C. Reynaud et al. /Journal of the European Ceramic Society 25(2005)589-597 50 051015202530354045 051015202530354045 Porosity(vol%) Porosity(vol%) 3.5 30 3221100 051015202530354045 051015202530354045 Porosity (vol%) Porosity(vol%) Fig. 6. Dependence on porosity of the mechanical properties of monolithic laminates(PFA= CS).(a) Youngs modulus; (b)modulus of rupture;(c) toughness;(d) fracture energy. The solid lines correspond to the best fit with Wagh's equations modulus with Ep= Eo(1-P)2. Such an equation was also Wagh et al. this value of 2 is characteristic of ceramics established by Wagh et al. 19 for a model derived from an densified without additives or applied pressure. However, previous analytical one developed by Wong et al.20 in ef- for materials hot-pressed or densified using sintering aids forts to explain charge and mass transport through the ran- leading to an intergranular glassy phase, mE takes value dom pore structure of rocks. The assumed ceramic structure reater than 2 is a three-dimensional. intertwined continuous network of Wagh et al. 22 derived, for the fracture properties, power are interconnected by small channels oore i A 3 material chains and open-pore channels. This assumption is laws with different exponents connected together by based on the fact that it is possible to fabricate ceramics with a very high porosity, as high as 93%, and that oper mog=mIC =mE+0.5 and mGIc =mE+I exist even at very low porosity(6%). This is consistent with The results from fits done with the exponents put at their the mainly open nature of the porosity in the present mate- neoretical values are reported in Table 2. The correlation rials where the pores introduced by the factors are fairly good The model developed by Wagh et al. 9. that takes into The fitting parameters obtained using a classical mean account the tortuosity of the porosity, describes the whole square method, are reported in Table 2 set of our experimental data of the mechanical properties The mE parameter(2.68), is greater than the value of over the entire porosity range(from P=0%to P=42%) 2 obtained experimentally by Blanks et al. 7 According to and appears to be well adapted to the present porosity mor- Table 2 Fi ers for the mechanical properties using Wagh's model Property Correlation 5. Fracture behaviour 2.68±0.08 5.1. Experimental results 590±15 0.98 4.34±0.09 The fracture behaviour of the laminar composite (LC) 46.4±2.0 was studied in 3-point bending for unnotched and notcheC. Reynaud et al. / Journal of the European Ceramic Society 25 (2005) 589–597 593 Fig. 6. Dependence on porosity of the mechanical properties of monolithic laminates (PFA = CS). (a) Young’s modulus; (b) modulus of rupture; (c) toughness; (d) fracture energy. The solid lines correspond to the best fit with Wagh’s equations. modulus with EP = E0(1 − P)2. Such an equation was also established by Wagh et al.19 for a model derived from an previous analytical one developed by Wong et al.20 in ef￾forts to explain charge and mass transport through the ran￾dom pore structure of rocks. The assumed ceramic structure is a three-dimensional, intertwined, continuous network of material chains and open-pore channels. This assumption is based on the fact that it is possible to fabricate ceramics with a very high porosity, as high as 93%,21 and that open pores exist even at very low porosity (6%). This is consistent with the mainly open nature of the porosity in the present mate￾rials where the pores introduced by the pore forming agents are interconnected by small channels.13 The fitting parameters obtained using a classical mean square method, are reported in Table 2. The mE parameter (2.68), is greater than the value of 2 obtained experimentally by Blanks et al.7 According to Table 2 Fitting parameters for the mechanical properties using Wagh’s model Property Extrapolated at P = 0 m Correlation factor E (GPa) 407 ± 7 2.68 ± 0.08 0.995 σR (MPa) 590 ± 15 3.18 0.98 K1C (MPa m1/2) 4.34 ± 0.09 3.18 0.99 G1C (J/m2) 46.4 ± 2.0 3.68 0.96 Wagh et al. this value of 2 is characteristic of ceramics densified without additives or applied pressure. However, for materials hot-pressed or densified using sintering aids leading to an intergranular glassy phase, mE takes value greater than 2. Wagh et al.22 derived, for the fracture properties, power laws with different exponents connected together by: mσR = mK1C = mE + 0.5 and mG1C = mE + 1 The results from fits done with the exponents put at their theoretical values are reported in Table 2. The correlation factors are fairly good. The model developed by Wagh et al.19,22 that takes into account the tortuosity of the porosity, describes the whole set of our experimental data of the mechanical properties over the entire porosity range (from P = 0% to P = 42%) and appears to be well adapted to the present porosity mor￾phology. 5. Fracture behaviour 5.1. Experimental results The fracture behaviour of the laminar composite (LC) was studied in 3-point bending for unnotched and notched