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  • 1.
    Andersons, J.
    et al.
    University of Latvia.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hojo, M.
    Ochiai, S.
    Kyoto University.
    Fibre fragment distribution in a single-fibre composite tension test2001Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 32, nr 4, s. 323-332Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Single fibre fragmentation tests are performed for brittle fibres with Weibull strength distribution and different surface treatments. The fragmentation process is modelled and closed-form expressions for break spacing distribution are obtained. The model accounts for the effect of finite fibre length on the initial fragmentation as well as for break interaction on the advanced fragmentation stage. It is assumed that the exclusion zone due to fibre-matrix interface failure and stress recovery in the fibre is linearly dependent on the applied load. This assumption is validated experimentally. The derived theoretical average fragment length dependence on applied load is used to determine the fibre strength distribution parameters and the effective interfacial shear stress for carbon/epoxy single fibre composites with different fibre surface treatment and for glass/vinylester single fibre composite. Fragment length distribution is predicted for several load levels. Predictions are in good agreement with experimental data

  • 2.
    Basso, Margherita
    et al.
    Politecnico di Milano, Department of Chemistry, Materials and Chemical Engineering “G. Natta”, Milan, Italy. Research Hub by Electrolux Professional, Pordenone, Italy.
    Piselli, Agnese
    Research Hub by Electrolux Professional, Pordenone, Italy. Politecnico di Milano, Department of Design, Milan, Italy.
    Simonato, Michele
    Research Hub by Electrolux Professional, Pordenone, Italy.
    Furlanetto, Riccardo
    Research Hub by Electrolux Professional, Pordenone, Italy.
    Pupure, Liva
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    De Nardo, Luigi
    Politecnico di Milano, Department of Design, Milan. INSTM—National Interuniversity Consortium of Materials Science and Technology, Firenze, Italy.
    Effect of food chemicals and temperature on mechanical reliability of bio-based glass fibers reinforced polyamide2019Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 157, s. 140-149Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents an experimental study to assess the effects of food chemicals and temperature on the mechanical performance of glass fiber reinforced bio-based polyamide. The diffusion of food chemicals was mainly driven by thermal energy, following Arrhenius law in all tested environments. Degradation of mechanical properties and decrease in reliability were assessed, due to the plasticization of polymer matrix. Secondary but not negligible effect on flexural strength degradation is given by the different chemical interaction between polymeric chains and molecules of food chemicals. Colour change was measured and resulted to be positively correlated to diffusion.

  • 3.
    Basso, Margherita
    et al.
    Politecnico di Milano, Department of Chemistry, Materials and Chemical Engineering, Milan, Italy;The Research Hub by Electrolux Professional, Pordenone, Italy.
    Pupure, Liva
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Simonato, Michele
    The Research Hub by Electrolux Professional, Pordenone, Italy.
    Furlanetto, Riccardo
    The Research Hub by Electrolux Professional, Pordenone, Italy.
    De Nardo, Luigi
    Politecnico di Milano, Department of Chemistry, Materials and Chemical Engineering, Milan, Italy;INSTM—National Interuniversity Consortium of Materials Science and Technology, Firenze, Italy.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Nonlinear creep behaviour of glass fiber reinforced polypropylene: Impact of aging on stiffness degradation2019Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 163, s. 702-709Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nonlinear creep behavior of one commercial short glass fiber reinforced polypropylene was investigated using tensile creep tests and stiffness degradation measurements. The impact of thermal aging and following quenching was evaluated on the latter mechanical property. Experimental results were modeled applying nonlinear viscoelastic model used by Pupure et al. (2013) and developed by Lou and Schapery [1,2]. Results showed that this model can describe nonlinear behavior of short glass fiber reinforced polymer composites, where microdamage is given by debonding of fiber-matrix interfaces already at low strains, where cracks propagate and lead to tensile creep fracture.

