Numerical simulation of matrix micro-cracking in short fiber reinforced polymer composites: Initiation and propagation

This paper presents a numerical simulation based analysis of micro-cracking in short fiber reinforced polymer composites. For this case, the conventional linear elastic fracture mechanics approach is shown not to be useful; instead, the Rice–Tracey ductile fracture model is shown to work well in the framework of the local approach to fracture. The model is first applied to the case of matrix cracking from the broken fiber end in a fiber fragmentation test of a single-fiber reinforced composite. The model predicts the measured conical crack path successfully, including the crack initiation angle and the kink formation as the crack propagates away from the fiber. Furthermore, the predicted dependence of the crack length on the nominal strain is found to be in qualitative agreement with measured data. Next the model is applied to micro-cracking in an aligned short fiber composite. The analysis predicts propagation of a matrix crack from the debonded fiber end towards the neighboring fiber at an oblique angle to the fiber axis. Before reaching the neighboring fiber, the crack is found to divert gradually towards the fiber axis. This behavior explains the so-called fiber-avoidance cracking mode reported in the literature. A parametric study is performed to reveal the dependence of the locally-averaged failure stress/strain on the fiber length and volume fraction.