Investigation on failure mechanisms of composite structures subjected to 3D state of stresses

Abstract

In this project, in cooperation with Airbus-France, an innovative failure approach to predict the rupture of composite structures subjected to complex 3D state of stresses has been proposed [1]. It was first necessary to understand the failure mechanisms occurring in L-angle specimens and to determine intrinsic out-of-plane strengths. The different out-of-plane failure mechanisms in composite laminated structures were identified by an experimental test campaign conducted on composite specimens subjected to different 3D states of stresses with different stacking sequences and thicknesses. This experimental test campaign has been performed on T700GC/M21 material and can be decomposed in three main batches of tests: Four Points Bending (FPB) tests on L-angle specimens, InterLaminar Shear Strength (ILSS) tests on plain laminated coupons, Unfolding Tests (UT) on L-angle specimens to validate the proposed mesoscopic 3D failure criterion. In each case, advanced measurement techniques was used (such as 3D Digital Image Correlation) in addition to standard investigation (strain gauge, LVDT measurements and micrographic analysis) in order to capture the different damage and failure mechanisms occurring during 3D loadings and to validate the FE computation. Due to the complexity of the problem, this study has been performed with a strong connection between experimental data and modeling with finite element analysis.