Abstract
A new ultrasonic imaging technique of microstructures in engineering materials is proposed, in which the shear waves back scattered by microstructures are detected by a point-focused transducer. By focusing the ultrasonic shear waves on a certain point on the micro structures such as interfaces of dissimilar materials and micro cracks, and extracting the back scattered signal in a particular frequency domain, the amplitude of the wave is mapped. The method is applied to image semi-closed fatigue crack surfaces, which are unable by usual ultrasonic imaging of reflected longitudinal or shear wave. Also, this method is combined with 2^<nd> harmonic measurement to visualize weakly bonded interfaces of spot welds.
