Craze Initiation Criterion in Glassy Polymers under High Pressure.

摘要

The initiation of crazes in glassy polymers is accounted for by a single criterion according to which crazing occurs when the maximum stress at the tip of a flaw (sigma(max)) reaches a critical value. This criterion can explain the initiation of crazes in polymethylmethacrylate and polystyrene tested in tension under superposed hydrostatic pressure. A single value of sigma(max) for each of the two polymers has been calculated and found to be independent of the applied hydrostatic pressure whether or not the polymer was exposed to the pressure-transmitting fluid. Our analysis predicts that relatively small stress-concentrations suffice for craze initiation even under remote compressivve stress states (negative first stress invariant). The predicted stress concentrations are in reasonable agreement with experimentally determined values. (Author)