Residual stresses in layered ceramic composites 1331 Pontion Fig 3. Compressive stress distribution in barrier layers made of alumina (left)and a mixture of alumina and zirconia(right) of Y-TZP/AlO3 composites. 0 0 Position across the layer lur Position across the layer [umg ressive stress distribution in barrier layers made of alumina (left)and a mixture of alumina and zirconia(right) of CE-TZP/Al2O3 composites. layers made of an oxide mixture the compressive barrier layers made of an oxide mixture crack stress was constant on position across the layer deflection not found. Observed changes were (Figs 3 and 4). The present results reveal that related to measurements of residual stress distribu- compressive stress distribution in barrier layers can tion in barrier layers be regarded as an important factor responsible for crack deflection in layered composites References 4 Conclu 1. Garvie. R. S. Hannink. R.H.J. and Pascoe. R. T. Ceramic steel? Nature(London), 1975. 258. 703-704 The aim of this work was to determine the residual 2. Marshall. D. B. Ratto. J J and Lange. F. F. Enhanced fracture toughness in layered microcomposites of Ce-Zro stress effects on the character of crack propagation and Al,O2.J. Amer. Cera. Soc.1991. 74. 2979-2987 in layered ceramic composites. During tests of controlled crack growth a distinct crack deflection nia composites Ceram. Bull. 1992.. 969-973 in alumina layers was observed The crack deflection 4. He. j and clarke. d.r. determination of the roscopic coefficients for chromium-doped sapphire angle was proportional to the layer thickness. In J.Am. Ceran.Soc.,1995,78,1347-1353layers made of an oxide mixture the compressive stress was constant on position across the layer (Figs 3 and 4). The present results reveal that compressive stress distribution in barrier layers can be regarded as an important factor responsible for crack de¯ection in layered composites. 4 Conclusions The aim of this work was to determine the residual stress e€ects on the character of crack propagation in layered ceramic composites. During tests of controlled crack growth a distinct crack de¯ection in alumina layers was observed. The crack de¯ection angle was proportional to the layer thickness. In barrier layers made of an oxide mixture crack de¯ection was not found. Observed changes were related to measurements of residual stress distribu￾tion in barrier layers. References 1. Garvie, R. S., Hannink, R. H. J. and Pascoe, R. T., Ceramic steel? Nature (London), 1975, 258, 703±704. 2. Marshall, D. B., Ratto, J. J. and Lange, F. F., Enhanced fracture toughness in layered microcomposites of Ce-ZrO2 and Al2O3. J. Amer. Ceram. Soc., 1991, 74, 2979±2987 3. Marshall, D. B., Design of high-toughness laminar zirco￾nia composites. Ceram. Bull., 1992, 78, 969±973. 4. He, J. and Clarke, D. R., Determination of the piezo￾spectroscopic coecients for chromium-doped sapphire. J. Am. Ceram. Soc., 1995, 78, 1347±1353. Fig. 3. Compressive stress distribution in barrier layers made of alumina (left) and a mixture of alumina and zirconia (right) of Y-TZP/Al2O3 composites. Fig. 4. Compressive stress distribution in barrier layers made of alumina (left) and a mixture of alumina and zirconia (right) of CE-TZP/Al2O3 composites. Residual stresses in layered ceramic composites 1331