Cyclic stress strain behavior of four nuclear pressure vessel materials

The constitutive equation under cyclic loading is needed for an inelastic analysis of nuclear components when the design requirement based on an elastic analysis is not satisfied. In order to characterize the cyclic stress strain behavior, a series of low cycle fatigue tests, each of which has a different strain sequence, are performed on four pressure vessel materials, namely A508 Cl. 2 steel, A533 Gr. B steel, SUS304 stainless steel and Inconel 600 alloy. It was found that the strain history dependence of cyclic stress-strain behavior of these materials is governed mainly by the cyclic softening and strain softening (strain hardening for SUS304 stainless steel). The phenomena of cyclic softening and strain softening can be evaluated by a simple model. SUS304 stainless steel and Inconel 600 alloy also show a period of cyclic hardening which is added to the cyclic softening and strain softening. The hysteresis loop of these materials can be approximated by cyclic stress strain curves obtained by the incremental step test