1452 T Lube et al. Journal of the European Ceramic Society 27(2007)1449-1453 maximum shielding=12 MPa m for 1=2.6 x alumina volume fraction 12 E三2598935,日 N, number of layer E22 Fig. 4. Influence of the AZ-composite chemistry on the maximum shielding of maximum shielding= 13 MPa m the outer A-layer. w. total thickness [ mm] e'=EA/E, elastic ratio 9>5×日 Fig 3. Influence of architecture on shielding.(a)N: number of layers and(b) kness optimal architecture Aopt is exclusively defined by the elastic constants. It also shows that shielding is more protective with a (a) A=121 low number of layers and for thicker specimens. However, for relatively thick layers the authors expect a non-uniform stress field within the layers(Saint Venant principle)and the stress E 16) Aa=(a-a)10, thermal mismatch field considered here(Eq (5)) would not apply The influence of the materials properties on the residual stress field is evident by Eq (5). Fig 4 presents the maximum shielding in A/AZ laminates for several compositions of the composite da=1.25 AZ. As one can observe the maximum for each composition is obtained for a different AoptAopt varies from 2.25 for 95 vol% 3 alumina to 2.7 for 50 vol% alumina. Properties of the different opposites were estimated by applying the rule of mixtures,to the values presented in Table 1 A more detailed analysis results in that exclusively the Youngs modulus ratio influences and not the thermal 0.25 expansion mismatch. Fig 5a reveals how a stiffer material than alumina in the inner layer will increase the toughness. It results com Fig. 5b, the higher the thermal mismatch is, the higher is (b) the compression in the outer layer and therefore, the higher is Fig. 5. Influence of the Young's modulus E and of the coefficient of thermal the shielding expansion a on the maximum shielding.1452 T. Lube et al. / Journal of the European Ceramic Society 27 (2007) 1449–1453 Fig. 3. Influence of architecture on shielding. (a) N: number of layers and (b) W: total thickness. optimal architecture λopt is exclusively defined by the elastic constants. It also shows that shielding is more protective with a low number of layers and for thicker specimens. However, for relatively thick layers the authors expect a non-uniform stress field within the layers (Saint Venant principle) and the stress field considered here (Eq. (5)) would not apply. The influence of the materials properties on the residual stress field is evident by Eq.(5). Fig. 4 presents the maximum shielding in A/AZ laminates for several compositions of the composite AZ. As one can observe the maximum for each composition is obtained for a different λopt. λopt varies from 2.25 for 95 vol% alumina to 2.7 for 50 vol% alumina. Properties of the different composites were estimated by applying the rule of mixtures, to the values presented in Table 1. A more detailed analysis results in that exclusively the Young’s modulus ratio influences λopt, and not the thermal expansion mismatch. Fig. 5a reveals how a stiffer material than alumina in the inner layer will increase the toughness. It results from Fig. 5b, the higher the thermal mismatch is, the higher is the compression in the outer layer and therefore, the higher is the shielding. Fig. 4. Influence of the AZ-composite chemistry on the maximum shielding of the outer A-layer. Fig. 5. Influence of the Young’s modulus E and of the coefficient of thermal expansion α on the maximum shielding