Papers by Author: Jian Guo Ning

Abstract: Based on the damage and Ottosen failure criterion, a dynamic constitutive model is proposed to investigate the mechanical behavior of concrete subjected to impact loading. The model predictions fit well with experimental results. So it can be used to simulate dynamic mechanical behavior of concrete

Abstract: The dynamic compression tests of reinforced concrete with different reinforcement ratios are carried out by split Hopkinson pressure bar (SHPB). Reinforced steel bar is placed along longitudinal and transverse direction. Experimental results show that reinforced concrete is non-linear and rate-dependent. With the enhancement of strain rate, the peak stress of reinforced concrete increases correspondingly

Abstract: This paper focuses on the situation of stress, strain and displacement of subgrade under the action of temperature and load. Carry out numerical simulation for strain problem of normal subgrade plane and compare the numerical results of stress field and displacement field to the analysis results obtained from predecessor, we can find that the distribution of every value is in conformity to its variation trend. The variation of stress and displacement shall be most violent at the top surface of subgrade, thus the effect of temperature and load on stress and displacement will decrease as the depth increases. Moreover, the capacity of calculation and visualization for program is developed greatly, which can supply beneficial assistance to engineering design and appliance.

Abstract: Fixed point iteration method for multi-particle unit cell’s boundary condition is presented. On the basis of this method, the macroscopic effective material parameters can be obtained from a microscopic point of view. Multi-particle unit cell models containing some important microstructure characteristics of TP-650 titanium matrix composites are established. The real displacement constrained conditions are applied on the multi-particle unit cell using this method, and the mechanical properties and fracture behaviors of the composites under tensile loading are simulated. A good agreement was obtained between the experimental results and the numerical predictions, which verifying the rationality of the FE models based on fixed point iteration method.

Abstract: SEM experimental system was employed to investigate the fracture behavior of particle reinforced metal matrix composites (91%wt tungsten alloys) by in-situ experiments. The fracture patterns of tungsten alloys under tensile loading were examined. Multi-particle unit cell models containing some important microstructure characteristics of tungsten alloys were established. By using fixed point iteration method, the displacement constraint conditions were applied on the multi-particle unit cell and the mechanical properties of tungsten alloys under tensile loadings were simulated. Comparison of the experimental results and the numerical predictions shows a good agreement between them, verifying the rationality of the FE models using the fixed point iteration method.

Abstract: The tensile properties of a titanium alloy reinforced with 3% by volume fraction of TiC particles and of an unreinforced titanium alloy are studied over a range of strain rates from 0.0001s-1 to 1300s-1 using quasi-static material testing system (MTS810) and split Hopkinson tensile bar apparatus. The experimental results show that both the TiCp/Ti composite and its matrix alloy exhibit an obvious strain-rate hardening property. But the high strain-rate sensitivity of the TiCp/Ti composite is significantly higher than that of the matrix. The high strain-rate sensitivity of the TiCp/Ti composite is considered to be originated from the high dislocation accumulation rate during dynamic deformation and the constraint of TiC particles on the surrounding matrix, which dramatically enhances rate of the matrix. Finally, a phenomenological dynamic constitutive relation is established considering the composite is elastic-perfectly plastic material.

Abstract: Based on the principle of the equivalent momentum of the corresponding elements for internal and external liners, annular shaped charge structure is proposed. The generatrix analytical equations for the external surfaces of the external liner and external charge are deduced. Experimental and numerical studies are conducted to investigate the formation and penetration process of the jet for the annular shaped charge under different initiation radiuses, and the initiation radius corresponding to the detonation wave front matched with the liner is optimized. At this radius, shaped charge can form an ideal cylindrical jet. Moreover, the diameter of the jet approximates the theoretical diameter of the jet, and has satisfactory symmetry and focus.

Abstract: At long standoff, a shaped charge with small cone angle will produce a jet with a high tip velocity and a low tail velocity, causing it to stretch and break up, so its penetration ability into multilayer metal targets is very weak, while the penetration depth of explosively formed projectiles is too low to penetrate into multilayer metal targets. On account of this, the large cone angle shaped charge, whose internal cone angle is about 100 degree, is proposed and designed in the paper. The sensitivity of penetration effect into targets to the cone angle of the liner is investigated by experiment. The results reveal that the shaped charge penetration into multilayer metal targets with large interval is more optimistic than that of the shaped charge with small cone angle and explosively formed projectiles. In numerical simulation, based on interface tracking algorithm known as markers on cell line to reconstruct material interfaces, jet penetration into metal targets is simulated in a two-dimensional multi-material Eulerian code. The numerical results are in good agreement with the experimental ones and also indicate the interface tracking algorithm has much better resolution for moving interfaces, especially effective for large deformation.

Abstract: Alumina have been investigated for its distinguished characteristics to be widely used in armor application. One-stage light gas gun were utilized to study the dynamic mechanical properties of alumina subjected to shock loading. Manganin gauges were employed to obtain the stress-time histories at the different Lagrange locations in alumina target. The Hugoniot curves of stress and pressure versus specific volume were fitted based on the experimental data. The compressive behaviors for AD90 alumina are shown to be from elastic to “plastic” below 12GPa and under more higher pressure it will be transferred to similar-fluid state. Adopting LS-DYNA finite element code the dynamic failure of alumina ceramic armor are simulated. It is concluded that nucleation and growth of great number of radial and axial cracks and lateral cracks play dominant role in fractured ceramic target under impact loading.

Abstract: The plate impact experiments have been conducted to investigate the dynamic behavior of 91W-6.3Ni-2.7Fe with three kinds grain sizes of 1− 3μm, 10 −15μmand 30 − 40μm . The stress-time history curves at different Lagrangian positions were obtained for tungsten alloys at different impact velocities. Lagrangian analysis technique was adopted to discuss the mechanical properties of the tungsten alloys under high strain rate. SEM was introduced to analyze the microstructure properties of tungsten alloys. The influence of grain size on the dynamic behavior of tungsten alloys under high strain rate was obtained and the stress-strain curves ( 4 5 1 10 ~ 10 s− ) of the tungsten alloys were given.