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无损检验对于保证和提高产品质量有着十分重要的作用。自三十年代初超声探伤出现以来,无损检验工作中所使用的超声波大都是用压电换能器获得的。为了把超声波传入被检验材料中去,必须有声耦合介质,比如油、水或其他耦合介质。接触法要求材料表面清洁且需达到一定的光洁度,探伤速度慢而且不经济;水浸法对于提高探伤速度和适应检验表面粗糙的材料具有许多优越性,但也存在不少缺点,特别是由于压电换能器的压电晶体居里点的限制及耦合介质的限制,所以对高温材料的检验很难实现。涡流探伤虽然解决了超声探伤中声耦合介质的问题,但是它只能检验材料的表面及近表面缺陷,不能检验材料的中心缺陷。
Non-destructive testing for the assurance and improve product quality has a very important role. Since the appearance of ultrasonic flaw detection in the early 1930s, most of the ultrasonic waves used in NDT have been obtained with piezoelectric transducers. In order to transmit ultrasonic waves into the material to be inspected, there must be an acoustic coupling medium, such as oil, water or other coupling medium. Contact method requires the material surface to be clean and to achieve a certain degree of finish. The inspection speed is slow and uneconomical. The water immersion method has many advantages for improving the inspection speed and for testing the surface roughness of the material, but there are many disadvantages, especially because of the pressure Electrical Transformer Piezoelectric Crystal Curie point limit and the limitations of the coupling medium, so the test of high temperature materials is difficult to achieve. Although eddy current testing to solve the problem of acoustic coupling medium ultrasonic flaw detection, but it can only test the surface of the material and near-surface defects, can not test the material center defects.