Investigation of Elastic Guided Waves for Ceramic Joint Evaluation.

摘要

The rapid development of ceramic technology has led to the widespread use of ceramics in applications traditionally reserved for metals. Many of these applications, however, require the use of ceramics bonded to other ceramics or to metals in order to achieve the requisite strength. The presence of unbonding in such ceramic joints can now be reliably detected by previously developed ultrasonic techniques, but what is needed is a nondestructive approach which is capable of assessing bond strength directly. A possible tool to achieve this goal is the use of guided elastic waves propagating in the braze layer of a typical ceramic joint. We describe the theory of guided waves in the center layer of a general three-layer solid. The secular determinant is found, and roots of the secular equation are determined numerically for cases of interest in ceramic joining. Both guided and leaky modes are described, and it is shown that dispersive Stoneley waves can occur for these materials. In addition, the evanescent nature of the guided waves in the bounding solids raises the possibility of determining the elastic properties of the oxygen depletion layer adjacent to the braze in oxide ceramics. Possible models for incomplete bonding and the effect of this condition in the ultrasonic parameters are also discussed. 16 refs., 10 figs.