A CONSTITUTIVE EQUATION OF CREEP, SWELLING AND DAMAGE UNDER NEUTRON-IRRADIATION APPLICABLE TO MULTIAXIAL AND VARIABLE STATES OF STRESS

A constitutive equation of creep, swelling and damage under neutron irradiation applicable to general conditions of stress. including stress change in direction as well as in magnitude, is developed. The creep related to irradiation is divided into irradiation-induced creep and irradiation-affected thermal creep. The irradiation-induced creep is formulated by taking account of the stress-induced preferential absorption (SIPA) mechanism and climb-controlled glide (CCG) mechanism and by postulating an isotropic tensor function of stress of order zero and order one which is also a function of neutron flux and neutron fluence. The irradiation-affected thermal creep, on the other hand, is modeled by extending the creep-hardening surface model of variable stress creep to include the effects of neutron irradiation and damage, The validity and utility of the proposed constitutive equation are discussed by applying it to the creep of type 316 stainless steel at 650-degrees-C subjected to some stress histories including reversed loading and non-proportional loading under different irradiation conditions.