An investigation of the effects of crack front curvature on the crack-tip opening displacement of A707 steel

This paper examines the effects of crack front curvature on the fracture toughness (crack-tip opening displacement) of A707 steel. Fracture mechanics specimens, in which the radii of curvature of the crack fronts are controlled in an effort to simulate potential variations in crack front profiles in fracture experiments, were produced by machining and fatigue pre-cracking. Three-point bend crack-tip opening displacements (CTODc) were measured in accordance with the ASTM E-1290 code. The results show that the critical CTODc increases with increasing crack front curvatures between 0.05 and 0.17 mm(-1). In all cases, stable crack growth and final catastrophic failure of the specimens are found to occur by transgranular ductile dimpled fracture, in which the ductile dimples are nucleated around MnS or Al-2(Mg)O-3 inclusions. The implications of the results are discussed for the measurement of critical CTODc in specimens with varying levels of crack front curvature.