Effects of rate. temperature and absorption of organic solvents on the fracture of plain and glass-filled polystyrene

The rate/temperature dependent fracture behaviour of plain and glass-filled polystyrene has been investigated over the crack speed (a) range of 10 -6 to 10 -2 m sec -1 and in the temperature (7-) range of 296 to 363 K. The Kc (a, T) relationships obtained, where Kc is the stress intensity factor at fracture, are shown to follow those given by the Williams/ Marshall relaxation crack growth model and the toughness-biased rate theory. Crack propagation in both materials is shown to be controlled by a ~-relaxation molecular process associated with crazing. Crack instabilities observed in plain polystyrene are analysed successfully in terms of isothermal-adiabatic transitions at the crack tip. Fracture initiation experiments are also conducted in which the effects of organic liquids on the fracture resistances of both plain/glass-filled polystyrene have been determined. Good correlations between K~ z (Ki being the crack initiation stress intensity factor) and 6s, solvent solubility parameter, of various liquid environments have been obtained, which give a minimum/~ value at 6s ~ (~p, where ~p is the solubility parameter of the polymer. For a given temperature, liquid environment and crack speed, the glass-filled polystyrene is shown to possess greater resistances to crack propagation than plain polystyrene.