Study On Dynamic Mechanical Behavior And Constitutive Model Of Fiber Reinforced Cemenitious Composites

Adding fibers to reinforce cementitious composites(CC)is an effective approach for overcoming the defect of the Cement-based materials like brittleness,bad crack resistance and low tensile strength.Polyvinyl alcohol(PVA)fibers reinforced cementitious composite(PVAFRCC)has been demonstrated that possesses tensile strain-hardening,large tensile strain and multiple-cracking behavior after the first crack,adding steel fibers to reinforce PVAFRCC can improve the resistance of PVAFRCC under impact loading,compressive strength and tensile strength,at present little work has been done on the dynamic properties of PVAFRCC and HFRCC.In this thesis the dynamic compression tests and splitting tests of PVAFRCC and HFRCC were conducted at different strain rates by using Split Hopkinson Pressure Bar(SHPB),the dynamic properties of PVAFRCC and HFRCC are studied,a new dynamic constitutive model is developed based on the analysis of experimental results and the second development for finite element software LS-DYNA was applied,at last the dynamic response of PVAFRCC and HFRCC are studied by numerical simulation.The works specific include the following:1.The design principle of PVAFRCC are considered.The fiber-bridging constitutive law of PVAFRCC was improved based on the results of single fiber pull out test,the first crack strength and the ultimate bridging strength are calculated more accurate by the improved law.The fiber-bridging constitutive law of HFRCC is developed by superposition principle,and the formulas of first crack strength are presented,the critical volume fraction of fibers for HFRCC is investigated.2.The dynamic compression tests and splitting tests of PVAFRCC and HFRCC were conducted at different strain states by using Split Hopkinson Pressure Bar(SHPB),the compressive strength,peak strain,toughness,splitting tensile strength,energy properties and the failure modes are analyzed,steel fibers can improve the dynamic compressive strength and dynamic tensile strength of HFRCC and PVA fibers can improve the compressive peak strain of HFRCC,different fiber content have certain effect on the toughness and energy properties.3.The relationship between dynamic compressive strength increase factor(DIF),dynamic strain increase factor(DEIF),dynamic tensile strength increase factor(DTIF)of HFRCC and strain rate are developed based on the analysis of experimental results and relative research,the dynamic constitutive model of PVAFRCC and HFRCC are developed,the improved HJC model considering the mechanism of reinforcing effect and toughening effect of fibers is developed,the dynamic tensile model is also developed by the static tensile introduced strain rate effect.4.The second development for finite element software LS-DYNA was applied,the program code of the dynamic constitutive model of PVAFRCC and HFRCC were compiled and the numerical examples validated that the model is correct and effective.5.The projectile penetration and low speed impact test of PVAFRCC and HFRCC target were simulated,the penetration depth,penetration speed-time curves and failure mode were analyzed and the impact times,deflection and failure mode under low speed impact were also investigated,at last the different fiber content effect on the resistance performance of PVAFRCC and HFRCC under impact loading were studied.