Geometric approach for detecting and locating multiple rivet notches in thin aluminum plates using ultrasonic Lamb wave scanning
This thesis describes work towards the detection of flaws in thin Aluminum plates using non-destructive evaluation (NDE) techniques. This approach requires the generation of an ultrasonic A0 and S0-Mode Lamb wave using an incident transducer excited with a tone burst centered at a near non-dispersive frequency. The relative distance between the transducer and the receiver is fixed so that both move along the same line on the plate. The arrival time information, coming from incident and reflected waves contain information associated with the location of reflection surfaces or potential flaws. The Hilbert-Huang transform is applied to the intrinsic mode functions which permit the computation of the signal energy as a function of time, proportional to the square of the amplitude of the analytical signal. A geometric method; Geometric Method I has been used in order to calculate the arrival times and amplitudes of the notch-reflected energy where in the coordinates of the source of the reflections outline the extent and relative direction of notches in two different scenarios. In a line scanning the set of predicted reflection points define the extent of the defect. The Lamb wave scanning approach is tested using 1.6mm-thick or 6061 T6 Aluminum alloy with multiple holes (3 holes) and notches (being on side of the three holes and also on both sides of the three holes) of various sizes from ¼&inches; to 1&inches; in length at multiple rivet holes on the plates. The results are summarized with defect maps that compare favorably to the actual holes and notches' locations on the plate. ^
Kaukuri, Nagaswaroopa, "Geometric approach for detecting and locating multiple rivet notches in thin aluminum plates using ultrasonic Lamb wave scanning" (2004). ETD Collection for University of Texas, El Paso. AAI1423690.