  • 4.
    Byström, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Influence of the inclusions distribution on the effective properties of heterogeneous media2003Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 34, nr 7, s. 587-592Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we investigate the effective conductivity of composite materials by means of the homogenization method. We concentrate on composites with circular or elliptic cylindrical inclusions. In particular, we are interested in the effect of the distribution of the cylinders in the continuous material on the effective properties. We compare rectangular and hexagonal distributions with random distributions for different volume fractions of the inclusions. We also study the effect of the number of inclusions in each periodic cell for the random structure as well as shape influence of the elliptical inclusions.

  • 5.
    Byström, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Helsing, Johan
    Kungliga tekniska högskolan, KTH.
    Meidell, Annette
    Narvik University College, 8505 Narvik, Norway.
    Some computational aspects of iterated structures2001Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 32, nr 6, s. 485-490Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We consider some computational aspects of effective properties for some multi-scale structures. In particular, we discuss iterated square honeycombs and another type of square honeycombs containing up to 4000 small discs randomly distributed inside each square. We present some numerical methods for estimating the effective conductivity with good control of the accuracy.

  • 6.
    Byström, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Jekabsons, Normunds
    Luleå tekniska universitet.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    An evaluation of different models for prediction of elastic properties of woven composites2000Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 31, nr 1, s. 7-20Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A critical analysis of two simple and convenient analytical models for calculation of elastic properties of woven fabric composites is performed. Predictions of these models are compared with results obtained using the method of reiterated homogenization and with experimental data for plain weave glass fiber and carbon fiber polyester composites. Three different scales are identified in the analysis. The first scale predictions, which are the tow properties (obtained by applying Hashin's concentric cylinder model, the Halpin-Tsai expressions or mathematical homogenization technique), are the most critical because they form the input information for woven composite modeling. It appears that the uncertainty in this information causes larger differences in predictions than the deviations between models of different degree of accuracy. This fact sets limits on the required accuracy of the models. Model comparisons reveal that the woven compoiste model based on isostrain assumption in the compoiste plane and isostress assumption for out-of-plane components is in very good agreement with both experimental data and the reiterated homogenization method, whereas the modified mosaic parallel model fails to describe composites with large interlaced regions.

  • 7.
    Carlson, Tony
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Asp, Leif
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Structural carbon fibre composite/PET capacitors: Effects of dielectric separator thickness2013Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 49, s. 16-21Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents an approach towards realising novel multifunctional polymer composites with combined structural and electric energy storing ability. A series of structural capacitors were made using three thicknesses of DuPont Mylar A thermoplastic PET as a dielectric separator employing carbon fibre/epoxy pre-pregs as structural electrodes. Plasma treatment was used as a route for improved epoxy/PET adhesion. The manufactured materials were mechanically and electrically tested to evaluate their multifunctional efficiency.The multifunctional materials developed show good potential for replacing steel, aluminium and other materials with lower specific mechanical properties but do not match the high specific mechanical and electrical performance of monofunctional composites and capacitors.

  • 8.
    Floruț, Sorin-Codruț
    et al.
    Politechnica University of Timisoara.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. NORUT, Department of Infrastructure Structures and Materials.
    Popescu, Cosmin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Stoian, Valeriu
    Tests on reinforced concrete slabs with cut-out openings strengthened with fibre-reinforced polymers2014Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 66, s. 484-493Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents the results of experimental investigations on reinforced concrete slabs strengthened using fibre-reinforced polymers (FRP). Eight tests were carried out on four two-way slabs, with and without cut-out openings. Investigations on slabs with cut-outs revealed that the FRP can be placed only around the edges of the cut-out when retrofitting the slabs whereas, in the situation of inserting cut-outs combined with increased demands of capacity, it is necessary to apply FRP components on most of the soffit of the slab. The proposed strengthening system enabled the load and deflection capacities of the FRP-strengthened slabs, in relation to their un-strengthened reference slabs, to be enhanced by up to 121% and 57% for slabs with and without cut-outs respectively.

