Contribution of the Strain Rate to the Generation of Residual Stresses During Deep Rolling and Machine Hammer Peening

Abstract

Deep rolling and machine hammer peening are widely applied mechanical surface treatments for improving the fatigue performance of high-strength materials by introducing compressive residual stresses and modifying the near-surface material state. Despite their industrial relevance, the effect of strain rate on material surface modification remains insufficiently understood, especially regarding its interaction with load-controlled deformation and depth-dependent material response. In this study, the effect of strain rate on the surface modification of AISI 4140 steel is investigated using explicit finite element simulations with a strain rate-sensitive constitutive model, supported by experimental residual stress validation. The depth-resolved quantification of plastic strain rate fields enables the continuous and impact-based loading modes in deep rolling and machine hammer peening to be compared within a consistent framework. The evolution of internal material loads and plastic strain rate fields is quantitatively analyzed under quasi-static conditions. A dedicated spatial-averaging framework is employed to extract numerically stable and physically representative plastic strain rate depth profiles beneath the treated surface, enabling the consistent quantification of maximum strain rates and the effective penetration depth. Results show distinct strain rate characteristics for each process. In machine hammer peening, the strain rate appears as transient, highly localized peaks governed by impact velocity–contact time coupling. Thus, the strain rate cannot be independently varied, limiting its suitability for isolated analysis. Therefore, deep rolling is used to assess the influence of strain rate on material surface modification. Under constant normal load, the rolling speed is varied to adjust the maximum plastic strain rate while preserving comparable contact mechanics. Maximum plastic strain rates of 101–103 s−1 are observed in the near-surface region. Depth-resolved analyses reveal that the strain rate primarily affects the accumulation and localization of plastic deformation in the near-surface and shallow subsurface layers, whereas its influence rapidly diminishes with increasing depth. The magnitude and penetration depth of compressive residual stresses are primarily governed by machining parameters such as applied load and tool geometry, while the strain rate acts as a process variable that influences the material response rather than directly controlling the residual stress state. Plastic strain rate was evaluated after the maximum equivalent strain converged, indicating quasi-static deformation. In deep rolling, strain rate can be tuned by speed at constant load; in machine hammer peening, it depends on impact conditions. Strain rate mainly affects near-surface plasticity, while residual stress is governed by load and tool geometry. Plastic strain rate was evaluated after the maximum equivalent strain converged, indicating quasi-static deformation. In deep rolling, strain rate can be tuned by speed at constant load; in machine hammer peening, it depends on impact conditions. Strain rate mainly affects near-surface plasticity, while residual stress is governed by load and tool geometry.