Osmotic Pressure-Filled Cracks

Abstract

In-service loss of load transfer is a slow process and, since it involves action by diffused water, the suggestion has been made that it proceeds by way of an interfacial failure process akin to stress corrosion in monolithic solids. It can occur without application of external stress. Debonded pockets in accelerated tests are often osmotic pressure-filled and propagate as cracks into the adjacent resin. It is demonstrated that osmotic pressure-filled cracks in polyester resin are elastic in nature and evidence is presented for concluding that their growth is by a slip/stick mechanism. An explanation involving crazing is offered to account for the alternate periods of crack blunting and sharpening. The appearance of fracture surface markings delineating positions of crack arrest are attributed to Griffith’s [1] observation that in a plate subjected to other than uniaxial tension perpendicular to the crack, the maximum stress concentration is close to but not at the crack tip. Measurement of crack profiles is used to determine the rate dependence of Young’s modulus and, by assuming that the periods of crack growth are adequately described by linear elastic fracture mechanics, an attempt is made to compare these periods for three different test temperatures.