| Concrete material is an important engineering material for infrastructure construction and national defense construction,it is inevitable to bear the static load,high temperature,high strain rate,dynamic load and other complex loads,in this environment,the concrete material can be competent for the safety requirements of the structure will directly affect the stability of the building itself,related to the safety of the lives and property of the people.Therefore,it is necessary to study the dynamic response,failure process and failure mechanism of concrete under high temperature and high strain rate loading.The research object of this paper is the commercial concrete material of C35 strength grade,which is the most commonly used in practical engineering.The research methods include two parts: experimental research and numerical simulation.The test,according to test requirements and processing of concrete specimen,the natural cooling after high temperature treatment of the specimens using the split Hopkinson pressure bar(SHPB-Split Hopkinson Pressure Bar)experimental study on the uniaxial and dynamic mechanical properties under passive confining pressure;numerical simulation aspects,H-J-C and other material models provided by ANSYS/LS-DYNA software,simulation of concrete SHPB test based on material parameters obtained from experiments.On the basis of the analysis,the process of crushing,fracture,stress and strain redistribution,so as to reveal the dynamic characteristics of the material.(1)Uniaxial dynamic compression performance was studied by SHPB test:the uniaxial compression tests were carried out at room temperature and at four different temperatures(8.58m/s,14.23m/s,18.36m/s)after three high temperature(200 ℃,400 ℃,600℃,800℃),results show:at the same temperature,the strain rate of concrete increases with the increase of impact velocity,the smaller the diameter of the specimen in the final failure mode and more dust;under the same impact velocity,when the temperature is below 400,with the increase of temperature,the peak stress and peak strain are improved to a certain extent at room temperature,however,when the temperature exceeds 400 degrees,the strength of concrete decreases sharply with the increase of temperature.(2)SHPB passive confining pressure test:the experiments were carried out at room temperature and after four high temperature(200℃,400℃,600℃,800℃)at three different loading rates(8.58m/s,14.23m/s,18.36m/s),results show:under the condition of passive confining pressure,the peak stress of concrete increases,however,due to the compression test of concrete specimens are not damaged,the specimen shape is well preserved,the reason is that in the course of impact,the crushing degree of the specimen is restrained due to the radial pressure of the sleeve on the hoop of the specimen.(3)Numerical simulation of dynamic behavior of concrete by using the method of numerical analysis:at the same temperature,with the increase of impact velocity,the crack initiation time is increased and the breaking degree increases at the same loading time;with the increase of heating temperature,the crack initiation time is increased and the breaking degree increases at the same loading time.For axial compression specimens,simultaneous radial expansion of axial compression,the tensile strain reaches the limit and the splitting failure occurs,with the coalescence of splitting cracks,the specimens are divided into several columns,redistribution of stress and strain on specimen,the stress gradually decreases to the edge of the diameter at the center,and has obvious characteristics of the circular diffusion.Under the action of passive confining pressure,the numerical simulation curves are basically consistent with the measured stress-strain curves of concrete.[] the following re refining concrete failure mode showed obvious correlation rate,at low strain rate,the failure modes of splitting failure,with strain rate increasing,failure mode is gradually transformed into crushing. |
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