Residual crashworthiness of CFRP structures with pre-impact damage – An experimental and numerical study

This study investigated the effect of transverse pre-impact damage on the load bearing capacity and failure behavior of square carbon fiber reinforced plastic (CFRP) tubes for axial crushing. The CFRP tubes were impacted transversely in different levels of impact energies to generate initial damage, and then the specimens were further crushed axially to evaluate the relation between transverse impact energies/positions and the residual axial crashworthiness. A finite element (FE) model was also developed to simulate the complex damage behavior of the CFRP tubes under these two different loading processes, based upon the continuum damage model (CDM) with user-defined material subroutine in Abaqus. A combined failure mode was observed in the transverse pre-impact tests, in which delamination was combined with partial or complete fiber breakage when increasing the impact energy from 10 J to 30 J. In the axial compression tests, two typical failure modes with circumferential fracture near the pre-impact position were identified for the damaged tubes, exhibiting significant difference from the progressive folding failure seen in undamaged tubes. Further, the damaged tubes yielded up to 38%, 58.5% and 58.3% reduction in terms of the peak load, mean load and energy absorption respectively in comparison with the specimens without pre-impact damages. It is also found that the residual crushing capacity decreased with increase in the transverse pre-impact energy; nevertheless the residual axial crushing properties were insensitive to single or double impacts on different circumferential positions. The failure modes of fiber breakage, delamination and matrix crack were investigated in detail by using the FE analysis.