Anisotropy Detection in Small Area of Materials using Surface Acoustic Waves (Basic Research on Utilization of Ultrasonic Reflectivity Measurement for Estimating Elastic Anisotropy)

An ultrasonic reflectivity measurement technique is applied to anisotropy detection within a small area of material. The ultrasonic reflectivity is microscopically measured using an ultrasonic microspectrometer with spherical-planar-pair lenses. The acoustic reflection coefficients of small area on a water-cubic (111) interface were measured for an incident wave at an angle θ to the normal and ɸ to some direction lying in the (111) surface. The reflection coefficients measured as a function of θ and ɸ were in good agreement with the theoretical calculation. This reveals that the microscopically measured reflection coefficient is reasonable and can be used as a promising detector of anisotropy in a small area. Furthermore, a mean reflection coefficient is defined for quantitative evaluation of elastic anisoropy in a small area of polycrystalline materials. It has been confirmed that, by performing numerical and experimental examinations with texture-controlled steels, the reflection coefficient measured in polycrystalline materials corresponds to the mean reflection coefficient.