  • 9.
    Gaff, Milan
    et al.
    Czech University of Life Sciences Prague (CULS).
    Babiak, Marián
    Czech University of Life Sciences Prague (CULS).
    Kačík, František
    Czech University of Life Sciences Prague (CULS), Technical University in Zvolen.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Turčan, Marek
    Czech University of Life Sciences Prague (CULS).
    Hanzlíka, Peter
    Czech University of Life Sciences Prague (CULS).
    Vondrová, Veronika
    Czech University of Life Sciences Prague (CULS).
    Plasticity properties of thermally modified timber in bending: the effect of chemical changes during modification of European oak and Norway spruce.2019Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 165, s. 613-625Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The plasticity of thermally modified European oak (Quercus robur L.) and f thermally modified Norway spruce (Picea abies Karst. (L.)) timber was evaluated in bending, and the plastic properties were related to the changes in chemical composition of the wood after modification. The objective was to gain new knowledge about the properties of materials in the plastic region of the force-deformation diagram in bending. A new software was developed (MATESS) and used to identify important characteristics of the material. This software eliminates shortcomings in current standards, such as simplifications in the evaluation of data when sufficiently sensitive measuring equipment is not available. The characteristics studied were: modulus of rupture (MOR), plastic potential (PP) chord modulus (CHM), the moduli of plasticity (EE), and the moduli of plasticity (EMV, EP). Extractives, lignin, cellulose, holocellulose, and hemicelluloses were analysed chemically to reveal the patterns that occur during the loading of the specimens. Thermal modification has different effects on the mechanical properties of oak and spruce, especially on CHM, EMV and EP, due to their different contents and structures of their chemical components. A strong correlation (r > 0.90) between hemicellulose content and MOR and Pp values was found for both species. The coefficients of determination indicated a very low dependence (r2 < 0.1) of MOR, PP, CHM, EE, EMV and EP, on the average density.

  • 10. Hejll, Arvid
    et al.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Motavalli, Masoud
    Technical University of Denmark.
    Large scale hybrid FRP composite girders for use in bridge structures: theory, test and field application2005Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 36, nr 8, s. 573-585Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents the manufacturing process and testing of large scale hybrid composite girders. The evaluation of the girders was a part of the European funded ASSET project. The bridge project, started in 1998 and finished in the autumn of 2002. The ASSET project has in brief covered the design, manufacture and construction of a fully polymer composite traffic bridge. The longitudinal girders are the most important part for the load carrying system of the bridge. Different types of girders were discussed, i.e. steel, concrete or FRP girders. Due to the advantages of FRP girders, for example; light weight, easy installation, superb durability and less maintenance compared to traditional materials it was decided to use FRP in the girders. However, before this could be carried out, tests were needed to verify theoretical calculations. Also a FE-analysis has been carried out, and this analysis is compared with an engineering analytical solution and tests. Both the numerical and the analytical theory correspond quite well with obtained test results.

  • 11.
    Hosseini-Hashemi, Sh.
    et al.
    School of Mechanical Engineering, Iran University of Science and Technology, Narmak, Islamic Azad University, Tehran South Campus, Islamic Azad University, Hamedan University of Technology, School of Mechanical Engineering, Iran University of Science and Technology, Tehran.
    Salehipour, H.
    School of Mechanical Engineering, Iran University of Science and Technology, Narmak.
    Atashipour, Seyed Rasoul
    School of Mechanical Engineering, Iran University of Science and Technology, Narmak.
    Sburlati, Roberta
    Department of Civil, Chemical and Environmental Engineering, Genoa University.
    On the exact in-plane and out-of-plane free vibration analysis of thick functionally graded rectangular plates: Explicit 3-D elasticity solutions2013Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 46, s. 108-115Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper exact closed-form solutions of 3-D elasticity theory are presented to study both in-plane and out-of-plane free vibrations for thick functionally graded simply supported rectangular plates. The solution procedure of the transverse vibration utilizes Levinson’s representation form to describe the displacement; in this way, the 3-D elasto-dynamic equations are written in terms of some suitable independent functions satisfying ordinary differential equations. A similar procedure is presented for in-plane vibration by introducing an appropriate displacement field. In each case, the obtained ordinary differential equations are analytically solved and boundary conditions are satisfied. The proposed solutions are validated by comparing some of the present results with corresponding results known in the literature as well as with 3-D Finite Element Method. Finally, the influence of inhomogeneity on the natural frequencies for a thick functionally graded rectangular plate is discussed.

