Failure process and damage behaviour of flattened Brazilian disc specimens based on micro-nonuniformity

To investigate the effect of cracks on the failure behavior of concrete under impact loading, the failure process and damage behavior of pre-crack flattened Brazilian discs under dynamic impact loading were systematically studied. A numerical model incorporating micro-heterogeneity of concrete was established based on split Hopkinson pressure bar experiments, enabling a quantitative analysis of the influence of different pre-crack inclinations and strain rates on secondary crack propagation and damage evolution, with consideration of the distribution characteristics of pre-cracks. The results show a significant positive correlation between dynamic tensile strength and strain rate, and a negative correlation of dynamic tensile strength with the inclination of pre-cracks. The model successfully simulated the realistic process of crack initiation, propagation, and penetration within the specimens based on micro-heterogeneity model. When the pre-crack inclination exceeded 60°, the propagation direction of the main crack was nearly perpendicular to the pre-crack, and the number of secondary cracks increased progressively with the pre-crack inclination. Additionally, by quantifying the damage degree of the specimens through the number of failed elements, it was determined that the damage degree was minimized when the pre-crack inclination was 45°. The research results can provide a theoretical basis for the dynamic safety design of concrete materials.