基于ABAQUS的油气缓冲器静压曲线摩擦力超差分析及排除

针对飞机起落架油气缓冲器制造过程中,出现的静压曲线试验摩擦力超差问题,通过建立缓冲器静压曲线试验受力模型,利用ABAQUS软件对模型进行有限元分析,得到在不同配合尺寸下,缓冲器密封组和导向部分两处配合部位的摩擦力仿真结果,找出了摩擦力超差的原因,并制定了相应的预防措施,经过实践验证,解决静压曲线试验摩擦力超差问题,表明该仿真分析方法可以用于指导飞机起落架油气缓冲器生产制造。

摩擦力判别函数的引入及应用

在涉及摩擦力的力学问题中,首次提出了摩擦力判别函数的概念．该函数的引入完善了库仑摩擦定律的表达式形式．为含有摩擦力、特别是对具有多处摩擦力的问题的清晰分析及解决提供了方便．应用该函数求解摩擦力问题时,无论研究对象处于何种状态、摩擦力的方向均可根据约束的性质作出任意假设,假设正确与否由摩擦力判别函数来确定．举例说明了该函数的适用性．

非临界摩擦力公式及其应用

对物体非临界摩擦力公式F=kf oΔxN,比例系数kf o与静摩擦系数μ之间的关系kf o1/kf o2=μ1/μ2做了进一步讨论,计算有摩擦的超静定问题.

铁路边大直径超深桩的施工质量控制

介绍广州市内环路国际标段A2.7标的桩基施工情况,阐述在地质条件复杂并在铁路边受火车振动外力影响且超深的情况下,完成大直径钻孔灌注桩施工的有效办法。

超薄膜流体摩擦的微观机制

为揭示超薄膜的特性与其微观结构的关系 ,运用分子动力学模拟的方法进行了研究。模拟系统采用云母晶面作为固体壁面 ,十六烷采用珠簧模型。模拟表明 ,超薄膜状态下流体出现了层状的类固态微观结构。采用固液比作为类固态与类液态的比例指标 ,发现等效粘度的上升是薄膜流体类固化造成的。模拟发现了摩擦力的非线性特性 。

Superplasticity of AZ31 magnesium alloy prepared by friction stir processing

Microstructure and tensile behaviors of AZ31 magnesium alloy prepared by friction stir processing（FSP） were investigated.The results show that microstructure of the AZ31 hot-rolled plate with an average grain size of 92.0 μm is refined to 11.4 μm after FSP.The FSP AZ31 alloy exhibits excellent plasticity at elevated temperature,with an elongation to failure of 1050% at 723 K and a strain rate of 5×10-4 s-1.The elongation of the FSP material is 268% at 723 K and 1×10-2 s-1,indicating that high strain rate superplasticity could be achieved.On the other hand,the hot-rolled base material,which has a coarse grain structure,possesses no superplasticity under the experimental conditions.

Forming mechanism of ultrasonic vibration assisted compression

To study the mechanism of ultrasonic vibration assisted forming,the static and vibration assisted compression tests of aluminum 1050 were carried out via a 25 kHz high-frequency ultrasonic vibration device.It is found that vibration reduces the flow resistance and improves the surface topography.The force reduction level is proportional to the ultrasonic vibration amplitude.By using numerical simulation of static and vibration assisted compression tests,the deformation characteristics of material were investigated.Throughout the vibration,the friction between the materials and tools reduces.The stress superposition and friction effects are found to be two major reasons for reducing the force.However,the force reduction because of stress superposition and friction effects is still less than the actual force reduction from the tests,which suggests that softening effect may be one of the other reasons to reduce the force.

