The fracture resistance of bi-axially orientated PMMA

The mechanical performance of the transparent polymer PMMA (polymethyl methacrylate) can be significantly enhanced by the process of bi-axial stretching during manufacture. However, few studies have reported on the fracture properties of bi-axially oriented PMMA. In this work, the fracture toughness and resulting surface morphology of bi-axially orientated PMMA has been investigated by testing single edge notch bend fracture specimens under quasi-static test conditions. The orientation of the specimens with respect to the stretching direction was systematically varied such that the effect of in-plane orientation and out-of-plane orientation was determined. The out-of-plane fracture resistance was shown to be enhanced compared to the in-plane resistance and compared to amorphous PMMA. Both out-of-plane and in-plane crack orientations had little effect on fracture resistance. Complex crack growth behavior and surface morphologies were observed in the out-of-plane direction. The results have important implications for the study of damage tolerance of transparent canopies in the aircraft industry.