Numerical simulation study of the strain rate effect on concrete in compression considering material heterogeneity

Abstract
The behaviour of brittle materials is generally known to be strain rate sensitive. There are different theories about the mechanisms under which the rate dependency of the material behaviour develops. Some recent studies suggest that the experimentally observed dynamic increase factor (DIF) in the compressive strength of concrete could be attributable to the dynamic response within the sample specimens, rather than a rate sensitive material property. This paper is aimed to provide another perspective from a mesoscale heterogeneity point of view. To this end, a robust mesoscale concrete model is employed to carry out numerical experiments at high strain rates. To best represent the loading conditions in actual dynamic tests, a numerical split Hopkinson pressure bar (SHPB) apparatus is set up, and the numerical experiment is performed in a similar fashion as a physical SHPB test. To allow for a direct observation of the relative contribution of the mesoscale heterogeneity, a companion homogeneous concrete model is also simulated. Comparison between the dynamic behaviour of the mesoscale and homogeneous models indicates that the heterogeneity in the concrete composite plays an important role, in addition to the dynamic inertia effect, in the dynamic enhancement of the apparent compressive strength of concrete.