A Finite-Element Analysis of Nonlinear Behavior of the End-Loaded Split Laminate Specimen

A finite-element analysis has been developed to evaluate the J-integral for the end-loaded split laminate specimen (ELS) used to characterize Mode II delamination fracture toughness of composites. The analysis includes the use of nonlinear beam theory to evaluate the J-integral from typical output data obtained using nonlinear beam elements. The beam elements include large deflections and rotations, midplane straining, and the effect of shear deformations. Several composite laminates going from unidirectional to multidirectional layups have been studied. The path independence of the J-integral using this analysis has been verified except for paths very close to the crack tip where the complex state of stress that develops at the crack tip invalidates beam theory approximations. For all the layups studied, midplane straining from the development of large rotations shows no significant effect on J. Furthermore, J has been found to be independent of shear deformations even when shear deformations are no longer negligible in the load-deflection response of the ELS. The effect of limited inelasticity on J, as is typical of multidirectional layups, has also been studied. This analysis illustrates the feasibility of evaluating the J-integral from simplified finite-element analyses, where global quantities away from the complex state of stress at the crack tip are used instead of local stresses and strains near the crack tip.