Influence of boundary conditions on the residual compressive strength of impacted thin-walled GFRP channel section profiles

Compression after impact (CAI) is a crucial assessment for the strength and stability of thin-walled structures. This study investigates the post-impact compressive behaviour of composite channel section profiles to bridge the gap between standard coupon-level testing and more complex structural configurations, where internal damage interacts with buckling phenomena under compressive loading. The profiles, made of eight-layer glass fibre reinforced polymer (GFRP) with a quasi-isotropic layup, were impacted at the corner (45° to the web) with energies of 20 J and 30 J, then subjected to axial compression. Finite element models were developed to simulate both the impact and compression stages in a single simulation. Four types of boundary conditions (BCs) were analysed: nodal displacement, U-shaped groove, V-shaped groove, and flat plate. The resulting force–shortening responses were compared with experimental results. The study found that boundary condition representation significantly influences the CAI response. In particular, simplified BCs using only nodal displacements failed to capture the contact interactions observed in experiments. Accurate modelling of the physical boundary constraints was shown to be critical for replicating the post-impact behaviour. This work demonstrates that structural-level fidelity, especially in boundary condition treatment, is essential for reliable prediction of CAI performance in composite structures.