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  • 1.
    Edgren, Fredrik
    et al.
    SICOMP AB, Swedish Institute of Composites.
    Mattsson, David
    Asp, Leif
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Formation of damage and its effects on non-crimp fabric reinforced composites loaded in tension2004Ingår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 64, nr 5, s. 675-692Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Non-crimp fabric (NCF) composites, manufactured by resin infusion techniques are one of the most promising next generation composite materials. They offer large potential for application in primary structures as they give excellent performance at low production costs. However, before NCF composites will be efficiently used in design, detailed understanding of governing micro mechanisms must be accumulated and described by predictive models. In the present study, NCF cross-ply laminates have been tested in tension. Intralaminar cracks caused in the 90° fibre bundle layers and their effect on laminate mechanical properties have been monitored. Occurrence of ‘novel' type of cracks propagating in the load direction (longitudinal cracks) is explained by a thorough FE analysis using an Representative Volume Element (RVE) approach, revealing stress concentrations caused by 0° fibre bundle waviness. Effects of damage on mechanical properties are modelled using modified micro mechanical models developed for analysis of conventional laminated composites. The analysis reveals mechanical degradation to be ruled by the crack opening displacement (COD). However, unlike traditional composites, transverse cracks do not generally extend through the entire thickness of the 90° layer, but are rather contained in single fibre bundles, limiting the COD

  • 2.
    Joffe, Roberts
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mattsson, David
    Compressive failure of non-crimp fabric composites: influence of bundle out-of-plane misalignment2004Ingår i: Mechanics of composite materials :: XIII international conference, May 16 - 20, 2004, Riga ; MCM 2004, 2004Konferensbidrag (Övrigt vetenskapligt)
  • 3.
    Joffe, Roberts
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mattsson, David
    Methodology for characterization of internal structure of NCF composite and its influence on mechanical properties2006Ingår i: Proceedings of the 3rd International Conference on Composites Testing and Model Identification: CompTest 2006, Faculty of Engineering, University of Porto, Portugal , 2006, s. 64-65Konferensbidrag (Övrigt vetenskapligt)
  • 4.
    Joffe, Roberts
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mattsson, David
    NCF cross-ply laminates: damage accumulation and degradation of elastic properties2006Ingår i: Fracture of Nano and Engineering Materials and Structures: Proceedings of the 16th European Conference of Fracture, Alexandroupolis, Greece, July 3-7, 2006 / [ed] E. E. Gdoutos, Encyclopedia of Global Archaeology/Springer Verlag, 2006, Vol. Paper 450, s. 1281-1288Konferensbidrag (Refereegranskat)
  • 5. Joffe, Roberts
    et al.
    Mattsson, David
    Modniks, Janis
    Institute of Polymer Mechanics, University of Latvia.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Compressive failure analysis of non-crimp fabric composites with large out-of-plane misalignment of fiber bundles2005Ingår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 36, nr 8, s. 1030-1046Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Failure initiation under compressive loading in non-crimpfabric composites containing bundles with out-of-plane orientation imperfections was analyzed using FEM in plane stress and linear elastic formulation. The bundle orientation imperfection in a composite unit was described by a sine function. Failure initiation strain was determined comparing failure functions corresponding to two alternative failure mechanisms: (a) plastic microbuckling in bundle due to mixed compressive and shear load; (b) plastic matrix yielding according to von Mises criterion. Parameters for compressive failure initiation analysis were bundle misalignment angle, fiber volume fraction inside the bundle and bundle volume fraction inside the composite unit. The support effect of the neighbouring material was analyzed varying boundary conditions and solving cases with particular configuration of surrounding material. Model prepreg tape GF/EP composite with different introduced levels of out-of-plane waviness of layers was used to validate the conclusions from parametric analysis.

