Acousto-Plastic Deformation of Metal by Nonlinear Stress Waves

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The present research project addresses the need to understand the Acousto-Plastic Effect (APE), which occurs when metal specimens are deformed (in compression or tension) and ultrasonic vibrations are superimposed. When the APE occurs, a remarkable transitory softening is observed. The research will address APE beyond the phenomenological descriptions presented in the current literature. Theoretical and numerical studies will be conducted to clarify the unusual metal morphology induced by ultrasonic vibrations. The research directly addresses the dynamic nature of the processes rather than treating the transitory metal softening effect by introducing an ad-hoc constitutive relation between strain and the apparent static stress. A comprehensive theoretical model is being developed for the evolving nonlinear stress waves. The model equations will be solved by using the space-time Conservation Element and Solution Element (CESE) method, a novel numerical framework for high-fidelity solution of nonlinear hyperbolic systems. Successful development of the theoretical and modeling capabilities will demonstrate a new paradigm for high-fidelity simulation of nonlinear stress waves in solids. The use of parallel computing for very large-scaled calculations could point to a new direction for high performance computation for material simulations. With in-depth understanding of the APE and the accurate modeling tool, implementation of high-power ultrasounds to various metal forming/joining processes could be achieved. The envisioned modeling tool could also be applied to various nonlinear wave problems, including seismic wave propagation in earth and ultrasonic propagation in biological tissues. The research project will foster a meaningful collaboration between researchers at the Ohio State University, and ultrasound specialists and materials scientists at the Ford Motor Company. Undergraduate and graduate students as well as practicing professions in the automotive industry will be integrated into the research project via educational outreach and direct training.