Exclusivity of strength-limiting extrinsic surface and hybrid flaws

Flexure strength-limiting flaw populations were examined in a sintered alpha-SiC having ∼6 vol% porosity comprised of homogenously distributed monosized (∼60-70 μm) pores. Bend bars were coarse-, medium-, and fine-finish ground with the intent to produce concurrent activity of intrinsic strength-limiting flaws (pores) and extrinsic strength-limiting flaws (machining damage) populations. However, this was not achieved as fractography showed that strength was always limited by a pore independent of the depth of machining damage in this material. The effects of strength-limiting flaw hybridization on 2-Parameter Weibull were then examined by positioning Knoop indents either directly on a pore present at the ground surface of the bend bars or away from them, and flexure loading those specimens to fracture. Fractography confirmed the suggestion in this case that a negative curvature in the Weibull distribution curve was associated with exclusive strength-limiting flaw populations (hybrid and surface flaw types). The interpretation of intrinsic and extrinsic exclusive flaw distributions is discussed in reference to the prospective selection of a ceramic for structural applications.