  • 12.
    Huang, Yongxin
    et al.
    Wind R&D Center, Siemens Energy.
    Talreja, Ramesh
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Statistical analysis of oblique crack evolution in composite laminates2014Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 65, s. 34-39Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A previously developed statistical model for transverse cracking in cross ply laminates is extended to oblique cracking in multidirectional laminates. The oblique cracks are assumed to form in a ply when the local in-plane tensile stress normal to fibers exceeds the transverse strength of the ply. This strength is assumed to have a statistical distribution given by a two-parameter Weibull function. The model is applied to a glass-epoxy [0/602/0/-602]s laminate in which cracking evolution of the four -600 plies in the middle of the laminate is examined. The local stress field in the cracked -600 plies is calculated by a three-dimensional finite element method based on a unit cell construction developed by Li et al. [1]. The measured crack density is found to agree well with that calculated by the statistical model

  • 13.
    Jekabsons, Normunds
    et al.
    Luleå tekniska universitet.
    Byström, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    On the effect of stacked fabric layers on the stiffness of a woven composite2002Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 33, nr 8, s. 619-629Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Most micromechanical models for stiffness prediction of woven composites assume independence of the Q-matrix on the number of fabric layers in the composite. For example, the moduli of single and 10 layer composites are assumed to be equal in the case when all layers have the same in-plane orientation. Although this statement is likely to be true for isotropic materials or even for unidirectional laminated composites, it may not be valid in some cases of woven composites. This paper contains experimental and theoretical investigations of plain weave carbon fiber/polyester composites. Specimens with one single and eight layers of fabrics are tested and observable differences of mechanical properties are obtained. The theoretical part of this article consists of derivation and application of several micromechanical models on these particular composites. The use of those simplified models finally allows us to find the main mechanisms which cause the observed effects.

  • 14.
    Marklund, Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Asp, Leif
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Olsson, Robin
    Swerea SICOMP AB, Mölndal.
    Transverse strength of unidirectional non-crimp: multiscale Modelling2014Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 65, s. 47-56Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A multiscale approach is used to predict transverse tensile and transverse compressive strength of unidirectional non-crimp fabric (NCF) composites. Numerical analysis on fibre/matrix scale is performed to obtain the transverse strength of the fibre bundle to be further used in an analytical mesoscale model to predict the strength of the unidirectional NCF composite. Design of unidirectional layer composites with the same fibres, interface, matrix and volume fractions as in the bundle is suggested as an alternative method for bundle strength determination. Good agreement of both methods for bundle transverse strength determination is demonstrated. The simple analytical model used on mesoscale gives accurate predictions of the tensile transverse strength whereas the compressive strength is underestimated. The necessity of including bundle waviness in models when bidirectional NCF composites are analyzed is demonstrated by FEM stress analysis and by experimental data showing differences in transverse cracking pattern due to bundle waviness.

  • 15. Mattsson, David
    et al.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Methodology for characterization of internal structure parameters governing performance in NCF composites2007Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 38, nr 1, s. 44-57Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mechanical performance of non-crimp fabric composites is very dependent on their internal meso- and micro-structure which is defined by the manufacturing process of the fabric and composite processing conditions. This paper identifies the most important parameters which control mechanical properties of these materials. The identification is based on experimental observations and available theoretical findings. Characteristics of the internal structure of non-crimp fabric composites are analyzed in context of their significance for in-plane elastic and failure properties. Methodology for determination of most typical geometrical parameters of composites using optical observations of cross-sections of manufactured laminates is described. The methodology is applied to characterize cross-ply and quasi-isotropic composite laminates. These results are analyzed and a comparison between the laminates is performed.

