Fan Qunbo

Study of ZrO2 phase structure and electronic properties

The phase structure and electronic properties of c-ZrO2, t-ZrO2 and m-ZrO2 are calculated and compared using density functional theory. By calculating the energies for different lattice constants, the crystal structures of the three zirconia polymorphs are optimised. The calculation results are in good agreement with related experimental data and the cohesive energies do reflect the relative phase stability of the three zirconia polymorphs. The valence electronic density of states and the charge distributions on some typical planes are presented and discussed to investigate the valence electronic structure, the special electronic properties, and the Zr–O bond strength. The calculation results in this paper would be helpful to further predict the zirconia phase transition and some basic physical properties.

Prediction of the intrinsic thermal conductivity of phonons in dielectric and semiconductor materials based on the density of the lattice vibration energy

A novel method is proposed to simulate the intrinsic thermal conductivity of the phonons in dielectric and semiconductor materials by introducing the concept of the density of the lattice vibration energy, which is a function of frequency and temperature. A quantitative relationship between the density of the lattice vibration energy and the mean free path of the phonons is established. The heat capacity and sound velocity can also be calculated by using the phonon density of states, the theoretical densities, and the elastic modulus. The thermal conductivities of some typical dielectric and semiconductor materials are then calculated, and it is found that the agreement with experimental data is good for some materials. In contrast to traditional semi-empirical methods, there is no need to input any experimental data.

Study of Flying Particles in Plasma Spraying

In this article, the trajectories of ceramic and metal particles in plasma spray are calculated by solving related momentum and energy equations. Meanwhile, the spatial distributions, temperatures, velocities, as well as diameters of the particles are measured by employing an online, in-flight particle sensor (DPV2000). The experimental and computational results are in good agreement. It has been found that the particle flying trajectories are dependent on material types and particle diameters, and in a plane vertical to the spraying axis, there is a certain corresponding relationship between the particle diameter and the particle velocity, as well as particle temperature.

Numerical simulation of temperature and velocity fields in plasma spray

Based on the turbulence jet model, with respect to Ar-He mixture plasma gas injecting to ambient atmosphere, the temperature filed and velocity field under typical working conditions were investigated. Given the conditions of I=900 A, FAr = 1.98 m3/h, FHe = 0.85 m3/h, it is found that both the temperature and the velocity undergo a plateau region near the nozzle exit (0–10 mm) at the very first stage, then decrease abruptly from initial 13 543 K and 778.2 m/s to 4 000 K and 260.0 m/s, and finally decrease slowly again. Meanwhile, the radial temperature and radial velocity change relatively slow. The inner mechanism for such phenomena is due to the complex violent interaction between the high-temperature and high-velocity turbulent plasma jet and the ambient atmosphere. Compared with traditional methods, the initial working conditions can be directly related to the temperature and velocity fields of the plasma jet by deriving basic boundary conditions.

Effects of Microstructural Factors on Adiabatic Shear Behaviors of Ti6441 Alloys

Abstract In term of newly developed titanium alloys Ti-6Al-4V-4Zr-Mo (Ti6441) modified from the commercial Ti-6Al-4V alloys, the adiabatic shear behaviors of equiaxed and lamellar microstructures were investigated. Unlike the Ti-6Al-4V alloys, Ti6441 alloys with the lamellar microstructure are less susceptive to adiabatic shear bands (ASBs), compared with the equiaxed one. In particular, the ASBs branch off in the lamellar microstructure, requiring additional energy by consuming metal bulk plastic deformation work. Besides, forced shearing experiment results show the lamellar microstructure exhibits outstanding dynamic ductility in contrast with the equiaxed one, though both microstructures perform the same strength value.

Modeling the Dynamic Damage Process of the SiC3d/Al Interpenetrating Phase Composites

In the current study, a 3D mesoscopic structure FE-Model of interpenetrating SiC3d/Al composite is built based on the digital image-based modeling technique together with optimized methods of three-dimensional mesh generation. Subsequently, the finite element method is proposed to simulate the dynamic damage process of the interpenetrating phase composites SiC3d/Al under dynamic axial crushing. The cracking process in micro 3D space is clearly presented in the current study. It is shown that the cracks initialization and propagation mainly appear in the region of interface between ceramic and metallic phase. Moreover, the ceramic phase attributes to the models damage predominantly. The method proposed in this paper would be of help in the microstructure design of Interpenetrating Phase Composites.

Numerical Simulation in relation to Adiabatic Shearing Behaviors in Titanium Alloy

The adiabatic shearing phenomena are commonly found in titanium alloys, but they are rarely simulated in the microstructure scale. In the current study, the macro-dynamic compression is implemented and the microstructures are successfully embedded into the macro model by introducing a multiscale simulation technique, thus help to reveal the adiabatic shearing deformation mechanism of titanium alloy. The simulation results show that for the equiaxed titanium alloy, the adiabatic shearing process is determined by the phase proportion outside the shear band instead of the phase proportion inside; the study further shows that within a certain proportion of α phase, with the increase of α phase proportion, the adiabatic shear sensitivity decreases.

Multiscale Numerical Simulation of the Shaped Charge Jet Generated from Tungsten-Copper Powder Liner

Formation process of the shaped charge jet of W-Cu powder liner was simulated with smoothed particle hydrodynamics (SPH) method of LS-DYNA software. With the digital image process technique and macro-micro coupling method, a multiscale finite element model was established, and the high speed deformation process of the microstructure driven by explosive detonation in the liner of shaped charge was successfully simulated. The Cu phases were susceptible to serious deformation while the tungsten phase has less deformation. Besides, the temperature field of the microstructure during the shaped charge deforming was calculated, and a discussion of the deformation mechanism of the liner was given. The methods proposed in this paper would be of help in microstructure design of shaped charge materials.

The influence of defects on the effective Young's modulus of a defective solid

It is difficult to establish structure-property relationships in a defective solid because of its inhomogeneous-geometry microstructure caused by defects. In the present research, the effects of pores and cracks on the Youngs modulus of a defective solid are studied. Based on the law of the conservation of energy, mathematical formulations are proposed to indicate how the shape, size, and distribution of defects affect the effective Youngs modulus. In this approach, detailed equations are illustrated to represent the shape and size of defects on the effective Youngs modulus. Different from the results obtained from the traditional empirical analyses, mixture law or statistical method, for the first time, our results from the finite element method (FEM) and strict analytical calculation show that the influence of pore radius and crack length on the effective Youngs modulus can be quantified. It is found that the longest crack in a typical microstructure of ceramic coating dominates the contribution of the effective Youngs modulus in the vertical direction of the crack.