Abstract
We have proposed two new estimation methods for the fracture toughness (KIC) of hard or brittle materials by each use of our newly derived two equations of σm=ψKICSmf1/2 and σd-1=σ0-1+Ka1/2 (σm: transverse-rupture strength of artificially un-notched test piece, ψ: shape factor, Smf: total macroscopic fracture surface area of one test piece, σd: maximum external fracture stress which operated on the fracture origin, σ0: intrinsic fracture strength, 2a: maximum fracture origin diameter, K: 2σ0-1ρ-1/2, which is nearly proportional to KIC-1, ρ: fracture origin tip radius). And we have clarified that these two equations and two methods are applicable to some hard or brittle materials such as high speed steel, WC-16.4vol%Co hardmetal, Si3N4 ceramics and Mn-Zn ferrite.
In this study, we clarified that the above two equations and two methods are applicable also to another eight kinds of hard or brittle materials such as WC-Co hardmetals, TiC- and Ti(C, N)-base cermets and Al2O3-base ceramics. The Ψ and K values for each material were clarified to be commonly about 14×103 m-3/2 and 0.70KIC-1 respectively, in the same way as for the above previously studied materials. Thus, it was concluded that the KIC of general new hard or brittle materials can be estimated from σm and Smf or σd and 2a by each use of the above two equations or modified equations where these concrete experimental values of Ψ and K were substituted, respectively.
