Defect identification and sizing by the ultrasonic satellite-pulse technique

Abstract

Type and size are the most important defect characteristics that need to be determined for reliable prediction of the remaining service lifetime of a defective structure or part. The analytical and supporting experimental results presented in this paper concern a universal ultrasonic defect-identificationand-subsequent-sizing method. The conceived satellite-pulse technique (SPT) is based on the interpretation, in terms of defect types and dimensions, of the separation in time-of-arrival between the specularly-reflected pulse and its tipdiffracted or tangentially-scattered "satellite" contained in the composite defect signal. Several alternate calibration procedures were also developed, any one of which enables the ultrasonic examiner to make the time scale of the oscilloscope read directly in terms of equivalent crack depth or void diameter as appropriate.

Strong Scatterers and 1-D Born Inversion

“…The scale factor of 3/4 comes from the two integrations which are used to convert the impulse response data in the time domain to the BR/ZOTSD signature, using the area/peak technique for radius estimation [12]. The resulting relationship is proposed for the null separation for voids in the BR/ZOTSD signature; T = 3/ 4 (1/c+ n/2v)d ( 2 ) where, for Titanium, c=6130 mjsec and v=0.87c for a range of voids [7,5 ] .…”

“…For example, the commercially used dB drop method [1) is based on the amplitude of the signal. Similarly the total duration of the signal is used to estimate the flaw size in the satellite pulse method [2]. There the duration is measured as the time between the front surface reflection and a suitable trailing wave (the "satellite" pulse).…”

Development of a Quantitative Flaw Characterization Module — A Status Report

“…For clarity, only the clockwise creeping wave is shown by the wavy line from Q1 to Q2 in Figure 3(b). The mode-converted (surface) waves produced by the incident bulk wave at the void's shadow boundaries circumvent it a number of times until they disappear into the background of irrelevant sources since their energy is continuously depleted by tangential radiation (8). Each time the clockwise creeping wave reaches point Q2' a tangentially scattered wave (S wave) is launched in the desired direction to be received by the shear-wave transducer.…”

“…The center frequency for the most appropriate longitudinal-wave transducer (optimum frequency fo) is determined from the average result of shear-wave measurements by the equation (8) where fo is in MHz and d s is in ~m. Table 2 transducers.…”

Ultrasonic Flaw Classification Using a Quasi-Pulse-Echo Technique

“…This difference is reflected in the fact that a significant mode-converted diffracted wave component can exist for a crack-like defect ( Although mode-converted diffracted responses contain significant information useful in the classification process, standard techniques have mainly employed specularly reflected signals of the same mode type. Even advanced techniques such as the satellite-pulse technique [1], a variation based on the Delta Technique [2] and the LLTtechnique [3] have not fully exploited these features.…”