MECHANICAL PROPERTIES MODELING OF POROUS CALCIUM PHOSPHATES CERAMICS

Macroporous Biphasic Calcium Phosphate bioceramics, for use as bone substitutes, have been fabricated by soft chemical hydrolysis, cold isostatic pressing and conventional sintering, using naphthalene particles as a porogen to produce macropores. The resulting ceramics are biphasic materials made of hydroxyapatite and beta-tricalcium phosphate containing various macroporosities and microporosities. Compression tests and three-point bending toughness tests were performed on samples covering the widest attainable ranges of porosities (53 different macroporosity/microporosity couples). Results are compared to previously proposed analytical models and hypotheses. The models describe the evolution of mechanical properties of a porous material, taking into account the separate influences of both macroporosity and microporosity. The strength model also considers macropores as critical flaws. The main results are the following: (i) the models are modified to improve the fitting with experiment, (ii) the macropores are actually identified as being linked to the critical flaws and (iii) the previous hypothesis is rejected, as the critical flaw size appears to increase with macroporosity. This phenomenon is interpreted by the existence of clusters of macropores, acting as critical flaws, which size increases with macroporosity.