Prediction and experimental validation of penetration depth of butt welds in thin plates using superimposed laser sources

In this paper, a methodology to measure penetration depth of butt welds in thin plates using laser generated ultrasounds is presented. The superimposed line sources (SLS) technique is used to generate narrowband ultrasounds. The signal processing procedure that combines wavenumber-frequency (k-ω) domain filtering and synthetic phase tuning (SPT) is used to reduce the complexity of Lamb wave signals. The reflection coefficients for different wavelengths corresponding to each wave mode are calculated. Cutcheck inspection is performed and critical dimensions of weld such as penetration depth, reinforcement height and bead width are measured. Regression analysis that includes stepwise regression and corrected Akaike's information criterion (AICc) is performed to build prediction models that use the reflection coefficients as predictors. The model predictions are validated using cutcheck results of validation experiments and the root mean square error (RMSE) is as low as 7.74% of the plate thickness.