Meso-FE modelling of textile composites: Road map, data flow and algorithms

Damage in textile composites is closely connected with the internal micro- and meso-geometry of the reinforcement, and reveals features, which are not present in the damage processes in classical laminates. This paper proposes a test sequence intended to characterise damage in textile composites - its initiation and development different scale levels: (1) Tensile tests on samples cut in characteristic directions of the textile reinforcement (machine, cross and bias), accompanied with acoustic emission (AE) registration and full-field strain measurement on the surface. The test produces stress-strain diagrams and identifies characteristic strain levels for post-mortem investigation: just after first damage e 1 ; well-developed damage e 2 ; just before the final fracture of the sample e 3 . Full-field strain measurement highlights the relation between strain concentrations (linked with the damage initiation) and the reinforcement structure. (2) Samples loaded up to e 1...3 3 are examined with CT and X-ray. This reveals the damage pattern and allows quantitative characterising of the damage development. (3) Optical and SEM examination of cross-sections through the damage sites, determined with X-ray, identifies local damage modes. The same strain levels are further used for setting up fatigue tests. The experimental protocol is applied for triaxial braided and quasi-UD composites.

Experimental methodology of study of damage initiation and development in textile composites

https://research-information.bris.ac.uk/ws/files/7225122/Lomov_Ivanov_Experimental_methodology.pdf

Experimental methodology of study of damage initiation and development in textile composites in uniaxial tensile test

Continuous and discrete approaches for forming simulations of textile performs both involve difficulties and drawbacks The semi-discrete method is an alternative based on a meso-macro approach It is based on specific finite elements made of a discrete number of the components of the textile at lower scale Their strain energy in the interpolated displacement field leads to the nodal interior loads of the element In this paper a new three node element is proposed It is made up of warp and weft fibres, the tensile and in plane shear energy of which are considered The directions of the warp and weft yarns are arbitrary with regard to the element sides That is very important in case of simultaneous multiply draping simulations and when using remeshing The determination of the material data necessary to the simulation from standard tensile and bias tests is straightforward A set of elementary tests and mono and multi-ply draping shows the efficiency of the approach

Simulations of textile composite reinforcement draping using a new semi-discrete three node finite element

https://www.composites.ugent.be/ftp/VanPaepegem_2010_Composites_Science_and_Technology_part_I.pdf

Local damage in a 5-harness satin weave composite under static tension: Part I - Experimental analysis

Formation of damage and its effects on non-crimp fabric reinforced composites loaded in tension

Damage in NCF composites under tension: Effect of layer stacking sequence

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. Discussion concerning advantages and disadvantages of the proposed methodology in terms of accuracy and usefulness along with practical recommendations of its application are presented.

Methodology for characterization of internal structure parameters governing performance in NCF composites

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.

Compressive failure analysis of non-crimp fabric composites with large out-of-plane misalignment of fiber bundles

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 and delaminations initiated from intralaminar cracks. The effective stiffness of a layer with damage is back-calculated comparing the in-plane stiffness of a symmetric reference cross-ply laminate with and without damage. The in-plane stiffness of the damaged reference cross-ply laminate was calculated in two ways: (1) using FEM model of representative volume element (RVE) and (2) using the analytical GLOB-LOC model. The obtained effective stiffness of a layer at varying crack density and delamination length was used to calculate the A, B and D matrices in the unsymmetrically damaged laminate. The applicability of the effective stiffness in CLT to solve bending problems was validated analyzing bending of the damaged laminate in 4-point bending test which was also simulated with 3-D FEM.

David Mattsson

Papers

Formation of damage and its effects on non-crimp fabric reinforced composites loaded in tension

Damage in NCF composites under tension: Effect of layer stacking sequence

Methodology for characterization of internal structure parameters governing performance in NCF composites

Compressive failure analysis of non-crimp fabric composites with large out-of-plane misalignment of fiber bundles

Effective stiffness concept in bending modeling of laminates with damage in surface 90-layers