Fracture behavior of a multilayered silicon nitride

The fracture behavior of a silicon nitride layered composite with alternating dense and porous layers was investigated under varying span-to-depth ratio in bending tests. Although the load-deflection curves always indicated a linear behavior, delamination cracks were often observed in central porous layers. During four-point bending, a complicated fracture mode and local stepwise crack extension were observed. In the high span-to-depth ratio region, the fracture stress was almost constant and a fracture origin was always confirmed in the dense layer on the tensile surface. As for three-point bending, the fracture was originated in the dense layer on the tensile surface by tensile stress followed by delamination.