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

摘要

In the previous studies on the room temperature transverse-rupture strength or fracture stress (sigma_m), fracture toughness (K_(IC): SEPB method) and fracture origin size (2a) of polycrystalline hard or brittle materials, we have semi-theoretically derived and experimentally verified two equations of sigma_m = PSI K_(IC)S_(mf)~(1/2) and sigma_d~(-1) = sigma_0~(-1) +Ka~(1/2): S_(mf) is the total fracture surface area of all fragments of one test piece, sigma_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 (sigma_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, sigma_m can be approximately estimated by use of sigma_m - S_(mf)~(1/2) correlation lines with a parameter of K_(IC) or equation sigma_m = PHI K_(IC)S_(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, sigma_m can be approximately estimated by use of sigma_d~(-1)-a~(1/2) correlation lines with a parameter of K_(IC) and by measuring 2a, etc., and by estimating K_(IC) in the same way as in Method I.