Cycle-Dependent Fracture of Polymethyl Methacrylate

The fatigue behavior of PMMA and its fracture surface appearance have been studied over a range of stresses giving lives from 2×103 to 3×107 cycles. It has been proved that PMMA fails in a cycle-dependent manner. However, the mechanism by which fatigue cracks are initiated in unnotched specimens remains uncertain. The appearances of the fatigue fracture surfaces of PMMA have a number of features in common with fatigue fractures in metals. Most notable is the appearance of striations or ripple markings which delineate successive positions of the fatigue crack front. As in metals, the striations are formed during stage-II crack propagation by the blunting of the crack tip on the tensile stroke followed by resharpening of the crack tip on the subsequent compressive stroke.