Cross Effect of Aluminium Tubes Subjected to Torsion and Tension

The flow stress in tension after torsional prestrain, for example, is higher than that in merely tensional loading. This phenomenon is called the cross effect, cross hardening or latent hardening. In the present study the cross effect was investigated with torsion-tension combined loading tests. It was observed that the cross effect as well as Bauschinger effect is a kind of delayed phenomenon due to change of stress path. We proposed a hypothesis that unconstrained Orowan loops around pile-ups produced during the preloading work as forest dislocations against moving dislocations on the cross-slip planes during the subsequent loading. Since the density of forest dislocations determines the flow stress, the free Orowan loops cause the cross effect for cross loading and also cause the Bauschinger effect for reverse loading. The above explanation for the cross effect was confirmed by the tension test after torsional and reverse torsional prestrains.