The possibilities of 2D detection of cracks via linear and nonlinear modulation methods implemented on the basis of a software technique have been demonstrated through examples of ultrasonic location of model objects containing cracks with different acoustic characteristics. It has been shown that the modulation method allows determination of the degree of opening of a crack and establishment of its boundaries, which change the passage of an ultrasonic wave as a result of excitation of bending vibrations in the object. The features of detecting an isolated crack and a cavity that lie on the same path of location are determined. It is shown that the joint use of linear pulsed location and the modulation technique allow the reliable detection of a cavity and a crack if the cavity lies in front of the crack on the path of location. If the first flaw is a crack, it is difficult to identify the type of the second flaw via the modulation technique, because the ultrasonic wave transmitted through the crack undergoes modulation. The level of reflection from the first flaw is an important factor during identification of the flaw type. If the reflection levels are comparable, a flaw characterized in terms of its nonlinear acoustic properties is easily detected against the signal from a flaw with linear properties, whereas it is difficult to detect a linear flaw against the background of a nonlinear flaw and necessary to use additional criteria, such as a change in the direction of the modulation phase. Two nonlinear flaws can be distinguished if the first initiates an appreciably weaker modulation in the parameters of the reflected ultrasonic wave than the second does. The developed modulation measurement method can be used as a means for the 2D detection of SIC cracks and cavities in pipelines. Scanning with an ultrasonic probe over the surface of a pipe allows the obtainment of new data on the acoustic characteristics of cracks and their spatial distribution that cannot be obtained via the linear ultrasonic-location method. (to be continued)
A modulation crack-detection technique. I. Software implementation method
Eine Modulationstechnik zum Rissnachweis. I. Software Implementierungsmethode
Russian Journal of Nondestructive Testing ; 42 , 12 ; 773-779
2006
7 Seiten, 8 Bilder, 10 Quellen
Article (Journal)
English
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