Interpretation of Irradiation Effects on the Fracture Toughness of a Pressure Vessel Steel in Terms of Crack Tip Stress Analysis

The model of Ritchie, Knott, and Rice [10], relating the critical tensile stress for initiation of unstable cleavage fracture of mild steel to the cryogenic temperature-dependence of plane strain fracture toughness (K_Ic), is applied to a pressure vessel steel, ASTM A533B. It is shown that the fracture criterion of achieving the critical tensile stress over a characteristic microstructural distance is essentially unaffected by neutron irradiation. Thus, it appears that the effects of irradiation on the temperature-dependence of K_Ic in the cleavage range can be quantitatively assessed solely in terms of the effects on the yield and flow properties of the material.