The Characterization of Weld Morphology Using Ultrasonics

Abstract

Welding is a complex manufacturing process, which involves significant physical and chemical changes in materials. Meanwhile, unexpected defects such as lack of penetration, undercutting, crater crack, burn-through and porosity may occur during manufacturing process. Therefore, the assessment of weld quality by means of nondestructive testing is needed. In this paper, the weld morphology is investigated by means of linear and nonlinear ultrasonics. The relationship between weld morphology and ultrasonic features (signal energy ratio extracted from linear ultrasonics and acoustic nonlinearity coefficient extracted from nonlinear ultrasonics) are built. Different penetration morphologies (bead, shallow penetration, excessive penetration, and burn-through) show different ultrasonic signatures. The microscopic observation is used to build the numerical models that validate the experimental measurements. The experimental and numerical results show that linear ultrasonics is influenced by the penetration morphology (shape, width and depth). The acoustic nonlinearity coefficient is influenced not only by the weld morphology but also heterogeneities (e.g. porosity) in the medium. The experimental and numerical results are used to build the regression models such that the ultrasonic features can be exploited to assess the weld morphology in situ without any destructive testing.