Constitutive Equations Study in Biaxial Stress Experiments

Abstract

An experimental study of high temperature creep constitutive equations is reported. The experiments are performed in uniaxial and biaxial (tension-torsion) state of stress. Stress drop experiments starting from a given plastic state (i.e., fixed creep rates, stresses and temperature) lead to the flow rules. It is so pointed out: that hardening is essentially kinematical (as well as creep induced anisotropy), that in steady creep the components of this hardening are proportional to those of applied stress. Then, constitutive equations can be derived from that, the identification of which is reduced to the determination of three hardening and recovery scalar functions and to the knowledge, easily open to measure, of the relationship between the equivalent strain rate and the effective equivalent stress. In the case of our experiments, this relationship is a power law.

The Overstress Dependence of Inelastic Rate of Deformation Inferred From Transient Tests

“…The overstress dependence of the inelastic deformation rate implies that zero creep rates should be found at other than zero stress. This has indeed been demonstrated in [19] where the locus of nearly zero creep rate is at a non zero stress for an FeCoV alloy after prior creep deformation at 953 K.…”

Analysis of Inelastic Behavior for High Temperature Materials and Structures

“…Hayhurst and Leckie (1990); Murakami and Sanomura (1985); Nikitenko (1984); Oytana et al (1982). Non-coincidence of the strain-trajectory and the stress state angles indicates the anisotropy of inelastic behavior and/or dependency of the inelastic strain rate on the kind of the stress state.…”

“…12.17b, coincides with the direction of the applied stress state characterized by the angle α. Experimental data are discussed in Murakami and Sanomura (1985); Nikitenko (1984); Oytana et al (1982). According to this one can assume that the creep rate tensor is coaxial and collinear with the stress deviator, i.e.ε ε ε = λs s s. Taking into account (12.6) and (12.8) the following relations can be obtained…”

Modeling of Creep for Structural Analysis

“…Different stress states leading to the same fixed value of the von Mises stress can be conveniently characterized by the angle α (stress state angle). [224,235,252], the direction of the strain trajectory characterized by the angel β, Fig. The results of creep tests under the combined loading can be conveniently presented as γ cr / √ 3 vs. ε cr curves (so-called strain trajectories), e.g.…”

“…Non-coincidence of the strain-trajectory and the stress state angles indicates the anisotropy of the creep behavior. The effects of the induced anisotropy are usually related to anisotropic hardening, [252,160,235], and damage processes, e.g. Examples for anisotropic tension-torsion creep are presented for a directionally solidified nickel-based superalloy in [246] and for a fiber-reinforced material in [280,281].…”