Matrix crack propagation criteria for model short-carbon fibre/epoxy composites

Linear elastic and elasto-plastic finite-element analyses have been used to investigate the initiation of a conical-shaped matrix crack from the end of a single sized carbon short-fibre embedded in an epoxy matrix subjected to tensile loading. A maximum hoop-strain criterion and the modified Rice and Tracey micro-void nucleation, growth, and coalescence model are used to predict the crack angle. In the later case the applied strain at failure is also predicted. When the effects of the thermal residual stresses induced during the fabrication process are included, the predicted cone angle of the crack decreases from 23 to 18°, according to the maximum hoop-strain criterion. By using the Rice and Tracey model a cone angle of 16° was predicted, with or without the inclusion of thermal residual stresses, whereas the failure strain of the composite was shown to increase from 0.14 to 0.3% when the thermal stresses were included.