Impacting Splitting Tensile Test And Simulation Of Hybrid Fiber Reinforced High Strength Concrete

The impacting resistance of concrete is an important factor that affects the structure security, splitting will happen sometimes in concrete under the impacting load. The strength and toughness of concrete can be improved by mixing steel fiber and polypropylene fiber into high strength concrete, thus impacting splitting tensile resistance of concrete can be improved. In order to study the impacting splitting tensile resistance of hybrid fiber reinforced high strength concrete(HFRHSC), impacting splitting tensile resistance of HFRHSC was studied by using the split Hopkinson press bar(SHPB) device for steel fiber-polypropylene fiber high strength concrete impacting splitting test.Firstly, using split hopkinson pressure bar (SHPB) device for impacting splitting tensile test of HFRHSC,and the steel fiber volume of HFRHSC fraction was 0%,2% and 4%. The polypropylene fiber volume fraction of HFRHSC was 0%,0.05%,0.1%. From the tests, the splitting tensile strength of HFRHSC was obtained at the strain rates range from from 2.03 s-1 to27.93.ss1. The influence of strain rate、fiber volume fraction on splitting tensile strength of concrete were analyzed, the results showed that HFRHSC splitting tensile strength would improve when the strain rate or the fiber volume fraction improved.Secondly, It was found that in the SHPB test that HFRHSC was strain rate sensitive material, before and after strain rate critical value(5s-1), the slope of DIF-strain rate curve was different. According to Mechanism of dynamic tensile strength of HFRHSC, in this paper, the relationship formula between DIF and strain rate of HFRHSC with two parameters of A and B was established, A and B showed the influence of solid material strain rate and free water strain rate on splitting tensile strength of HFRHSC. Compared with the conventional splitting tensile strength formula, which was established from macroscopic angle, the formula of the HFRHSC was calculated from the microscopic and macro angles.Thirdly, the difference and similarity of matrix strength, fiber volume fraction, splitting tensile strength, splitting failure pattern and energy dissipation of HFRHSC were compared and analyzed, the results showed that energy dissipation of C60 and C80 concrete were increased with the increase of incident energy; With the increase of fiber volume fraction, C60 and C80 concrete specimen energy dissipation were increased, and with the increase of incident energy, C60 and C80 concrete specimen energy dissipation in high fiber volume rate was increased significantly; The tensile strength of C60 and C80 concrete specimen were increased with the increase of the incident energy; the damage evolution of concrete consuming a lot of energy, which could lead to the project rod end energy significantly smaller than the incident rod end. Incident rod end doing more work to block,which could make the specimen contact with the incident rod end crushing more significantly than the specimen contact with the the incident rod end.Fourthly, using the LS-DYNA software for simulating the process of HFRHSC splitting, splitting process of specimens were recreated. The process of splitting stress distribution characteristics of specimen, the characteristics of energy dissipation and influence of fiber volume fraction on concrete splitting tensile performance were analyzed. The results showed that the HFRHSC fracturing did not meet the center cracking conditions;when specimen diameter direction was compressed, Stress homogenization time was related to the diameter size;the splitting of concrete consuming a lot of energy, which could make the specimen contact with the incident rod end crasing more significantly than the specimen contact with the the incident rod end;fiber reinforced the splitting tensile strength of concrete,and Hybrid fiber enhancement effect was better than the single fiber.