Cyclic plastic behaviour of primary heat transport piping materials: Influence of loading schemes on hysteresis loop

Cyclic plastic deformation behaviour of 304LN stainless steel and SA333 Gr.6 C–Mn steel has been investigated employing a constant, increasing and decreasing strain amplitude cycling. Influence of loading scheme on cyclic plasticity characterizing parameters such as cyclic hardening/softening and Masing behaviour are examined. Additional hardening is identified with change in loading scheme and the hardening/softening sustains a dependency of prior load history in both the materials. Masing behaviour is not a common phenomenon in many engineering materials and both the materials in this investigation exhibited a non-Masing behaviour, however, the degree of deviation from Masing varied with the loading scheme. Microscopic evidences to explain the non-Masing behaviour are presented. The experimental investigations show that change in yield stress alone could not be used to explain the hardening/softening behaviour. However, sufficient experimental support is gathered to show that the strain range effect (non-Masing behaviour) is due to change in yield stress and can be explained by a continuous distribution of yield levels.