Extension of Copper and Brass under Tension and Cyclic Torsion

摘要

A study is made of the axial creep in copper and brass at various temperatures under steady axial tension and cyclic transverse torsion. One object was to find why some metals like copper exhibit creep that resembles high-temperature creep in showing primary, secondary, and tertiary stages while other metals like brass show transient creep only. It is shown that the difference arises because of differences in fatigue processes induced by the cyclic strain. Another object was to determine how the metals hardened during creep in the axial and transverse directions. It is found that in the axial direction hardening occurs progressively during creep and depends only on the extension, while in the transverse direction cyclic hardening at first increases and then approaches a steady value which coincides with cessation of the transient creep. It is pointed out that it is difficult to reconcile this hardening with dislocation theories that attribute the creep to recovery and that the creep is more in keeping with certain continuum-mechanics theories of irreversible second-order effects. (Author)