  • 16.
    Melk, Latifa
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Emami, Nazanin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Mechanical and thermal performances of UHMWPE blended vitamin E reinforced carbon nanoparticle composites2018Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 146, s. 20-27Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ultrahigh molecular weight polyethylene (UHMWPE) is a known to be the material of choice for bearing components in joint arthroplasty. However, oxidation wear of UHMWPE components is considered to be a major drawback limiting the lifespan of implants. Vitamin E was considered as a promising antioxidant to prevent long-term oxidation and reduce the wear degradation of UHMWPE material. Nevertheless, there are limited results on the improvements of vitamin E on the mechanical and thermal properties of UHMWPE. In this study, we investigated the incorporation of 0.5–3 wt.% carbon nanoparticles: Multiwalled Carbon Nanotubes (MWCNTs), Graphene (GO) and Nanodiamonds (ND) on the mechanical and thermal properties of UHMWPE blended vitamin E (UHMWPE-E). Surface analysis of the composite powders showed well-dispersed carbon nanoparticles within the UHMWPE-E matrix. Thermogravimetric (TGA) and Differential Scanning Calorimetry (DSC) were used to study the thermal behavior of the nanocomposites. It was found that the addition of GO, MWCNTs and ND improved the thermal stability of the nanocomposites compared to neat UHMWPE-E. However, the addition of carbon nanoparticles had no significant effect on the crystallization parameters of the composites. In addition, the incorporation of MWCNT and ND improved significantly the fracture toughness of the composites. The addition of 0.7 wt.% ND and 1 wt.% MWCNT increased the fracture toughness from 5.93 MPa m1/2 for neat UHMWPE-E to 7.38 and 9.19 MPa m1/2 respectively. The enhanced fracture toughness and thermal stability of the nanocomposites could be due to the successful powder processing technique where an optimized mixing and ball milling parameters were used.

  • 17.
    Moreno, Silvia Suñer
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Tipper, Joanne
    Institute of Medical and Biological Engineering, University of Leeds.
    Emami, Nazanin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Ultra High Molecular Weight Polyethylene/Graphene Oxide Nanocomposites: Thermal, Mechanical and Wettability Characterisation2015Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 78, s. 185-191Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Numerous carbon nanostructures have been investigated in the last years due to their excellent mechanical properties. In this work, the effect of the addition of graphene oxide (GO) nanoparticles to UHMWPE and the optimal %wt GO addition were investigated. UHMWPE/GO nanocomposites with different GO wt% contents were prepared and their mechanical, thermal, structural and wettability properties were investigated and compared with virgin UHMWPE. The results showed that the thermal stability, oxidative resistance, mechanical properties and wettability properties of UHMWPE were enhanced due to the addition of GO. UHMWPE/GO materials prepared with up to 0.5 wt% GO exhibited improved characteristics compared to virgin UHMWPE and nanocomposites prepared with higher GO contents.

  • 18. Nordin, Håkan
    et al.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Testing of hybrid FRP composite beams in bending2004Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 35, nr 1, s. 27-33Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents tests where hybrid composite beams have been investigated. The hybrid beam consists of a glass fibre I-beam with carbon fibre strengthened bottom flange and a rectangular concrete block in the compressive zone. The interaction between the concrete and composite beam were obtained in two ways; casting in shear connectors of steel and bonding by epoxy adhesive. As a reference, a beam without concrete in the compressive zone was also tested. The idea of combining carbon, glass and concrete was to utilize the stiffness contribution from the carbon and the compressive strength from the concrete. The glass fibre I-beam would then take up the main part of the shear force. The results from the test showed that a good composite action could be achieved between carbon, glass and concrete. However, it could also be noticed, as expected, that an I-beam is not the ultimate form due to stability problems. In the tests, problems arose due to lateral instability, but this was solved by placing stiffeners manufactured from wood between the flanges of the Fibre Reinforced Polymer beam over the supports. With a few modifications of the hybrid beam it is believed, that it would be possible to create both a technical and economical hybrid profile that benefits from carbon, glass and concrete.

