Mesoscale simulation of natural fibre reinforced thermoplastics for crushing investigations

Kurzfassung

Global climate changes and recent energy crises raise challenges on the society which can be partially tackled by technological breakthrough. To address this issue, the reduction of carbon-based materials is required in new transportation system based on UN Sustainable Development Goals (SDG). Natural fibres such as flax or hemp offer a promising solution to improve the sustainability of transportation systems. However, they suffer from lower mechanical properties compared to carbon or glass fibres and from a high sensitivity to moisture. The present work aims at building a numerical framework and developing robust mesoscale models to potentially replace resource-intensive experimental material screening in pre-design phases. In particular, these models could help estimating the influence of fibre and resin types on the crushing or impact properties of natural fibre composites. In this study, compacted periodic mesoscopic unitcells of woven flax and hemp fibre reinforced thermoplastics are generated using a Python routine and simulated with the explicit solver in LS-DYNA. The models represent in detail the structure of the impregnated yarns embedded in pure resin material. The non-linear elastic-plastic material behaviour of the resin is simulated with the material model *MAT_PLASTICITY_COMPRESSION_TENSION to account for tension/compression asymmetry. In a first approach, the orthotropic consolidated tows are modelled with *MAT_ENHANCED_COMPOSITE_DAMAGE while delaminations are represented via a cohesive contact using a trilinear traction separation law. Additionally, the resulting mechanical properties under quasi-static in-plane loading are experimentally validated with various material tests on samples extracted from hot pressed plates. Benefiting from the potential of virtual testing, periodic sub-models of tubes are finally generated with a morphing algorithm and loaded under transient-dynamic crushing at 10 m/s. In simulation, the crushing behaviour of the investigated natural fibre composite is lowered by instable failure modes such as buckling as shown in Figure 1 at point C, highlighting the need for increased thicknesses. The developed numerical approach allows assessment of the specific energy absorption for various composite types and fibre/resin systems prior to any mechanical tests. It therefore helps accelerating material screening and lowering material expenses. The contribution will discuss key steps and methods for the model generation and validation.