Defect Detection in Aluminum Bars Using Impedance and Ultrasonic Attenuation

Aluminum alloys are mainly used to manufacture automated machinery and in aeronautic, automotive, and biomedical structures, as well as tools for functions requiring strength, lightness, and precise movements. Monitoring and characterization of this material is very important to guarantee quality for those structures. This study proposes a new methodology for nondestructive testing and characterization of these materials using attenuation of ultrasonic waves and electrical impedance of piezoelectric ceramic plates attached to aluminum alloy bars. Five solid aluminum bars measuring 250 mm $\times \,\, 50$ mm $\times \,\, 50$ mm were used; in four, three holes of varying diameters and depths were drilled to simulate defects, while one bar was left intact as a reference. Three piezoelectric ceramic plates measuring 12.7 mm $\times \,\,12.7$ mm $\times \,\,0.52$ mm were attached to each bar near the manufactured defects and at the same position in the reference sample. Electrical impedance was assessed, and attenuation of the ultrasonic waves was measured using a function generator to excite the ceramic plates with a single 20 Vpp sine pulse in transmit/receive and pulse-echo modes at 90, 145, 230, and 376 kHz. Broadband attenuation was assessed using two pairs of transducers with nominal center frequency of 500 kHz and 5 MHz. The signals were acquired using a Tektronix TDS2022 digital oscilloscope and then processed in MATLAB. The results showed the viability of this technique for identifying defects in metallic aluminum structures and characterizing these materials using lower frequencies.