Study of internal strain evolution in Zircaloy-2 using polycrystalline models: Comparison between a rate-dependent and a rate-independent formulation

In the present paper, an elasto-viscoplastic model is proposed to describe the behavior of hexagonal close-packed materials where multiple deformation modes, including plastic slip and twinning, coexist. The model assists in interpreting the experimental lattice strains whose evolution is often complex because of the many deformation modes involved. The proposed rate-dependent model is compared with a previously developed rate-independent model by studying the development of internal strains in a moderately textured Zircaloy-2 slab. The comparison shows that most of the inflexions that are experimentally observed are well reproduced by the proposed model and the qualitative and quantitative agreement is generally better with the new rate-dependent formulation.