A multi-layer model for residual stress relaxation aligned with microstructure evolution under thermal exposure and cyclic loading

Residual stress relaxation phenomena under thermomechanical conditions, particularly thermal exposure and cyclic loading, constitute critical determinants of fatigue performance in surface-treated engineering components. This study systematically investigates the thermal and cyclic relaxation mechanisms in shot-peened Ni-based superalloy GH4720Li through integrated experimental characterization and computational modeling. Through systematic characterization via X-ray diffraction (XRD) and electron backscatter diffraction (EBSD), we establish quantitative correlations between residual stress relaxation kinetics and concurrent microstructure evolution, particularly dislocation annihilation and grain boundary restructuring. Building upon these observations, a novel multilayer constitutive framework is developed to decouple the synergistic effects of microstructural evolution on residual stress relaxation dynamics. The model demonstrates predictive accuracy within 6.3 % for residual stress magnitudes and 3.3 % for characteristic depth parameters when compared to stabilized thermal exposure data. Under cyclic loading conditions, corresponding errors remain constrained to 15.5 % and 4.8 %, respectively. Such precision validates the model's capability to isolate microstructure-driven relaxation mechanisms from purely mechanical contributions. This multi-physics framework provides an unprecedented quantitative tool for optimizing surface-engineered components operating in combined high-temperature and cyclic loading environments, effectively bridging the gap between microstructure-aware modeling and industrial fatigue life prediction.