Low-velocity impact response of stitched composite plates: effects of geometry and support conditions

The present study investigates the transverse low-velocity impact response of stitched quadraxial non-crimp E-glass/epoxy composite plates with a symmetric (0°/+45°/90°/−45°)s stacking sequence through systematic variation of plate geometry and boundary conditions. Two distinct geometries, namely circular plates (clamped over a 76.2 mm diameter window) and rectangular plates tested at three support spans (40, 60, and 80 mm), are examined under impact energies ranging from 5 to 25 J using an instrumented drop-weight testing system. This structured experimental approach enables a direct comparison of the effects of geometry and bending compliance within the same material system. The findings indicate that both geometry and span length exert a substantial influence on the impact response. Increasing the span length has been shown to reduce bending stiffness, leading to lower peak loads and higher deflections. It has been demonstrated that circular plates exhibit intermediate stiffness behaviour, which can be considered as a compromise between the stiffer behaviour exhibited by short- and mid-span rectangular configurations. Furthermore, it was observed that penetration and perforation thresholds were only evident in circular plates, while rectangular plates remained below these limits within the investigated energy range. Post-impact visual inspection revealed distinct damage mechanisms depending on specimen geometry and boundary conditions.