<p>The Brazilian indirect tensile test is widely regarded as the most convenient method for measuring the tensile strength of rocks and brittle solids. However, its validity has been long debated amongst engineering geologists and material scientists for decades. Some studies suggest an overestimation of tensile strength, whilst others report underestimation or contradictory results. This study investigates these inconsistencies and tries to explore the influence of both material type and loading jaw curvature using experimental and numerical approaches. Brazilian samples from synthetic brittle material were prepared in laboratory and tested using jaws with varying curvatures. Results indicate that jaw curvature significantly affects the failure mode and estimated tensile strength. Specifically, increasing the jaw curvature led to the formation of a single central crack and a rise in estimated tensile strength, particularly at a jaw curvature of 0.8. To further assess material dependency, numerical modelling using the discrete element method was employed. First, the micro-properties of the bonded particle model were calibrated against physical experiments under different loading conditions. The numerical model was then validated for various jaw curvatures. Simulations of Brazilian discs with different brittleness indices revealed that material brittleness contributes to both tensile strength overestimation and underestimation. For flat-loading rims, cracks typically initiated near the rims, whilst increased brittleness reduced shear crack contributions. Higher jaw curvature shifted cracking zones towards the disc centre. However, excessive bond breakage at high brittleness indices altered failure modes from central cracking to crushing, leading to tensile strength overestimation.</p>