Nondestructive evaluation of spot welds using acoustic and thermographic imaging techniques

A series of laboratory experiments were conducted to determine the ability of acoustic and thermographic methods to evaluate the quality of individual spot welds and the structural integrity of spot-welded joints with andwithout adhesive. Test specimens consisted of spot-welded, adhesive-bonded, and weld-bonded lap joints in steel plates. The quality of the spot welds was altered by varying welding parameters. After nondestructive evaluation, the samples were peeled or subjected to mechanical tests to determine the strength of the welds. Results demonstrate that it is possible to detect defective spot welds in both the thermographic and acoustic images. Techniques are presented that allow identification of "stick" welds characterized by solid but weak contact. Methods to quantify the imaging results are being developed by comparing the acoustic and thermographic images to the data obtained from mechanical strength tests and modeling results.