Cyclic plasticity of nickel at low plastic strain amplitude: hysteresis loop shape analysis

The cyclic plasticity of nickel was studied by accomplishing room temperature fully-reversed fatigue experiments at constant plastic strain amplitudes of 1.0×10−4 and 2.5×10−4 on single crystal and polycrystal nickel with 290 μm grain size. The cyclic plasticity behavior within a hysteresis loop was analyzed by measuring shape characteristics of the loop. Parameters that were evaluated include the loop shape parameter, friction stress, back stress, and second derivative of stress with respect to total strain. Results indicate that these parameters correlate well with the development of dislocation substructures. In addition, at low plastic strain amplitude, polycrystal and single crystal hysteresis loops exhibit a distinct constriction. The constriction is more pronounced in single crystals cycled at the lower plastic strain amplitude.