A Study On Coupled Arithmetic Of High Efficiency And High Precision And Its Application On Material Impact Response

As a Lagrangian mesh-free particle method,smoothed particle hydrodynamics(SPH)gets an advantage over the conventional mesh method:it is very suitable for simulation of large deformation,fracture,and crush;and it can easily track material interfaces.In this article,SPH method is introduced,effects of kernel function and smooth length on simulation of stress waves are studied,and material spalling is simulated using SPH method.Steel fiber-reinforced concrete(SFRC)possesses higher strength and toughness than plain concrete,and therefore finds a wild range of application in military defensive structures and civil buildings.In this article,dynamic mechanic behaviors of SFRC,especially strain-rate sensitivity and fiber reinforcement effect,are carefully studied.Corresponding constitutive model is proposed.Taking advantage of both SPH method and FE method,FE-SPH coupled method possesses both high efficiency and high precision,and is very suitable for simulation of impact dynamics problems.In this article,FE-SPH coupled method is introduced;contact algorithm between FEM elements and SPH particles is carefully studied.Then the FE-SPH coupled method is adopted to simulate SFRC penetration problem.The reliability of coupled method is verified.The mechanism of SFRC penetration is investigated.The main contents of this article include:In Chapter 2,the basic ideas of SPH are expounded;the basic concepts,such as kernel approximation and particle approximation,are introduced.Conservation equations of continuum mechanics are discretized by SPH method in rectangular Cartesian coordinates.The essential issues in SPH simulation of impact dynamics problem,such as CFL condition,kernel function,changeable smooth length,particle search method and constitutive model embedding et al.,are studied.CSPM is introduced and its superiority is illustrated.In Chapter 3,FCT method is adopted into SPH method to deal with discontinuity surface,and the simulation result is compared with that of artificial viscosity method.Kernel function and smooth length's impacts on stress-wave simulation with SPH are studied.The kernel functions and smooth lengths suitable for stress-wave simulation are identified.45#steel spalling is simulated using CSPM.The time-history curves of free surface velocity obtained by experiment.FDM and CSPM,respectively,are compared.The comparison demonstrates that CSPM can simulate stress propagation and spalling in solid more accurately than ordinary FDM.In Chapter 4,the technology of SHPB test on SFRC,especially wave-shaper technology,is studied.It is shown that the wave-shaper reduce high-frequency component in incident wave,and help maintain constant strain-rate and stress uniformness.Dynamic behaviors of 6-fiber-content SFRC are investigated using SHPB,including strain-rate effect and fiber reinforcement effect on strength,critical strain and energy dissipation.The mechanisms of strain-rate effect and fiber reinforcement effect are analyzed.An new constitutive model for SFRC is proposed.A new dynamic increase factor equation for concrete is proposed on the basis of existing works.The embedding method of dynamic increase factor into constitutive equation is modified.A new visco-plastic damage-softening constitutive model for concrete is proposed.Properties of the new model,such as strain-rate sensitivity,damage evolution,strain-rate variation and unloading,are explored.It is shown that the new model for concrete is able to accurately describe dynamic behavior of concrete.Finally,Chapter 5 studies the FE-SPH coupled metho.The element-particle-transform method,element-element contact algorithm,particle-particle contact algorithm and element-particle contact algorithm are explained in detail.On the basis of study on SFRC dynamic behavior,the constitutive model of SFRC is embedded into two-dimensional FE-SPH coupled program.SFRC penetration problem is simulated.Penetration pictures are shown.Penetration mechanism is explained.Residual velocities obtained by experiment and simulation are compared,which verifies the efficiency of the program.