Numerical and Experimental Study of Flax-Basalt Composites Impact Behaviour

Fiber-reinforced composite materials are usually adopted for transportation applications, where the impact behavior is crucial for vehicle safety and protection. Therefore, since composites are characterized by low toughness and consequent poor damage resistance, several authors have investigated different approaches to improve the impact resistance, such for example the addition of rubber particles to the polymer matrix or the reinforcement hybridization to obtain a new material by exploiting the benefits of all its constituents. Hybridization gives the possibility to realize composites with more balanced and tailored properties by lowering the costs too. In this work, the low-velocity impact behavior of hybrid composites has been numerically and experimentally investigated. In particular, epoxy-based laminates based on only 16 basalt twill, only 16 flax twill, and 16 flax/basalt layers, alternatively stacked have been realized by the vacuum infusion process. Basalt and flax fibers can be both considered green fibers, having the first ones a mineral origin and the second one a natural source. Thus, their adoption combines the impact resistance of basalt fibers and the actual environmental sustainability issues. The experimental results showed the advantage of fiber hybridization and evidenced better impact performances for the hybrid composites than those of pure basalt and pure flax laminates. In addition to the experimental tests, to implement and optimize a predictive tool for the impact resistance behavior of composite laminates, Finite Element (FE) models were developed by using the LS-DYNA solver. The model consisted of 16 shell layers connected by cohesive elements to better reproduce the delamination phenomenon. The boundary conditions applied were the same as for the physical tests. It is known that, in the definition of numerical models, some parameters cannot be experimentally determined or are not available from the tests; therefore, a trial-and-error approach was properly used to select them. The numerical results showed a good reproduction of the experimental trend and can therefore be considered as a valid and capable tool for the impact behavior simulation of other hybrid solutions or different stacking sequences.