Propagating, evanescent and ZGV Lamb modes in high-performance anisotropic Cu-Al-Ni alloy plates

High-performance alloy materials are increasingly considered for various engineering applications due to their combination of desirable properties. However, the guided wave-based structural health monitoring of alloys is often challenged by their strong anisotropic nature, which makes it difficult to calculate the guided wave behavior and associate mode shapes. In this article, Lamb mode waves of Cu-Al-Ni alloy under uniaxial stresses are characterized by developing a novel numerical polynomial approach, which may provide an efficient way to solve problems concerning acoustic wave propagations. To facilitate understanding of the dispersion curve trajectories, the anisotropic phase transformation from cubic phase (austenite) to orthorhombic plate (martensite) is considered. The comparison of the evanescent mode trajectories between the cubic and orthorhombic alloys shows the presence of imaginary modes in the cubic phase, although they may not exist in the orthorhombic phase at specific frequencies. In the case of Lamb propagation in the cubic alloy, the dispersion curves oscillate strongly, creating crossings among multiple symmetric and antisymmetric modes. This study also concerns the second harmonic generation of Lamb mode pairs in cubic and orthorhombic alloys. Furthermore, effect of uniaxial stresses on Lamb dispersion curves in both phases are also identified and discussed. The results obtained may promote understanding and optimization of novel acoustic devices made of anisotropic materials.