Fracture toughness and fracture mechanisms of PBT/PC/IM blend |
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Authors: | Jingshen Wu Yin -Wing Mai Brian Cotterell |
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Affiliation: | (1) Centre for Advanced Materials Technology, Department of Mechanical Engineering, University of Sydney, 2006 Sydney, New South Wales, Australia |
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Abstract: | The static and impact fracture toughnesses of a polybutylene terephthalate/polycarbonate/impact modifier (PBT/PC/IM) blend
were studied at different temperatures. The static fracture toughness of the blend was evaluated via the specific fracture
work concept and the J-integral analysis. A comparison of these two analytical methods showed that the specific essential fracture work, W
e, was equivalent to the
obtained by the ASTM E813-81 procedure, representing the crack initiation resistance of the material. The discrepancy between
W
e and
of ASTM E813-89 was caused by the extra energy component in
consumed by a 0.2 mm crack growth. Impact fracture toughness was also analysed using the specific essential fracture work
approach. When the fracture was elastic, W
e was equivalent to the critical potential energy release rate, G
IC, obtained via LEFM analysis. Temperature and strain-rate effects on the fracture toughness were also studied. The increase
in impact toughness with temperature was attributed to two different toughening mechanisms, namely, the relaxation processes
of the rubbery particles and the parent polymers in a relatively low-temperature range and thermal blunting of the crack tip
at higher temperatures. The enhancement in static fracture toughness at temperatures below — 60 °C was thought to be caused
by plastic crack-tip blunting, but the monotonic reduction in yield stress was largely responsible for the toughness decreasing
with higher temperatures. The temperature-dependent fracture toughness data obtained in static tests could be horizontally
shifted to match roughly the data for the impact tests, indicating the existence of a time-temperature equivalence relationship. |
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Keywords: | |
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