In situ ultrasonic measurement of crack closure

Size Estimation of Fatigue Crack Appearing at Bolt Joints of Aluminum Alloy Plates by Synchronized SAW Measurement

“…The width and intensity of the terrace gradually increased with increasing number of fatigue cycles, which might be due to expansion of the fatigue crack. The saturation of the peak intensity at higher loads in the fatigue cycle was also reported by Rokhlin and Kim [6] in the SAW reflected from a crack measured at different loads in a fatigue cycle.…”

“…The ultrasonic monitoring technique has been developed to detect the initiation and expansion of the fatigue crack in the fatigue testing [4][5][6][7][8][9][10]. In most of these monitoring techniques, data were recorded under pausing the fatigue tester [4,7,8,10,11], and these measurements can be called as stationary ultrasonic measurements.…”

“…Min and Kato [12] carried out the real-time ultrasonic measurement during the fatigue testing of the aluminum alloy plate with a very small frequency (0.001 Hz) to obtain changes in the ultrasonic wave reflected from the specimen bottom in one fatigue cycle at different stages in the fatigue process. Rokhlin and Kim [6,9] carried out the in-situ ultrasonic measurement with the SAW to detect a crack initiated from a pit at different fatigue loads by stepping up/down a load in a fatigue cycle. These studies showed the effectiveness of the real-time ultrasonic measurement in a fatigue cycle, but also showed limitations of the real-time measurement: the frequency of the fatigue cycle should be very small, or the change in the loading should be stepwise.…”

Depth Evaluation of Fretting Fatigue Crack Appearing at Bolt Joints of Aluminum Alloy Plates by Synchronized Surface Acoustic Wave Measurement

“…8) These were carried out by pausing the fatigue tester, and it was unable to examine the change in the ultrasonic wave signal in a fatigue cycle. To overcome this difficulty, Min and Kato 11) and Rokhlin et al 9,10) carried out the real-time ultrasonic measurement during the fatigue testing of the specimen to obtain the change in the ultrasonic signals at any loading level in a fatigue cycle, but still remained limitations. The authors 12,13) presented the other way of the ultrasonic monitoring technique, called as the synchronized ultrasonic measurement, in which the ultrasonic pulse signal is generated in synchronization with the loading cycle in the fatigue testing to obtain the data at any stress levels in a fatigue cycle, and they evaluated a crack length from the change in the SAW intensity reflected from the fatigue crack with the stress level in the fatigue cycle.…”

“…Guan et al 16) also estimated the depth of the slot by the laser generated surface acoustic wave. Rokhlin and Kim 9,10) reported that there are different types of mode conversion of the surface acoustic wave at the root of the pit, and they estimated the depth of the pit by using the converted wave. These reports show the effectiveness of the mode conversion of the Rayleigh wave for evaluation of the crack depth.…”