Fluid transport into crazes under triaxial stress

The penetration coefficient of silicon oil (500 cS) into PS during tensile deformation was determined under a range of superposed hydrostatic pressure of 1 to 1200 bars. At atmospheric pressure, the liquid front, driven by a relatively high capillary pressure, was found to lag behind the "dry" craze tip front. The penetrability was observed to increase as a steep linear function of the pressure up to 80 bars at which the liquid front was forced to reach the craze tip front. At higher pressures, a stage of suppressed penetrability was observed which was associated with a substantial decrease in the craze size and density. The suppressed penetrability is explained on the basis of pressure induced "void" reduction competing with its pumping component. An effective axial strain analysis is presented to explain such a reduction. The effect of pressure on the maximum stress at the tip of a flaw, in conjunction with the distribution of surface defects, is found to account for the suppressed craze density at elevated pressures.