A new meso-scale modelling of static and fatigue damage in woven composite materials with finite element method

Aim of this work is to evaluate the fatigue damage in textile composites on meso-scale level. Pre-damage properties, damage thresholds and damage propagation of unit cell (UC) are calculated and validated by experiments. Quasi-static damage algorithm is further used to model the cycles of the fatigue loading. Model output is the computed SN curve of textile composites

Optimized flax preforms for composites, ECOCOMP

status: publishe

Finite element modelling of damage development during longitudinal tensile loading of coated fibre composites

In this paper, results of finite element calculations of the stress state near a broken coated fibre in unidirectional carbon fibre-epoxy matrix composites are presented. For this aim, a simplified two-dimensional axisymmetric model has been developed. A part of the model contains an equivalent composite medium and, to this end, elastic constants of a coated fibre composite were separately calculated and used as input data in this analysis. The influences of coating thickness, coating stiffness and assumed crack pattern on the stresses in the broken fibre and in adjacent, unbroken fibres are evaluated, and their possible impact on composite longitudinal tensile strength is discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.status: publishe

Biaxial tension and ultimate deformation of knitted fabric reinforcements

In this study, the behavior under biaxial tension of two types of glass knitted fabrics, a rib and a milano weft knit, was investigated. The tests were performed using a homemade biaxial tester, which is capable of applying displacement velocity in two orthogonal directions independently. The ultimate deformation in both wale and course directions was determined at different displacement ratios. Furthermore, geometrical models were developed for the rib knit to predict the ultimate deformation. Good agreement with experimental results was achieved. (C) 2001 Elsevier Science Ltd. All rights reserved.status: publishe

In situ polymerization of thermoplastic composites based on cyclic oligomers

The high melt viscosity of thermoplastics is the main issue when producing continuously reinforced thermoplastic composites. For this reason, production methods for thermoplastic and thermoset composites differ substantially. Lowering the viscosity of thermoplastics to a value below 1 Pa.s enables the use of thermoset production methods such as resin transfer molding (RTM). In order to achieve these low viscosities, a low viscous mixture of prepolymers and catalyst can be infused into a mold where the polymerization reaction takes place. Only a limited number of polymerization reactions are compatible with a closed mold process. These polymerization reactions proceed rapidly compared to the curing reaction of thermosets used in RTM. Therefore, the processing window is narrow, and managing the processing parameters is crucial. This paper describes the production and properties of a glass fiber reinforced polyester produced from cyclic oligoesters.status: publishe

Modelling of the interaction between matrix cracks and delaminations during impact of composite plates

This paper discusses the investigation of the transverse impact of plate-like composite specimens. It focuses on the initiation of delaminations at matrix cracks and on the interaction of delaminations with matrix cracks. This study shows that an accurate prediction of the development of matrix cracks and delaminations during impact requires the use of energy criteria, taking into account the appropriate fracture toughness values, depending on the interface and the mixed mode loading. Also, the accumulation of damage in the plate has to be taken into account when predicting the damage development. (C) 1996 Elsevier Science Limitedstatus: publishe

Optimisation of a GMT-based cold pressing technique for low cost textile reinforced thermoplastic composites

Much potential and interest exists for the fast processing of lightweight, inexpensive composite preforms in automotive and other transport applications. As a thermoplastic matrix is more suitable for mass production with short cycle times, a novel cost-effective glass fibre reinforced thermoplastic textile preform is developed. Weft-inserted warp knitting is used to produce this textile preform containing both the reinforcing fibres and the thermoplastic matrix material as split-film ribbons. The aim of the work is to establish a useful processing technique and to control those parameters which lead to the production of good quality composite parts. The current study is specifically directed at determining the feasibility of the GMT-based cold pressing technique for the manufacturing of this new type of thermoplastic composite. An experimental design method is used to develop a statistical model which gives response surfaces of the effects of the processing parameters on the mechanical performance of the final composite part. Processing variables are ranked in order of importance to determine the optimal processing window. An economical comparison with the use of long fibre reinforced GMT mats proves the cost-efficiency of this new continuous reinforced thermoplastic composite. (C) 1999 Elsevier Science Ltd. All rights reserved.status: publishe

Model of shear of woven fabric and parametric description of shear resistance of glass woven reinforcements

Forming simulations of textile preforms require a description of the shear resistance of the preform plies. Experimental determination of the shear diagrams is time consuming, costly and requires highly qualified personnel. Typical glass rovings exhibit quite consistent behaviour, described by diagrams for bending, compression and tension, in function of linear density of the rovings. Based on these representative diagrams, a parametrical study of the shear resistance of glass preforms has been carried out, using a model, which accounts for different sources of the fabric resistance to shear: friction, compression of the yarns, yarn (un)bending, Possible simultaneous action of shear and (pre)tension is taken into account. The model (validated against experimental data) generates shear diagrams for plain, twill and 5-harness satin square fabrics. The diagrams were then processed to create analytical expressions of the shear diagrams: T = T₀ + T₁ tanªγ, where T is the shear force, γ is the shear angle, a, T₀, and T₁ are parameters, tabulated as functions of yarn linear density, fabric tightness and pretension. The value of α was found to be close to 2 in all the cases. The resulting family of shear diagrams was verified against experimental data.status: publishe

Virtual textile composites software WiseTex: Integration with micro-mechanical, permeability and structural analysis

The internal geometry of textile reinforcements is an important factor of the reinforcement performance during composite manufacturing and in the service life of the composite material. When a 3D-shaped composite part is concerned, the reinforcement is locally deformed (compressed, stretched and sheared), and any model describing the internal geometry of the reinforcement should account for this deformation. The software package WiseTex implements a generalised description of internal structure of textile reinforcements on the unit cell level, integrated with mechanical models of the relaxed and deformed state of 2D- and 3D-woven, two- and three-axial braided, weft-knitted and non-crimp warp-knit stitched fabrics and laminates. It is integrated with modelling of resin flow, micro-mechanical calculations of properties of textile based composites and micro-macro analysis of composite parts, finite element models and virtual reality software. The paper describes this family of models, which use a unified description of the geometry of the reinforcement unit cell.status: publishe