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, 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/sub 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/sub Ic/ in the cleavage range can be quantitatively assessed solely in terms of the effects on the yield and flow properties of the material