A self-calibrating technique for the ultrasonic discrimination of solid-state welds

This paper presents the description and application of a self-calibrating technique for ultrasonic weld discrimination. A broad-band ultrasonic transducer is bonded to one side of the component containing the weld. The transducer transmits and receives short pulses in the pulse-echo mode. The received short pulses are processed to provide data on weld quality. The technique is self-calibrating in the sense that the capture of two waveforms in a single measurement provides enough information to remove the transducer transfer function and transducer bond losses. A key feature of the technique is the elimination of the deleterious effects of ultrasonic bond variability, which was found to be the major limitation for the materials investigated in this study. Another feature is the requirement of access to one side of the weld only. The technique is applied to solid-state welds involving two types of steel, i.e., martensitic and austenitic steel. For the martensitic steels, substantial improvement over previous studies was seen and first- and fourth-class welds could be discriminated. On the other hand, the austenitic steel welds are examples which demonstrate the need for still further improvements, since the discrimination between first- and fourth-class welds was only marginal.