Development of Two New Methods for Estimating Fracture Stree of Fractured Hard or Brittle Materials from Its Fragments

Abstract

In the previous studies on the room temperature transverse-rupture strength or fracture stress (σ_m), fracture toughness (K_IC: SEPB method) and fracture origin size (2α) of polycrystalline hard or brittle materials, we have semi-theoretically derived and experimentally verified two equations of σ_m=ψK_ICS_mf^1/2 and σ_d^-1 =σ₀^-1+Kα^1/2: S_mf is the total fracture surface area of all fragments of one test piece, σ_d is the maximum external stress on the fracture origin, etc..
In this study, based on the above each equation, we newly developed two methods for approximately estimating the fracture stress (σ_m) of the fractured test piece of hard or brittle materials from its fragments, whose fracture load and kind of material are both unknown. Method I: On condition that all the fragments are available, σ_m can be approximately estimated by use of σ_m-S_mf^1/2 correlation lines with a parameter of K_IC or equation σ_m =ψK_ICS_mf^1/2 and by measuring S_mf and estimating K_IC from the correlation line between K_IC and K_IC^HV (fracture toughness measured by IF method). Method II: On condition that the fragment including the fracture origin is available, σ_m can be approximately estimated by use of σ_d^-1-α^1/2 correlation lines with a parameter of K_IC and by measuring 2α, etc., and by estimating K_IC in the same way as in Method I.