Electrical arc contour cutting based on a compound arc breaking mechanism

Electrical arc contour cutting(EACC)is a novel high-efficiency material cutting process that applies arc plasma to perform efficient and economical contour cutting of difficult-to-cut materials.Compared to conventional electrical arc machining(EAM),this process can remove the allowance of open structures and plates in bulk mode,rather than entirely in the form of debris.Compared with existing contour cutting methods,EACC possesses the advantages of high cutting efficiency and a deep cutting depth.Particularly,a compound arc breaking mechanism(CABM),which integrates hydrodynamic force and mechanical motion,has been applied to control the discharge arc column in EACC,while also strengthening the debris expelling effect in the narrow discharge gap.The CABM implementation conditions were studied,based on arc column distortion images captured by a high-speed camera and simulation results of the flow field and debris distribution.A set of machining experiments was designed and conducted to optimize the performance of the proposed process.Finally,a SiC_(p)/Al metal matrix composite(MMC)space station workpiece was machined to verify the feasibility and efficiency of this process.

Effect of rapid cold stamping on fracture behavior of long strip S′phase in Al−Cu−Mg alloy

High-angle annular dark-field scanning transmission electron microscopy and selected area electron diffraction techniques were used to study the mechanism that underlies the influence of rapid cold-stamping deformation on the fracture behavior of the elongated nanoprecipitated phase in extruded Al−Cu−Mg alloy.Results show that the interface between the long strip-shaped S′phase and the aluminum matrix in the extruded Al−Cu−Mg alloy is flat and breaks during rapid cold-stamping deformation.The breaking mechanisms are distortion and brittle failure,redissolution,and necking.The breakage of the long strip S′phase increases the contact surface between the S′phase and the aluminum matrix and improves the interfacial distortion energy.This effect accounts for the higher free energy of the S′phase than that of the matrix and creates conditions for the redissolution of solute atoms back into the aluminum matrix.The brittle S′phase produces a resolved step during rapid cold-stamping deformation.This step further accelerates the diffusion of solute atoms and promotes the redissolution of the S′phase.Thus,the S′phase necks and separates,and the long strip-shaped S′phase in the extruded Al−Cu−Mg alloy is broken into a short and thin S′phase.

RESEARCH ON REPAIR SUPPORT FOR FLOOR HEAVE IN SOFT ROCK ROADWAY

The run-around of Xiagou subincline bottom is a soft rock roadway, its floor has heaved over 1 m. ln this paper, by electronic microscope scanning and X-ray diffraction analy-sis, the components of the soft rock are determined and the breaking mechanism of roadway is analyzed as well. Through finite element calculation and simulation model test, the reasonable repair support method is put forward.

Optical Trapping of a Single Molecule of Length Sub-1 nm in Solution

Plasmonic optical manipulation has emerged as an affordable alternative to manipulate single chemical and biological molecules in nanoscience.Although the theoretical models of sub-5 nm single-molecule trapping have been considered promising,the experimental strategies remain a challenge due to the Brownian motions and weak optical gradient forces with significantly reduced molecular polarizability.Herein,we address direct trapping and in situ sensing of single molecules with unprecedented size,down to∼5Åin solution,by employing an adjustable plasmonic optical nanogap and single-molecule conductance measurement.The theoretical simulations demonstrate that local fields with a high enhancement factor,over 103,were generated at such small nanogaps,resulting in optical forces as large as several piconewtons to suppress the Brownian motion and trap a molecule of length sub-1 nm.This work demonstrates a strategy for directly manipulating the small molecule units,promising a vast multitude of applications in chemical,biological,and materials sciences at the single-molecule level.

Study on the fragmentation of granite due to the impact of single particle and double particles

Particle Impact Drilling(PID)is a novel method to improve the rate of penetration(ROP).In order to further improve the performance of PID,an investigation into the effect of single and double particles:(1)diameter;(2)initial velocity;(3)distance;and(4)angle of incidence was undertaken to investigate their effects on broken volume and penetration depth into hard brittle rock.For this purpose,the laboratory experiment of single particle impact rock was employed.Meanwhile,based on the LS-DYNA,a new finite element(FE)simulation of the PID,including single and double particles impact rock,has been presented.The 3-dimensional(3D),aix-symmetric,dynamicexplicit,Lagrangian model has been considered in this simulation.And the Elastic and Holmquist Johnson Cook(HJC)material behaviors have been used for particles and rocks,respectively.The FE simulation results of single particle impacting rock are good agreement with experimental data.Furthermore,in this article the optimal impact parameters,including diameter,initial velocity,distance and the angle of incidence,are obtained in PID.

An Electrochemically Assisted Mechanically Controllable Break Junction Approach for Single Molecule Junction Conductance Measurements

We report an electrochemically assisted mechanically controllable break junction （EC-MCBJ） approach to investigating single molecule conductance. Electrode pairs connected with a gold nanobridge were fabricated by electrochemical deposition and then mounted on a homebuilt MCBJ platform. A large number of Au- molecule-Au junctions were produced sequentially by repeated breaking and reconnecting of the gold nanobridge. In order to measure their single molecule conductance, statistical conductance histograms were generated for benzene-l,4-dithiol （BDT） and 4,4＇-bipyridine （BPY）. The values extracted from these histograms were found to be in the same range as values previously reported in the literature. Our method is distinct from the ones used to acquire these previously reported literature values, however, in that it is faster, simpler, more cost-effective, and changing the electrode material is more convenient.

Unexpected current-voltage characteristics of mechanically modulated atomic contacts with the presence of molecular junctions in an electrochemically assisted-MCBJ

In this article, we report on the characterization of various molecular junctions＇ current-voltage characteristics （Ⅰ-Ⅴ curves） evolution under mechanical modulations, by employing a novel electrochemically assisted-mechanically controllable break junction （EC-MCBJ） method. For 1,4-benzenedithiol, the Ⅰ-Ⅴ curves measured at constant electrode pair separation show excellent reproducibility, indicating the feasibility of our EC-MCBJ method for fabricating molecular junctions. For ferrocene-bisvinylphenylmethyl dithiol （Fc-VPM）, an anomalous type of Ⅰ-Ⅴ curve was observed by the particular control over the stepping motor. This phenomenon is rationalized assuming a model of atomic contact evolution with the presence of molecular junctions. To test this hypothesized model, a molecule with a longer length, 1,3-butadiyne-linked dinuclear ruthenium（H） complex （Ru-1）, was implemented, and the Ⅰ-Ⅴ curve evolution was investigated under similar circumstances. Compared with Fc-VPM, the observed Ⅰ-Ⅴ curves show close analogy and minor differences, and both of them fit the hypothesized model well.