Failure criterion for brittle materials with U‐notches: Unification of characteristic length‐based and grain size‐based criteria

Abstract Here, the limitations of characteristic length‐based ( L chb ) and grain size‐based ( G b ) criteria with two or three parameters were pointed out employing the apparent toughness tests of 12 different ceramics at a large span range of U‐notch root radius ( ρ ) values. After comprehensively considering the potential influencing factors of stress intensity factor ( K c ), ρ divided by critical notch tip radius ( ρ c ) was proposed as the independent variable, and the data of 21 materials (covering ceramics, plastics, resins, rocks, and metals) was summarized and discussed to establish a simple and more applicable K c prediction model. Results indicated that K c / K Ic was a power function of ρ / ρ c with a power exponent n of 0.5 for ideal materials and less than 0.5 for actual materials. It was also found that ρ c can be calculated simply by K Ic 2 /(π σ 0 2 ), where σ 0 represented the inherent strength. This semiempirical criterion succeeded in unifying the L chb and G b criteria without introducing more parameters to increase the prediction accuracy of the K c at the U‐notch root for brittle materials like ceramics.