Experimental researches show that the strength of material increases
with strain rate. However, dynamic response of quasi-brittle materials
is significantly different under tensile and compressive loading. In
order to simulate this phenomenon, damage plasticity model is adopted
and enhanced with strain rate effect. Two different state variables as
equivalent strain rates are defined, one for compression and other one
for tension. Corrected strain rates are used instead of instantaneous
ones, in order to consider retardation of damage evolution. Simulations
of Split Hopkinson pressure bar (SHPB) are conducted to investigate
dynamic tensile strength of concrete specimens. Performance of the
proposed model is demonstrated by comparing with experimental results.
Furthermore, a parametric study is conducted and effects of different
parameters, such as dilatation angle, friction, thickness of the
specimen, shape of impulse and impedance mismatch, on the dynamic
increase factor are discussed in detail.