Shear strength tests of joined advanced ceramics

Advanced ceramics appear to be a very important resource for the development of many new technologies (fuel cells, nuclear fusion…) and in many manufacturing processes. An important issue in the construction of ceramic components is related to their joining methods. When size and complexity of the components grow, it is impossible to sintherize them in a single monolithic piece. It is necessary to join several parts: apart from mechanical joining systems, the primary solution is to use a material – that acts as adhesive – able to intimately join the two materials. The joining material needs to give sufficient mechanical strength, and to maintain resistance to external actions at high temperatures, as the adherend material is able to. In this paper, some results obtained in the Innovative Materials Laboratory (La.M.In.) of the II Faculty of Engineering of the Politecnico di Torino, will be shown. Since there is no unique method to measure the shear strength of the ceramics joints (the most important is ASTM C1469-00) and lack of agreement on a common test still exists, different testing methods were considered. One of the main difficulties is still to correlate the results from different tests: in fact, in each testing method the sample is subjected to different states of stress, and failure is induced differently. A thorough stress analysis has to be carried, by means of detailed finite elements models.