Cross Effect in Aluminium Tubes Subjected to Torsion and Tension

Abstract

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