Monolithic and composite ceramic machining flaw-microstructure-strength effects: model evaluation

A model giving the size, c, of flaws from machining of ceramics as c ∝ (E/H)1/3(F/K)2/3, where F= the vertical force on abrasive particles, and H, K, and E= respectively local values of hardness, fracture toughness (i.e. small crack values) and Youngʹs modulus is shown to be consistent with material, microstructural and machining parameter effects on flaws and strengths. Specifically this model is consistent with effects of machining flaw sizes on strengths due to effects of: (1) porosity and grain size in monolithic ceramics, (2) matrix grain size, and dispersed particle size and volume fraction in ceramic particulate composites, and (3) machining parameters such as grit size in monolithic and composite ceramics. Such a model emphasizes the role of microstructural and compositional dependence of properties impacting strengths via both flaw introduction as well as via flaw propagation to failure, which provides a broader perspective on strengths of typically machined ceramics.