Mesoscale Modelling of Confined Split-Hopkinson Pressure Bar Tests on Concrete: Effects of Internal Damage and Strain Rates

Abstract: The dynamic strength of concrete under complex loading conditions is a key consideration in the design and maintenance of infrastructures. To assess this mechanical property, Split Hopkinson Pressure Bar (SHPB) tests are typically adopted across a wide range of loading and confining conditions. In this study, mesoscale modelling based on the finite element method (FEM) is employed to simulate SHPB tests on three-phase concrete with realistic aggregate shape, in order to investigate the effects of loading ramp rate, internal friction, and confining pressure on the dynamic increase factor (DIF). Microscopic evidence to explain these effects is explored through analysing the distributions of the internal strain rate and local damage. As key results, increasing loading ramp rates, internal friction, and confining pressure can generally leads to higher DIF values. Only a higher loading ramp rate significantly amplifies the strain-rate effect on the DIF, as evidenced by pronounced increases in both internal strain rate and damage in the mortar and aggregate phases. In contrast, higher internal friction and confining pressure weaken the strain-rate effect on the DIF. Both can be attributed to the mortar phase, which shows a less pronounced increase in damage with increasing strain rate. This study enriches the understanding of the dynamic fracture of concrete toward complex loading scenarios.