  • 19.
    Pupurs, Andrejs
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Modeling mechanical stress and exfoliation damage in carbon fiber electrodes subjected to cyclic intercalation/deintercalation of lithium ions2014Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 65, s. 69-79Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Gradients in lithium ion concentration distribution in carbon fiber are accompanied by non-uniform fiber swelling leading to development of mechanical stresses. During lithium deintercalation these stresses may lead to initiation and growth of radial cracks in the fiber. The subsequent cycle of intercalation may result in arc-shaped cracks deviating from the tip of the radial cracks. These phenomena decrease the mechanical properties of fibers if used in structural batteries and reduce the charging properties of the battery by decreased diffusivity of lithium ions and by exfoliating layers on the fiber surface. The crack propagation and possible damage evolution scenarios are analyzed using linear elastic fracture mechanics. The crack geometry dependent ion concentration distributions and the elastic stress distributions were found using finite element software ANSYS.

  • 20.
    Quaresimin, Marino
    et al.
    Department of Management and Engineering, University of Padova.
    Carraro, P.A.
    Department of Management and Engineering, University of Padova.
    Mikkelsen, L.P.
    Department of Wind Energy, Technical University of Denmark, Risø Campus.
    Lucato, N.
    Department of Management and Engineering, University of Padova.
    Vivian, L.
    Department of Management and Engineering, University of Padova.
    Brøndsted, Povl
    Department of Wind Energy, Technical University of Denmark, Risø Campus.
    Sørensen, Bent F.
    Materials Department, Risø National Laboratory, Department of Wind Energy, Technical University of Denmark, Risø Campus, Danish Corrosion Centre.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Talreja, Ramesh
    Reprint of: Damage evolution under cyclic multiaxial stress state: a comparative analysis between glass/epoxy laminates and tubes2014Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 65, s. 2-10Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work an experimental investigation on damage initiation and evolution in laminates under cyclic loading is presented. The stacking sequence [0/θ2/0/-θ2]s has been adopted in order to investigate the influence of the local multiaxial stress state in the off-axis plies and the possible effect of different thickness between the thin (2-plies) and the thick (4-plies) layers. Results are presented in terms of S–N curves for the initiation of the first cracks, crack density evolution, stiffness degradation and Paris-like curves for the crack propagation phase. The values of the off-axis angle θ has been chosen in order to obtain local multiaxial stress states in the off-axis plies similar to those in previous studies for biaxially loaded tubes. Results concerning damage initiation and growth for these two specimen configurations are shown to be consistent for similar local multiaxial stress states

  • 21.
    Quaresimin, Marino
    et al.
    Department of Management and Engineering, University of Padova.
    Carraro, P.A.
    Department of Management and Engineering, University of Padova.
    Mikkelsen, L.P.
    Department of Wind Energy, Technical University of Denmark, Risø Campus.
    Lucato, N.
    Department of Management and Engineering, University of Padova.
    Vivian, L.
    Department of Management and Engineering, University of Padova.
    Brøndsted, Povl
    Department of Wind Energy, Technical University of Denmark, Risø Campus.
    Sørensen, Bent Fruergaard
    Department of Wind Energy, Technical University of Denmark, Risø Campus.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Talreja, Ramesh
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Damage evolution under cyclic multiaxial stress state: A comparative analysis between glass/epoxy laminates and tubes2014Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 61, s. 282-290Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work an experimental investigation on damage initiation and evolution in laminates under cyclic loading is presented. The stacking sequence [0/θ2/0/−θ2]s has been adopted in order to investigate the influence of the local multiaxial stress state in the off-axis plies and the possible effect of different thickness between the thin (2-plies) and the thick (4-plies) layers. Results are presented in terms of S–N curves for the initiation of the first cracks, crack density evolution, stiffness degradation and Paris-like curves for the crack propagation phase. The values of the off-axis angle θ has been chosen in order to obtain local multiaxial stress states in the off-axis plies similar to those in previous studies for biaxially loaded tubes. Results concerning damage initiation and growth for these two specimen configurations are shown to be consistent for similar local multiaxial stress states

