Strain-rate effect on the compressive strength of brittle materials and its implementation into material strength model

This paper studies the strain-rate effect on the compressive strength of brittle materials and its implementation into a material strength model. It shows that most of the current practices to consider strain-rate effect on the compressive strength of brittle materials using uniaxial stress data and loading path are questionable. It demonstrates that the rapid increase of the dynamic compressive strength between the transition strain-rate and the upper limit strain-rate in a SHPB test is correlated with the change of stress state in SHPB specimen, i.e. the stress state in SHPB specimen is changed from uniaxial stress state toward uniaxial strain state with the continuous increase of strain-rate from the transition strain-rate. Dynamic increase factor (DIF) based on experimental data under uniaxial strain state is recommended for the consideration of strain-rate effect on the compressive strength of brittle materials. An associated method to implement the uniaxial strain DIF into material strength model is also proposed and verified. Discussion on the DIF formulae and their implementations in several popular strength models of concrete-like materials is presented.