Further investigation on the dynamic compressive strength enhancement of concrete-like materials based on split Hopkinson pressure bar tests. Part II: Numerical simulations

Split Hopkinson pressure bar (SHPB) tests have been used widely to measure the dynamic compressive strength of concrete-like materials at high strain-rates between 10¹ and 10³ s⁻¹. It has been shown in companion paper (Zhang M, Wu HJ, Li QM, Huang FL. Further investigation on the dynamic compressive strength enhancement of concrete-like materials based on split Hopkinson pressure bar tests Part I: Experiments. Int J Impact Eng 2009;36(12):1327–1334) that the axial strain acceleration is normally unavoidable in an SHPB test on brittle materials. Axial strain acceleration introduces radial confinement in the SHPB specimens and consequently enhances the compressive strength of concrete-like specimens. This paper employs numerical simulation to further demonstrate that the unexpected radial confinement in an SHPB test is responsible for the increase of the dynamic compressive strength of concrete-like materials at strain-rates from 10¹ to 10³ s⁻¹. It confirms the observations in Zhang et al. (Zhang M, Wu HJ, Li QM, Huang FL. Further investigation on the dynamic compressive strength enhancement of concrete-like materials based on split Hopkinson pressure bar tests Part I: Experiments. Int J Impact Eng 2009;36(12):1327–1334) that the dynamic increase factor (DIF) measured in SHPB tests can be reduced either by using tubular SHPB specimens or by reducing the diameter of the SHPB specimen. A kinetic friction model is proposed based on kinetic friction tests and is implemented in the numerical model. It shows that it is necessary to use a kinetic friction model, rather than a constant friction model, for more accurate numerical simulation of SHPB tests.