  • 22.
    Sabau, Cristian
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Popescu, Cosmin
    Northern Research Institute – NORUT.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Schmidt, Jacob W.
    echnical University of Denmark, Department of Civil Engineering.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Strengthening of RC beams using bottom and side NSM reinforcement2018Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 149, s. 82-91Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The allowable strain in fibre reinforced polymers reinforcement is limited by design codes to avoid debonding. The near-surface mounted (NSM) reinforcement technique has been proven to produce better anchorage behaviour compared to externally bonded reinforcement solutions. However, NSM solutions do not always eliminate debonding issues, with concrete cover detachment (CCD) typically occurring in RC beams strengthened for flexure. This experimental study investigated the efficiency of side mounted (S) compared to bottom mounted (B) NSM bars to prevent CCD. The experimental results were compared to models available in the literature that predict the observed failure modes and the crack spacing in the NSM anchorage zone. Compared to B-NSM, the S-NSM solution was successful in avoiding brittle CCD failure and showed increased rotational capacity and energy dissipation at failure. Existing CCD debonding models were found to be conservative.

  • 23.
    Sas, Gabriel
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. NORUT, Department of Infrastructure Structures and Materials.
    Dăescu, Cosmin
    Politechnica University of Timisoara.
    Popescu, Cosmin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Tamás, Nagy-György
    Politechnica University of Timisoara.
    Numerical optimization of strengthening disturbed regions of dapped-end beams using NSM and EBR CFRP2014Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 67, s. 381-390Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a parametric investigation, based on non-linear finite element modeling, to identify the most effective configuration of carbon fiber reinforced polymers (CFRP) for strengthening reinforced concrete (RC) dapped end beams. Following a field application and laboratory tests, it focuses on effects of 24 externally bonded (EBR) and near surface mounted reinforcement (NSMR) configurations on yield strain in steel and the capacity and failure mode of dapped-end beams. The investigated parameters were the mechanical properties of the CFRP, the strengthening procedure and the inclination of the fibers with respect to the longitudinal axis. Two failure scenarios were considered: rupture and debonding of the FRP. The results indicate that high-strength NSM FRPs can considerably increase the capacity of dapped-end beams and the yielding strains in reinforcement can be substantially reduced by using high modulus fibers.

  • 24.
    Sburlati, Roberta
    et al.
    Department of Civil, Chemical and Environmental Engineering, Genoa University.
    Atashipour, Seyed Rasoul
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Atashipour, Seyed Abdolrahim
    Department of Civil, Chemical and Environmental Engineering, Genoa University.
    Reduction of the stress concentration factor in a homogeneous panel with hole by using a functionally graded layer2014Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 61, s. 99-109Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work aims at understanding the effect of a radially heterogeneous layer around the hole in a homogeneous plate on the stress concentration factor. The problem concerns a single hole in a plate under different far-field in-plane loading conditions. By assuming a radial power law variation of Young’s modulus and constant value for Poisson’s ratio, the governing differential equations for plane stress conditions, and general in-plane loading conditions are studied. The elastic solutions are obtained in closed form and, in order to describe localized interface damage between the ring and the plate, two different interface conditions (perfectly bonded and frictionless contact) are studied. The formulae for the stress concentration factors are explicitly given for uniaxial, biaxial and shear in-plane loading conditions and comparisons with interface hoop stress values are performed. The solutions are investigated to understand the role played by the geometric and graded constitutive parameters. The results are validated with numerical finite element simulations in which some simplified hypotheses assumed in the analytical model, are relaxed to explore the range of validity of the elastic solution presented. In this way the results obtained are useful in tailoring the parameters for specific applications.

