Effects of crack shape on fracture toughness in a high-strength structural steel

Cracks in standard laboratory testpieces may not always be representative of those found in structural components, which are often surface-breaking, part-through cracks. The work described in this paper attempts to compare the behaviour of both through- and surface-cracked testpieces, particularly in the ductile-brittle transition range. It was found, in general, that the maximum depth position of a surface crack was equivalent to a through-thickness crack of the same crack depth in terms of calculated stress intensity and crack opening displacement. The top surface, on the other hand, was found to exhibit larger values of critical stress intensity and crack opening displacement. The implications of these observations are discussed.