Shukui Li

Energy spectrums of bilayer triangular phosphorene quantum dots and antidots

We theoretically investigate the confined states of the bilayer triangular phosphorene dots and antidots by means of the tight-binding approach. The dependence of the energy levels on the size, the type of the boundary edges, and the orientation of the dots and antidots, and the influences of the electric and magnetic fields on the energy levels, are all completely analyzed. It is found that the energy level numbers of the bilayer dots and antidots are determined by the energy levels in two layers. The external electric field can effectively tune the energy levels of the edge states in both layers to move in opposite directions. With the increase of the magnetic field, the magnetic energy levels can approach the Landau levels of the phosphorene monolayer, the phosphorene bilayer, or both, depending on the specific geometry of the monolayer-bilayer hybrid phosphorene quantum dots. This research should be helpful for the overall understanding of the electronic properties of the multilayer hybrid phosphorene...

Dynamic Recrystallization in the Shear Bands of Tungsten Heavy Alloy Processed by Hot-Hydrostatic Extrusion and Hot Torsion

Abstract Hot-hydrostatic extrusion and hot torsion (HE+HT) were applied to the processing of the as-sintered tungsten heavy alloy (WHA). The dynamic mechanical properties of the WHA processed by HE+HT and the microstructural evolution within adiabatic shear band (ASB) were systematically investigated. The results show that the WHA susceptibility to ASB is much improved, and localized shear bands can be formed in specimens. TEM analysis of ASB shows that the multiplication and rearrangement of dislocation play dominate roles in the dynamic recrystallization (DRX) process within ASB of WHA, and the nano-scaled equiaxed-recrystallized grains within ASB can be formed via repeating the processes including dislocation multiplication, dislocation rearrangement and dislocation annihilation. The investigation result of observed DRX of the WHA firmly supports the rotational dynamic recrystallization (RDR) mechanism in metals.

Insensitive high-energy energetic structural material of tungsten-polytetrafluoroethylene-aluminum composites

Energetic structural material is a kind of materials that are inert under normal conditions but could produce exothermic chemical reaction when subjected to impact. This report shows a kind of energetic structural material of tungsten (W)-polytetrafluoroethylene (PTFE)-aluminum (Al) with density of 4.12 g/cm3, excellent ductility and dynamic compressive strength of 96 MPa. Moreover, 50W-35PTFE-15Al (wt%) can exhibit a high reaction energy value of more than 2 times of TNT per unit mass and 5 times of TNT per unit volume, respectively, but with excellent insensitivity compared with traditional explosives. Under thermal conditions, the W-PTFE-Al composite can keep stable at 773 K. Under impact loading, when the strain rate up to ∼4820 s−1 coupled with the absorbed energy per unit volume of 120 J/cm3, deflagration occurs and combustion lasts for 500 μs. During impact compressive deformation, the PTFE matrix is elongated into nano-fibers, thus significantly increases the reaction activity of W-PTFE-Al composites. The nano-fiber structure is necessary for the reaction of W-PTFE-Al composites. The formation of PTFE nano-fibers must undergo severe plastic deformation, and therefore the W-PTFE-Al composites exhibit excellent insensitivity and safety. Furthermore, the reaction mechanisms of W-PTFE-Al composites in argon and in air are revealed.

Adiabatic shear banding of hot-rolling Ti–6Al–4V alloy subjected to dynamic shearing and uniaxial dynamic compression

Effect of stress state including dynamic shearing and uniaxial dynamic compression on adiabatic shear banding (ASBing) of hot-rolling Ti–6Al–4V (TC4) alloy was investigated. The absorbed energy of specimen before failure was calculated to evaluate the susceptibility to adiabatic shear band (ASB) of TC4 alloy quantitatively. Results show that the susceptibility to ASB of hot-rolling TC4 alloy exhibits obvious anisotropy under both dynamic shearing and uniaxial dynamic compression conditions, but the anisotropy of susceptibility to ASB under dynamic shearing condition exhibits an opposite tendency with that under uniaxial dynamic compression condition. Under the condition of uniaxial dynamic compression, material shows the highest susceptibility to ASB when loaded along transverse direction (TD) of the hot-rolling TC4, while the lowest susceptibility when loaded along rolling direction (RD). However, under the condition of dynamic shearing, the material behaves in the opposite way, demonstrating the lowest susceptibility when loaded along TD of the hot-rolling TC4, while the highest susceptibility when loaded along RD.