  • 6.
    Joffe, Roberts
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mattsson, David
    Varna, Janis
    Damage tolerance of cross-ply non-crimp fabric composites2005Ingår i: The fifth Canadian international composites conference, CACSMA , 2005Konferensbidrag (Övrigt vetenskapligt)
  • 7. Mattsson, David
    Mechanical performance of NCF composites2005Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Composite materials are today in widespread use in the aerospace and marine industries due to their excellent strength and stiffness to weight ratio. In most marine and aerospace applications traditional composites (pre- impregnated tapes) are still the main choice for design of load bearing structures. Nevertheless, due to their high material costs and sensitivity to out-of-plane loads (eg impact), the use of composites manufactured from pre-impregnated tapes (prepregs) has so far been limited. Non-crimp fabric (NCF) based composites address both these concerns, without any significant drop in in-plane performance. In the presented thesis, the mechanical performance of NCF composites is investigated. NCF cross-ply composites have been tested in tension and the effect on mechanical properties due to intralaminar cracks in the 90° layer has been monitored. Effects of damage on mechanical properties are modeled using modified micro mechanical models developed for analysis of conventional laminated composites. The analysis reveals that the mechanical degradation is ruled by the crack opening displacement. Furthermore, NCF cross-ply composites response to tensile loading show large effect of the fabric layer stacking sequence: much larger elastic modulus reduction was observed in [0/90/0/90]S than in [90/0/90/0]S case. Since transverse cracks in 90°- bundles may give modulus decrease about 5%, the observed 40% stiffness reduction is attributed to failure and delamination of bundles oriented in the direction of the applied load. Analysis of micrographs shows extensive delaminations and 0°-bundle breaks. Transverse strain in bundles governs transverse cracking in NCF composites and FE analysis reveals that this strain may be significantly lower than the applied macroscopic strain component in the same direction. This feature is important for damage evolution modelling. Analysing by FEM the importance of media surrounding the bundle on average transverse strain it was found that a power law could be used to predict the average strain in bundles. A calculated H-matrix which establishes the relationship between strains in meso-element and RVE strains could then be used to calculate the “effective stiffness” of the bundle. This “effective stiffness” is the main element in simple but exact expressions derived to calculate the stiffness matrix of NCF composites. Failure initiation under compressive loading in NCF composites containing bundles with out-of plane orientation imperfections has been analyzed using FEM in plane stress and linear elastic formulation. The bundle orientation imperfection in a composite unit was described by a sine function. Failure initiation strain was determined comparing failure functions corresponding to two alternative failure mechanisms: a) plastic microbuckling in the bundle due to mixed compressive and shear load; b) plastic matrix yielding according to von Mises criterion. Parameters for compressive failure initiation analysis were bundle misalignment angle, fiber volume fraction inside the bundle and bundle volume fraction inside the composite unit. Mechanical performance of NCF 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 thesis 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 NCF composites are analyzed in context of their significance for in-plane elastic and failure properties. A methodology for the determination of the most typical geometrical parameters of composites using optical observations of cross-sections of manufactured laminates is described.

  • 8. Mattsson, David
    Multi-scale analysis of mechanical phenomena in NCF composites2003Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Mechanical phenomenon in Non Crimp Composites is studied in this thesis using a multiscale approach. This approach is choosen due to the architecture of the composite which is heterogenic both on micro as well as mesoscale. Homogenization is therefore performed on three different length scales: micro-scale which homogenizes the fiber/matrix structure, meso-scale where the bundle structure is homogenized into layers creating a homogeneous material and macro-scale which considers the representative volume element. Volume average stress and strain relations are used for the development of both the iso-strain and Partial iso-strain method. These methods are approximate analytical methods using a method of dividing the composite into elements in which the stiffness matrices can be determined. The elements consist of a number of subelements were the material is already homogenized. In this case, the iso-strain method only considers stress in the composite whereas the Partial iso-strain model considers both stress in the composite and also the stress and strain developing in different elements in the composite. Out-of-plane orientation of fiber bundles are also analyzed in terms of stiffness. In this case homogenization is performed using a slightly different approach than in the case were the fiber bundles only have in- plane orientation. Instead of using CLT for the determination of each elements stiffness matrix, volume average of the stiffness matrices for the subelements within the elements is performed, using the assumption of iso- strain in the element. Preliminary calculations are performed with the object of determining a knock-down factor for the determination of strain level in the 90º bundles, which are the most possible locus for failure. Parametric studies on 90º bundle strain are also performed, analysing the importance of media surrounding the 90º bundle, the stiffness ratio between the lower sub- elements in two different elements and the volume content of bundle in the layer. The stiffness-damage relationship for a cross-ply NCF composite is also monitored experimentally and modelled. For this purpose, analytical micro- mechanics models used for analysis of conventional laminated composites are modified and tensile tests are performed. Secondly, RVE based models of the composite meso-structure implemented in FEM are developed. RVE analysis is to provide information on stress and strain concentrations caused by the material heterogeneity and, hence, allow for explanations to damage mechanisms observed in tests. A study of the compressive failure initiation in an imperfect element of NCF composite is conducted. FEM based parametric study is performed on the mesoscale to identify the microscale and mesoscale parameters governing failure initiation in an NCF element containing fiber bundle with a certain degree of out-of-plane waviness which is surrounded by matrix and supported by different layers. As two competitive failure mechanisms plastic microbuckling in the bundle and yielding in the matrix are considered. To verify the conclusions "a model NCF composite" with predetermined out-of- plane waviness is designed, tested in compression and analyzed theoretically.

