A new localized inverse identification method for high temperature testing under resistive heating: Application to the elastic‐viscoplastic behaviour of L‐PBF processed In718

Abstract

The mechanical behaviour of the nickel‐based superalloy In718, as processed from laser powder bed fusion (L‐PBF) additive manufacturing, is characterized at high temperature, from 800 to 1100°C. Samples built by L‐PBF are submitted to sequences combining uniaxial tensile load at different prescribed velocities, and relaxation steps of different durations, operated under resistive heating under vacuum, with a home‐developed testing machine. Tests are equipped with force evolution measurement, with infra‐red field imaging and thermocouples to capture the non‐uniform temperature distributions induced by resistive heating, and with digital image correlation to capture the non‐linear displacement fields. An inverse finite element strategy is developed to identify the parameters of a temperature‐dependent elastic‐viscoplastic behaviour model. The strategy is based on (i) direct finite element simulations of tests, (ii) a cost function expressing the distance between calculated and measured quantities, and (iii) a minimization algorithm. Direct numerical simulations are performed on a limited part of the working zone of samples, the zone of interest, with applied boundary conditions provided by DIC records and with an imposed temperature distribution provided by infra‐red imaging. The cost function is based on the force evolution only, for a series of different tests operated at different nominal temperatures. Optimum values of constitutive parameters are obtained by minimizing the cost function value, which is achieved with the home‐developed optimization platform MOOPI. Finally, the identified parameters are discussed with respect to the literature.