it is shown that the present method can provide accurate results. Finally, the effects of power of functionally graded material (FGM), plate thickness, inner to outer radius ratio and boundary conditions on the deflection and stresses of a functionally graded annular sector plate are studied.

  • 13.
    Karimi, Paria
    et al.
    Department of Engineering Science, University West, Trollhättan, Sweden.
    Sadeghi, Esmaeil
    Department of Engineering Science, University West, Trollhättan, Sweden.
    Åkerfeldt, Pia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ålgårdh, Joakim
    Department of Engineering Science, University West, Trollhättan, Sweden. Powder Materials & Additive Manufacturing, Swerea KIMAB AB, Kista, Sweden.
    Andersson, Joel
    Department of Engineering Science, University West, Trollhättan, Sweden.
    Influence of successive thermal cycling on microstructure evolution of EBM-manufactured alloy 718 in track-by-track and layer-by-layer design2018Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 160, s. 427-441Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Successive thermal cycling (STC) during multi-track and multi-layer manufacturing of Alloy 718 using electron beam melting (EBM) process leads to a microstructure with a high degree of complexity. In the present study, a detailed microstructural study of EBM-manufactured Alloy 718 was conducted by producing samples in shapes from one single track and single wall to 3D samples with maximum 10 longitudinal tracks and 50 vertical layers. The relationship between STC, solidification microstructure, interdendritic segregation, phase precipitation (MC, δ-phase), and hardness was investigated. Cooling rates (liquid-to-solid and solid-to-solid state) was estimated by measuring primary dendrite arm spacing (PDAS) and showed an increased cooling rate at the bottom compared to the top of the multi-layer samples. Thus, microstructure gradient was identified along the build direction. Moreover, extensive formation of solidification micro-constituents including MC-type carbides, induced by micro-segregation, was observed in all the samples. The electron backscatter diffraction (EBSD) technique showed a high textured structure in 〈001〉 direction with a few grains misoriented at the surface of all samples. Finer microstructure and possibility of more γ″ phase precipitation at the bottom of the samples resulted in slightly higher (~11%) hardness values compared to top of the samples.

  • 14.
    Larker, Richard
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Anevik, K.
    Luleå tekniska universitet.
    Kristiansson, S.
    Loberg, Bengt
    Luleå tekniska universitet.
    Heat treatments of the low-expansion superalloy Incoloy 909 for application in ceramic/metal joints and in metal matrix composites1992Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 13, nr 1, s. 11-15Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Increasing efficiency demands on gas turbines have promoted the development of superalloys with low thermal expansion up to intermediate temperatures, to reduce the need of cooling for preservation of efficient clearances between rotating and stationary parts. These materials are also of prime interest for joins to engineering ceramics such as silicon nitride and silicon carbide, and as a matrix with W or SiC fibres in metal matrix composites (MMC). The paper deals with the thermomechanical and microstructural stability of Incology 909 during possible joining and densification treatments. Thermal expansion behaviour and joining/densification temperatures suitable for retaining the desired structure of the superalloy are presented.

  • 15.
    Malmelöv, Andreas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Hållfasthetslära.
    Hassila, Carl-Johan
    Applied Materials Science, Uppsala University, SE-751 03 Uppsala, Sweden.
    Fisk, Martin
    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.
    Wiklund, Urban
    Applied Materials Science, Uppsala University, SE-751 03 Uppsala, Sweden.
    Lundbäck, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Hållfasthetslära.
    Numerical modeling and synchrotron diffraction measurements of residual stresses in laser powder bed fusion manufactured alloy 6252022Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 216, artikkel-id 110548Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Residual stresses in metal additive manufactured components are a well-known problem. It causes distortion of the samples when removing them from the build plate, as well as acting detrimental with regard to fatigue. The understanding of how residual stresses in a printed sample are affected by process parameters is crucial to allow manufacturers to tune their process parameters, or the design of their component, to limit the negative influence of residual stresses. In this paper, residual stresses in additive manufactured samples are simulated using a thermo-mechanical finite element model. The elasto-plastic behavior of the material is described by a mechanism-based material model that accounts for microstructural and relaxation effects. The heat source in the finite element model is calibrated by fitting the model to experimental data. The residual stress field from the finite element model is compared with experimental results attained from synchrotron X-ray diffraction measurements. The results from the model and measurement give the same trend in the residual stress field. In addition, it is shown that there is no significant difference in trend and magnitude of the resulting residual stresses for an alternation in laser power and scanning speed.

