On viscoplasticity of irradiated steels

Milan V. Mićunović

The irradiation of steels by neutrons appears during many modern technological processes. Experiments promoted division of neutrons into [9] super cool, very cool, thermal, resonant, intermediate, fast, high-energetic and relativistic groups according to their energies. As one of the mast important examples we may mention periodic intensive neutron bombardment of the first wall blanket of nuclear reactors. During such a process there appears the class of thermal, resonant, intermediate and fast neutrons where nuclei may be treated as fixed with respect to moving neutrons. This permits application of classical mechanics concepts. From the whole bundle of processes which accompany neutron irradiation we are mainly concerned here with their interaction with dislocations (as microscopic cause of plasticity) as well as voids (microscopic cause of damage like thermal creep). For continuum mechanics type considerations their influence on inelastic constitutive equations is of primary concern. .Such an influence is the subject of this paper where we analyze finite thermoplastic strains at time rates which do not allow time independent idealization. Microstructural changes of steel structure are here described by internal variables approach with incompatible strains as opposite to the approach with compatible strains and inelastic memory.