Fatigue fracture of polycarbonate

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Abstract
The fatigue fracture process in polycarbonate can be different for cracks grown from notches and from surface crazes. During the discontinuous crack growth process (which occurs during the very slow crack growth regime), full‐width cracks grown from notches have a very different crack tip plastic zone when compared to that observed in localized cracks grown from surface crazes. These localized surface cracks have a pair of sharply defined shear bands at the crack tip (forming the “epsilon” plastic zone) that are absent from notched‐grown cracks, The presence of the shear band pair in this plastic zone produces two major modifications. The discontinuous crack growth is extended to higher stress intensity ranges due to the (crack tip) craze stabilization by the shear band pair. Moreover, a shear fatigue fracture mode, absent in the notched specimens, occurs upon termination of the discontinuous growth process. The implications of this comparison are that estimates of fatigue lifetimes of smooth samples based on fatigue crack growth data (on notched specimens) may be erroneous.

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