In this paper, thermomechanical couplings at the grain scale in metallic polycrystals are studied during the deformation process through an original experimental setup and improved calibration tools and full-field treatments. In order to perform intragranular thermomechanical analysis in a metallic polycrystal at the grain scale, a crystallography-based technique for the projection of the temperature and displacement fields on a polynomial basis is proposed. It enables intragranular coupled analysis of strain and temperature full-field data. Macroscopic, mesoscopic and granular analysis are then conducted and it is shown that the determination of a macroscopic yield stress as well as a critical resolved shear stress in grains is possible. Early local microplastic activity is therefore thermomechanically confirmed.