  • 16.
    Müller, Michael
    et al.
    Department of Additive Manufacturing and Printing, Fraunhofer Institute for Material and Beam Technology, Winterbergstraße 28, 01277 Dresden, Germany; Institute of Materials Science, Faculty of Mechanical Science and Engineering, TUD Dresden University of Technology, Helmholtzstr. 7, 01069 Dresden, Germany.
    Enghardt, Stefan
    Institute of Materials Science, Faculty of Mechanical Science and Engineering, TUD Dresden University of Technology, Helmholtzstr. 7, 01069 Dresden, Germany.
    Kuczyk, Martin
    Department of Additive Manufacturing and Printing, Fraunhofer Institute for Material and Beam Technology, Winterbergstraße 28, 01277 Dresden, Germany; Institute of Materials Science, Faculty of Mechanical Science and Engineering, TUD Dresden University of Technology, Helmholtzstr. 7, 01069 Dresden, Germany.
    Riede, Mirko
    Department of Additive Manufacturing and Printing, Fraunhofer Institute for Material and Beam Technology, Winterbergstraße 28, 01277 Dresden, Germany.
    López, Elena
    Department of Additive Manufacturing and Printing, Fraunhofer Institute for Material and Beam Technology, Winterbergstraße 28, 01277 Dresden, Germany.
    Brueckner, 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, Winterbergstraße 28, 01277 Dresden, Germany.
    Marquardt, Axel
    Department of Additive Manufacturing and Printing, Fraunhofer Institute for Material and Beam Technology, Winterbergstraße 28, 01277 Dresden, Germany; Institute of Materials Science, Faculty of Mechanical Science and Engineering, TUD Dresden University of Technology, Helmholtzstr. 7, 01069 Dresden, Germany.
    Leyens, Christoph
    Department of Additive Manufacturing and Printing, Fraunhofer Institute for Material and Beam Technology, Winterbergstraße 28, 01277 Dresden, Germany; Institute of Materials Science, Faculty of Mechanical Science and Engineering, TUD Dresden University of Technology, Helmholtzstr. 7, 01069 Dresden, Germany.
    Microstructure of NiAl-Ta-Cr in situ alloyed by induction-assisted laser-based directed energy deposition2024Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 238, artikkel-id 112667Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The development of new high temperature materials for coatings as well as structural components is an important topic to contribute to a higher efficiency and sustainability of e.g. gas turbine engines. One promising new class of high temperature materials are NiAl-based alloys. Within this study, the microstructure and microhardness of NiAl-Ta-Cr alloys with varying Cr and Ta content were investigated. Graded specimens were fabricated by laser-based directed energy deposition utilizing an in situ alloying approach by mixing elemental Ta and Cr as well as pre-alloyed NiAl powder. Thermodynamic calculations were performed to design the alloy compositions beforehand. Inductive preheating of the substrate was used to counter the challenge of cracking due to the high brittleness. The results show that the cracking decreases with increasing preheating temperature. However, even at 700 °C, the cracking cannot be fully eliminated. Scanning electron microscopy, X-ray diffraction and electron backscatter diffraction revealed the formation of the phases B2-NiAl, A2-Cr and C14-NiAlTa within NiAl-Ta and NiAl-Cr alloys. For NiAl-Ta-Cr compositions, deviations regarding the phase formation between calculation and experiment were observed. Maximum hardness values were achieved within the NiAl-Ta and NiAl-Ta-Cr systems for the eutectic compositions at 14 at.-% Ta with maximum values above 900 HV0.1.

