Study On Anti Explosion And Anti Penetration Properties Of SFRC And Evolution Of Stress Wave

With the rapid development of national defense,many new research topics have occurred in the field of explosion and penetration.As a typical protective engineering material,steel fiber reinforced concrete(SFRC)has been more and more widely used in the field of anti explosive and anti penetration engineering because of its strength and toughness better than conventional concrete.In the engineering application research of anti explosion and penetration of SFRC,it involves the constitutive theory of materials,wave mechanics,damage mechanics,numerical calculation and so on.So there are still very high academic value and practical value in this field.On the basis of the SFRC specimen with the steel fiber content upto 6%developed by improving the technology,the contact explosion and penetration experiments of SFRC materials were launched as well as the static and dynamic compression and splitting tensile test.The influence of the steel fiber to the mechanical properties of the SFRC is analyzed and summarized.And the problem of the penetration of the SFRC target is also carried out.In the experiment and numerical calculation,the relevant constitutive parameters of the material are selected,and the penetration law and the mechanism of penetration resistance are analyzed and summarized.At the same time,the stress wave evolution in the viscoelastic material is studied.The research results and innovation points of this paper are as follows:By improving the blending process of steel fiber concrete,the steel fiber content of SFRC is up to 6%.The compression and splitting tensile tests of SFRC in the quasi static condition are carried out by MTS experimental system.The impact compression test of SFRC under high strain rate is developed by using the separated Hopkinson pressure bar(SHPB).Based on the experimental results,the strain rate effect of SFRC and the effect of steel fiber content on its mechanical properties were analyzed.The results show that when the steel fiber content is 6%,the splitting strength can be increased by 106%,while the compressive strength can be increased by 61%.With the increase of the strain rate,the strength enhancement factor DIF will increase,while the increase of DIF increases with the increase of the steel fiber content.At the same time,based on the dynamic experimental data of materials,a new damage viscoplastic constitutive model of SFRC is proposed,and the constitutive parameters of the material in the model are optimized when the integral curve of the constitutive is approximated by the experimental curve step by step using the successive least squares method.The method is simple and clear,which can be used widely.The strain rate effect,strain rate jump effect,unloading nonlinear hysteresis effect and damage softening effect of SFRC material are well reflected.The contact explosion tests were performed on the circular SFRC slabs of different volume fractions with RDX charges placed on their surfaces.And the laws of anti blasting and anti spalling were summarized and numerical simulation was carried out.The volume of spalling pit decreases rapidly with the increase of steel fiber fraction with a decline of 80%when the fraction is 6%,which is same as the crack density.Based on the experimental results,the fitting formulae are given,which can be used to predict individually the change tendencies of the blast crater volume,the spalling pit volume and the crack density in slabs with the increase of the steel fiber fraction.The new formulae of the thickness of damage region are established,whose predictions agree well with our test results and others.It is essential to overall consider both the thickness of the damage and the diameter on the explosive-resistant performance of SFRC.The anti-blast and anti-spall abilities of SFRC are firstly enhanced and then decreased with the increase of steel fibre content,and the anti-spall ability has a significant decrease compared with anti-blast ability.The formulae for estimating the degree of the local damage of SFRC were improved adequately considering material properties,external loads and environments etc.The reinforcing mechanism is analyzed,and the formulae of the fracture toughness and the volume of the spalling pit with steel fibre fraction are established separately according to fracture mechanics theory and dimensional analysis.The results show that the damage level and the anti-blast ability have the relation between spear and shield under the same load.Moreover,the deliberate attempt makes the two theory viewpoints unified and gives us a further understanding of the strengthening mechanism of steel fibre,which is significant both in science and engineering.Experimental research and numerical calculation of anti penetration of SFRC target have been carried out.Firstly,according to the experimental results,the anti penetration law of SFRC is summarized.Based on the negative acceleration time-history curve in the existing experimental data and HJC constitutive model,the anti-penetration problem of soil and concrete composite target is simulated by LS-DYNA.The numerical simulation optimization method is used to optimize the material parameters in the constitutive model according to how the numerical results are in agreement with the experimental results.The numerical results of the numerical simulation results are in good agreement with the experimental results,which proves that the method is feasible and the material parameters are reasonable.Related material parameters,the ability of anti-penetration of composite targets with different configurations of SFRC-concrete-soil is investigated.The results show that the energy absorption effect of composite target can be enhanced by optimizing the structure of the target or the protective layer,thereby not only enhancing its ability to resist penetration,but also reducing the amount of material,which is intended to lay the foundation for improving the design of composite targets.To study the influence of the motion attitude of special-shaped projectile on its stability and penetration effect,a series of numerical simulations were carried out,which focused on the tendency and regularity of ballistic trajectory of special-shaped projectile with different obliquity and angle of attack.The simulation results indicate that the larger the pitch angle,the smaller the effect of the attitude angle of the projectile;the effect of high attack angle on attitude angle of special-shaped projectile is much greater than that of pitch angle change,and the direction of attack angle plays an important role;There is the best combination of pitch angle and attack angle,so that the penetration effect is the best.The stability of special-shaped projectile motion is studied preliminarily,which can provide the basis and reference for trajectory control design.A new viscoplastic constitutive model is proposed by assuming both the volume strain and strain bias of the material as the sum of the transient elastic strain and the lag viscoplastic strain.As a special case of this model,based on the constitutive model of one dimensional Maxwell viscoelastic material,a three-dimensional Maxwell body constitutive model with double viscosity is proposed and applied to the propagation of one dimensional strain stress wave in the target plate.The characteristic lines and relations of wave propagation are obtained,and the analytic expression of shock wave attenuation in the target plate is given.The numerical calculation of the propagation of one-dimensional strain wave is carried out by the characteristic line method,and some enlightening conclusions in theory and engineering application are obtained.