Analysis of Optimal Loading Angle in Dynamic Flattened Brazilian Disc Splitting Test for Concrete

The mechanism of crack expansion in conventional Brazilian discs is clearly obtained with the help of numerical simulations, and the direction of crack expansion is related to the loading speed. Then the relationship between the stress field and the platform angle was given quantitatively based on the theoretical analysis. To obtain the accurate tensile strength of self-compacting concrete under the premise of numerical simulation and theoretical analysis, flattened Brazilian disc (BD) splitting tests with six loading angles were carried out by using the split Hopkinson pressure bar (SHPB) loading system. The crack initiation mode and fracture propagation mode of specimens under different loading angles and loading rates were analyzed through digital image correlation (DIC) and strain gauges. When the loading angle lies between 28 degrees and 30 degrees, the specimens easily meet the requirement of central cracking under high loading rates. The experimental results were well explained with theoretical analysis from a view of dimensionless Griffith's equivalent stress. The dynamic tensile strength measured from the non-central crack mode in flattened BD splitting tests underestimates the inherent dynamic tensile strength.