    Fulltekst (pdf)
    fulltext
  • 17.
    Pakharenko, Viktoriya
    et al.
    Centre for Biocomposite and Biomaterials Processing, Graduate Department of Forestry, John H. Daniels Faculty of Architecture, Landscape and Design, University of Toronto, Toronto, ON M5S3E8, Canada.
    Sameni, Javad
    Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ON M5S3G8, Canada.
    Konar, Samir
    Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ON M5S3G8, Canada.
    Pervaiz, Muhammad
    Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ON M5S3G8, Canada.
    Yang, Weimin
    School of Mechanical and Industrial Engineering, Beijing University of Chemical Technology, 100029, China.
    Tjong, Jimi
    Centre for Biocomposite and Biomaterials Processing, Graduate Department of Forestry, John H. Daniels Faculty of Architecture, Landscape and Design, University of Toronto, Toronto, ON M5S3E8, Canada.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ON M5S3G8, Canada.
    Sain, Mohini
    Centre for Biocomposite and Biomaterials Processing, Graduate Department of Forestry, John H. Daniels Faculty of Architecture, Landscape and Design, University of Toronto, Toronto, ON M5S3E8, Canada. Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ON M5S3G8, Canada .
    Cellulose nanofiber thin-films as transparent and durable flexible substrates for electronic devices2021Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 197, artikkel-id 109274Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work reports for the first time an exceptionally high thermal stability of cellulosic nanofibers films at 190 °C after a 5 h exposure, a threshold required for their design and manufacturing in flexible electronic devices. A long-term durability validation of a flexible cellulose nanofiber over a period of 10 years exposure under ambient condition validated their life-span over a long period of operating condition. Arresting quinoid oxidative reactions pathways and thermal degradation of lignin or lignin-less cellulose are demonstrated to be two fundamental routes to enhance thermal processing of cellulose nanofiber substrates and to achieve long service life of energy devices made from them. One of the main highlights of this work is the first time validation of a long operating service life for a light-emitting device made from a cellulose nanofibers substrate, while continuously illuminating the fabricated prototype under ambient condition for an equivalent of 10 years. The unique durability of this flexible substrate will have potential applications in flexible lighting, energy and sensing devices. © 2020 The Authors

  • 18.
    Parareda, Sergi
    et al.
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, 08243 Manresa, Spain; CIEFMA – Department of Materials Science and Engineering, EEBE, Universitat Politècnica de Catalunya-BarcelonaTech, 08019 Barcelona, Spain.
    Casellas, Daniel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, 08243 Manresa, Spain.
    Mares, Marc
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, 08243 Manresa, Spain.
    Mateo, Antonio
    CIEFMA – Department of Materials Science and Engineering, EEBE, Universitat Politècnica de Catalunya-BarcelonaTech, 08019 Barcelona, Spain.
    A damage-based uniaxial fatigue life prediction method for metallic materials2023Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 231, artikkel-id 112056Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Determining the fatigue behaviour of metallic materials using standardised testing methods is costly and time-consuming. Therefore, several methods have been proposed to shorten the testing time and improve the fatigue optimisation of materials and components. This work presents a new fatigue testing method based on fatigue damage monitoring that allows determining the fatigue resistance in a short time and with few specimens. The presented method, named as the stiffness method, monitors the inelastic strains as an indicator of fatigue damage evolution. Strain measurements were carried out by digital image correlation techniques and showed to effectively follow damage evolution during fatigue tests. Results are convincing and more evident to obtain and discuss than other monitoring techniques, like temperature dissipation. In addition, the method overcomes the main limitations of the existing fast testing methods by avoiding the utilisation of complex apparatus, like infrared cameras or acoustic emission sensors. The approach has been validated in ten different metallic materials, as titanium and aluminium alloys, carbon steels, and stainless steels. The estimated fatigue limit was compared with values obtained following standardised tests, showing excellent agreement. Results allow pointing out the stiffness method as an efficient and effective tool for rapidly determining the fatigue behaviour of metallic materials.

    Fulltekst (pdf)
    fulltext
  • 19. Rezaei, Fateme
    et al.
    Ynus, R.
    Ibrahim, N.A.
    Effect of fiber length on thermomechanical properties of short carbon fiberreinforced polypropylene composites2009Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 30, s. 260-263Artikkel i tidsskrift (Fagfellevurdert)
  • 20.
    Saeidi, Kamran
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Neikter, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Olsen, J.
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Shen, Zhijian James
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    316L stainless steel designed to withstand intermediate temperature2017Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 135, s. 1-8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Austenitic stainless steel 316L was fabricated for withstanding elevated temperature by selective laser melting (SLM). Tensile tests at 800 °C were carried out on laser melted 316L with two different strain rates of 0.05 S− 1 and 0.25 S− 1. The laser melted 316L showed tensile strength of approximately 400 MPa at 800 °C, which was superior to conventional 316L. Analysis of fracture surface showed that the 316L fractured in mixed mode, ductile and brittle fracture, with an elongation of 18% at 800 °C. In order to understand the mechanical response, laser melted 316L was thermally treated at 800 °C for microstructure and phase stability. X-ray diffraction (XRD) and Electron back scattered diffraction (EBSD) of 316L treated at 800 °C disclosed a textured material with single austenitic phase. SEM and EBSD showed that the characteristic and inherent microstructure of laser melted 316L, consisting of elongated grains with high angle grain boundaries containing subgrains with a smaller misorientation, remained similar to as-built SLM 316L during hot tensile test at 800 °C. The stable austenite phase and its stable hierarchical microstructure at 800 °C led to the superior mechanical response of laser melted 316L.

