During the processing of laminar ceramic, biaxial residual stresses ca
n arise due to differential thermal contraction between unlike layers.
A tensile stress can cause preexisting flaws to extend across the lay
er and into the adjacent layers and then tunnel until they meet either
another crack or a free surface. A previous analysis has shown that f
or a given residual stress there is a critical layer thickness, below
which no tunnel cracks will exist, regardless of initial flaw size. He
re, the previous analysis was modified to take into account the crack
extension into adjacent layers. To determine the validity of the analy
sis, laminates composed of alternating layers of zirconia and alumina/
zirconia were fabricated by a sequential centrifugation technique. The
composition of the alumina/zirconia layer was varied to change the bi
axial, tensile stresses in the zirconia layer. Observations were then
made to determine the critical layer thickness for tunnel cracks and t
heir extension into the adjacent layers. These observations were compa
red to the theoretical predictions.