1989 Volume 38 Issue 428 Pages 490-495
Tensile tests of Si3N4/S45C bonding bar-type specimens, which were jointed by metallizing method, were carried out in laboratory air at room temperature. Then, the relation between the fracture stress and the appearance of fracture surface was investigated in detail.
Generally, the crack initiation site was at the bonding part, and the crack propagated into the ceramic. In this case, the following relation was observed between the fracture stress, σf (MPa) and the square root of the mist area, √Ah(mm).
σf=540(√Ah)-0.47
Furthermore, the size effect was recognized on the fracture stress and the following equation was deduced for the fracture stress, σf (MPa) based on fracture mechanics and fractography.
σf=25.8/√d
where d(m) is the diameter of specimen.
When the diameter of specimen increased, the crack initiated in the ceramic in some of the specimens. In this case, the fracture stress was low. The reason was considered that the bonding-induced residual tensile stress increased with increasing the diameter of specimen and/or the value of residual stress was remarkably different at each specimen.
