Zirconia/ veneer bi-layered components are extensively used in dental restoration technology to improve resistance of tooth’s surface from decay. The direction of the fracture propagation at the interface of zirconia and veneer is investigated in this paper. Finite element analysis is performed on a bi-material four point bend specimen in different geometries, and the fracture initiation angle is obtained using maximum tangential stress (MTS) criterion. The effect of specimen geometry on the fracture initiation angle is discussed. Because an interface crack may propagate through interface or kink into one of the materials, some comments are given to determine under which condition “interface de-bounding” will be happened.

Silicon/glass bi-materials are used in micro-assembly and packaging of micro-electromechanical systems (MEMS) and micro-electronics devices. In this paper, maximum tangential stress (MTS) concept is used for determination of the fracture initiation angles of silicon/ glass bi-material notches. First, the MTS criterion is analytically formulated for a bi-material notch problem. Then, the criterion used for prediction of fracture initiation angles of some experimental data given in literature for silicon/ glass bi-material notches. In addition, the modified MTS (MMTS) criterion, which considers the effect of I-stress, was compared with the MTS criterion and the experimental data. It was shown that MMTS criterion provides more accurate results than the MTS criterion for estimation of the fracture initiation angle.