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Fracture tests have been conducted on polycarbonate in the elasto-plastic and fully plastic regimes. The fracture behavior was well characterized by the J-integral. The value of the J-integral at the initiation of crack growth, corresponding to JIc, was 2.1 kN/m (12.2 psi∙in.) for the 1981 ASTM Test Method for JIc, a Measure of Fracture Toughness (E 813-81), and 3.3 kN/m (19 psi∙in.) for the 1987 ASTM (E 813-87). It was found that the value of the J-integral at 2% crack growth, 4.4 kN/m (25 psi∙in.), corresponded well with values of KIc in the literature. It is suggested that the value of J at 2% crack growth may be a better parameter to characterize fracture than J at initiation. The value of the J-integral at popin or unstable fracture, 7.3 kN/m (41 psi∙in.), was consistent for all the experiments. No effect of crack length or thickness was observed for any of these values of J. Two difficulties with the use of the 1987 standard were found. The first was that the data did not coincide with the blunting line. More crack growth was measured than predicted by the blunting line. The second was that a valid data point between the 1 and 1.5-mm offset lines could not be experimentally obtained because of the nature of crack growth in polycarbonate.
elastic-plastic fracture, test methods, polycarbonate, J, -integral, fracture toughness
Principal engineer, Southwest Research Institute, San Antonio, TX