Prefabricating uniaxial residual stress with decoupled plastic strain: theoretical modelling and experimental validation

Residual stress evolution poses a long-standing challenge in evaluating structural integrity and service performance of mechanical components, owing to both the complex spatial distribution of residual stress and, more fundamentally, its inherent coupling with plastic strain. This paper proposes a prefabrication specimen that decouples the control ofresidual stress and initial plastic strain by introducing structural geometry as an additional design variable, supported by theoretical derivation, numerical simulations, and experimental validation. Leveraging inhomogeneous elastic–plastic deformation, a structural configuration with strips of varying dimensions is designed to generate a self-equilibrated, uniaxial residual stress field upon tensile loading and unloading. The theoretical framework reveals that the magnitude of residual stress and the level of initial plastic strain can be systematically varied by independently tailoring the geometric ratios of the strips and preload in tensile loading. The residual stress field can significantly exceed yield strength of the material through careful dimensional design. Finite element simulations and experiments on AA7050 aluminium alloy and TC4 titanium alloy, including X-ray diffraction measurements of residual stress, validate the feasibility and effectiveness of the decoupling specimen. As discussed in conjunction with further thermal exposure tests on AA7050 specimens, the prefabricated structure readily enables direct exposure to thermal, fatigue, and thermo-mechanical service conditions. This approach provides a robust experimental basis for investigating stress-driven versus microstructure-driven relaxation mechanisms, paving the way for fundamental research on residual stress evolution.