The fracture morphology of fast unstable fracture in polycarbonate
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Fracture tests were conducted on polycarbonate using compact tension specimens. With the aid of fractographic analysis techniques the effects of various geometric and test parameters on the fracture-surface morphology were studied. Four distinct regions were identified on the fracture surface: (i) initiation region, (ii) mist region, (iii) mirror region, and (iv) banded region. The extent of the mist region was found to depend inversely on the ratio of the initial crack length, a, and the specimen width, W. The fracture morphology also was affected by changes in the test temperature and externally applied compressive loads, but it did not exhibit any significant trends as a function of the loading rate. A qualitative model, called the “critical thickness craze crack interaction” (CCI) model, was developed to explain the micromechanisms involved in the fracture process. This model is based on the proposition that the various features on the fracture surface are generated by the interaction of the crack with a critical thickness craze, where the latter is that part of the main craze which has a thickness greater than some critical thickness, d.
KeywordsFracture Surface Crack Length Polycarbonate Compressive Load Initial Crack
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