Viscoplastic Behavior of a Notch Root at 650°C: ISDG Measurement and Finite Element Modeling

Abstract

Viscoplastic behavior of the nickel-based superalloy, Inconel 718, at a notch root has been investigated by conducting isothermal tensile, creep and cyclic elastoplastic tests at 650°C which is the working temperature of the material in aircraft engines. A laser-based interferometric technique was extended to measure biaxial strains over a gage length of 150 μm at the notch root; the computer controlled system permits real-time measurements. A thin-film pure silicon coating and an argon atmosphere were used to prevent oxidation of the reflective indentations that serve as the strain gages. The measured strains were used to evaluate the Bodner-Partom constitutive model which was incorporated into the ABAQUS finite element code. Material constants in the model were determined from uniaxial tests on smooth specimens. The predicted strains agree reasonably well with the measured ones for all three kinds of loadings.