Masing behavior in copper single crystals fatigued under load control

In a previous paper it was demonstrated that copper single crystals cycled under load control do not saturate in plastic strain once PSBs have nucleated. Thus, a powerful tool for describing and analyzing information from the stress-strain hysteresis loop is lost. This paper approaches the details of the cyclic stress-strain response using Masing behavior as a tool for understanding the microstructural changes that prevent saturation from occurring. It is shown that under constant amplitude load control copper single crystals do not strictly exhibit Masing behavior. However, Masing behavior is observed in crystals that do saturate because the cycling conditions are not such as to lead to the nucleation of PSBs. This implies that the microstructure is constantly evolving meaning, that the number of PSBs is increasing throughout life. The change in the microstructure is gradual and Masing behavior can be said to apply to the first degree. Under variable amplitude load control, however, copper single crystals exhibit Masing behavior if the current load is lower than the previous load. This implies that the previously established microstructures are capable of supporting the deformation specified at the current load amplitude.