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The tooth surface friction has an important impact on the tooth surface contact stress and the tooth surface contact fatigue life. In the estimation of the contact fatigue life of the tooth surface, the influence of the friction force of the tooth surface is often ignored, which is not conducive to the accurate prediction of the contact fatigue life of the tooth surface. In order to accurately predict the contact fatigue life of the tooth surface, the R-S-N curves are fitted based on the three-parameter Weibull distribution and the nominal stress method according to the tooth surface contact fatigue test data of 18CrNiMo7-6 gear material. By calculating the contact stress on the tooth surface, the time-varying friction factor is introduced, and the influence of the time-varying friction factor on the contact fatigue life of the tooth surface is analyzed. Finally, the tooth surface contact fatigue test is used to verify the validity. The results show that the contact fatigue limit of tooth surface estimated by the traditional nominal stress method is large due to the influence of the time-varying friction factor, and the influence of the friction factor on contact fatigue life of tooth surfaces decreases with the increase of stress.

BackgroundIn the injection and extraction Kicker power supply system of High Intensity Heavy-ion Accelerator Facility (HIAF), the transmission efficiency and stability of the control event directly affect the working performance of the power supply.PurposeThis study aims to develop the Kicker power supply communication system for precise control of hundreds of IGBT (insulated gate bipolar transistor) switches in the bipolar solid-state PFN-Marx generator of HIAF-Kicker power supply, hence to provide a gigabit readback path for the waveform data obtained by the high-speed acquisition system.MethodsBased on a digital controller with kernel Xilinx Kintex-7 FPGA (field programmable gate array) chip, the UDP (user datagram protocol) stack described by hardware language as the core of data communication was employed by the system. The scheme of intercepting waveform pulse and its front and back parts for transmission was adopted to improve the communication efficiency and save the system resources. The optical control signals required by the multi-channel power supply were provided by the controller via the connecting optical fiber daughter boards. The shielding case was added to reduce electromagnetic interference and enhance the stability of data transmission.ResultsThe data transmission test shows that the system meets the precise control demand of hundreds of IGBT switches, and the data transmit speed satisfies the needs of gigabit data readback.ConclusionsThe performance of designed system meets the communication requirements of Kicker power supply.

the formation mechanism of micro-pitting had been described in this paper,the action relationships of various influencing factors had also been analyzed,and the three main action mechanisms of local contact stress,film thickness ratio of lubricating oil and micro mechanical properties for materials had been regularized.Based on elastohydrodynamic lubrication theory and previous test results for Newtonian fluids,the reasonable calculation method of film thickness for lubricating oils had been determined.Through comparative calculations,the specific effects of oil types,lubricating oil temperatures,transmission torques and gear speeds on the oil film thickness had been analyzed.Combined with the micro-pitting design of gear transmission,feasible ideas and operational methods for lubrication improvements and optimizations had also been given.Finally,through the experimental designs,the correctness of the theoretical analysis had been verified,and the basic data for the anti micro-pitting design of the combination for gears of 18 CrNiMo7-6（material）+ISO-VG220（Lubricating oil） had been goted.

The gearbox of rack test for the Three Gorges ship lift is low speed heavy duty four stages transmission,and need frequent fast reversing operation in the process of test,due to the influence of the gear meshing backlash,elastic torsional deformation of shaft and elastic deformation of gear tooth and other factors,the operation performance of gearbox will be changed during reversing process,especially the output speed and torque. In order to analyze the influence on the transmission performance of gearbox,the calculation models of the influence of the gear meshing backlash and the elastic torsional deformation of the shaft on the rotational speed are setup respectively,the output speed of the gearbox in the reversing process is calculated and compared with the output speed of gearbox measured by experiment,which verifies the accuracy of the calculation model and the test data.

The surface roughness of traditional grinding gear has the typical anisotropy characteristic in microcosmic direction. After the barrel finishing of the tooth surface,the micro-surface is isotropic. According to the Hertz theory and the theory of contact fractal strength of gears,the influence of microstructure contact stress calculation was discussed. The contact stress limit of the traditional grinding gear and the barrel finishing gear was obtained by gear contact fatigue strength comparison test. The results show that the isotropic finishing process can make the micro-texture of the tooth surface tend to be isotropic,and improve the contact fatigue strength of the gears,which provides a reference for the life design and reliability design of the gear.

The background and necessity about the construction of the public service platform for gear strength and reliability test technology of strengthening foundation engineering project of the Ministry of Industry and Information Technology are briefly introduced. The function of eight sub- platforms are outlined. The key generic technology research and demonstration application progress are introduced. It has guiding significance for the design,manufacture,testing etc. of the gear production.

The frequency response analysis of gearbox housing of large- sized bridge crane is carried out under the excitation frequency,and the displacement response curves of every bearing bore on the housing and the greatest response position of the housing are obtained. The results show that when the meshing frequencies under the rated speed,the natural frequency of the housing can be avoided and it should not cause the resonance.

The hole defects can easily occur in magnesium alloy castings that are prepared by low pressure lost foam casting (LP-LFC) process when the process parameters such as vacuum, pouring temperature and filling velocity are not properly selected. In this study, the forming mechanism of the hole defects in AZ91D magnesium castings by LP-LFC process was investigated. The shape, location and surface appearance of the hole defects were observed using optical microscopy and scanning electron microscopy, and the chemical composition on the surface of the holes was analyzed using energy spectrometer. The result indicates that there are two types of hole defects, i.e., the pyrolysis products related hole defects, including concentrative hole and blow hole defects, and slag related hole defects. The concentrative hole and the blow-hole defects were formed either by the liquid-EPS degradation products entrapped in the molten metal under the condition that the pouring temperature is equal to or lower than 730 ℃, or by the hindered transport of EPS pyrolysis products. Some irregular shape hole defects were caused by slag or by coating slough entrapment when the pouring temperature is equal to 750 ℃ and the filling velocity is equal to or greater than 100 mm·s-1. To reduce or eliminate the hole defects, the vacuum and filling velocity must be properly chosen to ensure that the metal front profile exhibits convex shape and in laminar current state, and the pouring temperature should be just high enough to ensure that the molten melt has adequate heat energy to complete the foam pyrolysis and to fully occupy the mould. For AZ91D magnesium castings in this study, the parameters should be 730 ℃ pouring temperature, 0.02-0.03 MPa vacuum and 80 mm·s-1 filling velocity.

Objective: To explore application value of iterative metal artifact reduction (iMAR) algorithm in reducing the artifacts from abdominal metal implants. Methods: The CT images of 32 patients with abdominal metal implants were reconstructed with both iMAR and filtered back projection (FBP) algorithm, respectively. Subjective image quality was assessed by two independent radiologists. Objective image quality indic including signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and artifact index (AI) were calculated by the noise values measured at the most severe level of artifacts near metal implants on images of both iMAR and FBP algorithms. Difference in subjective and objective image quality assessment between iMAR and FBP algorithms was compared. Results: The overall subjective quality score of iMAR images was significantly higher than FBP images (3.656±0.475 vs. 2.156±0.618, P