Observations of fibrous fracture modes in a prestrained low-alloy steel

Abstract

Crack-opening displacement (COD) tests have been performed on prestrained QIN (HY-80) low-alloy steel. In specimens containing fatigue precracks the COD is largely insensitive to prestrains below 0.17, but a significant reduction in COD occurs at higher prestrains. Measurements of the yield-stress variation with tensile strain have enabled the effects of prestrain on fracture toughness to be estimated. Apart from a small initial increase, the general effect of prestrain is to reduce fracture toughness. The decrease in toughness with prestrain is accompanied by the development of zig-zag fractures. Crack growth appears to be intermittent and occurs by a process of shear decohesion along paths corresponding to either the spiral slip-lines emanating from a blunted cracktip, or, at lower displacements, the straight slip-lines emanating from a sharp crack.