Experimental Study on the Reduction Effect of Pit Texture on Disassembly Damage for Interference Fit

After remanufacturing disassembly,several kinds of friction damages can be found on the mating surface of interference fit.These damages should be repaired and the cost is closely related to the severity of damages.Inspired by the excellent performance of surface texture in wear reduction,5 shapes of pit array textures are added to the specimens’surface to study their reduction effect of disassembly damage for interference fit.The results of disassembly experiments show that the order of influence of texture parameters on disassembly damage is as follows:equivalent circle diameter of single texture,texture shape and texture surface density.The influence of equivalent circle diameter of single texture and texture shape are obviously more significant than that of texture surface density.The circular texture with a surface density of 30%and a diameter of 100μm shows an excellent disassembly damage reduction effect because of its perfect ability of abrasive particle collection.And the probability of disassembly damage formation and evolution is also relatively small on this kind of textured surface.Besides,the load-carrying capacity of interference fit with the excellent texture is confirmed by load-carrying capacity experiments.The results show that the load-carrying capacity of the excellent texture surface is increased about 40%compared with that of without texture.This research provides a potential approach to reduce disassembly damage for interference fit.

High-speed train cooperativecontrol based on fractional-ordersliding mode adaptive algorithm

Purpose–This study aims to propose an adaptive fractional-order sliding mode controller to solve the problem of train speed tracking control and position interval control under disturbance environment in moving block system,so as to improve the tracking efficiency and collision avoidance performance.Design/methodology/approach–The mathematical model of information interaction between trains is established based on algebraic graph theory,so that the train can obtain the state information of adjacent trains,and then realize the distributed cooperative control of each train.In the controller design,the sliding mode control and fractional calculus are combined to avoid the discontinuous switching phenomenon,so as to suppress the chattering of sliding mode control,and a parameter adaptive law is constructed to approximate the time-varying operating resistance coefficient.Findings–The simulation results show that compared with proportional integral derivative(PID)control and ordinary sliding mode control,the control accuracy of the proposed algorithm in terms of speed is,respectively,improved by 25%and 75%.The error frequency and fluctuation range of the proposed algorithm are reduced in the position error control,the error value tends to 0,and the operation trend tends to be consistent.Therefore,the control method can improve the control accuracy of the system and prove that it has strong immunity.Originality/value–The algorithm can reduce the influence of external interference in the actual operating environment,realize efficient and stable tracking of trains,and ensure the safety of train control.

Structural Design of High-precision Positioning System in Weak Signal Environment Based on UWB and IMU Fusion

Aiming at the problem that indoor positioning technology based on wireless ultra-wideband pulse technology is susceptible to non-line-of-sight effects and multipath effects in confined spaces and weak signal environments,a high-precision positioning system based on UWB and IMU in a confined environment is designed.The STM32 chip is used as the main control,and the data information of IMU and UWB is fused by the fusion filtering algorithm.Finally,the real-time information of the positioning is transmitted to the host computer and the cloud.The experimental results show that the positioning accuracy and positioning stability of the system have been improved in the non-line-of-sight case of closed environment.The system has high positioning accuracy in a closed environment,and the components used are consumer-grade,which has strong practicability.

Discharge Characteristic of Micro-Arc Oxidation on Aluminum Alloy under the Changing Electrolyte Temperature

The electrolyte temperature has a great influence on the performance of the coating prepared by micro-arc oxidation (MAO). The behavior of MAO discharge in the changing electrolyte temperature has been investigated. Compared to constant electrolyte temperature in conventional MAO process, the process has different discharge characteristics under the changing electrolyte temperature. The amplitude of pulse voltage was detected to study the change of discharge characteristic under the constant-current control of MAO power supply. Three successive discharge stages were differentiated by the variable the pulse voltage versus process time. Since there were significant changes in the sound, the sound signals were acquired and the audio analysis was used to describe the changing of the MAO discharge at different stages. Optical emission spectroscopy (OES) was employed in situ to unveil how the micro-discharge changed with the temperature increasing. Scanning electron microscopy (SEM) was used to characterize the morphology of the coatings on 6N01 aluminum alloy prepared by normal process with the constant-temperature control of the MAO electrolyte and by the process under the changing electrolyte temperature. A mode of film growth and micro-discharge was given to describe the effects of the changing electrolyte temperature in the whole MAO process.

Research of Surface Coating Influence on Loose Life of Bolt

The rust⁃proof ability relate to the reliability of bolt connection,and the painting is the most simple and effective rust⁃proof method in industry.Because of lacking general standard,there are different coating thicknesses painted on the surface of workpieces,which influences the loose life of connecting bolt.For the longer loose life,Three kinds of applied coatings(primer coating,primer+top⁃coat coating,primer+intermediate⁃coat+top⁃coat coating)in industry are tested in the experiment,and the best coating is found.All the conclusions gotten by analyzing the testing phenomenon of every coating shown in experiment,have profound meaning for practical industry application.

Mechanical Properties of Resistance Spot Welded Components of High Strength Austenitic Stainless Steel

Resistance multi-spot welding （MSW） in column, triangle and tetragonal symmetry arrangements was prepared using cold-rolled 301L high-strength sheets, and their static and fatigue properties were in- vestigated. The effects of spot welds on the fracture strengths and fatigue limits were discussed. The results show that the static strengths can be estimated using an inherent linear relationship formula of the load versus the welding area. It was based on the 28%-33% volume fraction of α′ martensite induced at the interfacial spot weld fracture because of the failure deformation. The fatigue limits of the MSW nonlin- early increase with the number of spot welds. The arrangement of spot welds in the MSW significantly affects the average fatigue limit of each spot weld; its 26% maximum reduction occurred in the triangle, and the interaction stress between spot welds led to its 18% reduction in the tetragonal symmetry. The calculated fatigue stress of all MSW loadings with their mean fatigue limits was 230-270 MPa.