Zhong HAN
,
Yusheng ZHANG
材料科学技术（英）
Nanostructured (ns) materials, i.e., polycrystalline materials with grain sizes in the nanometer regime (typically below 100 nm), have drawn considerable attention in the past decades due to their unique properties such as high strength and hardness. Wear resistance of ns materials, one of the most important properties for engineering materials, has been extensively investigated in the past decades. Obvious differences have been identified in friction and wear behaviors between the ns materials and their corresponding coarse-grained (cg) counterparts, consistently correlating with their unique structure characteristics and mechanical properties. On the other hand, the superior tribological properties of ns materials illustrate their potential applications under contact loads. The present overview will summarize the important progresses achieved on friction and wear behaviors of ns metallic materials, including ultrafine-grained (ufg) materials in recent years. Tribological properties and effects on friction and wear behaviors of ns materials will be discussed under different wear conditions including abrasive wear, sliding wear, and fretting wear. Their correlations with mechanical properties will be analyzed. Perspectives on development of this field will be highlighted as well.
关键词:
Nanostructured metals
,
metals
,
Friction
,
Wear
,
Mech
刘小明
,
由小川
,
柳占立
,
庄茁
金属学报
利用分子动力学方法模拟了刚性金刚石压头在Ni单晶体上的滑动过程, 讨论了压入深度对
摩擦力的影响(压入深度对滑动过程中压头下方的微结构演化(能否发射位错环)有很大影响). 结
合摩擦过程中的塑性行为和能量耗散机制, 解释了产生摩擦力锯齿形曲线的原因, 证实了位错的形
核及湮灭是黏--滑机制的原因之一. 不同滑动速度对摩擦力影响的模拟表明, 压头的滑动速度决定
了压头下方位错环的运动和演化形式: 在高速滑动下, 形成的位错环依次沿着滑移面很快向Ni单晶
基体内扩展; 在低速滑动下, 压头下方产生的位错环互相发生作用, 在材料的亚表面形成较低能量的
大位错环, 由此产生的塑性变形主要集中在材料的亚表面.
关键词:
纳米尺度
,
Friction
,
Molecular dymamics
,
Stick-slip mechanism
,
Dislocation loop
Mohamed KHARRAT
,
Maher DAMMAK
,
Amine CHARFI
材料科学技术（英）
Fibre-matrix interface is known to have contribution to the mechanical performance of fibre-reinforced composite by its potential for load transfer between the fibre and the matrix. Such load transfer is of great importance in dentistry when a post is used for fixing a ceramic crown on the tooth. In this study, a pull-out test was carried out to analyse the interfacial properties of a steel fibre embedded in a polyester and epoxy matrices. It was found that the fibre-matrix interface is debonded on the whole embedded length when the fibre stress reached the debonding stress. Then, the fibre stress fell down to the initial extraction stress required to pulling out the debonded fibre from the matrix. Both debonding stress and initial extraction stress initiated a linear increase with the implantation length after the debonding stress reached horizontal asymptotes. To analyse the fibre-matrix load transfer before debonding, an analytical shear-lag model was adopted to in this test conditions. Fitting the experimental results with the analytical model provided the interfacial shear strength. By considering the Coulomb friction at the fibre-matrix interface during the fibre extraction process, an analytical model which considers Poisson's effects on both fibre and matrix, was developed. In this model, knowledge of the initial extraction stress of the fibre provides the residual normal stress at the fibre-matrix interface.
关键词:
Fibre
,
null
,
null
,
null
,
null
,
null
,
null
桑瑞鹏
,
周晖
,
温庆平
,
金俨
,
郑军
宇航材料工艺
doi:10.3969/j.issn.1007-2330.2009.06.013
模拟月球表面极端高低温环境,对空间飞行器机构活动部件常用固体自润滑材料进行极端温度环境存贮实验.通过拉伸强度、压缩强度、弯曲强度、冲击强度、摩擦磨损等性能研究,评价固体自润滑材料在月面极端高低温环境下的生存适应能力.结果表明,两种典型空间用固体自润滑材料模拟三个月球日经历极端温度环境存储实验后,各项性能都未发生明显变化.
关键词:
润滑
,
月面
,
极端温度
,
力学性能
,
摩擦
叶呈武
,
张绪虎
,
张艳秋
,
高阳
,
丁水
宇航材料工艺
使用ANSYS软件对重载条件下服役的自润滑推力轴承进行了摩擦性能模拟,并对计算进行了地面试验验证和研究.结果表明:小于0.4mm厚的自润滑轴衬有利于减少轴承接触面的应力,降低摩擦因数,减少轴衬的厚度,提高轴衬材料的压缩强度、热导率等有利于降低轴衬材料的工作温度,提高轴衬的使用寿命.Nomex/PTFE复合自润滑材料的摩擦因数随载荷的增加而稳定降低,在145 MPa的重载荷下出现0.017极低摩擦因数.
