Multi-impact mechanical behaviour of short fibre reinforced composites

High velocity transverse impact on reinforced composites is a matter of interest in the automotive, aeronautical and biomedical sectors. Most existing studies have addressed this problem by single isolated impacts; however, this work deals with the distinction between single, sequential and simultaneous impacts on composite structures. This paper proposes an experimental methodology to study the mechanical behaviour of materials under single and multi-impact loadings. The overall objective is to investigate the mechanical response of short carbon fibre reinforced PEEK when is subjected to single and multiple high velocity impacts. Experimental tests are conducted covering impact velocities from 90 m/s to 470 m/s. Energy absorption, damage extension and failure mechanisms are compared to assess additive and cumulative effects in high velocity impact scenarios. Experimental results show that the specific deformation and fracture mechanisms observed during multi-hitting events change with impact velocity. Compared to the behaviour of unreinforced thermoplastics, short fibre reinforced composites present significant limitations at velocities close to the ballistic limit, but multi-hit capability is observed at high impact velocity when the damage is mainly local. As key conclusion, the ballistic limit obtained in single impact test cannot be extrapolated to sequential and simultaneous tests. Multi-impact tests, especially close to the ballistic limit, are necessary to guarantee the structural integrity of composite structures in realistic impact scenarios.