Temperature dependence of fracture toughness JIC and ductility for BCC materials in the transition region

The temperature dependence of ductility, strength and fracture toughness for a BCC material undergoing predominantly linear elastic behavior at low temperatures and elastic-plastic behavior at higher temperatures is examined. A model, based on ductile fracture mechanisms involving void nucleation followed by cavity growth and void coalescence, is developed to relate the fracture toughness parameter JIC with temperature. Two general equations for linear elastic and elastic plastic regimes of JIC versus temperature T, are obtained. Applications of this model to experimental data obtained on a carbon steel show that JIC varies with T2 at low temperatures and with T at higher temperatures, thus defining a transition temperature.