  • 21.
    Samarjy, Ramiz Saeed Matti
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. University of Mosul, College of Engineering, Department of Mechanical Engineering.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Using laser cutting as a source of molten droplets for additive manufacturing: A new recycling technique2017Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 125, s. 76-84Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new variant of additive manufacturing is proposed which involves transferring molten droplets via a laser beam to a substrate. The droplets are generated by laser remote fusion cutting of a supply sheet that could be a waste material, for recycling purposes. The laser-induced ablation pressure at the cutting front continuously drives melt downwards below the supply sheet in the form of a liquid column. Droplets separate from the column and solidify as a track on a substrate below. The droplets, surrounded by vapour, had in this case an average diameter of 500 μm and a speed of 2 m/s, with deviations up to 50%. Sound clad tracks were generated on steel and aluminium substrates. In the case of a copper substrate discontinuous clad tracks were produced as a result of poor wetting. The droplet jet had a small divergence of about 5°, which is suitable for controlled deposition. The transmitted part of the laser beam interacted with the clad track but did not affect the process result. High speed imaging was found to be a suitable tool for qualitative and quantitative analysis of the technique.

  • 22.
    Samarjy, Ramiz Saeed Matti
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander F.H.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Laser-induced boiling and melt transfer from a metal edge2017Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new technique for additive manufacturing was recently presented, by depositing droplets as a continuous track on a substrate, where the droplets were ejected from laser remote fusion cutting of a metal sheet. For the here presented approach, the droplets are instead ejected from the sheet edge, termed the machining mode, which is compared to cutting. Here the transmitted part of the laser beam does not hit and interact with the deposited track because of lateral dislocation. High speed imaging has shown that laser-induced boiling, which drives the melt downwards, causes asymmetric conditions in the machining mode by lateral pushing of the generated drop jet under the sheet, where the melt even can attach. Compared to machining, the cutting mode keeps less deviation of the drop trajectories, higher precision and a smoother surface finish. It was demonstrated that the edge conditions after machining are sufficient to repeat the process. This enables additional technique opportunities, including recycling of a whole sheet of waste metal. By the aid of high speed imaging from two different perspectives, the melt flow behaviour, the drop jet precision as well as process trends with respect to parameters, drop ejection and deposition were studied.

  • 23.
    Somberg, Julian
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Gonçalves, Gil
    Centre for Mechanical Technology and Automation (TEMA), University of Aveiro, Portugal.
    Sánchez, María Soria
    Institute of Material Science of Barcelona, Spain.
    Emami, Nazanin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Chemically expanded graphite-based ultra-high molecular weight polyethylene nanocomposites with enhanced mechanical properties2022Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 224, artikkel-id 111304Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Chemically expanded graphite (CEG) has recently been identified as promising reinforcement for polymer composites with the ability for commercial up-scaling. In this work, silane and polydopamine functionalized CEG were successfully synthesized and employed to prepare ultra-high molecular weight polyethylene (UHMWPE) nanocomposites with an enhanced interfacial compatibility. Characterisation of the functionalized CEG indicated a significant oxygen reduction, which gave rise to a restoration of the graphitic structure. The polydopamine functionalized CEG showed an enhanced exfoliation and dispersion in organic solvents and the polymer matrix with respect to the non-modified CEG. The silane functionalized CEG provided a higher affinity towards the matrix with polymer chains covering the CEG sheets on the fracture surfaces. The addition of functionalized CEG enhanced the mechanical properties of the UHMWPE matrix with an increase in micro-hardness of up to 25% and storage modulus of up to 58%. Furthermore, the hydrophobicity of the composites was significantly enhanced with an increase in water contact angle from 98.6° for the pure polymer to 119° for 5 wt% silane functionalized CEG. Preliminary wear experiments indicated the potential of the composites for tribological applications with a decrease in wear rate of up to 99% under water lubricated conditions.

