抄録
Current ultrasonic flaw inspection and material characterization techniques are reviewed in view of structural integrity of materials used for atomic and steam power stations. In addition to the conventional ultrasonic flaw inspection with angle-beam shear transducers, more accurate flaw sizing techniques are introduced, i. e., Time-of Flight Diffraction and phased array transducers. Another promising technique is the use of cylindrical guide waves in pipes. Numerical results of circumferential guided wave propagation with semi-analytical finite element method show that the guided wave corresponding to S2 mode of the Lamb wave is most effective to evaluate crack initiated from the inner surface of pipes. The transmitted wave amplitude drops about 10% for a crack of which depth is 5% of the wall thickness. To evaluate material degradation prior to macro crack extension, the possibility of nonlinear ultrasonics is demonstrated for sintered powder metals with longitudinal wave and a closed surface fatigue with the leaky Rayleigh wave.
