SUBCRITICAL CRACK-GROWTH IN GLASSES UNDER CYCLIC LOADS - EFFECT OF HYDRODYNAMIC PRESSURE IN AQUEOUS ENVIRONMENTS

The effect of hydrodynamic pressure developed in the wake of a crack g rowing in a brittle material under cyclic loads in an aqueous environm ent is considered. The pressure acts in opposition to the movement of the crack faces, thus shielding the crack lip from the applied loads. A general hydrodynamic fluid pressure relation based on a one-dimensio nal Reynolds equation, which is applicable to a crack with an arbitrar y crack opening profile, is developed. The model is modified to accoun t for side flow through the thickness of the sample and cavitation nea r the crack tip. Both effects significantly modify the hydrodynamic pr essure distribution. Finally, the resulting hydrodynamic pressure rela tions are combined with a fracture mechanics model to account for the change in the near-tip stress intensity. Resulting predictions of the cyclic crack-growth rate are found to be in good agreement with measur ed values for a borosilicate glass tested at various frequencies in a water environment. (C) 1997 Acta Metallurgica Inc.