Modeling the damage behavior of superplastic materials H.S. da Costa-Mattos Laboratory of Theoretical and Applied Mechanics, Department of Mechanical Engineering, Universidade Federal Fluminense, Niterói/RJ – Brazil G. Minak, F. Di Gioacchino, A. Soldà Department of Mechanical Engineering and Materials Science, University of Bologna, Bologna – Italy Abstract The present paper is concerned with the modeling of superplasticity phenomenon in metallic materials using a continuum damage theory. The goal is to propose a one-dimensional phenomenological damage model, as simple as possible, able to perform a mathematically correct and physically realistic description of plastic deformations, strain hardening, strain softening, strain rate sensitivity and damage (nucleation and growth of voids) observed in tensile tests performed at different strain rates. Only two tensile tests at different controlled strain rates are necessary to obtain all the material parameters that appear in the theory. Examples concerning the modeling of tensile tests of a magnesium alloy at different strain rates are presented and analyzed. The results obtained show a very good agreement between experimental results and model prevision. Keywords: superplasticity, strain rate sensitivity, magnesium alloy, tension/compression testing, continuum damage mechanics. 1 Introduction A wide class of materials – metals, ceramics, intermetalics, nanocrystaline, etc – show superplastic behavior under special processing conditions. Although, up to now, there is no precise physical def- inition of superplasticity phenomenon in metallic materials, from a phenomenological point of view, superplasticity can be defined as very high deformations prior to local failure. In the case of tensile tests under controlled strain rate, this means very high elongations of the specimens before rupture. The deformation process is generally conducted at high temperature and the strain can be 10 times the obtained under room temperature. Superplastically deformed material in tensile tests gets thinner in a very uniform manner, rather than forming a ’neck’ (a local narrowing) which leads to fracture. The most important characteristic of a superplastic material is its high strain rate sensitivity of flow stress that confers a high resistance to neck development and results in the high tensile elongations Mechanics of Solids in Brazil 2009, H.S. da Costa Mattos & Marcílio Alves (Editors) Brazilian Society of Mechanical Sciences and Engineering, ISBN 978-85-85769-43-7