Table of Content

10 July 2017, Volume 28 Issue 13

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Research Progresses on Interfacial Stick-slip Frictions

SONG Baojiang1,2;YAN Shaoze1,2

2017, 28(13):  1513-1522. 

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The recent progresses in stick-slip friction on both of macroscopic and microscopic scales were reviewed. The friction properties embodied by the macroscopic stick-slip phenomenon, the discovery of the microscopic stick-slip phenomenon and the influence factors of the microscopic stick-slip friction were introduced. The achievements of the modeling researches and experimental studies in the field of stick-slip frictions were summarized. This paper gave a brief perspective to the focus studies on stick-slip frictions and proposed the ideas that exploring the interface friction behavior from microscopic and mesoscopic scales is the developing trend in the area of stick-slip frictions.

Structure Optimization and Isolating Performance Analysis of Spaceborne Camera Isolator

LIU Shiping1;XIONG Qi1;LI Shiqi1;WANG Yue2

2017, 28(13):  1523-1527,1534. 

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Based on the principles of large damping loss of viscoelastic material under the action of shear forces, a spaceborne camera isolator was preliminarily designed. By using the orthogonal experimental design method and finite element analysis, the influences of the structural parameters of the isolator on the natural frequencies and modal loss factors were explored in detail, the structure of the isolator was optimized accordingly. The finite element model of the camera vibration isolation system was established, the mechanics strength was checked and the vibration isolation performances were analyzed. The results show that the camera vibration isolation system may meet the mechanics environmental tests of the satellite launching stage by using the isolators, and have better vibration isolation effectiveness.

Gearbox Fault Diagnosis Based on RB-SSD and MCKD

HE Qun1;GUO Yuangeng1;WANG Xiao1,2;REN Zonghao1;LI Jimeng1

2017, 28(13):  1528-1534. 

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When a rotating part of the gearbox failed, the periodic fault impulse components in the vibration signals were easily submerged by the harmonic components and the strong background noises, thus leading to the challenging difficulties in the fault feature extractions. To address this issue, a new fault diagnosis method was proposed based on RB-SSD and MCKD herein. Firstly, the low-resonance components of the signals were separated from the harmonic components and the noises using RB-SSD method, and then the MCKD method was employed to the low-resonance components to further highlight the periodic impulse components. Finally, the envelope spectrum analysis was performed to diagnose the faults. The evaluation results from simulations, experiments and engineering applications demonstrate that the proposed method may extract effectively and highlight the periodic fault impulse components from noisy vibration signals, thus providing accurate and reliable diagnosis results.

Numerical Analysis of Cavitation Effects of Self-excited Oscillation Pulse Nozzles and Jet Forms

WANG Zhaohui1;HU Ya'nan1;RAO Changjian1;DENG Xiaogang2

2017, 28(13):  1535-1541. 

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Based on the cavitation effects of the self-excited oscillation pulsed nozzles and multi-phase flow model, a cavitation model of the self-excited oscillation pulsed jets was established. The axisymmetric physical model of the chamber was built according to the self-excited oscillation chamber structures and its geometric parameters. The breakup of cavitation bubbles, two-phase distributions in the chambers, turbulent kinetic energy distributions and velocity distributions in an oscillation period of 100ms were obtained by numerical calculations. The results show that: in 1.02-2.37ms, the radii of cavitation bubbles decrease rapidly and the bubbles begin to do radial motions to form the accelerating jet on the bubbles surface. In 2.69-4.67ms, the bubbles start to crush when the pressures of cavitation bubble surfaces reach the limit breaking value. In the beginning of 25ms, the strong turbulent kinetic energy is formed at the contact interface between the main jet and air, and the center vortex area in self-excited oscillation chamber gradually grows up. Continuous jet in the outflow field is cut into the multiple jet and the jet velocity reaches a stable value about 30-40m/s near the axis of injection. In 40-90ms, the central cavitation airbag in the chamber has been formed and begins to block the movements of main jet, and the large cavitation area appears in the nozzle's outlet channel and the maximum turbulent kinetic energy is concentrated in the downstream of the lower nozzle exits. In the later period of oscillation, the velocity of main jet tends to be stable and the diffusion effects are weakened as the main jet interacts with the air and the penetration distances of the jet increase.

