Application of an Equation Representing Reciprocal Fracture Strength versus Square Root of Fracture Origin Size to the Estimation of Fracture Toughness of Hard or Brittle Materials

Abstract

In the past study on the transverse-rupture strength (σ_m) of WC-10mass%Co hardmetal, the authors had derived an equation of σ_d^-1=σ₀^-1+Kα^1/2 (σ_d; the external stress which operated on the fracture origin at the moment of fracture, σ₀; the intrinsic fracture strength, K; 2σ₀^-1ρ^-1/2, ρ; the effective tip radius of microstructural defect which acted as the fracture origin, a; the half of the major-axis length of the fracture origin), and also had clarified that this equation holds on various kinds of hard materials. Furthermore, the slope value (K) of the σ_d^-1-α^1/2 regression line was suggested to have a correlation with the fracture toughness (K_IC) in a similar way as the slope of σ_m-S_mf^1/2 regression line (S_mf; total macroscopic fracture surface area of fragments). In this study, this suggestion was investigated on four kinds of hard or brittle materials such as high speed steel, WC-10mass%Co hardmetal, Si₃N₄ ceramics and Mn-Zn ferrite. It was found that the K has surely a strong correlation with K_IC, and K_IC can be expressed by an unified equation of K_IC??0.7K^-1.