Post-buckling and First-ply Failure of Thin-walled Frames and Columns Made of Composite Materials

First-ply failure (FPF) of composite thin-walled columns and frames is investigated in the buckled structure. Elastic behavior is assumed during the pre-buckling and buckling states, and along part of the post-buckling equilibrium path. The Tsai-Hill criterion is employed to identify failure of one ply at one specific location. The technique of analysis is based on evaluation of the post-buckling elastic path, and using FPF as a constraint in the analysis. The structure is modeled using a few degrees of freedom to include local and/or overall buckling modes. The theoretical results are compared with experimental bounds and show good agreement for local. buckling of isolated columns. There are no experimental results for frames in the literature, but theoretical results are presented for a simple case with asymmetric bifurcation.