IMPULSE-RESPONSE METHOD TO PREDICT ECHO RESPONSES FROM TARGETS OF COMPLEX-GEOMETRY .3. APPLICATION TO NONDESTRUCTIVE TESTING

A theoretical model has been proposed for predicting the radiation of transient ultrasonic pulses, their scattering by targets of complex shape, and their reception. [A. Lhemery, ''Impulse-response method to predict echo responses from targets of complex geometry. Part I. Theory,'' J. Acoust. Sec. Am. 90, 2799-2807 (1991)]. Its computer implementation and experimental validation have also been considered [A. Lhemery and R. Raillon, ''Impulse-response method to predict echo responses from targets of complex geometry. Part II. Computer implementation and experimental validation,'' J. Acoust. Sec. Am. 95, 1790-1800 ( 1994)]. The accuracy of the model allows its application to a problem arising in classical NDT pulse-echo methods, namely, the discrimination of small defects and misoriented cracks. The echo-response from these two types of defects can produce the same B- or C-scan images in certain circumstances, leading to the possibility of serious misinterpretations. First, the relative importance of both the geometric and the electroacoustical parameters involved in the echo-forming mechanism is determined by a computer study conducted with our model's implementation. Simple relations are found between the echo responses of the two kinds of defects. Insight gained from modeling such responses has led to the development of a new signal processing method to identify the defect. An example of its efficiency on measured waveforms is given.