reduced during further quenching. As can be seen from Fig. 4, the mono- lithic material shows a sharp change between one temperature and the next. For the laminate composite, however, it seems like there is a more gradual change between no cracks and failure. The reason for this phe- nomenon is due to the residual compressive stresses resisting the crack growth and decreasing the chances of complete breakdown of the ma- terial considerably [39].
According to above analysis, if the indents are made into the cross section of laminated TSG ceramics, the crack-growth behavior will de- pend on the on the position of indents located in compressive layers or in tensile layers. It can be inferred that: (1) if the indents were made in the compressive layers, the cracks would begin to propagate in the parallel direction at low temperature differences whereas the transversal cracks did not propagate much at the same temperatures differences; (2) in the tensile layers the inverse phenomena would hap- pen due to the inverse stresses. That to say, transversal cracks would propagate easily and grow unstably at low temperature differences. At the same temperatures difference, the parallel cracks were rather stable. The transversal cracks stopped propagating when they had reached the compressive layers.