The True Triaxial SHPB Simulation System Based On Four-dimensional Spring Model

The split Hopkinson bar test(SHPB)is a common method to study the dynamic properties of materials at medium strain rates.In this paper,a triaxial SHPB numerical simulation system is constructed based on the 4D-LSM.The main contents include three aspects: stress wave propagation characteristics in square rods,the mechanical modeling system of SHPB,the numerical verification of the simulation system,and the inversion of rock dynamic parameters.The main contributions are as follows:(1)Firstly,the stress wave propagation and the dispersion effect in the square rod is investigated.The influence of parameters is investigated by using the DLSM,which obtained the parameters and wave characteristics.Secondly,we correct the wave dispersion effect by algorithm,which can correct different waveform.The result shows that the wave correction effect with less frequency components is better,which lays the foundation for the triaxial SHPB.(2)Secondly,the reconstruction method and mechanical model of the triaxial SHPB numerical model is established.We propose a step-by-step modeling method,which solves the trouble of 3D contact incompatibility and computer memory overflow.Meanwhile,we establish the linear and discontinuous contact for the contact face,and contact model is verified.Then a modified Zhao-Brown contact criterion is proposed as a nonlinear contact model.Finally,based on the triaxial SHPB numerical system,we carry out a parameterization study,which obtained the dynamic fluctuation law and the recommended model parameters of the triaxial SHPB.(3)Finally,aiming at the issue of rock dynamic failure under the initial geo-stress,the confining pressure and the slot device in the physical equipment is simulated,which verified the effectiveness of the numerical simulation system.After that,the triaxial SHPB system is used to study the dynamic characteristics of rock under dynamic compression conditions.The numerical results show that as the confining pressure increases,the dynamic strength of the rock will increase accordingly,and the dynamic strength loaded by the combination of dynamic and static loading is greater than that of the dynamic impact loading.The relevant conclusions are consistent with the observations of physical experiments.For 4D-LSM,a modified Mohr-Coulomb dynamic constitutive model is also added,and a method to calibrate model parameters based on triaxial experimental data is proposed.Aiming at the limitation of the computing of the inversion problem,we propose an acceleration scheme based on CPU-GPU heterogeneous parallel technology.