A modified size effect model for brittle nonmetallic materials

Formulae of both existing size effect models for brittle materials, `effective volumeʹ and `effective surfaceʹ were theoretically derived for bar specimens with rectangular and circular cross-sections, for three- and four-point bending load configuration, respectively. Additionally, a modified model called `effective shell modelʹ is introduced. Exemplarily three- and four-point bending tests were performed on bar specimens of different sizes of a leucite reinforced glass ceramic material. The results were analyzed based on the three size effect models. It was found that the defect population of the specimens could be characterized better with the effective surface than with the effective volume model. The new effective shell model improves the statistical reliability even more.