FRACTURE-BEHAVIOR OF A MULTILAYERED SILICON-NITRIDE

The fracture behavior of a silicon nitride layered composite with alte rnating dense and porous layers was investigated under varying span-to -depth ratio in bending tests. Although the load-deflection curves alw ays indicated a linear behavior, delamination cracks were often observ ed 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 const ant and a fracture origin was always confirmed in the dense layer on t he tensile surface. As for three-point bending, the fracture was origi nated in the dense layer on the tensile surface by tensile stress foll owed by delamination.