On the bulk compaction of brittle granular materials, Part III: Brittle-to-ductile transition and yield strength^*

A new and simple method is presented that enables the estimation of the yield strength (σ_y) of brittle materials (e.g., ceramics, glasses). It results from the combination of sufficiently high-stress compaction of their granular form, postmortem analysis of the crushed particles to identify the critical particle size corresponding to their brittle-to-ductile transition, and the use of a developed and simple analytical expression. This method was an outcome from Part I of this three-paper series. To execute it, a granular brittle material is compacted to a sufficiently high stress, whereby the acting comminution produces both a fraction of particles having a sufficiently small size formed by ductile or plastic-like deformation and a remaining fraction of larger particles formed from brittle fracture. Postmortem microscopy is then used to identify the smallest particle size whose morphology indicates it formed from brittle fracture (d_B2D). The brittle material's σ_y can then be estimated using a combination of the d_B2D, Kendall's and Griffith's theories, a priori knowledge of the material's fracture toughness (K_Ic), and a fracture mechanics shape factor constant (Y) using σ_y = √((32 π K_Ic²)/(3 Y² d_B2D)). The method's development and its use to estimate σ_y for several vitreous silicates, α-quartzes, and NaCl are provided.