Experimental correlation between ductility and J-integral in the transition region of 1045 steel

A study of the variation of fracture toughness jIC and ductility, measured under both tensile loading and biaxial plane strain (bulge) loading, of AISI 1045 steel in the annealed condition, in the transition temperature range of −60 to 25°C was carried out. This temperature range delineates the changes in behavior from linear elastic to elastic-plastic behavior for this steel. It was found that the variation of jic with temperature shows a transition at about −20°C while the bulge ductility only has a marked transition below −40°C. These trends are explained in terms of the effect of material properties, namely the flow stress, on crack blunting, while the bulge ductility is correlated with the total strain to cause significant crack growth to take place. In the elastic-plastic region, a linear relationship between jIC and bulge ductility was found to occur.