Inter-ply stitching optimisation of highly drapeable multi-ply preforms

An efficient finite element model has been developed in Abaqus/Explicit to solve highly non-linear fabric forming problems, using a non-orthogonal constitutive relation and membrane elements to model bi-axial fabrics. 1D cable-spring elements have been defined to model localised inter-ply stitch-bonds, introduced to facilitate automated handling of multi-ply preforms. Forming simulation results indicate that stitch placement cannot be optimised intuitively to avoid forming defects. A genetic algorithm has been developed to optimise the stitch pattern, minimising shear deformation in multi-ply stitched preforms. The quality of the shear angle distribution has been assessed using a maximum value criterion (MAXVC) and a Weibull distribution quantile criterion (WBLQC). Both criteria are suitable for local stitch optimisation, producing acceptable solutions towards the global optimum. The convergence rate is higher for MAXVC, while WBLQC is more effective for finding a solution closer to the global optimum. The derived solutions show that optimised patterns of through-thickness stitches can improve the formability of multi-ply preforms compared with an unstitched reference case, as strain re-distribution homogenises the shear angles in each ply

Analyse et simulation de la mise en forme de composites thermoplastiques

ORLEANS-BU Sciences (452342104) / SudocSudocFranceF

Simulation of continuous fibre reinforced thermoplastic forming using a shell finite element with transverse stress

International audienceA shell finite element with transverse stress is presented in this paper in order to simulate the forming of thermoplastic composites reinforced with continuous fibres. It is shown by an experimental work that many porosities occurs through the thickness of the composite during the heating and the forming process. Consequently the reconsolidation i.e. the porosity removing by applying a compressive stress through the thickness is a main point of the process. The presented shell finite element keeps the five degrees of freedom of the standard shell elements and adds a sixth one which is the variation in thickness. A locking phenomenon is avoided by uncoupling bending and pinching in the material law. A set of classical validation tests will prove the efficiency of this approach. Finally a forming process is simulated. It shows that the computed transverse stresses are in good agreement with porosity removing in the experiments

Modeling and simulation of the progressive failure in composites structures for automotive application

peer reviewe

Experimental and numerical analysis of interply porosities in composites thermoforming

Effective forming of Continuous Fiber Reinforced Thermoplastic Composites requires a detailed understanding and modeling of the forming mechanisms and the development of computational techniques for process simulation. A re-compaction stage is performed at the end of the process in order to avoid interply porosities. The through the thickness behaviour of the composite during forming and consolidation is analysed by a shell finite element with pinching degrees of freedom. This element avoids a locking due to pinching by a modification of the constitutive relation

Analyse expérimentale et simulation numérique de la reconsolidation lors de la mise en forme des CFRTP

International audienceUne expérience de formage montre que de nombreuses porosités sont induites dans un multipli à fibres continues et matrice thermoplastique pendant la mise en forme. Il est essentiel pour la qualité de la pièce finale qu'une phase de reconsolidation efficace termine la fabrication. Dans cette étape, un effort de compression suffisant doit être appliqué de sorte que la contrainte normale transverse dans chaque pli amène la consolidation. Dans l'objectif de prévoir la consolidation par simulation du procédé, un élément fini de coque à contrainte transverse est proposé pour la modélisation de chaque pli. La comparaison d'une simulation de mise en forme dans le cas d'une pièce en Z montre que la contrainte transverse calculée est en bonne corrélation avec la présence ou non de porosités observés expérimentalement

Analyse expérimentale et simulation numérique de la reconsolidation lors de la mise en forme des CFRTP

National audienc