Fatigue Fracture of Polymethylmethacrylate

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Abstract
Two distinct fracture morphologies have been observed in commercial grade polymethylmethacrylate (PMMA) cycled to failure at room temperature in uniaxial loading. In extruded PMMA the fatigue striations are concentric with one origin, increasing in spacing until final fracture occurs. Some of the fatigue striations are serrated owing to the crack being stalled by flaws which are inherent to the material. The region of fatigue crack growth is flat and glassy smooth. In cast PMMA the fatigue striations occur in many localized regions near the surface and are not serrated. There is no apparent regularity to the striations on a scale comparable to the extruded PMMA. It is concluded that the differences in the fatigue fracture surfaces between cast and extruded PMMA reflect a difference in molecular weight.