Experimental and numerical evaluation of size dependent strength in fused silica ceramics

Ceramic materials exhibit brittle behaviour, which limits their use as structural elements under tensile loading. Bending and indirect tensile tests are commonly used to evaluate the mechanical properties of ceramics. Each test produces different stress fields within the specimen, and these effects can be analysed using Weibull statistical theory. This study evaluates the influence of different testing methods and effective volume on the mechanical strength of slip-cast fused silica ceramics by integrating Weibull statistical analysis with micro-CT-based defect characterization and finite element method (FEM) simulations. Although previous studies have examined three-point bending, four-point bending, and Brazilian tests individually, this study integrates these methodologies to provide a comprehensive understanding of size effects and microstructural influences on mechanical behaviour. A FEM-based computational approach was developed to determine the effective volumes of the specimens, and results obtained from analytical and numerical methods were compared. The Weibull modulus was approximately 9 and showed increased consistency with a total of 50 samples. While Weibull modulus values remained similar across test methods, significant differences were observed in characteristic strengths, mainly due to variations in effective volume. Larger effective volumes resulted in lower strength because of the higher probability of critical defects. The intrinsic strength, independent of stress state and specimen geometry, remained consistent for all tests. Furthermore, the study demonstrates that the effective volume calculation procedure based on numerical analysis can be applied to complex test geometries and various loading conditions, establishing a direct relationship between testing methods, specimen geometry, and size effects.