Torsion shear strength of ceramics joined by brittle or ductile materials

Assessing the shear strength of a joined ceramic or CMC is an essential task in components design. Indeed, what is needed for design purposes, is the true shear strength, while several standard tests only give conventional values, disregarding multiaxiality and non-uniformity of the actual stress distribution. If used under proper conditions, torsion test has the advantage of producing a state of pure shear stress with a known distribution in the joint section. A distinction must be done whether the joining material is brittle or ductile. In case of brittle behavior, the stress concentration factor due to the specimen geometry must be taken into account; moreover, since the stress state is intrinsically biaxial, failure may occur out of the joint section. In case of ductile behavior, the non-linear effect of plasticity must be included. The talk discusses these aspects and proposes a procedure suitable to assess the pure shear strength of joined ceramics.