Damage and failure mechanisms in composite bolted joints

This study's overall goal is to develop methods to accurately predict the strength of notched composite laminates. Empirical analyses of notched composite test data led to an understanding of failure mechanisms. Trends in ultimate strength versus layup parameters were extracted from several DoD test programs. A test program with incrementally loaded, notched coupons was conducted to track sub-critical damage. Damage states at near-ultimate loads were correlated to the ultimate strength trends. These trends were then attributed to specific matrix damage types. Detailed finite element analyses of composite bolted joint configurations were conducted using solid element models with nonlinear material properties. Sensitivity studies were conducted to determine the mesh refinement needed for converged peak stresses. At the loads corresponding to initial damage in the incremental notched tests, linear and nonlinear finite element analysis consistently predicted peak ply stresses which were significantly higher than ply strengths derived from unidirectional coupon tests.