Part II: Fracture strength and elastic modulus as a function of porosity for hydroxyapatite and other brittle materials

Part I of this paper discussed the Weibull modulus mm, versus porosity PP behavior of brittle materials, including HA. While the Weibull modulus mm deals with the scatter in fracture strength data, this paper (Part II) focuses on two additional key mechanical properties of porous materials, namely the average fracture strength 〈σf〉〈σf〉, and Young’s modulus EE, for PP in the interval from P≈P≈ zero to P≈PGP≈PG (the porosity of the unfired compacts). The 〈σf〉〈σf〉 versus PP data for HA from this study and the literature data for alumina, yttria stabilized zirconia (YSZ) and silicon nitride are described well by functions of ϕϕ, where ϕ=1−P/PG=ϕ=1−P/PG= the degree of densification. A similar function of ϕϕ applies to the 〈E〉〈E〉 versus P behavior of HA from this study and data from the literature for alumina, titanium and YSZ. All of the data analyzed in this study (Part II) are based on partially and fully sintered powder compacts (excluding green powder compacts), thus the 〈σf〉/σ0〈σf〉/σ0 versus ϕϕ and 〈E〉/E0〈E〉/E0 versus ϕϕ relationships may apply only to such specimens.

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► Fracture strength σfσf, Young’s modulus EE, versus porosity PP, HA and other ceramics.
► From green porosity PGPG to P≈0P≈0, equations similar to σfσf and EE versus PP.
► σfσf and EE versus PP expressed as (1−P/PG)n(1−P/PG)n, with n≈1n≈1 for each material.
► Power law function may apply to many partially sintered brittle materials.