Control Method of LVRT for Hydraulic Wind Turbines Based on Pressure Feedback

AI Chao1,2;ZHANG Liang2;CHEN Lijuan2;KONG Xiangdong1,2

2017, 28(13):  1542-1547,1553. 

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Combined with the control requirements of hydraulic wind turbine LVRT, in order to realize power rapid adjustment in the processes of LVRT, a control method of LVRT was proposed based on pressure control, namely adding pressure control loop in the original LVRT control loop. Simulations were carried out based on AMESim and MATLAB/Simulink, and control method was verified by the experiments on the 30kV·A hydraulic wind turbine platform. Finally, it shows the proposed control method may realize the fast adjustments of power, and effectively restrain the grid-connected speed impacts, which lays a theoretical foundation for the engineering applications of the hydraulic wind turbines.

Analysis of Main Influence Factors for Slip Ring Combined Rotating Seals Based on 3D Contact

ZHU Xiaohua;JING Yang

2017, 28(13):  1548-1553. 

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The calculation which applied the traditional 2D FEA to generalize the maximum contact stress on a single-contact line of the sealing ring to the whole contact surface was not an accurate algorithm. In view of it, a more accurate and effective contact stress calculation method was proposed based on the 3D simulation model herein. Some different 3D models of the combined sealing ring were established through simulating the actual working conditions, and the method was used to analyze the effective contact stress distribution under the different effect factors of the dynamic seal characteristics, such as the reciprocating motion speeds, the revolving speeds, the medium pressures, the O-ring compressions, the thicknesses of the slip rings and the slottings on the moving contacts. The results show that the slottings on the moving contacts, the thicknesses of the slip ring, the O-ring compressions and the medium pressures have a great influence on the values of effective contact stresses; when the reciprocating motion speeds and the revolving speeds of inner shaft exceed a critical value, they have an influence on the values of the effective contact stresses. The results of this paper provide a reference for the optimization design of slip ring combined seals.

Effects of Diesel Engine Combustion Chamber Matching Parameters on Wall Impinging Spray Characteristics

HAO Jing;HE Bangquan;JIN Chao

2017, 28(13):  1554-1560. 

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The effects of different injector nozzle angles, impinging distances between nozzle and piston top surface, the combustion chamber reentrant radius and convexity angles on spray characteristics after diesel impinging on the combustion chamber walls were investigated through schlieren photography with high speed digital camera. The results show that, for the injectors and pistons in experiments, the proper nozzle angle is as 75°. The mixing of fuel and gas after wall impingements may be promoted by increasing nozzle angle, but too large nozzle angle will increase the risk of fuel impinging on cylinder heads and cylinder liners. The proper impinging distance is as 4.2mm (15°CA before top dead center of compression stroke). Smaller impinging distances may prompt spray droplet collision and bounding in the pit area, and larger impinging distances may hinder the reaction of air in the central region of combustion chambers. In addition, moderate increasing the reentrant radius may promote the mixing of fuel and air, and hence reduce wall wetting in the combustion chambers. Suitable changes of the convexity angles may control the spray diffusion velocities in the center zones of combustion chambers after diesel impingements.

A Novel Weak-coupling Three-translation Parallel Robot Mechanisms and Its Kinematics Analysis

ZHU Wei;DAI Zhiming;LIU Xiaofei;SHEN Huiping;ZHU Xiaorong;HE Baoxiang

2017, 28(13):  1561-1566,1607. 

