Crack detection in aluminum parts by using ultrasound-excited infrared thermography

• Ultrasonic IR thermography can detect ‘kissing’ cracks in heavy aluminum structures.
• Thick aluminum beams should be supported at two ends and be stimulated in the middle.
• Temperature signals and signal-to-noise ratio reach maximums at times under 0.5 s.
• 1D and 2D wavelet transform is a convenient image enhancing technique.

Ultrasound-stimulated IR thermography, thanks to its large-area imaging capability, high test productivity and safety, is a powerful tool for the inspection of cracks in heavy aluminum structures. In thick aluminum parts, the most important defect detection parameters are the differential temperature signal and signal-to-noise ratio (SNR), which typically reach their maximums at shortly (under 1 s) after the beginning of the ultrasonic excitation. In the IR inspection of non-metals, the ultrasonic excitation may be relatively long, while in the case of highly-conductive aluminum, short-pulse (burst) stimulation (from 0.4 to 1 s) is sufficient The crack detectability can be improved by evaluating temperature images at the times when maximum SNR values occur. Further enhancement of test results can be achieved by applying some data processing algorithms which can be 1D, i.e. applied to temperature evolutions in time, or 2D, i.e. applied to spatial coordinates, or a single image.