Fracture Toughness of Polycarbonate
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概要
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Fracture toughness tests have been carried out on extruded sheets of polycarbonate bisphenol A. The variations of fracture toughness, K_<1c>, with temperature, strain rate and crack direction in the partially orientated sheet, were studied. Slow bend tests provided quasi-static K_<1c> data whilst dynamic initiation values were obtained from instrumented Charpy impact tests. In both types of test high speed crack velocity measurements were made using conductive silver grids applied to the specimens. The variation of K_<1c> with strain rate and temperature was found to be small and in general agreement with expectations from the relaxation properties of polycarbonate. Notch acuity was found to have little effect in that values of K_<1c> and crack velocity from specimens having the standard Charpy notch were similar to values obtained from sharp cracked specimens. Some anisotropy was present in the material and gave rise to a small difference in K_<1c> values according to the direction of crack propagation relative to the extrusion direction. Crack velocity showed considerable dependence upon orientation, and fracture mode was also influenced such that the transition from stable growth to fast fracture occurred at much lower temperature when the crack path orientated at 90°to the extrusion direction. It was thought that dynamic toughness, K_d, was influenced more than K_<1c> by partial orientation of amorphous regions in the material and that the relaxation time for re-orientation was probably significant here.
- 社団法人日本材料学会の論文
- 1974-01-15