Mode-selective resonance ultrasound spectroscopy of a layered parallelepiped

The resonance frequencies of mechanical free vibration of a three-layer material calculated by a discrete-layer model and measured by acoustic-resonance methods were compared. The material was composed of an aluminum parallelepiped sandwiched by two stainless-steel parallelepipeds. The discrete-layer model developed here used linear Lagrange basis functions through the layered dimension and continuous global power-series basis functions in the plane perpendicular to the layer thickness. Using such a basis function for the layer-thickness direction allows discontinuity in the elastic properties across the interface between dissimilar layers. The resonance frequencies were measured using two methods: mode-selective electromagnetic acoustic resonance (EMAR) and resonance ultrasound spectroscopy (RUS). The measurements agreed with the calculations typically within 1%. The EMAR method allows the selective detection of vibrational modes possessing particular displacement patterns. This selectivity was supported by the model calculation. Thus, using the EMAR method makes mode identification clear and this is essential for developing and improving the model calculation of such a complicated structure. Internal friction was also measured by the two acoustic methods, which reveals the mechanical-contact effect on the internal-friction measurement in the RUS method.