Nonlinear surface acoustic wave characterization of single crystal copper: A molecular dynamics study

The elastic nonlinearity of materials causes high-amplitude surface acoustic waves (SAWs) to experience nonlinear sharpening during propagation, potentially causing material microstructure damage or modification. For plastic materials, it occurs in the form of surface shear slip. Therefore, the nonlinear SAW method can be used to characterize the mechanical properties (elastic constants and yield strength) of single crystal copper. This paper aims to investigate this extreme nonlinear evolution phenomenon of SAWs from a microscopic perspective by establishing a molecular dynamics (MD) model of high-amplitude SAW propagating on the surface of single crystal copper. Initially, a uniaxial tensile simulation was performed to calculate the critical yield stress of the material. By comparing with the theoretical value, the applicability of the selected EAM potential function was determined. Subsequently, the MD models of high-amplitude SAW in the three crystal directions of (100)[110], (110)[100] and (111)[112] were established using this potential function, and the yield strength of single crystal copper was successfully determined. The reliability of this method was verified by comparing the data with the uniaxial tensile testing results. Additionally, considering the anisotropy of the crystal, which may have an impact on the nonlinear evolution of SAW, the quantitative characterization of nonlinear evolution was achieved by solving the second-order nonlinear coefficients for SAW in the three crystal directions. The results indicate that the (111)[112] orientation exhibits the greatest degree of nonlinearity. In summary, this study provides new insights into the application of extreme nonlinear SAWs in materials characterization.