Yujun Xue

Fluorescence of silicon nanoparticles prepared by nanosecond pulsed laser

A pulsed laser fabrication method is used to prepare fluorescent microstructures on silicon substrates in this paper. A 355 nm nanosecond pulsed laser micromachining system was designed, and the performance was verified and optimized. Fluorescence microscopy was used to analyze the photoluminescence of the microstructures which were formed using the pulsed laser processing technique. Photoluminescence spectra of the microstructure reveal a peak emission around 500 nm, from 370 nm laser irradiation. The light intensity also shows an exponential decay with irradiation time, which is similar to attenuation processes seen in porous silicon. The surface morphology and chemical composition of the microstructure in the fabricated region was also analyzed with multifunction scanning electron microscopy. Spherical particles are produced with diameters around 100 nm. The structure is compared with porous silicon. It is likely that these nanoparticles act as luminescence recombination centers on the silicon surface. The small diameter of the particles modifies the band gap of silicon by quantum confinement effects. Electron-hole pairs recombine and the fluorescence emission shifts into the visible range. The chemical elements of the processed region are also changed during the interaction between laser and silicon. Oxidation and carbonization play an important role in the enhancement of fluorescence emission.

Separating and Reconstructing Techniques of Cylindricity Error by Three-point Method

The mathematical model of and the solution to cylindrical form error separation are presented in this paper. The roundness, the radius error of different cross sections and the initial coordinates of the least square centers of measured cross sections can be separated by this technique. Meanwhile, the rotation motion error of spindle and the rectilinear motion error of guide way can be separated effectively. Based on the periodicity of roundness error, a method of solving the roundness of measured cross sections is put forward by means of system of linear equations without using the Fourier transform of discrete data. According to the separated process of the above errors, the reconstruction datum of cylindrical surface and the mathematical formula to reconstruct measured cylindrical form are established

Fabrication and Tribological Behavior of Ni-ZrO2 Nanocomposite Coatings Prepared by Electrodeposition in Ultrasonic Field

Ni-ZrO2 nanocomposite coatings were fabricated by electrodeposition from a modified Watt’s type electrolyte containing ZrO2 nanoparticles, where an ultrasonic field was imposed during electrodeposition process. The weight percent of ZrO2 in coatings and the surface morphology of coatings were examined. The microhardness and tribological properties of Ni-ZrO2 nanocomposite coatings and pure Ni coating were investigated. The results show that ultrasonic agitation can greatly affect the microstructure and the tribological behavior of Ni-ZrO2 nanocomposite coatings. The Ni-ZrO2 nanocomposite coatings record variable ZrO2 contents and surface morphologies by modifying ZrO2 concentration in electrolyte and ultrasonic parameters. The Ni-ZrO2 nanocomposite coating fabricated with ultrasonic agitation exhibits finer grains and more compact structure compared to pure Ni coating and the Ni-ZrO2 nanocomposite coating fabricated without ultrasonic agitation. The dispersed ZrO2 nanoparticles in coatings and ultrasonic agitation during electrodeposition synthetically contribute to the grain refinement of the coatings. Therefore, the Ni-ZrO2 nanocomposite coating by ultrasonic electrodeposition exhibits high microhardness and excellent tribological behavior. In general, the improvement in friction and wear properties of Ni-ZrO2 nanocomposite coatings can be attributed to the homogeneously dispersed ZrO2 nanoparticles and the finer-grained structure.Copyright

Optimum control for active steering of vehicle based on H ∞ model following technology

This paper introduces a new control scheme for active steering of vehicle. An ideal reference model followed by the four-wheel steering (4WS) vehicle is established resulting from the front-wheel steering (FWS) vehicle, and an H∞ optimum controller for the 4WS vehicle is designed based on model following technology. The dynamic simulation is performed to verify control effect of the H∞ controller, and the result shows that the H∞ controller can apply to the 4WS vehicle system. It can not only minimize the sideslip angle of the 4WS vehicle to zero value, but also keep the yaw rate of the 4WS vehicle in accordance with the FWS vehicle. The handleability is further improved for 4WS vehicle.

Virtual Prototype of the Tunnel Boring Machine and Movement Simulation in DIVISION MOCKUP2000i2

The virtual reality is a multi-functional, interactive and immersible technology. As an advanced engineering design technology, the virtual reality technology (VRT) has been widely used in large mining machinery design and manufacturing. The system is based on DIVISION Mockup2000i2 software. Virtual prototype of the Tunnel Boring Machine (TBM) is studied in this paper. In addition, the movement simulation of TBM is completed in DIVISION Mockup2000i2. Firstly, CATIA software is adopted to build the parts of TBM. The TBM is assembled in CATIA too. Secondly, the THEOREM software is applied to convert the assembled model of TBM to another format which can be identified in DIVISION MOCKUP2000i2 software.

Analysis for Thermal Characteristics of High-Speed Angular Contact Ball Bearing under Different Preload

A large amount of heat is produced due to the friction between components within the bearing, resulting in an increase in temperature of the bearing system. The value of the preload directly affects the temperature of the bearing, and will affect the performance of bearing. Based on ball bearing of quasi-statics and thermal analysis, the heat generation of the high speed angular contact ball bearing is calculated and analyzed under different preload, rotation speed and contact angle. The temperature distribution of the bearing under steady state condition is obtained by using ANSYS for the numerical simulation of the bearing different conditions, and the influence rule of preload on heat generation of bearing is given. The research results provide a reference for the temperature distribution of rolling bearing and its application research.

