Direct and indirect test techniques for measuring the tensile strength of brittle materials, an experimental study

To address challenges associated with measuring the tensile strength of brittle materials, a comparative analysis was conducted on several specimens and a new test specimen. The new test method is a symmetrical bend disc (SBD) that can be prepared from in-field cores. Evaluations were performed employing direct tension, Brazilian disc, and three-point bending beam specimens. The samples were made of cement paste, a foundational construction material. The findings indicated that the tensile strength values derived from the direct tension test yielded the lowest estimates (1.93 ± 0.2 MPa), whereas those from the three-point bending beam were 2.71 ± 0.05 MPa, and those from the Brazilian disc ranged from 2.02 to 2.33 MPa. In comparison, the tensile strength recorded for the SBD ranged from 2.01 to 2.39 MPa. Analysis shows that specimen geometry and loading configuration have a significant effect on the measured tensile strength, so that by adjusting the thickness-to-diameter (t/D=0.3) and span-to-diameter (S/D=0.8) ratios, the exact value of tensile strength measured by direct tensile strength can be obtained. In these cases, the diameter value (100 and 150 mm in this study) also affects the results. After the experimental tests, numerical simulations were undertaken to investigate the stress distributions and fracture patterns characteristic of the specimens. Results showed that, compared with BD as the standard test method, which exhibits significant gradients in compressive-tensile strengths resulting in high coefficients of variation (about 10 %), while SBD exhibits lower gradients and lower coefficients of variation (about 4 %).