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A weak-coupling three-translation parallel robot mechanisms was introduced, which was composed of two RRPaR branches and one PPaP. Firstly, the topological structural characteristics and DOF of the mechanism were analyzed through POC(position and orientation characteristics) theory. Secondly, the forward and inverse solutions of the mechanism and the model of velocity and acceleration were derived. Based on the speed Jacobi matrix, the singular positions of the mechanism were analyzed. According to the inverse solution equations and the main constraints of the mechanism, 3D polar boundary search method was used to draw the 3D solid and sectional drawings of the mechanism. The displacement, velocity and acceleration curves obtained from the solid model and mathematical model were basically consistent, which verified the correctness of the motion equations. The mechanism has the advantages of good decoupling performance, simple structure and flexible movement, and has the advantages of partial decoupling and large working spaces in the longitudinal direction of movement, and is suitable for the automatic operations of the automata structures for production lines.

Research on Anti-lock Control of Electro-hydraulic Braking Systems Based on Agents

NIU Limin;ZHOU Yazhou;YANG Hongyuan

2017, 28(13):  1567-1573. 

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For the dynamic response characteristics differences between the motor regenerative braking forces and the hydraulic braking forces and the nonlinear characteristics of the electro-hydraulic braking systems of a battery electric vehicle, an anti-lock braking method was proposed based on Agents for electro-hydraulic braking systems. The motor regenerative braking forces and hydraulic braking forces were distributed according to unilateral concession strategy, competition strategy and cooperative strategy of the Agent based braking systems which was composed of motor Agent, hydraulic braking Agent and ABS Agent. MATLAB/Simulink simulation results show that the front wheel is always ahead of the rear wheel into the lock trends by cooperation among Agents under emergency braking conditions, besides, the Agent based braking system may identify road adhesion accurately to distribute the motor regenerative braking forces and the hydraulic braking forces, braking stability and adaptive ability of the braking systems are promoted.

Multi-objective Collaborative Optimization Method for Mechanical Systems Based on Coupling Analysis and Weighted Satisfaction Degree

MA Jun;WU Liuyang;HE Wenbin;MING Wuyi;CAO Yang

2017, 28(13):  1574-1579. 

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Aiming at the mechanical system optimization result reliability problems caused by design variables coupling relation, based on weighted degree of satisfaction and coupling relation, a mechanical system multi-objective collaborative optimization method was proposed. At first, the coupling model for design variables of mechanical systems was established. And then, using maximum-minimum satisfaction function, considering sub-objective weighting factors, a weighted multi-objective collaborative optimization evaluation function was build. At last, the applications of mechanism-structure multi-objective collaborative optimization design of shield type hydraulic support four-bar prove the method may simplify optimization solution processes and improve the optimization result reliability.

Multi-objective Optimization of Drilling Parameters Based on Pareto Optimality

WANG Kai;WANG Rongpeng;LIU Yu;SONG Guiqiu

2017, 28(13):  1580-1587. 

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A multi-objective optimization of drilling parameters method based on Pereto principle was put forward to optimize horizontal directional drill machine. The optimization model of drill parameters was developed. Modifications were made based on NSGA-Ⅱ due to the deficiency of penalty function method in handling constraints. Therefore, an effective constraints handling strategy utilizing constrained domination principle was introduced. To prevent premature, and accelerate the convergence speed towards optimal Pareto front, the original crowding distance calculation method was modified based on the niche concept. A new adaptive crossover and mutation strategy was put forward. Finally, the modified algorithm was applied to optimization model of drilling parameters which was built based on a coal mine. The results show that the modified algorithm has better convergence and distribution compared with NSGA-Ⅱ and MOPSO when solving test problems. The distribution of solution set is evenly when applying the algorithm to solve optimization model of drilling parameters. It improves the mechanical drilling speed effectively, extentes the life of drilling and decreases the energy ratio of drilling.

Influence Analysis of Structural Parameters on Transfer Characteristics of High-power Permanent Magnet Eddy-current Coupling

LI Yanmin;CAI Shuo;YAO Jianfeng;CHENG Junzhi

2017, 28(13):  1588-1592. 

