Abstract
As an important parameter for concrete, fracture energy is difficult to accurately measure in high loading rate tests due to the limitations of experimental devices and methods. Therefore, the utilization of numerical methods to study the dynamic fracture energy of concrete is a simple and promising choice. This paper presents a numerical investigation on the influence of loading rate on concrete fracture energy and cracking behaviors. A novel rate-dependent cohesive model, which was programmed as a user subroutine in the commercial explicit finite element solver LS-DYNA, is first proposed. After conducting mesh sensitivity analysis, the proposed model is calibrated against representative experimental data. Then, the underlying mechanisms of the increase in fracture energy due to a high strain rate are determined. The results illustrate that the higher fracture energy during dynamic tension loading is caused by the wider region of the damage zone and the increase in real fracture energy. As the loading rate increases, the wider region of the damage zone plays a leading role in increasing fracture energy. In addition, as the strain rate increases, the number of microcracks whose fracture mode is mixed mode increases, which has an obvious effect on the change in real fracture energy.
Highlights
Concrete is one of the most widely used building materials
Concrete materials are mainly subjected to static loads in a structure, but under certain special conditions, such as explosions and earthquakes, concrete can be subjected to dynamic loads
Conducted three-point bending tests on concrete at different loading rates, and the results showed that fracture energy tends to decrease with increases in loading rate at lower loading rates, but it increases when the loading rate is increased at higher loading rates
Summary
Concrete is one of the most widely used building materials. Generally, concrete materials are mainly subjected to static loads in a structure, but under certain special conditions, such as explosions and earthquakes, concrete can be subjected to dynamic loads. It has been embraced that for medium strain rates, a slight moderate increase can be observed until the threshold of approximately 10 s−1 is reached, and at such a strain rate, an abrupt increase in fracture energy can be noticed This method can test the tensile properties of concrete at high strain rates, strong assumptions on the material behaviors are introduced to facilitate data processing [21], and it is not clear whether the incident compressive wave will affect the material before the tensile wave returns [13]. All the experimental studies on concrete fracture energy show that there is a definite correlation between loading rate and fracture energy, due to the limitations of the experimental techniques available as well as the difficulty of achieving accurate measurements, experimental data are very scattered. The reasons for the increase in concrete fracture energy are discussed from three aspects: the influence of rate-dependent material description, the region of the damage zone, and the failure mode of microcracks
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