In this fourth paper of a series on the effective elasticproperties of alumina-zirconia composite ceramics the influence of porosity onthe effective tensile modulus of alumina and zirconia ceramics is discussed. Theexamples investigated are alumina and zirconia ceramics prepared from submicronpowders by starch consolidation casting using two different types of starch,potato starch (median size D50 =47.2 µm) and corn starch(median size D50 =13.7 µm). The dependence of effective tensilemoduli E, on the porosity f, measured for porositiesin the ranges of approx. 19-55 vol.% and 10-42 vol.% for alumina and zirconia,respectively, using a resonant frequency technique, was evaluated by fittingwith various model relations, including newly developed ones. A detailedcomparison of the fitting results suggests the superiority of the new relationE/E0 = (1 - f)·(1 - f/fC),developed by the authors (with the tensile modulus of the dense ceramic materialE0 and the critical porosity fC),over most other existing fit models. Only for special purposes and well-behaveddata sets the recently proposed exponential relation E/E0 = exp [-Bf/(1- f)] and the well-known Phani-Niyogi relation E/E0= (1 - f/fC)Nmight be preferable.