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The working principles and advantages of permanent magnet eddy-current coupling were introduced for high-power couplings. The magnetic circuit was analyzed,torque of the coupling was calculated by reluctance method, the relationship among structural parameters（the thickness of copper, the thickness of magnetizer, the length of air gap, the thickness of permanent magnet, the number of permanent magnet , relative speed）with torque was obtained. The distribution of the magnetic field and eddy current of the coupling was obtained by Ansoft Maxwell, and the influences of the structural parameters on the torques and axial forces were analyzed.

Reliability Analyses of Gear Transmission Errors of Steering Mechanism of Gun Using MDCRSA

BAI Yali1;ZHANG Yi1;JI Min2;LIU Wenqiang3

2017, 28(13):  1593-1600. 

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To more accurately show the gear transmission errors of the steering mechanism of the gun (GTESMG)，reliability analysis of the GTESMG was carried out from a probabilistic perspective by considering multiple factors and dynamic loads. According to GTESMG's practical applications and theoretical researches，MDCRSA were proposed and the mathematical model of this algorithm was established based on a quadratic function， the detail description of the algorithm was given herein. Then an illustrative real project was used to validate the algorithm in some aspects. The simulation results show that when the design value of GTESMG is as 10′，the reliability is as 0.990，it may meet the requirements of a steering mechanism of gun. Through the comparisons with traditional five analysis methods which were used to evaluate the reliability of gun， the results show that MDCRSA has higher precision and higher efficiency in the reliability analysis of GTESMG. These strengths are likely to become more prominent with increasing simulation times. This research provides an effective and excellent method for the reliability analysis of GTESMG，moreover，the MDCRSA offers a useful insight for designing the reliability of complex gun assemblies.

Remanufacturability Analysis Method for Engine Crankshafts Based on Shaft Center Trajectory

WANG Yulin;HU Jinqiang;KE Qingdi;SONG Shouxu

2017, 28(13):  1601-1607. 

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The uncertainty of the remanufacturing blank qualities was analyzed by the theory of predecisional remanufacturing. A remanufacturability analysis method was presented based on shaft center trajectory. This method extracted the characteristic parameters of the shaft center trajectory of the same engine crankshaft under different wear conditions by using the moment invariant algorithm. The mapping relationship among the characteristic quantity and wear quantity was established to determine the remanufacturability of the engine parts so that the quantification of crankshaft wear under any conditions might be realized. The test results show that the method has high precision for identifying the wear of the crankshafts. It provides a more accurate criterion to find the optimal remanufacturing time in the service period of the crankshaft. At the same time, it provides a solution to the uncertain control problems of remanufacturing blank qualities in the service period with the same batch product failures.

Effects of Mechanical Shocks on Mechanics Properties and Microstructures of High Hardness Laser Cladding

ZHENG Lijuan;FU Yuming;WANG Haoping;QI Tong

2017, 28(13):  1608-1612. 

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In order to reduce the defects of high hardness alloy cladding layers, a new technique for the laser cladding processes was presented. The Ni based, Fe based and Co based three kinds of high hardness alloy cladding layers were prepared on the surfaces of 45 steel. The effects of mechanical shocks on the mechanics properties and microstructures of the cladding layers were compared and analyzed. Research results show that the surface cladding quality of cladding layers may be improved by loading the mechanical shocks, restrian cracks. Mechanical shocks have different impacts on mechanics properties of cladding layers of different materials. Ni65WC specimen may withstand the maximum load increased by 26.2%, but the total elongation is reduced by about 37%, the ratio of the maximum load to the Fe90 sample may be increased to 21.3%, and the total elongation is also approximately improved, the ratio of the maximum load to the Sti6+3%WC sample may be increased to 9.04%, no obvious changes in the total elongation. Mechanical impacts make the microstructure significantly refined, micro hardness improved.

Carbon Emission Assessments of Cutting Processes Driven by 3D Models

ZHANG Lei;JIANG Shixin;ZHANG Weiwei

2017, 28(13):  1613-1619,1627. 

