Residual strain effects on bridging stress of cracked and delaminated fiber metal laminates

An analytical model is developed that accounts for the effects of both residual thermal strain and residual post-cure stretching strain in the prediction of the bridging stress and the crack opening displacement (COD) of cracked and delaminated fiber metal laminates. Two GLARE® tensile specimen configurations with center cracks in the aluminum layers, one with elliptically shaped delaminations and the other with rhomboidally shaped delaminations, are analyzed with the governing solutions of the analytical model. The shear deformations at the delamination front of either the resin rich region at the metal-fiber layer interface or the fiber layer itself are modeled. Analytical results show that the presence of residual thermal strain reduces the bridging stress while residual post-cure stretching strain increases the bridging stress. A high post-cure stretching level, inducing a greater bridging stress for lowering the COD and also affecting crack closure at crack tips, can result in an increased fatigue life. The use of either of the two shear models has negligible effect on the calculated bridging stress and COD. The analytical results are correlated with available test data of CODs for validating the analytical model. Copyright © 2010 by ASTM International.