  • 25. Täljsten, Björn
    et al.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Strengthening concrete beams for shear using CFRP-materials: evaluation of different application methods2000Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 31, nr 2, s. 87-96Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents different methods and tests for the application of carbon fibre reinforced plastic (CFRP) fabrics and tapes to concrete beams. The purpose of the tests were twofold; first to study the shear force capacity of the beams both before and after strengthening; and second, to examine three different ways of applying the fabrics. These were: two hand lay-up systems, one vacuum injection system and one pre-preg system. The total number of beams tested was eight. The test results proved that a very good strengthening effect in shear could be achieved by bonding fabrics to the face of concrete beams. However, a lot of energy was released at failure, which led to brittle failures. The tests also showed that the techniques which used hand lay-up were preferable as compared to other systems, even though the fibre weight fraction was considerably less. However, the vacuum injection system was the most environmentally friendly method.

  • 26.
    Zhuang, Linqi
    et al.
    Department of Aerospace Engineering, Texas A&M University, Texas A&M University, College Station.
    Pupurs, Andrejs
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ayadi, Zoubir
    Institut Jean Lamour, Nancy Universite, Science et Ingénierie des Matériaux et Métallurgie (SI2M), Institut Jean Lamour, Nancy, Laboratoire de Science et Génie des Surfaces, EEIGM, Institut Jean Lamour, SI2M, EEIGM 6 Rue Bastien Lepage, F-54010 Nancy, Institut Jean Lamour, University of Lorraine, EEIGM 6 Rue Bastien Lepage, F-54010 Nancy, University of Lorraine, F-54010, Nancy.
    Fiber/matrix debond growth from fiber break in unidirectional composite with local hexagonal fiber clustering2016Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 101, s. 124-131Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Energy release rate (ERR) for fiber/matrix debonding in composite with local fiber clustering, subjected to axial tension, has been investigated numerically by a 3-D finite element (FE) model. In the model, broken fiber is central in a hexagonal unit which is embedded in an effective composite. Fiber/matrix debond with circular front is assumed to be originated from the fiber break. The effect of the local fiber clustering on ERR is studied by varying distance between the broken fiber and the neighboring fibers. For very short debonds as well as for long debonds (almost steady-state growth) the ERR was calculated by both the J integral and the Virtual crack closure technique (VCCT). Results show that the debond growth is Mode II dominated and that the ERR strongly depends on the angular coordinate. The local fiber clustering has larger effect on the angular variation for shorter debonds and the effect increases with larger local fiber volume fraction. The results obtained from the 3-D hexagonal model are compared with those obtained previously using 5-cylinder axisymmetric model developed by the same authors. The ERR values from 5-cylinder axisymmetric model could be considered as upper bound for the 3-D hexagonal model.

  • 27.
    Zrida, Hana
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Marklund, Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ayadi, Zoubir
    Institut Jean Lamour, SI2M, EEIGM 6 Rue Bastien Lepage, F-54010 Nancy.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Master curve approach to axial stiffness calculation for non-crimp fabric biaxial composites with out-of-plane waviness2014Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 64, s. 214-221Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of 0∘-tow out-of-plane waviness on the biaxial Non-Crimp-Fabric (NCF) composite axial stiffness is investigated. Homogenizing, the bundle mesostructure of the NCF composite is replaced by layers. Then the composite is represented by a laminate with flat layers with effective stiffness properties representing the curved 0∘-layer and the 90∘-layer with varying thickness. It is shown that the NCF composite knock-down factor characterizing the stiffness degradation has almost the same dependence on wave parameters as the knock-down factor for the curved 0∘-layer. Numerical analysis showed that 90∘-layer knock-down factor versus amplitude curves for different wavelength can be reduced to one master curve which can be described by a one-parameter expression with the parameter dependent on the used material. This observation is used to obtain high accuracy for analytical predictions for knock-down factors for cases with different wavelength and amplitudes based on two FE calculations only.

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