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

Abstract

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 ( T ) range of 296 to 363 K. The K c (a, T) relationships obtained, where K c 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 β -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 i 2 ( K i being the crack initiation stress intensity factor) and δ s , solvent solubility parameter, of various liquid environments have been obtained, which give a minimum K i 2 value at δ s ≈ δ p , where δ 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.