Temperature and rate dependent fracture in glass‐filled polystyrene

The rate and temperature dependent fracture behavior of glass‐filled polystyrene has been investigated over the crack speed range of 10¹³ to 1 mm/sec and in the temperature range 283 to 396°K for three environmental conditions: (i) air; (ii) water; and (iii) hot water exposure at 363°K and subsequent drying. Relationships between fracture toughness (K_c), crack speed and temperature have been obtained experimentally and analysed according to the concepts of fracture mechanics and reaction rate theories. Crack propagation in air is shown to be controlled by a β‐relaxation process associated with crazing. Activation energies of 200 ∼ 210 kj/mole in air and 80 ∼ 120 kj/mole in water are reported. At a given temperature and crack speed, the glass‐filled polystyrene is shown to display smaller crack propagation resistances in a water environment when compared with the air results. Specimens subjected to hot water exposure and then tested after drying also possess less cracking resistance. This toughness degradation phenomenon is a result of the damaging effects of the water which penetrates into the glass‐filled composite.