Effect of crack size on fracture of high yield stress materials

Abstract

The paper considers the behaviour of (brittle) high strength materials for which the onset of crack extension and fracture instability are coincident in a fracture mechanics type test where the crack is sufficiently long that the plastic deformation, which is associated with the onset of crack extension, is highly localized to the vicinity of the crack tip. A theoretical analysis shows that both the J integral at the onset of crack extension and the effective fracture toughness decrease below their long crack values as the pre-existing crack size decreases. However, the predicted decreases are only small (≲515%) as the pre-existing crack size decreases to a level at which the applied stress approaches the tensile yield stress of the material. The theoretical predictions are consistent with the experimental results obtained by Wilshire and Knott.