Energy transfer mechanism in ultrasonic impact and its single-cycle equivalent experimental methodology

Ultrasonic impact treatment is extensively employed to improve the surface quality and fatigue performance of engineered components. However, existing methodologies are limited by their inability to accurately characterize the transient behavior within a single impact cycle, which hinders the development of theoretically grounded parameter optimization. This paper investigates the stress wave propagation mechanism during single-cycle of ultrasonic impact and proposes an equivalent impact experimental analysis method for single-cycle ultrasonic impact treatment grounded in one-dimensional impact stress wave theory. The key innovation lies in decoupling the complex high-frequency process into a controllable single-cycle event based on a rigorously derived energy equivalence principle. An energy transfer model based on stress wave propagation was established, and the equivalence conditions for the impact parameters were subsequently derived. Complementary finite element models of ultrasonic impact treatment and equivalent impact treatment were constructed. Validation was performed via an equivalent impact test platform using 6061-T6 Aluminum Alloy and 45 # steel. The stress wave history curve measured in the equivalent impact test closely replicates the theoretical ultrasonic impact curve, with errors in maximum amplitude and pulse width within 4.4% and 5.4% respectively. Comparison between simulation and equivalent impact test results reveals maximum depth and diameter errors below 3.7% and 7% respectively, with maximum residual stress error below 5.5% and hardness errors within 5.2% at different orientations. Electron Backscatter Diffraction analysis confirms highly consistent grain size distribution between the two techniques. This study lays a theoretical foundation for the visual investigation into the mechanism of ultrasonic impact and offers new insights for the exploration of various ultrasonic-based processes.