Abstract
This paper analyzes the relationship between the rates of change of elastic strain energy, the strength during the concrete failure process, and proposes that the increased dynamic strength of concrete was caused by the hysteresis effect of energy release—according to the basic principle of energy conversion. Dynamic Brazilian disc tests were carried out on concrete specimens, with diameter of 100 mm, by using the split Hopkinson pressure bar. Test results were obtained through using a gas gun, with an impact pressure of 0.15 MPa, 0.20 MPa and 0.25 MPa, respectively. The dynamic failure process of concrete is then reproduced by numerical calculation methods. Finally, the energy characteristics during the concrete failure process at different strain rates are studied, and the enhancement mechanism of the dynamic strength of concrete is verified. The results showed that the dynamic tensile strength of concrete increased by 9.79% when the strain rate increased by 61% from 60.25 s−1; and when the strain rate increased by 92.8% from 60.25 s−1, the dynamic tensile strength of the concrete rose by 46.28%. The rates of change of both input energy and dissipated energy meet at the peak stress of the material. The increases in rates of change for the two kinds of energy were not synchronized, so excess input energy could be stored as concrete strength increased. As a result, the extra energy stored after peak stress led to a higher degree of concrete fragmentation and greater kinetic energy of the fragment. These results offer research directions for improving the dynamic strength of concrete.
Highlights
As the most commonly used building material, concrete is employed widely in various civil and military buildings, such as high-rise residential buildings, bridges, tunnels, hydropower stations, and military bunkers
When the strain rate was increased by 61% from 60.25 s−1, the dynamic tensile strength rose by 9.79%; and when the strain rate was increased by 92.8% from 60.25 s−1, the dynamic tensile strength of the concrete rose by about 46.28%
From 71.19 s−1, the dynamic tensile strength of the concrete was increased by 18.38%; and when the strain rate was increased by 72.34% from 71.19 s−1, the dynamic tensile strength of the concrete was increased by 70.8%
Summary
As the most commonly used building material, concrete is employed widely in various civil and military buildings, such as high-rise residential buildings, bridges, tunnels, hydropower stations, and military bunkers. A century has passed and many researchers have conducted a large number of experiments using dynamic loading equipment [2,3,4] to study the effect of strain rate on the dynamic strength of concrete. Hao et al [13] studied the effects of the end friction confinement and inertia on the compressive properties of concrete under impact loads in the SHPB test, proposed an empirical formula. The findings of previous studies revealed that, a large number of researchers believe that the increased dynamic strength of concrete is caused by radial inertia and end friction effects, it seems that there is a lack of understanding with regard to the mechanisms of both radial inertia and friction. Numerical methods were applied to reproduce the dynamic Brazilian disc test of concrete and the energy conversion process during the dynamic failure of concrete specimens was analyzed to verify the proposed enhancement mechanism of the dynamic strength of concrete
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