Preparation of ultra-fine grain Ni-Al-WC coating with interlocking bonding on austenitic stainless steel by laser clad and friction stir processing

The ultra-fine structured Ni?Al?WC layer with interlocking bonding was fabricated on austenitic stainless steel by combination of laser clad and friction stir processing (FSP). Laser was initially applied to Ni?Al elemental powder preplaced on the austenitic stainless steel substrate to produce a coating for further processing. The as-received coating was subjected to FSP treatment, processed by a rotary tool rod made of WC?Co alloy, to obtain sample for inspection. Microstructure, phase constitutions, hardness and wear property were investigated by methods of scanning electronic microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) microanalysis, and X-ray diffraction (XRD), hardness test alongside with dry sliding wear test. The results show that the severe deformation effect exerted on the specimen resulted in an ultra-fine grain layer of about 100μmin thickness and grain size of 1?2μm. Synergy between introduction of WC particles to the deformation layer and deformation strengthening contributes greatly to the increase in hardness and friction resistance. An interlocking bonding between the coating and matrix which significantly improves bonding strength was formed due to the severe deformation effect.

Application of ultra-smooth composite diamond film coated WC-Co drawing dies under water-lubricating conditions

A specific revised HFCVD apparatus and a novel process combining HFCVD and polishing technique were presented to deposit the micro-and nano-crystalline multilayered ultra-smooth diamond（USCD） film on the interior-hole surface of WC-Co drawing dies with aperture ranging from d1.0 mm to 60 mm.Characterization results indicate that the surface roughness values（Ra） in the entry zone,drawing zone and bearing zone of as-fabricated USCD coated drawing die were measured as low as 25.7,23.3 and 25.5 nm,respectively.Furthermore,the friction properties of USCD films were examined in both dry sliding and water-lubricating conditions,and the results show that the USCD film presents much superior friction properties.Its friction coefficients against ball-bearing steel,copper and silicon nitride balls（d4 mm）,is always lower than that of microcrystalline diamond（MCD） or WC-Co sample,regardless of the lubricating condition.Meanwhile,it still presents competitive wear resistance with the MCD films.Finally,the working lifetime and performance of as-fabricated USCD coated drawing dies were examined under producing low-carbon steel pipes in dry-sliding and water-lubricating conditions.Under the water-lubricating drawing condition,its production significantly increases by about 20 times compared with the conventional WC-Co drawing dies.

DETERMINATION OF PRESSURIZING CURVE AND COMPUTER CONTROL OF THICKNESS THINNING FOR SUPERPLASTIC BULGING

This paper proposes the assumption that the flow with viscous friction is the stretch of part of the sheet that lies along the walls of a die during the process of superplastic bulging according to superplastic flow equation and geometrical model of bulging of a sheet into a long trapezoid groove or truncated cone, by introducing the friction-factor P which describes the friction effect on the process. Also, the paper proposes the method of controlling thickness nonuniformity and develops the equipment which for uniform thickness of bulging, is automatically controlled with a computerl it also analyzes the important innuence of lubrication on thickness distribution of bulging materials. By the assumption, the relationship between bulging pressure and time is obtained in bulging of a sheet into the groove and cone, and p-t curve of multi-mould-cavity complicated bulging is discussed based on the analysis of single-mould-cavity bulging characteristics.

Frictional characteristics of sheet metals with superimposed ultrasonic vibrations

The forming performance of sheet metals in the deep-drawing process with ultrasonic vibrations can be improved by the surface effect between the sheet metal and the die.A sheet metal friction test with ultrasonic vibrations is performed to explore the cause of the surface effect.The frictional characteristics are investigated,and the corresponding friction expressions are established based on the contact mechanics and the elastic–plastic contact model for rough surfaces.Friction is caused by the elastic–plastic deformation of contacting asperities under normal loads.The actual contacting region between two surfaces increases with normal loads,whereas the normal distance decreases.The normal distance between the contacting surfaces is changed,asperities generate a tangential deformation with ultrasonic vibrations,and the friction coefficient is eventually altered.Ultrasonic vibrations are applied on a 40Cr steel punch at the frequency of 20 kHz and the amplitude of 4.2μm.In the friction tests,the punch is perpendicular to the surface of the magnesium alloy AZ31B sheet metals and is sliding with a relative velocity of 1 mm/s.The test results show that the friction coefficient is decreased by approximately 40%and the theoretical values are in accordance with the test values;Ultrasonic vibrations can clearly reduce wear and improve the surface quality of parts.

