Papers by Author: Li Sheng Liu

Abstract: Modeling of heat and electrical current flow simultaneously in thermoelectric convertor using classical theories do not consider the influence of defects in the material. This is because traditional methods are developed based on partial differential equations (PDEs) and lead to infinite fluxes and stress fields at the crack tips. The usual way of solving such PDEs is by using numerical technique, like Finite Element Method (FEM). Although FEM is robust and versatile, it is not suitable to model evolving discontinuities since discontinuous fields are mathematically singular at the crack tip and required an external criterion for the prediction of crack growth. In this paper, we follow the concept of peridynamic (PD) theory to overcome the shortcomings above. Therefore, the main aim of this paper is to develop the peridynamic equations for the generalized Fourier’s and Ohm’s laws. Furthermore, we derived the peridynamic equations for the conservation of energy and charge for the coupled thermoelectric phenomena.

Abstract: Peridynamic simulations have been carried out to perform the slope stability analysis. A slope is first modelled with discretized particles in 2D. Then the non-ordinary state-based Peridynamic model is utilized. In order to obtain a more realistic behavior of the soil, Drucker-Prager constitutive model is used to describe the mechanic properties of soil. Results show great agreements with the FEM results, while provides the dynamic slide progress in the post-failure process.

Abstract: The Phan-Thinen and Tanner (PTT) model was used to describe the co-extrusion behavior of tread rubber which is made up of two components. To investigate the effects of upper and lower channels on simulation results, two kinds of Finite Element (FE) models were established. One of them contained the upper and lower channels, while another did not. Comparison between the computational results and corresponding test data illustrates that the difference of these two models is obvious, which suggests that the consideration of upper and lower channels play an important role in analysis on polymer’s co-extrusion process. Besides, we also analyzed the effects of wall slip coefficients on co-extrusion products. The results show that the decreasing of wall slip coefficients can reduce the extrusion swell phenomenon effectively, but it may bring out the distorting of the corner parts of co-extrusion section shape. Therefore, various factors need to be comprehensive taken into account in the selection of wall slip coefficients.

Abstract: One common and prominent reason for the tube explosion issue of pipe network is the water hammer. Because the pressure levels caused by water hammer are far exceeding the pressure range of the pipe limit. Since a great loss has been caused by water hammer damage, an important influence factor (shape of pipe) on the phenomena associated with water hammer have been performed by using the platform of numerical simulation software CFX. Analysis of the results show that the vortex and reflux phenomena appear in elbow pipe, different shape of pipe will lead to various flow regime. The pressure caused by shape is slight and can be negligible compared to the normal pressure. But it does has influence on period, 90-degree elbow will reduce 0.01s in period.

Abstract: Water hammer can occur in any fluid pipeline systems. The pressure caused by water hammer are far exceeding the pressure range of the pipe limit, and it can lead to the failure or fracture of the pipeline. Since a great loss has been caused by that, two influence factors (flow velocity and roughness of the pipe-wall) associated with water hammer have been performed by using the numerical simulation software CFX. Analysis of the results show that each factor effects differently in waveform, amplitude, period, attenuation of the water hammer wave. The different velocities only influences the peak of pressure wave but not the waveform and period. The pressure reduction as the increase of roughness can be neglected compared to the normal pressure.

Abstract: The shear property of the thermoelectric material Bi₂Te₃ is inextricably linked with its layer structure. By the molecular dynamics method, the mechanism of shearing deformation was studied in this paper. In the simulation, cubic single-crystal simulation cells with different layer directions inside were adopted, ensuring that the c axis of crystal lattice can be along, across and 45^o deviated from the shear stress. Compared with all the calculation models, the results show that when the shear stress increases, slip occurs along the Te1-Te1 adjacent layers which are connected by the weak van der Waals bonding, and ultimately leads to structural fracture. Furthermore, size effect and loading modes can also impact the behavior of shearing deformation, however, in very different ways. Future efforts should be focused on the influence of the creation and motion of defects during the deformation as well as temperature effect and strain rate effect.

Abstract: In this paper the sensitivity of strain rate and size effect with different particle volume fraction in SiCp/Al Composite were studied through the experiment. Specimens with 40% and 30% SiC particle volume fraction were made. There are three types of particle sizes in each volume fraction. The sensitivity of strain rate and the effect of particle size in Al matrix composites reinforced with the different volume fraction were investigated, using the split Hopkinson pressure bar and Instron5882 universal material testing machine. The surface microstructure of the specimens in each composite was examined using optical microscopy and SEM. Through the strain-stress curves, the sensitivity of strain rate can be obtained. The experimental results show that the sensitivity of strain rate increases with the increasing of particle volume fraction. At the same volume fraction, the size effect were observed obviously and higher flow stresses were obtained in the composites reinforced with small particles than that in the composite with large particles.

Abstract: The size effect on particles reinforced metal matrix composites (MMCp) was investigated by a numerical method. A numerical multi-particles unit cell model has been constructed to carry out numerical analysis. In this model, circle particles were randomly placed in matrix according to uniform distribution, the sizes of particles in the paper were classified into 4 groups: 6μm, 13.5 μm ,50μm, and 100μm respectively. For investigating the effect of particles’ size on the plastic behavior of MMCp, the Griffith fracture criterion and the damage of ceramic particles were considered. Result showed that there was a close relationship between the particle size and the deformation behavior of the composites. Yield strength and plastic work hardening rate of the composites increase with decreasing particle size. The predicted stress–strain behaviors of the composites were in agreement with the experimental results.

Abstract: The dynamic compressive behavior of Al2O3 (10% vol.) / TiB2 ceramic composite had been tested by using a split Hopkinson pressure bar in this paper. The results show that the main failure modes of the ceramic composite include crushed failure and split fracture along the loading direction. The former is the typical compressive failure of brittle materials. The later is tensile failure along the flaws produced during the composite manufacturing. The numerical simulation was also used to study the effect of the diameter/length ratio of the samples on the experimental results. The effect of the deformation in the bars’ ends, which contacted with the samples, was also studied in the numerical models.

Abstract: Dynamic response and fracture of high strength boride/alumina ceramic composite were investigated by split Hopkinson pressure bar (SHPB) experiment in this paper. The compressive stress–strain curves and dynamic compression strength of the composites were tested. The surface’s microstructure of fractured composites were examined by using scanning electron microscope (SEM) to investigate the fracture mechanism. The results show that boride/alumina has high dynamic compressive strength and high Young’s modulus. The main fracture mode of the material is the fracture of the ceramic grains. The micro-voids and flaws, generated during the sintering and manufacturing of material and mechanical process of specimen, decrease the strength of the material because they provide the source of crack expansion when the material undergoes the dynamic loadings.