Progressive failure of notched and unnotched composites under biaxial tension-compression

Abstract

Although most tests on composites are conducted uniaxially, they are subjected to multi-axial loads in real-life applications. In this thesis, the behavior of unnotched and open-hole unidirectional carbon epoxy crossply laminates under various off-axis biaxial tension-compression loadings is studied using a mixed experimental and numerical approach. Strain measurements made using digital image correlation technique in cruciform test specimens show overall good correlation with finite element predictions based on the micromechanics of failure theory and material property degradation method. The necessity for adopting an aligned mesh concept where element edges are aligned with ply fiber direction for accurate prediction of progressive failure patterns is illustrated. The capability of the finite element model in predicting critical and sub-critical damage mechanisms governing failure in these laminates is assessed. Furthermore, the detrimental effect of off-axis loading and the introduction of an open-hole in carbon epoxy crossply laminates under the biaxial loading are investigated quantitatively.