Resulted from the multiply scattered ultrasonic pulse in polycrystalline media, the structure noise is an essential obstacle to ultrasonic flaw detecting in coarse grained metals. The early research shows that the scattered energy is of higher concentration nearby the transmitter. The fact leads to an idea of preferable separated transmitter-receiver transducers to be used in case of coarse grained metals. Experiments show that there is a certain amount of time when it is free of structure noise on the receiver and the amount is proportional to the distance between the transmitter and receiver. The velocity the structure noise approaches the receiver seems to be about 0.85 of that of the longitudinal waves(Vl). Analysis shows that the abnormal velocity is resulted from the structure noise excited by a head wave propagating under the surface and the highest velocity of the structure noise is equal to Vl /3.
Publication Source: Trends in NDE Science & Technology; Proceedings of the 14th World Conference on Non-Destructive Testing, New Delhi, 8-13 December 1996.Vol. 1, pages 113 - 116 Publisher:Ashgate Publishing Company
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