Effects of Lamellar Microstructure Characteristics on Quasi-static and Dynamic Deformation Behavior of Ti 6Al-4V-4Zr-Mo Alloys

Abstract The influences of lamellar microstructure characteristics on quasi-static tensile properties and dynamic compression deformation behavior were studied for newly developed titanium alloy Ti-6Al-4V-4Zr-Mo. To tailor the microstructure characteristics, the lamellar microstructure was obtained by be solution treatment at 960 °C and underwent subsequent aging treatments at 700 and 570 °C, respectively. Results show that as the aging temperature decreases, the size of α colonies and the width of α plates present a declining trend. Correspondingly, the slip length of dislocation becomes relatively shorter, resulting in the increase of quasi-static deformation capability. Dynamic compression tests also show that the lamellar microstructure aged at 570 °C with α colonies and α plates in smaller size, which induces the propagated path of crack easily bifurcate and deflect, presents higher dynamic fracture strain, in contrast with the lamellar microstructure aged at 700 °C.

Adiabatic shear banding of hot-extruded tungsten heavy alloy under cryogenic temperature

The effect of cryogenic temperature on adiabatic shear banding (ASBing) of tungsten heavy alloy (WHA) processed by hot-hydrostatic extrusion was investigated. Results show that, when the initial temperature is decreased, the dynamic flow stress, the critical failure time, and the dynamic failure energy of specimens show an increasing tendency, while the susceptibility to ASB of WHA shows a decreasing tendency, which is characterized by decreased shear strain and increased width of shear bands. Microstructure analysis shows that the number of microcracks within ASB exhibits an increasing tendency with decreased initial temperature, and the dynamic recrystallization (DRX) process within ASB is evidently suppressed at the lower temperature. As a result of the lower temperature, the motion and rearrangement of dislocation are effectively suppressed, which is mainly responsible for the incomplete DRX process within ASB and decreases susceptibility to ASB.

Bending mechanical property and failure mechanisms of woven carbon fiber-reinforced aluminum alloy composite

Copper-coated woven carbon fiber-reinforced aluminum alloy composite was prepared by spark plasma sintering (SPS). Microstructure, three-point bending mechanical property, and the failure mechanisms of the composite were investigated. Microstructure observation shows that the carbon fibers bond compactly with matrix alloy. Compared with the matrix aluminum alloy, the bending strength, ductility, fracture energy, and cracking resistance of the composite are evidently improved. Microstructure analyses reveal that the high specific strength of carbon fibers and transfer of stress from matrix alloy to carbon fibers are responsible for the increase of the composite bending strength. The expanding of cracks is restrained, and cracking resistance of the composite is improved by adding woven carbon fiber. Attributed to the carbon fibers’ debonding, cracks deflection, and multipath propagation mechanisms, the fracture energy of the composite increases.

Quantum transport through a quantum dot structure side coupled with many quantum-dot and Majorana-bound-state pairs

We theoretically investigate the electron transport properties of a wheel-like quantum dot (QD) structure with a central QD side coupled with many pairs of QD and Majorana bound states (MBSs) by using the nonequilibrium Green’s function method. For clarity, we concentrate our researches on the parameter regime where interdot couplings is much smaller than the inter-MBS and MBS-QD couplings, which ensures the conductance peaks induced by them distinguishable. In the absence of the interdot couplings among the side QDs, the increase of the MBS-QD pair number is equivalent to the increase of the interdot coupling in the QD structure including one central QD and one MBS-QD pair. It is shown that as a response the interval between two side symmetrical peaks will be enlarged, and the MBS-QD couplings will bring into being a zero-bias conductance peak which can be split into two symmetrical sub-peaks by the nonzero inter-MBS couplings. In the presence of the interdot couplings among the side QDs, they make serio...

Dynamic behaviors of fiber reinforced aerogel and Mg/aerogel composites

The dynamic behaviors of glass fiber reinforced silica aerogel and the Mg/aerogel composites are experimentally investigated using spilt Hopkinson pressure bars. For the purpose of comparison,dynamic responses of hydrogel are also investigated. Incident wave shaping experiments are designed to investigate the shaping effects of aerogel and Mg/aerogel structures. Results show that the fiber reinforced aerogel exhibits significant strain rate strengthening and strain hardening behavior. The strength of the investigated aerogel exhibits evidently size effect: strength of aerogel shows an increasing tendency with the size of sample due to the special nano-porous network structure of aerogel. The incident wave shaped by the composite structure of Mg/aerogel is obviously weaker than that of single magnesium alloy or aerogel, indicating a better protective capacity of Mg/aerogel composite structures.

Strain rate-dependent and temperature- dependent compressive properties of 2DCf/SiC Composite

Effects of strain rate and temperature on dynamic behaviors of 2DCf/SiC composite were investigated by improved Split Hopkinson Pressure Bars (SHPB) using pulse shaper. Results show that the shape of incident wave changes from rectangle to triangle after using pulse shaper in SHPB testing. The dynamic compressive strength of the composite increases with strain rate increasing from 500s–1 to 1700s–1, while shows decreasing tendency with strain rate rising from 1700s–1 to 2750s–1, indicating a maximum dynamic strength at strain rate of about 1700s–1. The 2DCf/SiC composite exhibits higher strength and better ductility at elevated temperature in the range of 460°C~500°C compared with that at room temperature.