  • 9. Mattsson, David
    et al.
    Joffe, Roberts
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Damage in NCF composites under tension: effect of layer stacking sequence2008Ingår i: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 75, nr 9, s. 2666-2682Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Non-crimp fabric (NCF) cross-ply composites response to tensile loading is investigated showing large effect of the fabric layer stacking sequence: much larger elastic modulus reduction was observed in [0/90/0/90]S than in [90/0/90/0]S case. Since transverse cracks in 90°-bundles may give modulus decrease about 5%, the observed 40% stiffness reduction is attributed to failure and delamination of bundles oriented in the direction of the applied load. Analysis of micrographs shows extensive delaminations and 0°-bundle breaks. FE calculations showed that failure of 0°-bundles at the surface is energetically more favorable. However, the fracture resistance of surface bundles is higher due to smaller bundle waviness and the density of bundle cracks on the surface was not larger than inside. Two possible reasons for the higher stiffness reduction in the [0/90/0/90]S NCF composite were suggested: (a) If two imperfect 0°-bundle layers are separated by a 90°-bundle layer their resistance to failure is lower than when they are situated next to each other; (b) the effect of each surface 0°-bundle break on the composite stiffness is larger (due to less constraint from the surrounding material the opening of surface bundle breaks is much larger).

  • 10. 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 composites2007Ingår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 38, nr 1, s. 44-57Artikel i tidskrift (Refereegranskat)
    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.

  • 11. Mattsson, David
    et al.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Average strain in fiber bundles and its effect on NCF composite stiffness2007Ingår i: Journal of engineering materials and technology, ISSN 0094-4289, E-ISSN 1528-8889, Vol. 129, nr 2, s. 211-219Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Transverse strain in bundles governs transverse cracking in noncrimp fabric (NCF) composites. Finite element (FE) analysis shows that this strain may be significantly lower than the applied macroscopic strain component in the same direction. This feature is important for damage evolution modeling. The isostrain assumption which in different combinations is widely used in stiffness models is inadequate because the strain in different mesoelements (bundles of different orientation and matrix regions) is assumed the same. Analyzing by FEM the importance of media surrounding the bundle on average transverse strain it was found that an increasing ratio of the bundle transverse stiffness to the matrix stiffness leads to a decrease of the strain in the bundle. An increase of the stiffness in the same direction in adjacent layers leads to an increase of the transverse strain in the bundle. Higher bundle volume fraction in the layer leads to larger transverse strain in the bundle. These trends are described by a power law and used to predict the average strain in bundles. The calculated H matrix which establishes the relationship between strains in the mesoelement and representative volume element strains is used to calculate the "effective stiffness" of the bundle. This effective stiffness is the main element in simple but exact expressions derived to calculate the stiffness matrix of NCF composites. Considering the three-dimensional (3D) FE model as the reference, it was found that all homogenization methods used in this study have sufficient accuracy for stiffness calculations, but only the presented method gives reliable predictions of strains in bundles.

  • 12. Mattsson, David
    et al.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Formation of damage and its Effect on Non-crimp Fabric Reinforced Composites Loaded in Tension2004Ingår i: MACM 2004 conference proceedings: Proceedings of the Tenth International Conference on Marine Applications of Composite Materials, Composites education association , 2004Konferensbidrag (Refereegranskat)
  • 13. Mattsson, David
    et al.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Krasnikovs, A.
    Stiffness degradation in Non-Crimp fabric composite in tension due to damage2004Ingår i: From nano-scale interactions to engineering structures: ECCM 11, 11th European Conference on Composite Materials ; May 31 - June 3, 2004, Rhodes, Greece / [ed] Costas Galiotis, Rhodos: European Society for Composite Materials , 2004Konferensbidrag (Refereegranskat)
  • 14.
    Pupurs, Andrejs
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Loukil, M.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Swerea.
    Mattsson, David
    Swerea.
    Damage development and stiffness reduction in laminates in out-of-plane loading2014Ingår i: 16th European Conference on Composite Materials, ECCM 2014: Seville, Spain, 22 - 26 June 2014, European Conference on Composite Materials, ECCM , 2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    Simple approach based on Classical Laminate Theory (CLT) and effective stiffness of damaged layer is suggested for bending stiffness determination of laminate with intralaminar cracks in surface 90-layers. The effective stiffness of layer with cracks as a function of crack density is back-calculated comparing in-plane stiffness of laminates with and without damage. The accuracy of the CLT and effective stiffness approach is demonstrated comparing with bending stiffness results from FEM simulated 4-point bending test on laminate with damage. Analytical model for damaged laminate stiffness is presented which gives similar values for effective stiffness as FEM calculations for unit cell. Effect of local delaminations initiated from transverse cracks is analyzed.

  • 15.
    Varna, Janis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Lundmark, P.
    Mattsson, David
    Megnis, M.
    Luleå tekniska universitet.
    Constitutive models for composite laminates with matrix cracks and fiber breaks2005Ingår i: Proceedings of the International Conference on Fracture and Damage Mechanics IV, 2005, s. 597-604Konferensbidrag (Refereegranskat)
1 - 15 av 15
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