Study On Dynamic Compression Performance Of Hybrid Fiber Reinforced Concrete

Hybrid fiber reinforced concrete (HFRC) is a kind of high-performance composite concrete, which is made by mixing two or more different performance and different size fiber into the concrete matrix. Engineering industries draw attention to the perfect mechanical properties and durability of fiber reinforced concrete. And the steel fiber reinforced concrete (SFRC) has been used in highway pavement, protective structure, airport runway and many other fields. As being the improvement of SFRC, it is worth to discuss and study whether HFRC has better application value in these above fields, and whether HFRC appears more excellent mechanical properties under impact or explosion loading.This paper has carried on deep research to the dynamic compression mechanics property of HFRC and production mechanism of strain rate effect through combining the experimental analysis with numerical simulation. The conclusion of this paper can also provide the experimental and theory basis of the dynamic compression mechanics property of HFRC, it is helpful for the further application in practical engineering. The main research works and achievements are as follows:Firstly, the static compression performances of HFRC and SFRC are researched on the basis of the static compression tests. The result shows that the static compression strengths of HFRC have little difference from that of SFRC. But the failure patterns of the HFRC test specimen is better than that of the SFRC test specimen, the crazing and peeling of the former are lighter.Secondly, the impact compression tests in four strain rates (21s-1,43s-1, 65s-1,116s-1) were done by usingΦ74mm split Hopkinson pressure bar (SHPB), and the dynamic stress-strain curves in four different strain rates were obtained. The failure patterns in different strain rates were collected and described.Thirdly, the experimental results were analyzed comprehensively by considering the strain rate effect of main mechanics parameters (compressive strength, peak strain, peak toughness), and the influence of strain rate on the failure patterns of concrete were discussed. The dynamic material properties of HFRC and SFRC with the same content of steel fiber are compared with each other. The result shows that the dynamic strength and toughness of the former is better than that of the later. The mechanism of strain-rate hardening of concrete was analyzed from the crack propagation and interaction of cracks, and from the damage evaluation modes under different stain rate.Fourthly, a finite element model was built for the dynamic compression test by using ANSYS/LS-DYNA software to simulate this test, the incident waves, reflected waves and transmitted waves are gained from this numerical simulation. And results show that the numerical simulations are accordant with the testing result. By comparing waveform extracted from different positions of the test sample, the uniformity of axial stresses during tests is confirmed.The stress-strain curves in four different strain rates was reconstructed using the extracted waveform, which were compared with the test results. Damage models of the test specimen in different time are obtained and the differences of failure patterns between high strain rate and low strain rate are explained.