Cyclic stress–strain response of textured Zircaloy-4

Abstract

In this paper, the cyclic stress–strain response of textured Zircaloy-4 is investigated at room temperature in an incremental step test using fully reversed tension–compression loading under strain control. The material exhibits an asymmetry of stress response in both rolling and transverse directions, and the corresponding cyclic stress–strain curves can be expressed by a power law relation. Furthermore, phenomenological friction and back stresses are derived from an analysis of hysteresis loop shapes using the Cottrell scheme. It has been shown that the magnitude of the phenomenological friction stress in compression is always higher than that in tension for either rolling or transverse direction. While the magnitude of the phenomenological back stress, being independent of the loading direction, increases much more rapidly in transverse direction than that in rolling direction with increasing the plastic strain amplitude, and the trend in both directions can be expressed by a logarithmic relation. A further discussion suggests that (i) the intergranular thermal stress in the material is responsible for the difference in the phenomenological friction stress between tension and compression, thus leading to the asymmetry of stress response; (ii) the increase of the saturated stress with the plastic strain amplitude stems from the back stress that is primarily a direct consequence of the plastic strain incompatibilities between grains; (iii) the different performance between rolling and transverse directions results from the texture effect.