On-Line Monitoring Method for Fatigue of Mechanical Structure Parts

Fatigue failure was a typical failure form of mechanical structure parts, elastic modulus drop was an important characteristic of structural material occur fatigue, so a new mechanical structure fatigue monitoring online method was proposed. Firstly, a test device that could impose cyclic load with adjustable frequency and amplitude on cantilever beams was designed; secondly, a stress measurement system based on Fiber Bragg Grating sensor to monitor structural state of fatigue was developed; thirdly, a method to calculations stress based on this system was described; finally, the online method was used in the elastic modulus drop. Introduction Under the action of alternating load, the material properties of the mechanical structure show the regularity of the attenuation process. It contains the occurrence of fatigue cracks, the development, the formation of macro cracks, peeling off and fracture. Fatigue damage has become an important factor that leads to the failure of the mechanical structure. According to statistics, project of fatigue fracture damage, accounted for 50% ~ 90% of all mechanical damage and fatigue damage and fatigue damage fracture is the most common form of failure of mechanical structure [1]. The damage caused by fatigue is more and more outstanding in engineering failure. Therefore, how to monitor the fatigue information in the early stage of the fatigue phenomenon is an urgent problem to be solved in the engineering field. In order to be able to timely access to the service of machinery structure fatigue status information, only to rely on to parts of the structure were measured periodically is unable to meet the requirements. It requires long-term on-line fatigue monitoring of mechanical structure with the new monitoring device and test methods [2,3]. In this paper, a test device is designed to monitor the fatigue damage state of the mechanical structure. The precision control of the applied load frequency and amplitude is realized by means of the device; the strain measurement system based on Fiber Bragg grating(FBG) sensor is used to realize the load condition of the cantilever beam and the effective monitoring of the strain response. The fatigue damage state of the cantilever beam is obtained by analyzing and processing the measured data. The experimental results show that the measurement system is effective in monitoring the fatigue damage of the existing mechanical structures. Fatigue Monitoring Test Device Cantilever beam material is 45 steel. Cantilever beam specimen is subject to bending stress, in addition to its fixed end, the suspension section of the same force, but because of different interface size, making the stress on the cross section different. In order to cause the cantilever beam specimen to be prone to fatigue, the section of the suspension section becomes smaller. The shape of the specimen of the cantilever beam is shown in figure 1. The design can reduce the load of the fatigue damage in the sample; the purpose is the connecting rod fatigue damage will not occur in the load 398 transfer. It can prevent the connecting rod is fracture prior to the cantilever beam specimen due to fatigue damage. The loading mechanism is a crank mechanism, which is the core mechanism of the mechanical body part of the test device, which not only can realize the conversion of the rotary motion to the complex linear motion, but also can realize the adjustable load size[4]. Crank more hours, in order to increase the mechanical strength of the crank, the crank is changed into a disc shape. Its working principle is shown in figure 2.

Analysis on Calculation of Transverse Swing Amount of Mine Hoisting Container under Flexible Constrains

Increasing transverse swing of container has a direct impact on safety of multi-rope friction mine hoist. Under the strain of flexible guide, increasing transverse swing is related with parameters of mine hoisting system. Take hoist container under strain of steel rope guide as the research object, considers increasing hoist speed of hoist container, increasing load of steel rope terminal and lateral stiffness of steel rope guide and other parameters to establish a solving equation of increasing swing amount of container, and then analyze transverse swing amount of hoist container under different parameters of tension of guide rope, hoist speed and load on the terminal of hoist steel rope. Research shows: lateral stiffness of guide rope is inversely proportional to transverse swing amount of hoist container under flexible strains; hoisting speed and increasing load of steel rope terminal have greater effect on increasing swing amount of container in the middle segment of guide than in the starting and ending point.

Development of On-Line Condition Monitoring System for Wind Turbines in Plant Level

The maintenance cost of wind turbines has become the significant challenge for the wind power enterprise. One available way to reduce the cost is to monitor the wind turbines and make preventative maintenance. In this paper, an on-line condition monitoring system for wind turbines in plant level was presented. A 4-level monitoring structure was designed for the system, and the network communication was used to transmit the data efficiently. A high performance digital signal processor (DSP) was used as the processing core in the signal acquisition device. A computer software was also developed for data analysis and remote management of the monitoring device. The vibrations, temperature, and some other information of the turbines were gathered synchronously. The monitoring center in wind farm, the data center of wind power enterprise and the remote service center of equipment supplier can know the operation condition of wind turbines well. It would be useful for wind power enterprise to obtain the operation condition of wind turbine and reduce the cost of maintenance.Copyright

Strength analysis for pre-stressed bolted joints of turntable bearings

This paper describes a calculation model for pre-stressed bolted joints used to connect turntable bearing to the flanges. A traditional pre-stressed bolted joint calculation model is described and its insufficiencies for the direct application on turntable bearings are pointed out. The suggested stress analysis is done by modeling the most loaded single bolt segment of the turntable bearing assembly, applying the preload and the working load on it. The alternating stress in the bolt is done by finite element analysis. The results show that the alternating load of the bolt is significantly decreased and is lower than the fatigue limit of the bolt under the condition of the larger tightening force. Therefore, it should be possible to increase the preload in the conditions that the maximum stress of bolt is below its yield limit stress situation.