The effect of thermo-oxidation on matrix cracking of cross-ply [0/90]S composite laminates

The present article focuses on the effects of thermo-oxidation on matrix cracking in cross-ply [0/90]S composite laminates. IM7/977-2 carbon/epoxy samples were firstly aged at 150 °C under 1.7 bars of oxygen for 24 h, 48 h and 96 h, respectively. Quasi-static tensile tests were then carried out on un-aged and aged samples. The number of matrix cracks was counted during the tensile tests in order to establish the evolution of the crack density as a function of the applied stress and a numerical model was employed to evaluate the critical energy release rate of un-aged and aged laminates. A reduction of the critical energy release rate of aged samples was measured compared to un-aged sample. Scanning Electron Microscopy (SEM) observations were carried out by replicas of the sample surfaces in order to identify a possible relationship between the thermo-oxidation induced damage at the local scale and the onset of matrix cracking at ply scale.