Compound bifurcations in the buckling of a delaminated composite strut

An analysis of the buckling and post-buckling of a delaminated composite strut is presented using a simple 4 degree of freedom nonlinear Rayleigh-Ritz formulation. Bifurcation analysis indicates that instability occurs in general at an asymmetric point of bifurcation. Depending on the depth of delamination both thin-film and overall buckling can occur in the post-buckling range, the transition being seen at a point of secondary bifurcation. For certain combinations of parameters this becomes a stellar bifurcation, associated with a double eigenvalue, where there are three possible subsequent routes for the post-buckling. The method used is fast and reliable and can be readily extended to modelling a composite with several layers.