Matrix failure in composite laminates under tensile loading

The failure envelope of the matrix in composite laminates under tensile loads has not received much attention in literature. There are very little to no experimental results to show a suitable failure envelope for this constituent found in composites. With increasing popularity in the use of micromechanical analysis to predict progressive damage in composite structures, it is important that matrix behaviour under tension is modelled correctly. In this paper, the authors present and test a new biaxial specimen design to investigate tensile matrix failure in composite structures. Through the use of micromechanical analysis, the authors developed a method in which the matrix stresses at failure can be extracted. Comparing to the existing off-axis test, it was shown that the presented specimen design and test methodology can improve the accuracy of the obtained matrix failure stresses, i.e., the matrix failure envelope for EP280 resin. Additionally, the results indicate that matrix failure takes place earlier than that predicted by von-Mises failure criterion and that the 1st Stress Invariant criterion can better predict matrix failure under tensile loading.