Cyclic stress-strain response of polycrystalline nickel

Abstract

Constant plastic strain amplitude fatigue experiments were conducted at room temperature on polycrystalline nickel (290 μm grain size) at plastic strain amplitudes from 2.5 × 10 −5 to 2.5 × 10 −3. Cyclic deformation behavior was characterized by analyzing the cyclic hardening response, evaluating the evolution of the shape of the hysteresis loop, and optical and transmission electron microscopy observations. The results indicate that the cyclic stress-strain (CSS) curve has a pronounced bulge or region of reduced slope extending from a plastic strain amplitude of approximately 2 × 10 −4 to 8 × 10 −4. This region of reduced slope is caused by the localization of plastic strain in persistent slip bands (PSBs). It is also shown that plastic strain amplitude has little influence on the friction stress of cyclically saturated nickel; however, the back stress increases with increasing plastic strain amplitude. A comparison of the cyclic deformation characteristics of polycrystalline nickel with those of copper indicates that these materials exhibit similar fundamental cyclic behavior on both a macroscopic and microscopic level.