Constitutive modelling and formability prediction of Inconel-718 sheet at elevated temperatures for space applications

Abstract

ABSTRACT In this work, uniaxial tensile tests of Inconel-718 (IN718) sheets were performed at elevated temperature domain of 773-1023K and a deformation rate between 0.001-1s-1. A substantial reduction in maximum stress was observed at 923K indicating a decrease in peak load by approximately 75.6% and 8.5% in contrast to room temperature (303K) and 773K respectively. Further, different constitutive models, namely Cowper-Symonds (CS), Mechanical Threshold Stress (MTS), and Johnson-Cook (JC), were established to envisage the stress-strain behaviour. The CS model predicted flow stress response better with the correlation coefficient, average absolute error, and standard deviation of 0.98, 4.09% and 6.14% respectively. Also, formability experiments were performed at higher temperatures of 773K and 923K using stretch forming test facility. The highest dome height was noted at 923K signifying an improvement in limiting dome height (LDH) by 32% with respect to 303K. Further, thermo-mechanical numerical simulations of the process were successfully carried out, integrating established constitutive models independently. The predicted formability parameters, such as maximum attained load and surface strain distribution, were validated with the experimental data. The CS constitutive equation predicted the deformation behaviour close to the experimental results and, therefore, was considered as the appropriate model.