The environmental stress-crazing and cracking in polystyrene under high pressure

Abstract

Tensile experiments on polystyrene (PS) in various pressure-transmitting fluids were performed up to 4.0 kbar to study the effects of test media on the mechanical behavior of amorphous polymers under pressure. The fracture stress of PS in silicon oil environment was found to depend strongly on the viscosity of oil and the strain rate of tensile tests. As the strain rate increases, the fracture mode at 2.5 kbar was observed to change from brittle to ductile at some critical strain rate, a rate which shifts to a higher value with decreasing viscosity of silicon oil. In addition, creep fracture experiments conducted at 2.5 kbar in silicon oil with different viscosities suggested that the environmental effects are governed by the rate of diffusion of the environmental liquid into the tensile specimen. Fourier transform infrared measurements performed on specimens fractured in silicon oil environment under pressure proved that the penetration of liquid takes place mainly through the porous structure of the crazes. It was also found, surprisingly, that water, which hardly affects the mechanical behavior of PS at atmospheric pressure, becomes a significant stress-cracking agent under higher pressure.