Papers by Author: Yang Wang

Abstract: Although the nanostructure machining by AFM probe assisted with laser has gain a great progress, few studies has been done on the optical fiber probe guiding the continuous laser to irradiate on AFM probe to machining nanostructure. Using this technology to create nanodot and nano-groove was presented in this paper. The law of how the experiment parameters influenced the results was summarized in the paper. The scale of nanodot is about 450nm, and nano-groove is about 40nm. When the fabrication is completed, the wear of the AFM probe was observed by SEM and drew a conclusion. In the method of nano machining by AFM Probe combining with a CW Laser, there will be a combined field to achieve the fabrication, and the method is better than mechanical characterization with AFM probe.

Abstract: The effect of rare earth element yttrium on cyclic oxidation behavior of Co-10Cr-10Al alloys in ambient atmosphere of 1 atm at 1073K was investigated. The results indicated that the addition of 0.05 at.% Y in the alloy enhanced the formation of protective oxide scales with compact smooth surface, and improved cyclic oxidation resistance of the alloy. On the contrary, the addition of 0.1-0.3 at.%Y greatly increased the oxidation rate of the alloy, with formation of a rapidly growing Co oxides layer with the porous and rough surface appearance.

Abstract: Obtaining narrower kerf and smaller heat affected zone (HAZ) is a difficulty in laser cutting carbon fiber reinforced plastic (CFRP) composites. In order to solve this problem, the experiments used a semiconductor UV laser to cut CFRP have been done and how laser parameters (include pulse power, repetition frequency, cutting speed and direction) influent the width and HAZ of kerf have been achieved. In the meantime, compared with infrared laser cutting CFRP, the quality of CFRP cut by different wavelength laser has been investigated. The results show that owing to CFRP has the characteristic of anisotropy, laser cutting direction is the most significant factor that affects the quality of kerf cut by UV laser. The study also found that owing to high single photon energy, the narrower kerf and smaller HAZ around kerf can be get by UV laser cutting CFRP, nevertheless, it can’t be achieved by infrared laser cutting CFRP.

Abstract: Laser-assisted machining (LAM) is a hybrid cutting process in which a laser beam is used to heat and soften the workpiece locally in front of the cutting tool edge. The rapid temperature rise at the shear zone reduces the yield strength and work hardening of the workpiece, which makes the plastic deformation of difficult-to-machine materials easier during machining. LAM provides a reduction in the cutting forces/specific cutting energy, longer tool life, better surface integrity, and high productivity over traditional cutting. This paper presents the technical characteristics, material removal mechanism and the application of machining hard-to-machine material in LAM. The latest development of LAM and future scope are summarized in this paper.

Abstract: Dip-pen nanolithography (DPN), based on atomic force microscope (AFM) system, is an effective method for nanoscale science and engineering, and the potential applications of DPN will be shown in the field of nanomechanics, nanomaterials, nanobiotechnology, nanomedicine. And the novel combined-dynamic mode DPN (CDDPN), rather than mostly used contact mode DPN or tapping mode DPN, becomes the important tool for the fabrication of nanodots with the direct-writing method of depositing the ink onto the hard silicon surface at the predetermined position, which is presented in the corresponding experiments. In addition, the size of nanodots gradually decreases in the diameter with the increase of the number of nanodots in the case of AFM tip dipping in ink once. However, the size in height does not monotonically reduce as the reduction of the ink, which is affected by the interaction among the relative humidity, AFM tip, substrate material, surface roughness, etc. For the better nanolithography quality of the nanodot, the nanolithography process, under the optimized process parameters, is accomplished once without the intermediate scan imaging process as much as possible.

Abstract: Theoretical, experimental and simulation researches are investigated to study the phenomenon of edge chipping in laser assisted milling (LAML) of silicon nitride ceramics. To consider the crack evolution and influencing factors of edge chipping, the Extended Finite Element Method (XFEM) is used to model the process of chipping crack with the advantage of independent of the mesh and needless to remesh with the crack growth. The chipping width measured from experiments are loaded as initial boundary conditions to build the XFEM model, and the results show the edge chipping reduces with cutting forces decreasing and edge toughness increasing. The model reveals the edge chipping of workpiece reduces at elevated temperature through softening and toughening mechanisms.

Abstract: It is bigger that SRa_dcv of the micro-pits image based on square area scrambling, and the uniformity of micro-pits distribution is not very good. An improved method is presented that presetting the minimum interval of the micro-pits, and setting positions of these micro-pits randomly, then optimizing the positions of the micro-pits by area scrambling. SRa_dcv of the micro-pits image generated in this method will be much smaller, and the uniformity of the micro-pits distribution will be very good.

Abstract: Mathematical model including design variables, constraint conditions and target functions is raised on the basis of problem description. Using the mathematical model, area scrambling micro-pits image design methods are presented. The methods can generate square area scrambling micro-pits image based on square-aligned-array arrangement, square area scrambling micro-pits image based on square-staggered-array arrangement, and area scrambling micro-pits image based on equilateral hexagon-array arrangement. The uniformity of the last one is the best.

Abstract: Two image generating algorithms based on square partial scrambling are raised to implement micro-pits with approximate uniformity distribution of YAG laser texturing roll. Micro-pits can be uniformly distributed to ensure the area-uniformity of the micro-pits distribution. Micro-pits can be partial scrambled and optimized according to the evaluation standard to ensure the direction-uniformity of the micro-pits distribution.Partial scrambling image generating algorithms based on square-aligned-array arrangement and square-staggered-array arrangement are both effective image generating algorithms of uniformity distribution. The latter is more effective.

Abstract: By employing a generalization of the conservation law for momentum using the finite difference time domain (FDTD) method, the feasibility of using a near-field optical fibre probe to create near-field optical trapping is investigated. Numerical results indicate that the scheme is able to trap nanoparticles with diameters of tens of nanometres in a circular shape with lower laser intensity. Using the built system with a tapered metal-coated fibre probe, 120 nm polystyrene particles are trapped in a multi-circular shape with a minimum size of 400 nm. They are at a resolution of λ/7 (λ: laser wavelength) and d (d: tip diameter of fiber probe), respectively.