Hysteresis loop shape in fatigue of CuZn alloys

Hysteresis loop shapes in 70Cu30Zn, 75Cu25Zn and 80Cu20Zn alloys were studied as a function of strain amplitude and holding stress during load interruptions. Three loop shapes, designated as I, II and III, were found. The strain amplitude at which transition from Shape I to Shape II and Shape II to Shape III occurs, decreases with decreasing Zn content. The characteristic shapes of these loops were considered to arise from Zn segregation to dislocations and from Bauschinger stress behavior as a function of half-cycle strain. Holding during cycling produced anisotropic loop shapes. The magnitudes of these distortions increased with holding time, eventually producing burst and yielding behavior. Explanations for anisotropic loop shapes were also based on Zn segregation to dislocations and on changes in Bauschinger stress as a function of half-cycle strain.