Multiaxial loading on a 3D woven carbon fiber reinforced plastic composite using tensile-torsion tests : Identification of the first damage envelope and associated damage mechanisms

This study focuses on the experimental identification of the first damage envelope in a 3D woven composite with polymer matrix, under mull-axial loadings including combined in-plane tension and out-of-plane shear loadings (sigma-tau envelopes). Proportional Tensile-Torsion tests on rectangular bars were performed to induce different multiaxial stress states. To enable envelopes identification, onset of the first damage has been evaluated thanks to the correlation of various and complementary investigation measurement techniques, such as Stereo-Digital Image Correlation (Stereo-DIC), Acoustic Emission (AE) and in-situ microscopic observations. In addition, a specific data reduction process has been used to manage accurate quantification of the stress state induced by the multiaxial loadings. Based on these findings, both sigma(11)-tau(13) and sigma(22) -tau(23) envelopes were identified on a 3D woven composite material with polymer matrix. Using microscopic observations, damage mechanisms (type and localization) related to the mull-axial loadings were identified. In addition, thanks to the strain fields measured by the Stereo-DIC on the material surface, particular relations between the mull-axial loadings and the 3D woven architecture have been established.