Impact Characteristics Of Hybrid Fiber Strain Hardening Cementitious Composites

In recent years,strain-hardened cementitious composites(SHCC)made from Polyvinyl alcohol(PVA)fibers or Polyethylene(PE)fibers have attracted much attention because of their high ductility,crack resistance and excellent durability.Two or more fibers are added to the material to complement each other.Taking advantage of their respective advantages is one of the important technical aiming to improve fiber reinforced cementitious composite materials.In this paper,steel fibers are mixed with PVA and PE fibers,respectively.Based on the study of the effects of different amounts of mixed fibers on the static mechanical properties of cementitous materials,the dynamic mechanical properties of mixed fibers on cementitous materials are explored through drop weight tests and split Hopkinson pressure bars(SHPB)tests.The influence law is analyzed,and the action mechanism of steel fiber is analyzed.By designing the type,amount and water-binder ratio of the cementitious material,ordinary strength grade SHCC and high strength grade SHCC are prepared.Among them,ordinary strength SHCC is prepared by using PVA and PE fibers.The compressive strength is 47MPa-56 MPa,high strength.Grade SHCC is made of PE fiber,and the compressive strength is 100MPa-110 MPa.Then the influence of steel fiber on the mechanical properties of SHCC is studied.The main research contents and results are as follows:Through uniaxial tensile test results,it was found that the incorporation of steel fibers can increase the ultimate tensile stress of PVA-SHCC and high-strength PE-SHCC.Steel fibers can significantly increase the magnitude of stress growth in the early stages of stretching.However,for ordinary strength PE-SHCC,although the hybrid steel fibers increase the initial tensile stress,excessive hybrid steel fibers will reduce the ultimate tensile stress.Hybrid steel fibers can significantly reduce the crack width of PE-SHCC(10% ? 30%).In addition,in high-strength PE-SHCC,hybrid steel fibers can significantly improve compressive strength.The drop weight test found that the flexural impact performance of hybrid PE-SHCC was better than that of hybrid PVA-SHCC.The incorporation of steel fibers caused the dynamic force-displacement curve of PVA-SHCC to deviate significantly from the static force-displacement curve,but this effect was not shown in hybrid PE-SHCC.From the perspective of energy absorption,under the action of flexural impact,the hybrid steel fiber makes the energy absorption of PVA-SHCC larger,and the hybrid steel fiber will also make the PVA-SHCC displacement smaller under the impact.Through SHPB test,it is found that compared with ordinary strength,high-strength SHCC has lower sensitivity to strain rate.Under the same working conditions,steel fiber significantly improves the impact resistance of ordinary strength SHCC,and can especially compensate for the attenuation of the stress softening section after SHCC peak stress.PE-SHCC has better impact resistance than PVA-SHCC.Comprehensive analysis of the static and dynamic mechanical properties of SHCC,the research results found that the optimal ratio of ordinary strength SHCC hybrid fibers is 2PVA + 0.25% steel fibers,and the optimal ratio of hybrid fibers in high strength SHCC is 1.5% PE + 0.5% steel fibers.In addition,the total amount of mixed fibers should not exceed 2%.