VISCOPLASTIC BEHAVIOR OF A NOTCH ROOT AT 650-DEGREES-G - ISDG MEASUREMENT AND FINITE-ELEMENT MODELING

Viscoplastic behavior of the nickel-based superalloy, Inconel 718, at a notch root has been investigated by conducting isothermal tensile, c reep and cyclic elastoplastic tests at 650 degrees C which is the work ing temperature of the material in aircraft engines. A laser-based int erferometric technique was extended to measure biaxial strains over a gage length of 150 mu m at the notch root; the computer controlled sys tem permits real-time measurements. A thin-film pure silicon coating a nd an argon atmosphere were used to prevent oxidation of the reflectiv e indentations that serve as the strain gages. The measured strains we re used to evaluate the Bodner-Partom constitutive model which was inc orporated into the ABAQUS finite element code. Material constants in t he model were determined from uniaxial tests on smooth specimens. The. predicted strains agree reasonably well with the measured ones for al l three kinds of loadings.