Unified compliance-based correction for indirect tensile strength in Brazilian disc, ring, and modified seesaw tests

The indirect tensile strength values obtained from the Brazilian disc (BD), Brazilian ring (IR) and modified seesaw test (MST) are highly sensitive to specimen geometry, stress concentration and compliance of the loading system and are not readily comparable. This study suggests a unified compliance-based analytical framework for consistent evaluation of the indirect tensile strength for these three testing configurations. To validate the proposed framework, experimental tests were conducted on dark grey granite specimens, and finite element modelling was carried out under the same boundary and contact conditions. The results indicate that the Brazilian disc configuration gives the highest apparent tensile strength due to the stress concentration effect of the platens, while the Brazilian ring and modified seesaw test give lower tensile strength due to the reduced stress concentration. The measured tensile strength was decreased by up to 12.93% for the Brazilian disc and 9.60% for the modified seesaw test when compliance correction was applied, highlighting the need to consider loading-system compliance. In addition, the stiffness of the specimens was determined to be greater at lower inner-to-outer diameter ratios and less at higher ratios. The proposed framework offers a common analytical foundation for understanding indirect tensile strength for various specimen geometries and loading conditions. It enhances the reliability and consistency of tensile strength measurement and offers practical guidance for the design, comparison and standardization of indirect tensile testing methods for brittle geomaterials.