Dynamic increase factors of concrete-like materials at very high strain rates

Strain rate effects on the compressive and tensile strengths of a concrete-like material play an important part in the construction of its dynamic constitutive model. So far no data for the same material covering a wide range of strain rates were reported in the literature, not to mention the data for compression at strain rates greater than 10(3) s(-1). This paper presents a combined theoretical and experimental study on the dynamic increase factors of concrete-like materials at very high strain rates. First, a method is proposed to determine dynamic increase factor for a concrete-like material in compression due to strain rate effect only (that is to say to eliminate the inertial (containment) effect) at very high strain rates (>10(3) s(-)(1)) by in-depth analysis of its Hugoniot elastic limit (HEL). Then, various material tests (i.e. quasi-static uniaxial compression and tensile tests, SHPB and SHTB tests, plate impact test and dynamic compression-shear test) were performed on a certain type of cement mortar in a wider range of strain rates (i.e. 10(-5) s(-)(1) - 10(6) s(-)(1)). Finally, the test data are compared with the previously proposed semi-empirical equations for dynamic increase factors. Furthermore, the plate impact test results for ultra high performance concrete (UHPC) available in the literature are also analyzed using the proposed method. Dynamic increase factor for tension at strain rate of 10 (3) s(-)(1) is obtained indirectly by the relationship between dynamic uniaxial tensile strength and dynamic shear strength through the shear wave tracking (SWT) technique which is based on dynamic compression-shear test. It is found that dynamic increase factor for concrete-like materials in compression due to strain rate effect only can be regarded as a constant at very high strain rates. It is also found that the previously proposed semi-empirical equations can accurately describe the strain rate sensitive behavior of concrete-like materials in both tension and compression.