关键词:
摩擦
,
自润滑材料
,
推力轴承
,
数值模拟
Jihui WANG
,
E.Wieers
,
L.M.Stals
,
J.P.Celis
材料科学技术（英）
MoSx coatings were prepared by bipolar-pulse DC unbalanced magnetron-sputtering system with the variation of coating thickness at different Ar pressures. The composition and surface morphology were determined by using energy dispersive X-ray and scanning electron microscopy; the structural characterisation was analyzed by X-ray diffraction. The friction and wear properties were investigated by fretting tests in air with less than 10% and 50% relative humidity.At 0.40 Pa pressure, (002) basal plane orientation was formed throughout the coatings. At 0.88 Pa and 1.60 Pa pressures, (002) basal plane orientation was only noticed in the first stage of coating growth (around 0.20 µm in thickness), and then edge orientations with their basal planes perpendicular to the surface would be evolved in the coatings. Humidity has a minor influence on the coatings that have (002) basal plane orientation, whereas the tribological properties of MoSx coatings with edge orientations are greatly affected by humidity. The mechanisms of coating growth and friction and wear processes are discussed.
关键词:
MoSx coating
,
null
,
null
,
null
Mustafa BOZ
,
Adem KURT
材料科学技术（英）
Friction-wear properties of the ZrSiO4 reinforced samples were measured and compared with those of plain bronze based ones. For this purpose, density, hardness, friction coefficient wear behaviour of the samples were tested. Microstructures of samples before and after sintering and worn surfaces were also investigated by scanning electron microscopy (SEM), and the wear types were determined. The optimum friction-wear behaviour was obtained in the sample compacted at 500 MPa and sintered at 820oC. Density of the final samples decreased with increasing the amount of reinforcing elements (ZrSiO4) before pre-sintering. However after sintering, there is no change in density of the samples including reinforcing elements (ZrSiO4). With increasing friction surface temperature, a reduction in the friction coefficient of the samples was observed. However, the highest reductions in the friction coefficients were observed in the as-received samples containing 0, 5% reinforced ZrSiO4. The SEM images of the sample indicated that while bronze-based break lining material without ZrSiO4showed abrasive wear behaviour, increasing the amount of ZrSiO4resulted a change in abrasive to adhesive wear mechanism. All samples exhibited friction-wear values, which were within the values shown in SAE-J661 standard. With increasing the amount of reinforcing ZrSiO4, wear resistance of the samples was increased. However samples reinforced with 5% and 6% ZrSiO4showed the best results.
关键词:
Friction materials
,
null
,
null
,
null
,
null
He YANG
材料科学技术（英）
Cold ring rolling is an advanced but complex metal forming process under coupled effects with multi-factors, such as geometry sizes of rolls and ring blank, material, forming process parameters and friction, etc. Among these factors, friction between rolls and ring blank plays an important role in keeping the stable forming of cold ring rolling. An analytical method was firstly presented for proximately determining the critical friction coefficient of stable forming and then a method was proposed to determine the critical friction coefficient by combining analytical method with numerical simulation. And the influence of friction coefficient on the quality of end-plane and side spread of ring, rolling force, rolling moment and metal flow characteristic in the cold ring rolling process have been explored using the three dimensional (3D) numerical simulation based on the elastic-plastic dynamic finite element method (FEM) under the ABAQUS software environment, and the results show that increasing the friction on the contact surfaces between rolls and ring blank is useful not only for improving the stability of cold ring rolling but also for improving the geometry and dimension precision of deformed ring.
关键词:
Cold ring rolling
,
null
,
null
,
null
Hongwu ZHANG
,
Zhao ZHANG
材料科学技术（英）
Rate-dependent constitutive model was used to simulate the friction stir welding process. The effect of the viscosity coefficient and the process parameters on the material behaviors and the stress distributions around the pin were studied. Results indicate that the stress in front of the pin is larger than that behind the pin. The difference between the radial/circumferential stress in front of the pin and that behind it becomes smaller when the material gets closer to the top surface. This difference increases with increasing the viscosity coefficient and becomes smaller when the welding speed decreases. The variation of the angular velocity does not significantly affect the difference.
关键词:
Friction stir welding
,
stir
,
welding
,
Finite
,
element
,
met
