An improved lagrangian thermography procedure for the quantification of the temperature fields within polycrystals

Abstract

Polycrystalline metallic materials are made of an aggregate of grains more or less well oriented with respect to the loading axis. During mechanical loading, the diversity of grain orientations leads to a heterogeneous deformation at the local scale. It is well known that most of the plastic work generated during the deformation process reappears in the form of heat, whereas a certain proportion remains latent in the material and is associated with microstructural changes. To access the local stored energy during deformation processes, experimental energy balances are needed at a suitable scale. Thus, simultaneous measurements of thermal and kinematic fields were made in-house at the microstructural scale of a 316L stainless steel submitted to a macroscopic monotonic tensile test. The aim of the present study is to propose a complete calibration strategy allowing us to estimate the thermal variations of each material point along its local and complex deformation path. This calibration strategy is a key element for achieving experimental granular energy balances and has to overcome two major experimental problems: the dynamics of each infrared focal plane array sensor that leads to undesired spatial and temporal noise and the complexity of the local loading path that must be captured by simultaneous complementary measurement. The improvement of such a multifield strategy is crucial for performing properly the experimental and local energy balances required to build new energetically based damage criteria.