D. J. Buchanan, R. A. Brockman, University of Dayton Research Institute, Dayton, OH; R. John, US Air Force Research Laboratory, Wright-Patterson AFB, OH
Shot peening is a commonly used surface treatment process that imparts compressive residual stresses into the surface of metal components. Compressive residual stresses retard initiation and growth of fatigue cracks. During the component loading history, the shot-peened residual stresses may change during cyclic loading, or during elevated temperature static loading, such as thermal exposure and creep. In these instances, taking full credit for compressive residual stresses would result in a nonconservative life prediction. As a result, designers are reluctant to incorporate any compressive residual stresses into fatigue life predictions of turbine engine components, subject to elevated temperatures and inelastic loading conditions.This research describes a methodical approach for characterizing and modeling residual stress relaxation under elevated temperature loading, near and above the monotonic yield strength of IN100. The model incorporates the dominant creep deformation mechanism, coupling between the creep and plasticity models, and effects of prior plastic strain. The initial room temperature residual stress and plastic strain profiles provide the initial conditions for relaxation predictions using the coupled creep-plasticity model. Model predictions correlate well with experimental results on shot-peened dogbone specimens subject to cyclic and creep loading conditions at elevated temperature. The predictions accurately capture both the shape and magnitude of the retained residual stress profile.
Summary: This research describes a series of experiments on mechanical behavior of IN100 with prior plastic strain that forms the basis of a constitutive model for accurately predicting relaxation of shot-peened residual stresses. The model successfully predicts residual stress relaxation of shot-peened laboratory specimens subject to stresses at yielding and under sustained loads.
