Buckling analyses of composite laminated panels with delamination

Abstract

Buckling response of composite laminated panels with an arti cial delamination was numerically investigated. Implementation of the nite-element models required a previous study on the simulation of fracture mechanisms under general mixed-mode loading conditions with the use of cohesive elements. To pursue this aim, a methodology based on numerical analyses and parametric studies of the DCB (Double Cantilever Beam) and ENF (End Notched Flexure) tests on AS4/PEEK laminates was developed. Comparison to available experimental data enabled to determine a reduced set of parameters which, controlling the response of cohesive elements and the variable discretization pattern over the model, provided a good compromise between accuracy and computational cost in both single-mode delamination cases. Validation of the obtained set of parameters took place through the simulation of the MMB (Mixed-Mode Bending) test at three di erent mode ratios. Good agreement with experimental measurements found in literature suggested extending the usage of the found set in more complex problems, such as delamination buckling of a damaged HTA/6376C plate, whose fracture-related properties are comparable to those of AS4/PEEK. Through a careful de nition of the geometric imperfection, the adopted nonlinear static approach showed to yield predictions of the failure load in good agreement with experimental results reported in literature. Finally, a qualitative study was conducted about the reduction of compressive strength caused by delaminations of di erent sizes, shapes and through-the-thickness locations within an AS4/PEEK panel. Conclusions showed to be consistent with similar previous works conducted by other authors, evidencing a reduction of the compressive strength with the delamination size and depth. On the contrary, no signi cant in uence of the delamination shape (circular or square) was observed.