The relation between the fracture toughness of plates and the thickness of the shear lips

Abstract

Single edge-cracked plate tension fracture toughness specimens were machined from Comsteel 3140 and an Atlas steel of approximately the same grade. Specimens were fatigue-precracked, quenched. and then tempered at various temperatures. Tensile specimens were machined from the same stock and heat treated with the fracture toughness specimens. Yield stress (0.2% offset), σ y , was determined from the various tensile specimens, and fracture toughness. K c , from the fracture toughness specimens. The average thickness of the shear lips, t 8, was measured on the fracture toughness specimens. Over the range of relative fracture toughness (0.12 ⩽ K c / σ y ⩽ 0.55) it was found that t 8 could be related to K c and σ y through t 8 = 0.18 ( K c / σ y ) 1·9. A rationale for this result is that t 8 is approximately equal to the radius of the plane stress plastic zone at and near the free surface of the plate specimens, r y , which is estimated from analysis as r y = ( 1 2 π) ( K c / σ y ) 2 = 0.16 ( K c / σ y ) 2. The application of the result to failure analysis is discussed.