Effect of ultrasonic assisted friction stir welding on microstructure and mechanical properties of AZ91-C magnesium alloy

The influence of ultrasonic vibrations on microstructure and mechanical properties of the AZ91-C magnesium alloy after ultrasonic assisted friction stir welding(UaFSW)in comparison with conventional friction stir welding(FSW)was investigated.The FSW was applied at the rotational speed of 1400 r/min and welding speed of 40 mm/min and no defects were observed.Using the same welding parameters,the process was carried out with inducing ultrasonic vibrations to the weld line at the amplitude of 15μm.The microstructure of the specimens was observed with optical and scanning electron microscopy.The results indicate that a very fine microstructure is obtained in UaFSW with respect to that of conventional FSW.Moreover,β-Mg17Al12 coarse dendrites are segregated to very fine and partly spherical particles that homogeneously distribute inα-Mg matrix.This remarkably-modified morphology of microstructure attributed to severe plastic deformation comes from ultrasonic vibration and friction stirring effect.Tensile and hardness tests were performed to evaluate the mechanical properties of the welds.According to the results,the vibration greatly improves the mechanical properties of the conventional FSW joint.The tensile strength and hardness are increased from 195 MPa and HV 79 in conventional FSW to 225 MPa and HV 87 in UaFSW,respectively.

Surface wear resistance properties of Ta+N implanted W_(18)Cr_4V high speed steel

High-speed steel W18Cr4V is commonly used in industries such as blade and mould manufacturers because of its high level of hardness and toughness, M-hardness and resistance, Ion implantation is an effective method to improve the wear resistance of W18Cr4V. In our investigation, Ta and Ta＋N ion implantation was performed on W18Cr4V high-speed steel. The surface properties after implantation were evaluated by measuring friction coefficients while the cabonyl phase of the surface was analyzed by X-ray diffraction analysis. It was found that the friction coefficients of the treated samples were much lower. Samples implanted with Ta＋N had a lower friction coefficients than samples implanted only with Ta. This can be attributed to the formation of a new chemical compound, Fe7Ta3, on both surfaces. An even harder chemical compound, FerN, was formed on both surfaces of Ta＋N implanted samples.

Superplastic behavior of friction-stir welded Al-Mg-Sc-Zr alloy in ultrafine-grained condition

The present work was undertaken to improve superplastic ductility of friction-stir welded joints of ultrafine-grained(UFG)Al-Mg-Sc-Zr alloy.In order to suppress the undesirable abnormal grain growth,which typically occurs in the heavily deformed base material,the UFG material was produced at elevated temperature.It was suggested that the new processing route could reduce dislocation density in the UFG structure and thus enhance its thermal stability.It was found,however,that the new approach resulted in a relatively high fraction of low-angle boundaries which,in turn,retarded grain-boundary sliding during subsequent superplastic tests.Therefore,despite the successful inhibition of the abnormal grain growth in the base-material zone,the superplastic deformation was still preferentially concentrated in the fully-recrystallized stir zone of the material.As a result,the maximal elongation-to-failure did not exceed 700%.

Investigation on the factors influencing the thickness distribution of superplastic-formed components

In the superplastic sheet forming process, the uniformity of the sheet's final thickness distribution is vital for ensuring the good mechanical quality of the formed components. The influences of the component shape and the contact friction on the final thickness distribution were investigated in this work by using finite element method on a series of axisymmetric models. It was concluded that shape optimization and friction elimination are required to get uniform thickness distribution, and eventually to improve the mechanical quality of the formed components. The constitutive equation of the Ti-6A1-4V superplastic material was also determined on the basis of experimental data.

