The cyclic behavior of polycrystalline material was studied by using variable strain amplitudes. It was found that specimens which were tested at incremental strain amplitudes experienced the same stress as that which existed under conventional constant-strain amplitudes. However, specimens which were tested using decremental strain amplitudes experienced a strain history effect upon the stress, as compared with constant strain amplitude conditions. Transmission electron microscopic observations showed that incremental loading produced a dislocation wall structure which was similar to that found using constant amplitudes. Under decremental loading conditions, the cellular dislocation structure which formed at higher strain amplitudes recovered to give a labyrinth structure. This degeneration process was found to be incomplete, and the dislocation structure remained in the form of dense dipolar walls.

C.D.Liu, M.N.Bassim: Physica Status Solidi A, 1995, 149[1], 323-30