Plasticity Considerations in Probabilistic Ceramic-to-Metal Joint Design

A new probabilistic failure criterion was developed for the design of high-temperature ceramic-to-metal joints. The essential feature of the theory is the inclusion of the energy dissipated during plastic deformation of the adjacent braze layer in the joint. A large number of bimaterial interface fracture simulations were performed for different crack positions and orientations near the bimaterial interface to determine the effect on stresses in the ceramic near the interface. The effective stress values were then ported to a probabilistic failure analysis code, which permitted simple inclusion of the new failure criterion. Brazed joints were made and failure tested in torsion to verify the failure criterion. Results show that the new failure critertion more closely approximates the failure of the ceramic-to-metal joints over the entire range of ultimate loads, and is a significant improvement in the failures criteria previously used for this type of joint design. Aspects of the failure criterion, material systems, residual stresses, mechanical behavior, and strength predictions will be presented.