高硅铝合金焊接现状及展望

文章主要介绍了几种高硅铝合金的焊接方法,对比了目前常用的各种焊接方法的优缺点,并对未来高铝合金的焊接的方法进行展望。

Ultrasonic Linear Motor with Anisotropic Composite

An idea to make up the vibrating body of ultrasonic motor with anisotropic composite is proposed and a linear piezoelectric motor is developed in this paper. Relative problems such as actuating mechanism, resonant frequency are discussed theoretically. According to the feature that impulse exists between the elastic body of composite ultrasonic linear motor and the base, an impulse analysis is presented to calculate the motor′s friction driving force and frictional conversion efficiency. The impulse analysis essentially explains the reason why the ultrasonic motor has great driving force, and can be applied to analyze the non-linear ultrasonic motor.

Underwater friction stir welding of ultrafine grained 2017 aluminum alloy

2017 aluminum alloy plates with an ultrafine grained （UFG） structure were produced by equal channel angular processing （ECAP） and then were joined by underwater friction stir welding （underwater FSW）. X-ray diffractometer （XRD）, transmission electron microscope （TEM）, scanning electron microscope （SEM） and microhardness tester were adopted to investigate the microstructural and mechanical characteristics of the FSW joint. The results indicate that an ultrafine grained microstructure with the mean grain size of-0.7 Ixm is obtained in the weld nugget by using water cooling. However, The FSW joint exhibits softening compared with the ultrafine grained based material and the heat affected zone （HAZ） has the lowest hardness owing to the coarsening of the strengthening precipitates.

Saint-Venant Fractional Equation and Hydraulic Gradient

The overall objectives to support analytically the mathematical background of hydraulics, linking the Navier-Stokes with hydraulic formulas, which origin is experimental but have wide and varied application. This, leads us study the inverse problem of the coefficients of differential equations, such as equations of the porous medium, Saint-Venant, and Reynolds, and accordingly with the order of derivatives. The research led us to see that the classic version suffers from a parameter that reflects the fractal and non-local character of the viscous interaction. Motivated by the concept of spatial occupancy rate, the authors set forth Navier-Stokes＇s fractional equation and the authors obtain the fractional Saint-Venant. In particular, the hydraulic gradient, or friction, is conceived as a fractional derivative of velocity. The friction factor is described as a linear operator acting on speed, so that the information it contains is transferred to the order of the derivative, so that the same is linearly related to the exponent of the friction factor. It states Darcy＇s non-linear law. The authors take a previous result that describes the nonlinear flow law with a leading term that contains a hyper-geometric function, whose parameters depend on the exponent of the friction factor and the exponent of the hydraulic radius. It searches the various laws of flow according to the best known laws of hydraulic resistance, such as Chezy and Manning.

Microstructural evolution and hot tensile behavior of Mg−3Zn−0.5Zr alloy subjected to multi-pass friction stir processing

The microstructures and hot tensile behaviors of ZK30 alloys subjected to single-and multi-pass friction stir processing(FSP)were systematically investigated.Following single-pass FSP(S-FSP),coarse grains underwent refinement to 1−2μm,with a distinct basal texture emerging in the stir zone(SZ).Additionally,second-phase particles were fragmented,dispersed,and partially dissolved.Multi-pass FSP(M-FSP)further enhanced the homogeneity of the microstructure,reduced texture intensity differences,and decreased the fraction of second-phase particles by 50%.Both S-FSP and M-FSP SZs demonstrated superplasticity at strain rates below 1×10^(−3)s^(−1)and at temperatures of 250−350℃.The S-FSP SZ exhibited an elongation of 390%at 250℃and 1×10^(−4)s^(−1),while the M-FSP SZ achieved an elongation of 406%at 350℃and 1×10^(−3)s^(−1).The superplastic deformation of SZ was co-dominated by grain boundary sliding(GBS)and the solute-drag mechanism in S-FSP and mainly by GBS in M-FSP.