A CREEP DAMAGE MODEL FOR INITIALLY ISOTROPIC MATERIALS WITH DIFFERENTPROPERTIES IN TENSION AND COMPRESSION

A continuum damage mechanics model for the dislocation creep response associated with the growth of parallel planar mesocracks in initially isotropic materials is presented. The model describes simultaneously d ifferent damage development in tension, compression and torsion, damag e-induced anisotropy, as well as different creep properties in tension , compression and torsion. The proposed constitutive equation for cree p and the damage growth equation contain joint invariants of the stres s tensor and the second-order damage tenser. The determination of the material parameters required in the proposed equations, from a series of basic experiments, is shown. Theoretical predictions are compared w ith experimental data for a multiaxial stress state of various materia ls in the primary, secondary and tertiary creep state under proportion al and non-proportional loading. (C) 1998 Elsevier Science Ltd. All ri ghts reserved.