A framework for macroscale modelling of inelastic deformations in 3D-woven composites

The use of 3D-woven composite materials has shown promising results. Along with weight-efficient stiffness and strength, they have demonstrated encouraging out of plane properties, damage tolerance and energy absorption capabilities. The widespread adoption of 3D-woven composites in industry however, requires the development of efficient computational models that can capture the material behaviour. The following work proposes a framework for modelling the mechanical response of 3D-woven composites on the macroscale. This flexible and thermodynamically consistent framework, decomposes the stress and strain tensors into two main parts motivated by the material architecture. The first is governed by the material behaviour along the reinforcement directions while the second is driven by shear behaviours. This division allows for the straightforward addition and modification of various inelastic phenomena observed in 3D-woven composites. In order to demonstrate the applicability of the framework, focus is given to predicting the material response of a 3D glass fibre reinforced epoxy composite. Prominent non-linearities are noted under shear loading and loading along the horizontal weft yarns. The behaviour under tensile loading along the weft yarns is captured using a Norton style viscoelasticity model. The non-linear shear response is introduced using a crystal plasticity inspired approach. Specifically, viscoelasticity is driven on localised slip planes defined by the material architecture. The viscous parameters are calibrated against experimental results and off axis tensile tests are used to validate the model

Evaluation of damage initiation models for 3D-woven fibre composites

Three dimensional (3D) fibre-reinforced composites have shown weight efficient strength and stiffness characteristics as well as promising energy absorption capabilities. In the considered class of 3D-reinforcement, vertical and horizontal weft yarns interlace warp yarns. The through-thickness reinforcements suppress delamination and allow for stable and progressive damage growth in a quasi-ductile manner. With the ultimate goal of developing a homogenised computational model to predict how the material will deform and eventually fail under loading, this work proposes candidates for failure initiation criteria. The criteria are evaluated numerically for tensile, compressive and shear tests. The extension of the LaRC05 stress based failure criteria to this class of 3D-woven composites is one possibility. This however, presents a number of challenges which are discussed. These challenges are related to the relative high stiffness in all directions, which produce excessively high shear components when projected onto potential off-axis failure planes. To circumvent these challenges, strain based criteria inspired by LaRC05 are formulated. Results show that strain based failure predictions for the simulated load cases are qualitatively more reasonable

Predicting damage initiation in 3D fibre-reinforced composites – The case for strain-based criteria

Three dimensional (3D) fibre-reinforced composites have shown weight efficient strength and stiffness characteristics as well as promising energy absorption capabilities. In the considered class of 3D-reinforcement, vertical and horizontal weft yarns interlace warp yarns. The through-thickness reinforcements suppress delamination and allow for stable and progressive damage growth in a quasi-ductile manner. With the ultimate goal of developing a homogenised computational model to predict how the material will deform and eventually fail under loading, this work proposes candidates for failure initiation criteria. It is shown that the extension of the LaRC05 stress-based failure criteria for unidirectional laminated composites, to this class of 3D-reinforced composite presents a number of challenges and leads to erroneous predictions. Analysing a mesoscale representative volume element does however indicate, that loading the 3D fibre-reinforced composite produces relatively uniform strain fields. The average strain fields of each material constituent are well predicted by an equivalent homogeneous material response. Strain based criteria inspired by LaRC05 are therefore proposed. The criteria are evaluated numerically for tensile, compressive and shear tests. Results show that their predictions for the simulated load cases are qualitatively more reasonable