2014. . No. 4(66) - Dec 2014, pp. 11-14
Evaluation of the defect real size in products with bilateral access
For products with bilateral access a new technique of real defect size evaluation has been developed. The technique is based on an amplitude shadow method of testing. Several independent pairs of transducers are used to avoid ambiguity of measurements; the pairs of transducers provide entrance of ultrasonic waves at different angles. A three-dimensional image of a defect can be achieved with layer-by-layer scanning of a defective section.
Modelling of an acoustic tract (approximations of beam geometry) with the use of a specially developed program has been carried out for different models of railhead defects.
Modelling of different situations together with experimental researches has made it possible to optimize main parameters influencing on defect sizing accuracy. Selected sizes of transmitting and receiving transducers, optimal operating threshold, and specially developed technique for setting the testing sensitivity were realized in a mockup of a pulsed ultrasonic flaw detector. For practical realization of this approach the new way of acoustic contact providing has been offered and implemented on real objects with poor surfaces for entry/receipt of ultrasound waves.
Experimental researches carried out on real defects and models of defects (more than 50 defective sections of railhead) with the mockup have shown satisfactory accuracy and repetition of measurements. The considered approach has restrictions; nevertheless the operation experience shows its practical suitability and satisfactory accuracy in many practical situations.
The approach for real defect size evaluation offered in the article can be applied to any objects with bilateral access.
Keywords: non-destructive testing, ultrasonic flaw detection, defect sizing
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