Inelastic Anisotropy of Inconel 718: Experiments and Mathematical Representation

Abstract

A generalized threshold function for viscoplastic materials, which can also serve as a yield function in rate-independent plasticity, is suggested for materials that exhibit a strength differential and/or a permanent volume change. The motivation for this type of a threshold function is that experiments, at both 25 and 650°C, on the nickel-based alloy Inconel 718 indicate that higher stresses occur in compression than in tension. Similar results have been obtained for martensitic steels and other metallic alloys at 25°C. A general approach for determining the inelastic flow dependence on each of the three stress invariants (I1,J2, and J3) is to follow stress paths where only one invariant is changing. Two classical experiments that do this are hydrostatic pressure and pure torsion, however many others are possible. Unfortunately, these stress paths generally require three-dimensional stress states, which are difficult to obtain in the laboratory. Thus, for experimental expediency, tests involving axial-torsional loading of thin-walled tubes can be used to determine the significance of the first and third stress invariants, I1 and J3, respectively. [S0094-4289(00)01303-7]

Integrating the Pressure-Sensitive Nonassociative Plasticity by Exponential-Based Methods

“…They also deduced that there should be a nonassociative flow rule with employing a plastic potential to have a good agreement with experiments. The same results were also concluded by Chait [10] for Titanium alloys, and by Gil et al [11], Iyer and Lissenden [12], and Lewandowski et al [13] for nickel base alloys such as Inconel 718.…”

“…(1) and (22), the plastic multiplier is acquired, as follows: = èP (12) áP = 0 ^ ¿P = èP Merging Eqs. (11) and (12), the subsequent connection will form éP = ys' (13) To regulate the evolution of the back stress, the succeeding Chaboche's nonlinear kinematic hardening is adopted…”

Constitutive Modeling of Creep and Damage Behaviors of the Non-Mises Type for a Class of Polycrystalline Metals

“…Namely, we may take a phenomenological approach that considers a difference in the macroscopic damage rate between tension and compression, instead of a physical one that distinguishes explicitly between underlying micromechanisms. This is analogous to the macromechanical attempts to describe the strength differential effect in tension and compression (Hirth and Cohen, 1970;Drucker, 1973;Iyer and Lissenden, 2000).…”