Numerical Analysis Of Material Properties Of Freeze-thaw Concrete Under Impact Load

In recent years,with the development of engineering construction in high cold area in China,the research on freeze-thaw damage of cement concrete has been paid more and more attention.Especially,the damage of concrete structure caused by impact loads such as earthquake,explosion and accidental impact of vehicles is increasing day by day.The research on the impact resistance of freeze-thaw concrete has become an important issue to be solved in civil engineering structure.In view of this research is still in the exploratory stage,this paper mainly uses the numerical simulation method to study the dynamic mechanical properties of freeze-thaw concrete materials under different strain rates.In this paper,the micro model of concrete material under different strength and freeze-thaw cycles is analyzed by finite element method,and the plastic damage model of concrete is established.The temperature field,thermal stress and other parameters are considered comprehensively.Through data analysis and fitting,the change rules of stress,strain and damage degree of C30 and C40 concrete with the increase of freeze-thaw cycles are obtained Compared with the actual indoor freeze-thaw test,the feasibility of the simulation method is verified.As a common test method to study the mechanical properties of concrete under impact load,the applicability of SHPB test has been widely recognized.In this paper,the finite element dynamic software LS-DYNA is used to simulate the SHPB test of several concrete specimens before and after freezing and thawing,and four different bullet impact velocities are used respectively,so as to obtain the stress-stress of several groups of specimens under different high strain rates Variation curve,damage evolution rule and failure criterion.In this paper,the establishment process of the model,the selection of material parameters,the definition of contact relationship and the mesh division of the model are described in detail.Several commonly used dynamic constitutive models of concrete and the definitions of various parameters of HJC model used in this paper are also briefly introduced.The simulation results are compared with the experimental data in the references,and the results show that the constitutive model is suitable for the prediction of the impact load resistance of concrete materials after freeze-thaw.In order to study the dynamic effect of freeze-thaw damage and high strain rate on cement concrete,this paper uses PFC discrete element software to establish a micro model for uniaxial compression calculation.Six different compression rates are applied to calculate the dynamic response results of freeze-thaw concrete under different strain rates,and the surface equations of initial modulus and compressive strength are fitted,and Mo is drawn The microscopic parameters of the discrete element model are inversely calculated by nomogram.Referring to the indoor test data,combining the curve relations of different strain rate,freeze-thaw cycle times,initial modulus and compressive strength parameters,the curved surfaces of C30,C40,C50 and C60 concrete under the joint action of the two parameters are fitted.