Buckling strength of square composite plates with geometrical imperfections: Preliminary results

Tests have been performed on square composite plates under in-plane compression. Theplateshad a width-to-thickness ratio close to the value for which the elastic critical load and the load for compres-sive fibre failure over a complete section would be equal, giving the maximum sensitivity to initial geometric imperfections. Some of the plates were manufactured with no intentional imperfections or defects, others with an intentional initial out-of-plane geometric imperfection. An advanced digital photogrammetry measurement system was used to monitor deformations of the tested plates. The responses were also calculated by means of geometrically non-linear finite element analysis. With the assumption of rotationally fixed edges, the calcu-lated elastic critical loads were significantly higher than those deduced from the measurements. Closer ex-amination revealed that the loaded edges of the plates rotated significantly during the tests. It was found nec-essary to include in the analysis the observed variation of edge rotation with applied in-plane displacement. Although material non-linearity was not modelled, some conclusions concerning the failure sequence were drawn from the analyses.