1985 Volume 3 Issue 4 Pages 875-881
The present study proposes a method of ultrasonic nondestructive evaluations of flaws in surface layer which can hardly be detected by the conventional methods, of ultrasonic testing due to lapping of both surface and flaw echoes. The echo patterns for various types of flaws in the surface layer of steel test specimens are measured with a single focusing probe and theoretically analysed by theory of sound, from which the effects of the water distance and the flaw depth on the echo pattern are clarified. Moreover, the applicability of this method with scanning device for inspection of flaws in welds is confirmed by microscopic examination. A summary of the results is as follows.
When the focus of the ultrasonic beam is beneath the position of flaw, there appear two peaks in the echo pattern which are corresponding to the surface echo and the flaw echo, respectively. As the focus approaches to the flaw position, the peak of flaw echo disappears. This peak of echo consists of multiple echoes and is most conspicuous when the ultrsaonic beam is mostly focused by its multiple reflection and thus its sound pressure is highest. The echo height of flaw depends upon the flaw depth and water distance, and the peak position in the echo pattern is independent from the flaw depth under the constant water ditsance. According to the peak profile of scanning detection for weld interfaces of clad, there are two types of echo patterns, that is, wave-shaped and flat-shaped patterns reflected at interspersed flaws and flat-shaped flaws, respectively.