ULTRASONIC EVALUATION OF SPOT WELD QUALITY.

A novel ultrasonic method for evaluation of shear strength of a spot weld is based on an analytical expression which relates the transmission coefficient of Lamb waves passing through a spot weld nugget to the nugget diameter. The use of an ultrasonic spectroscopic method for determining nugget size is also discussed. A fracture mechanics model is introduced to correlate fracture load to the nugget dimension. This model predicts that failure load is proportional to the squared nugget diameter. While the model is valid only when the weld fails through the nugget, the proportionality of the failure load to the square of the diameter holds also when failure occurs in the base metal.