Study On The Static-dynamic Mechanical Propertie Of Heterogeneous Composite Materials

As one of the most important construction materials, concrete is widely used in the civil engineering and national defense construction for the purpose of anti-knock and anti-penetration. Therefore, study of the mechanical properties of concrete under the impact load and high pressure has important military significance. This article study the static and dynamic mechanical properties of concrete comprehensively by means of experiments, theory and numerical simulation. Some iconic results have been achieved as follows:1) At home for the first time, the comprehensive and systematic experimental study and theoretical research have been carried out on the dynamic and static mechanical properties of plain concrete. A scientific definition and description which is related to the strain rate effect, hydrostatic pressure effect, the damage evolution and the volume compression properties has been given for concrete material under impact load. A dynamic damage constitutive model has been presented for concrete subjected to high pressures, large strains and high strain rate. In this model, the material equivalent yield strength is expressed as a function of the hydrostatic pressure, damage and strain rate. The piecewise function yield criterion established in this paper can be more universal and rigorous than Mohr-coulomb; The exponential pressure-related yield criterion established in this paper is different from that in HJC model adopted by the sortware Ls-dyna which needs to artificially assume two yield surfaces, the "complete material" and the "crushed material". The exponential yield criterion is more accurate to portray the entire damage process from the "complete material" to the "crushed material" through the evolution of the damage D. Therefore, this yield criterion is more scientific and rigorous in mechanics, moreover, the material parameters involved in this model are easier to determine.The piecewise state equation established in this paper is convenient to be used in engineering analysis; While the polynomial state equation proposed in this paper is more suitable for the refined calculation.2) In this study, the material damage is divided into two types the compression-shear damage and tensile damage; The damage evolution equation of concrete is derived based on the "equivalent micro-void system","equivalent micro-crack system" and "growth model with existing nucleus" by the microscopics statistics method. The relevant material parameters in the equation is determined according to the experimental data, the number of material parameters involved is less and physical meaning of each parameter is clearer, the damage evolution equation is simpler in the form and easier to apply. This is a significant progress compared to some description of the damage definition and damage evolution equation widely used in the current research.3) Based on the yield function in stress space and the modified Drucker’s postulate, new incremental constitutive relations and the calculation routine are presented by means of the internal variables theory. The constitutive relations are suitable for the hardening materials, ideal plastic materials and the softening materials as well, and very convenient for the use to dynamic problems, especially the high-speed impact problems.The discussion on our constitutive relations show that:only for the yield criteria independent of pressure, the volume deformation is purely elastic, and hence the calculation of the pressure and deviatoric stress can be decoupled completely, this is the so-called "hydrodynamic-elastic-plastic model"; while for the pressure dependent yield criteria with the pressure deviatoric stress coupled effect, such as concrete-like materials, the plastic volumetric deformation always exists, so the development of the pressure and deviatoric stress must be fully coupled, the "hydrodynamic-elastic-plastic model" is not suitable.4) The "radius of generalized regression" constitutive algorithm and strict increment constitutive algorithm are put forward to apply to concrete material, And the calculation process is given out in detail. A general proof of the "radius regression method" widely used in engineering calculations is presented, and the applicability and limitation of the method are pointed out, which has innovation significance in theory and engineering application. The incremental constitutive algorithm proposed by strictly based on the incremental constitutive theory is original, concise and practical.5) based on the results of dynamic constitutive containing damage for C40concrete, combined with some experimental results of C50concrete, and referred to the relevant existing experimental data, the C40～C50concrete containing damage dynamic constitutive relation and corresponding material parameters are given to expand the application range of research results for C40concrete. 6) By the heterogeneous composite material constitutive relation theory as guidance, An equivalent dynamic constitutive relation and the calculation method of equivalent corresponding material parameters for reinforced concrete are given,which are the basis of equivalent engineering calculation of penetration and detonation.