Fracture of polymethylmethacrylate at low temperatures

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Abstract
The deformation and fracture of polymethylmethacrylate (PMMA) at low temperatures has been studied with particular emphasis on fracture at 78°K. Surface steps (of maximum height ∼ 1500 Å) perpendicular to the tensile axis are evident on fractured specimens. The formation of the steps results from the generation and growth of crazes within the material. Fracture is nucleated at these surface steps and, consequently, the fracture process in PMMA is not due to pre-existing flaws in the material but is nucleated by these defects which are generated by the applied stress. It can, therefore, be concluded that fracture in PMMA at all temperatures below T g involves characteristic plastic deformation processes. It is suggested that the low and high-temperature crazes are a consequence of the same process; the difference in morphology is a reflection of the difference in molecular mobility at the respective temperatures.