  • 24.
    Thomas, Reny Thankam
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Del Río de Vicente, Jóse Ignacio
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Zhang, Kaitao
    Fibre and Particle Engineering Research Unit, University of Oulu, P.O. Box 4300, FI-90014 Oulu, Finland.
    Karzarjeddi, Mohammad
    Fibre and Particle Engineering Research Unit, University of Oulu, P.O. Box 4300, FI-90014 Oulu, Finland.
    Liimatainen, Henrikki
    Fibre and Particle Engineering Research Unit, University of Oulu, P.O. Box 4300, FI-90014 Oulu, Finland.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Size exclusion and affinity-based removal of nanoparticles with electrospun cellulose acetate membranes infused with functionalized cellulose nanocrystals2022Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 217, artikkel-id 110654Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Membrane filtration and affinity-based adsorption are the two most used strategies in separation technologies. Here, µm-thick multifunctional and sustainable composite membranes of electrospun cellulose acetate (CA) infused with functionalized, anionic, and cationic cellulose nanocrystals (CNCs) with enhanced wettability, tensile strength, and excellent retention capacities were designed. CNCs could uniformly impregnate into the three-dimensional CA network to effectively improve its properties. The impregnation of cationic CNCs at 0.5 wt% concentration drastically increased the tensile strength (1669%) while maintaining high permeation flux of 9400 Lm-2h-1 which is remarkable with cellulose modified electrospun membranes. The membranes infused with anionic CNCs exhibited a particle retention efficiency of 96% for 500 nm and 77% for 100 nm latex beads whilst the cationic CNC membranes exhibited a combined particle retention strategy using selectivity and size exclusion with a retention of >81% with 100 nm latex beads and 80% with ∌50 nm silver nanoparticles. We envision that the developed multifunctional membranes can be utilized for affinity-based and size-exclusion filtration to selectively trap bacteria or substances of biological significance.

  • 25.
    Volpp, Joerg
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Elongated cavities during keyhole laser welding2021Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 206, s. 109835-, artikkel-id 109835Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During laser beam deep penetration welding, the characteristic keyhole occurs that enables efficient energy absorption due to multiple reflections. Since this welding mode usually shows high dynamic behaviour, often a high amount of weld imperfections like spattering or porosity occur. Elongated keyholes during buttonhole, a.k.a donut welding, have shown the possibility to create smooth welding tracks when controlled variations of energy input were induced, e.g. beam oscillation. It was observed that the elongated keyholes can maintain themselves due to the balancing effects of the melt pool surface tension, which can form a catenoid shape that does not require any additional forces to be stable. Basic theoretical descriptions of the catenoid shape keyholes were derived. However, the complex system requires a more detailed investigation of the effect of the metal plume and the melt flows in order to explain the opening and maintenance effects of the elongated keyholes.

    Therefore, this work examined different modes of elongated keyholes, comparing traditional non-oscillating keyholes to keyholes formed by different beam scanning strategies. Analysis was made mainly by observations with high-speed-imaging and theoretical considerations to explain the phenomena of elongated keyholes. The observations showed that extended keyholes are not necessarily related to a reduced occurrence of imperfections and not either to the formation of perfect catenoid shapes. The keyhole front is deformed where the laser beam impacts and the rear wall is impacted where the vapour plume strikes. The opening of an elongated keyhole is likely related to the keyhole vapour plume that pushes the keyhole rear wall rearwards, while the non-affected rear wall parts do not collapse the keyhole due to the balancing nature of the second curvature of the rear wall.

  • 26.
    Zhou, Xiaojian
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Sethi, Jatin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Geng, Shiyu
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Berglund, Linn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Frisk, Nikolina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Aitomäki, Yvonne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Sain, Mohini
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Dispersion and reinforcing effect of carrot nanofibers on biopolyurethane foams2016Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 110, s. 526-531Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, carrot nanofibers (CNF) were used to enhance the performance of biobased castor oil polyol polyurethane nanocomposite foams. A method of dispersing CNF in the polyol was developed and the foam characteristics and CNF reinforcing effect were studied. Co-solvent-assisted mixing resulted in well-dispersed CNF in the polyol, and foams with 0.25, 0.5 and 1 phr CNF content were prepared. The reinforced nanocomposite foams displayed a narrow cell size distribution and the compressive strength and modulus were significantly elevated and the best compressive strength and modulus were reached with 0.5 phr CNF. Similarly, the modulus of the solid material was also significantly increased based on theoretical calculations. When comparing the foam performance, compressive strength and stiffness as a function of the density, the nanocomposite foams performs as commercial rigid PU foam with a closed cell structure. These results are very promising and we believe that these foams are excellent core materials for lightweight sandwich composites.

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