Structural response of stiffened composite panels with circular delamination: Buckling and post-buckling analysis

Abstract

Abstract This study investigates the structural response of composite stiffened panels containing a circular delamination under axial compression. A comprehensive finite element model was developed using a cohesive-zone interface formulation and couples it with local and global buckling responses. The model was validated against experimental data with errors below 6% for both critical buckling and ultimate failure loads. A stiffened panel configuration close to the previously experimentally tested one was used to investigate the influence on buckling load and ultimate load due to delamination diameter, depth, and position on the skin plate. The results demonstrate that diameter is the most dominant parameter, accounting for up to 54% effect on buckling load and 77% on ultimate load. This was followed by depth, which notably affects stiffness (by up to 18%) and strength (by 6%). The interaction between diameter and depth was also significant, contributing to 27% effect on buckling load and 15% on ultimate load. In contrast, the influence of delamination position within the tested range was lesser than 2%. A key finding is the close correlation between post-buckling stiffness degradation, residual strength, and energy absorption capacity. This enables establishing the post-buckling stiffness ratio as an early-warning indicator of delamination-induced instability.