Abstract
Porous brittle materials are used as filters, catalyst supports, solid oxide fuel cells
and biomedical materials. However the literature on the Weibull modulus, m, versus
volume fraction porosity, P, is extremely limited despite the importance of m as a
gauge of mechanical reliability. In Part I of this study, m is determined for 441 sintered
hydroxyapatite (HA) specimens fractured in biaxial flexure for 0.08 ≤ P ≤ 0.62. In this
study, we analyze a combined data set collected from the literature that represents work
from a total of 17 different research groups (including the present authors), eight different
materials and more than 1560 oxide and non-oxide specimens, the m versus P plot is “Ushaped”
with a wide band of m values for P < 0.1 (Region I) and P > 0.55 (Region III), and a
narrower band of m values in the intermediate porosity region of 0.1 < P < 0.55 (Region II).
The limited range of m (∼ 4 < m < 11) in Region II has important implications since Region
II includes the P range for the majority of the applications of porous brittle materials. Part
II of this study focuses on the P dependence of the mean fracture strength,< σf >, and the
Young’s modulus E for the HA specimens tested in Part I along with literature data for other
brittle materials. Both < σf > and E are power law functions of the degree of densification,
φ, where φ = 1 − P/PG and PG is the green (unfired) porosity.