Damage in textile laminates of various inter-ply shift

Deformation mechanisms and failure of textile laminates are strongly affected by inter-layer configurations – a mutual shift of the plies. To model it within a traditional framework, one must construct a representative volume element (RVE), which includes all the plies. This is a time consuming and computationally expensive work. As an alternative, the paper suggests boundary conditions (BC) imitating the interaction with the surrounding non-periodic media. This makes possible analysis on a single unit cell of one ply. The proposed BC respect inter-ply configurations, account for the number of plies, distinguish the ply position, and reproduce the meso stress state with a good accuracy. The BC are constructed through (1) averaging of the known periodic solutions with respect to the ply shifts, (2) separation of the solution to the outer and inner ply cases, (3) energy equilibrium of heterogeneous and effective media. The unit cell finite element (FE) modelling is validated by reference full scale solution on the entire laminate

Fibre distribution inside yarns of textile composite: gemetrical and FE modelling

This article addresses the experimental investigation and modelling of the uneven fibre distribution inside yarns of a textile composite. The test data is given for the tri-axial carbon-fibre braid; a considerable irregularity is revealed for the fibre distribution along and across the yarns. The importance of this effect for the damage resistance is illustrated with a simple finite-element (FE) model. The geometrical modelling of the internal geometry is also discussed

FE modelling of a structurally stitched multilayer composite

Finite-element models are presented for a typical structurally stitched carbonfibre composite. The term 'structural' means that the stitching yarn is thick enough to form a through-the-thickness reinforcement. The influences of different model features are revealed. The stitching, on the one hand, is shown to increase the stiffness, especially its out-plane component. On the other hand, it creates prominent stress-strain concentrators

Internal structure of structurally stitched NCF preform

The paper addresses the experimental investigation of the unit cell architecture in a structurally stitched multilayer carbon-fibre preform. Each layer is a multiaxial multiply non-crimp fabric (NCF) knit with a non-structural stitching. The term “structural” presumes here that the stitching yarn does not only consolidate the plies (as the non-structural one does) but also forms a 3D reinforcement. One stitching technique — tufting — is studied, with 120 tex aramide yarn. The experimental data reveals a considerable irregularity of the piercing pattern and fibre distribution

Local damage in a 5-harness satin weave composite under static tension, part II: meso-FE modelling

International audienceThis study forms the second part of a paper on the local damage analysis in a thermo-plastic 5-harness satin weave composite under uni-axial static tensile load. The experimental observations of Part I are confronted with the meso-FE simulations. Part II describes the following steps regarding the unit cell meso-FE modeling starting from: 1) Construction of the unit cell geometrical model; 2) Estimation of the homogenized elastic constants of the unit cell using different boundary conditions; 3) Evaluation of the local stress and damage behavior of the unit cell using meso-FE simulations. The aim of the numerical analysis is to investigate the dependency of local ply stress and damage profiles on the adjacent layers of the laminate

Progressive damage in stitched composites: Static tensile tests and tension-tension fatigue

The paper describes progressive damage in static tensile tests and tension-tension fatigue in structurally stitched carbon/epoxy NCF composites, in comparison with their non-stitched counterparts. Analogies between damage development in quasi-static tension and tension-tension fatigue are analyzed and links between the damage initiation thresholds in quasi-static tests and fatigue life are established

Forming simulation of a thermoplastic commingled woven textile on a double dome

This paper presents thermoforming experiments and FE simulations of a commingled glass-PP woven composite on a double dome geometry, with the aim of assessing the correspondence of predicted and experimental shear angles. Large local deformations - especially in-plane shear, i.e. relative rotation between the two yarn families – occur when draping a textile on a three dimensional part and eventually unwanted phenomena like wrinkling or tearing may occur. The macroscopic drape behaviour of a weave is generally subdivided into: 1) The high tensile resistance along the yarn directions, expressed as non-linear stress-strain curves, and 2) The shear resistance, expressed as non-linear shear force versus shear angle curves. The constitutive model is constituted of a dedicated non-orthogonal hypo-elastic shear resistance model, previously described in [1, 2], combined with truss elements that represent the high tensile resistance along the yarn directions. This model is implemented in a user subroutine of the ABAQUS explicit FE solver. The material parameters have been identified via textile biaxial tensile tests at room temperature and bias extension tests at 200°. Thermoforming experiments are performed on a rectangular blank with the warp direction along the second symmetry plane of the tool, with a preheating temperature of 200°C, a constant mold temperature of about 70°C, and a blankholder ring. It was concluded that the shear angles were fairly well predicted for this particular case study, which could be expected in view of the fact that no wrinkles had formed during the thermoforming experiment