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Among the several methods available for the measurement of the fracture toughness (K Ic ), the surface-crack-in-flexure (SCF) has the advantages of being based on an easy-to-produce short (application relevant) crack size of defined geometry with a naturally sharp crack tip. The production of ready-to-test cracked specimens is fast and uncomplicated, rendering accurate results with low scatter. However efficient and reliable, the procedural steps for the obtainment of a valid crack need revisions, especially on aspects concerning the polishing depth, the removal of lateral cracks, the obtainment of an appropriate crack geometry, and the use of adequate solutions for the geometry factor. In this study we attend to these issues by systematically polishing a large number of specimens of two ceramic materials having very distinct subsurface Knoop crack systems to assess the effect of remnants of lateral cracks. By evaluating the geometry factor of the median precrack along the entire crack front, we provide valid ranges for the crack geometry regarding the crack-surface intersection angle as resulting from the polishing depth, extending the applicability of the Strobl et al. solution to shallow cracks in detriment of the Newman and Raju formula that is poised to overestimations of K Ic of up to 10%. Our results debunk the belief that lateral cracks affect the obtained K Ic , but demonstrate the necessity of a minimum polishing depth for the attainment of valid crack geometries.

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