On Interaction of Elastic Waves with “Semitransparent” Defects

The issues of identifying discontinuities that partially transmit ultrasonic waves are examined. Such defects are widespread in various products and welded joints of metals and plastics. Examples of “semitransparent” defects include lacks of fusion, “dead spots”, slag and other foreign inclusions in welded joints, flokens and oxide films in forgings and rolled products, etc. Moreover, even such well-studied defects as cracks can also partially transmit ultrasonic waves. However, to calculate and adjust the parameters of ultrasonic testing, hollow model reflectors (various drills, grooves, etc.), which do not transmit ultrasound, are traditionally used. The present article states that for the purposes of defect sizing, it is necessary to correctly calibrate and configure the flaw-detector–transducer kit taking into account the peculiarities of detecting defects of various types, including ones that are “semitransparent” for ultrasonic waves. To develop models of artificial reflectors imitating defects semitransparent for ultrasound, it is proposed to classify such semitransparent defects into three groups, viz., defects with filling, intermittent structures, and clogged weld. The main features of defects of these types are considered. Possible approaches to calculating the acoustic paths of ultrasonic flaw detectors when identifying defects of the three indicated types are described. It is noted that analytical and numerical methods can be used for calculating defects with filling; numerical methods should be preferred for intermittent structures; and analytical methods are better suited to defects of the clogging type.