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To solve the problems of product development cycle extended caused by the traditional carbon emission assessment methods, taking shaft cutting processes as the research object, a model of cutting process features of input-process-output were proposed based on the cutting characteristics of typical machine tools. On the basis of analyzing the typical machining characteristics and the factors of carbon emissions, the quantitative formulas of carbon emissions in cutting processes were established and a carbon emission quantitative assessment method of components was proposed based on the Pro/E. Firstly, Pro/E was used to describe the characteristics of components and then extracted the informations of models to calculate the carbon emissions. Secondly, combined with manufacturing process plans and the quantitative formulas of carbon emissions, the carbon emissions of the components were quantified in design phases.


A Method for On-line Differentiating Operations and Energy Consumption States of CNC Machines

WANG Chao;LIU Fei;TUO Junbo

2017, 28(13):  1620-1627. 

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The energy consumption states of machine tools were made up of a series of energy consumption state nodes and processes. There were still some key state nodes might not be differentiated. Based on the systematic analyses of energy consumption states and state nodes in machining processes, a new method for differentiating energy consumption states of CNC machines was proposed to differentiate all kinds of energy consumption states of the machines by synthesizing power informations and CNC system communication informations, which solved differentiating problems, such as distinguishing the cutting starts, over state nodes, and finish machining states et al. The effectiveness and practicality were verified on FANUC CNC machine tools.

Fatigue Properties and Crack Propagation Behaviour of Friction Stir Crack Repaired 2A12 Aluminum Alloy

WANG Lei1,2;SHAN Yongfeng2;REN Jungang3;HUI Li1,2;ZHOU Song2

2017, 28(13):  1628-1632. 

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The friction stir repaired experiments were conducted on pre-cracked 2A12 aluminum alloy plates, and the samples were heat-treated after repairing. The tests of fatigue life and crack propagation were carried out respectively on the repaired specimens and the heat-treated specimens to study the changes of the fatigue performance. The results show that the fatigue life of repaired specimens after heat-treatment increases by 34.79%. Fatigue lives of repaired and heat-treated specimens account for 36.98% and 49.89% of the base metals. The crack growth rates of repaired specimens are higher than that of base metals, and the heat treatment may reduce the crack growth rates of repaired specimens. Fatigue fractures show that crack sources of the base metals mostly initiate at the surfaces or sub-surfaces, but the crack sources of repaired and heat-treated specimens mainly initiate at the boundaries between the repaired zones and base metals, and more than one crack sources are found. There are no cleavage river patterns in repaired zones of repaired specimens, however, the dense and compact fatigue striations may be found, which are similar to the base metals. The repaired specimens are composed of massive little equiaxed dimples in finial fracture zones, while for the repaired specimens after heat-treatments, the dimples are different in sizes but distribute uniformly.

Effects of La2O3 on AZ91D Magnesium Alloy Laser Cladding Layers by Al-Cu Powders

SUN Qi;LI Zhiyong;ZHU Rundong;LIU Chekai

2017, 28(13):  1633-1637. 

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Al-Cu coatings with different additions of La2O3 were cladded on AZ91D magnesium alloys using Nd: YAG laser. Surface morphology, microstructure and phase structure of the cladding layers were investigated with the aid of scanning electron microscope, energy disperse spectroscopy and X-ray diffraction technology. The results show that the grain sizes of the coatings may be refined with the additions of La2O3 in Al-Cu powders and the properties of the cladding layers are improved. Intermetallic compounds Mg17La2 and LaAl3 are generated in the cladding layers. Micro-hardness distributions and friction coefficients of the cladding layers were tested by micro-hardness tester and sliding wear testing machine. Al-Cu coatings with the addition of 1.2% La2O3 have the dramatically refined grains and the highest micro-hardness, which leads to the excellent performance of the cladding layers. The average friction coefficients of the cladding layers with La2O3 additions are lower than that without La2O3 additions or magnesium matrix. Obviously, the friction coefficients of cladding layers may be reduced by the additions of La2O3, thus the wear resistance of the cladding layers is improved.