Crack Bifurcation at the Surface of Laminar Ceramics That Exhibit a Threshold Strength

Previous literature has shown that when a crack extends across a compressive layer within a two‐phase laminar ceramic, the crack can bifurcate under special conditions. These special conditions appeared to require that a second crack (known as an edge‐crack) had to preexist along the center line of the compressive layer. Here, it is shown that a crack can exhibit bifurcation without the formation of an edge‐crack. It was found that a critical combination of residual compressive stress and layer thickness exists in which edge‐cracking of the layer does not occur, yet the crack bifurcates when entering the compressive layer. Additionally, it was observed that crack bifurcation only occurs within the surface region of the compressive layer, while within the bulk, the crack extends straight across the compressive layer. These observations strongly suggest that the stresses on the surface of the compressive layer, which are known to be different from those within the bulk, will encourage crack bifurcation.