Modeling delamination characteristics and influence in a laminated plate with a part-through hole

Abstract

A laminated composite pressure vessel subjected to a concentrated laser ablation process has been investigated. The primary goal of this research was to investigate the role of delamination in the failure process. A layered structural finite element methodology was developed which modeled each lamina of a laminate explicitly with structural finite elements. A kinematic constraint was incorporated to provide laminate behavior, which enforced the continuity of displacements at ply interfaces. Delamination behavior was provided by selectively deactivating the kinematic constraint. In order to measure the propensity for delamination extension, a virtual crack closure technique was used. Crack tip closure forces were calculated in the form of internal forces at ply interfaces resulting from the constraint. In order to gain insight into the delamination characteristics of the pressure vessel problem, the notched tensile bar (NTB) was used as a simplified approximation for the pressure vessel problem. The NTB also provided verification steps for the layered structural finite element methodology. Stacked beam and plate element models of the NTB provided total strain energy rates which compared very well with an analytical solution and with 2-D continuum finite element solutions. Overall, the results of the beam and plate finite element models demonstrate the ability of the layered structural finite element methodology to reflect the characteristic trends of delamination behavior. The pressure vessel problem was then investigated using the layered structural finite element methodology, where a flat laminated plate, with a part-through hole, under unequal bi-axial loading represented the pressure vessel. A specific model of an eight layer laminate with a hoop/helix layup of [0°/0°/[plus or minus] 77°/0°/0°/[plus or minus] 77°] with a 1.0 cm diameter part-through hole of variable depth was investigated under a variety of delamination configurations. The delamination behavior indicated stable, non-uniform strain energy release rate distributions, with a decreasing tendency to grow with an increase in delamination length or part-through hole depth. Finally, the influence of delamination upon the lamina stresses results in stress redistribution and intensification.