Nonlinear modeling of delaminated struts

A phenomenological overview of the buckling and postbuckling of fully and partially delaminated struts is developed using a simple four-degree-of-freedom nonlinear Rayleigh-Ritz formulation. Bifurcation analysis indicates that instability occurs in general at an asymmetric point of bifurcation. After bifurcation, realistic solutions are seen to follow the stable part of the postbuckling path, with the unstable branch being denied by contact between the contributing laminates. Depending on the geometry and position of the delamination, thoroughly stable (thin-film), effectively neutral (overall), or potentially unstable (mixed-mode) buckling can occur in the postbuckling range. Numerically obtained equilibrium solutions of the model are found to compare well with those obtained using the finite element code ABAQUS. Critical delamination depths, where the response undergoes a change in form, are discovered at positions of secondary bifurcation. The multiplicity of equilibrium solutions that arise at such points are seen to cause possible problems of path selection for standard finite element routines.