Ultrasonic Model for Solid State Weld Evaluation

Abstract

Ultrasonic techniques have classified good and poor solid state welds in several studies [1,2,3]. A number of different types of solid state welds such as pinch welds, inertia welds, and diffusion bonds, have been evaluated with various ultrasonic feature extraction and pattern recognition techniques. The results of these studies have presented trends in the features needed to determine bond quality, but there is no physical explanation as to why certain features of the ultrasonic wave forms are influenced by the bond quality. An appropriate physical model that complements the experimental results would help explain the acoustic interactions measured. One model for the solid state weld is that the acoustic interaction with the bond line is controlled by the effective compliance of the interface. We have designed an experiment to examine this model. In our experiment, two blocks made from a high glass transition temperature (Tg) epoxy are joined together with a thin, lower Tg epoxy interlayer. If the temperature of the specimen is held below the Tg of the low temperature epoxy, then the interlayer compliance ratio across the interface can be changed by varying the temperature. Ultrasonic data are acquired at each temperature and, thus, each compliance ratio. This ultrasonic data can be compared with theoretical predictions from the compliance model.