PREDICTING NON-LINEAR SHEAR DEFORMATION AND FAILURE IN 3D FIBRE-REINFORCED COMPOSITES

Other conference contribution, 2019

A class of composite materials with fully 3D fibre-reinforcements have shown weight efficient strength and stiffness characteristics, as well as promising energy absorption capabilities. In fact, Khokar et al. \cite{khokar} have demonstrated that, in bending, such a 3D-CFRP I-beam has two to three times the specific energy absorption capability of a steel I-beam with equivalent geometry. Note, the considered woven reinforcement has both horizontal and vertical weft yarns interlacing warp yarns in a grid-like set. This fibre network suppresses delamination and allows for stable and progressive damage growth in a quasi-ductile manner. While the considered 3D fibre-reinforced composite shows promise, developing a computationally efficient material model is crucial to supporting the material's widespread adoption across multiple industries. With the ultimate goal of developing a macroscale homogenised model to predict how the material deforms and eventually fails under loading, this work proposes a candidate for a phenomenologically based orthotropic viscoelastic damage model.

Previous experimental results indicate that this class of 3D fibre-reinforced composites exhibits linear material behaviour when loaded along one of the three nominal fibre directions. Shear loading however, produces a prominent non-linear response. This is likely due to the viscoelastic behaviour and damage of the polymer. In order to capture both the aforementioned linear and non-linear behaviours, a model inspired by crystal plasticity with viscoelastic slip planes is proposed. Specifically, a Norton type viscoelasticity model driven by shear tractions in preferred material planes is adopted. These planes are determined by the three reinforcement directions. As such, viscoelastic strain strictly develops when there is pronounced shear loading in these planes.

To enable the model to account for material degradation and failure, the components of the stiffness tensor  are assumed to degrade in accordance with pertinent damage modes. For this purpose models for unidirectional laminated composites such as Maimi et al. (extended to 3 reinforcement directions,) as well as those for 3D fibre-reinforced composites Marcin et al. explored. The applicability of the proposed model is assessed against results from mechanical experiments carried out under tensile, compressive and shear loading.