汽车镀锌钢板泥浆附着的腐蚀行为与机理

为了提高汽车用热浸镀锌钢板的质量,防止泥浆附着腐蚀,延长其服役寿命,对镀锌钢板和基材进行了泥浆附着试验.采用SEM观察微观腐蚀形貌,以XRD分析产物成分,通过阻抗谱分析等技术研究了其腐蚀行为和腐蚀机理.结果表明:腐蚀初期,腐蚀速度逐渐加快,锈层厚度不断增大,锈层成分和厚度对镀锌钢板的腐蚀速度影响很大;镀锌钢板、基材的锈层电阻和电荷转移电阻都呈现先增后减的变化趋势;泥浆中的溶氧量和较高的Cl-含量对腐蚀速度都有很大的影响.     

滑移隔震支座的试验研究及力学模型

通过滑移隔震支座的试验研究,探讨了静摩擦系数、动摩擦系数的变化趋势及滑动摩擦系数的影响因素,研究滑移隔震支座的恢复力特性。试验研究表明:静摩擦系数和动摩擦系数都与竖向压力的大小有关,随着竖向压力的增大而逐渐减小;滑动摩擦系数随滑动速度的增大而增大;滑动摩擦系数与频率有关,总的趋势是随着激励频率的增大,摩擦系数增大;滑移隔震支座加硅脂润滑后摩擦系数明显降低;高频激励下摩擦滑移隔震支座的恢复力模型宜采用理想弹塑性模型,低频激励下宜采用刚塑性模型。最后,指出已有摩擦力模型存在的缺陷,并根据试验结果建议了一个新的摩擦力模型,分析表明该模型与试验数据拟合较好。     

影响热浸镀锌钢板锌花形成的因素

使用低碳钢板进行热浸镀锌试验,利用扫描电镜观察了含铅镀锌层的微观形貌与组织,根据Zn-Pb相图,对含铅镀层的凝固过程进行了分析.通过试验研究了冷却速度对锌花大小的影响,当冷却速度在0～25 K/s时,随冷却速度增大,锌花尺寸从10 mm逐渐减小到1 mm,并分析其原因,得出:铅影响锌结晶过程和锌花形态,锌枝晶生长方向取决于形核位置,冷却速度对锌花尺寸有显著影响,锌花尺寸与冷却速度呈负指数增长的关系.     

铜基粉末冶金列车闸瓦材料的摩擦磨损性能研究

在MM-1000型摩擦试验机上测试了铜基粉末冶金列车闸瓦材料在不同制动条件下的摩擦磨损性能.试验证明:该材料具有较高的摩擦系数0.43～O.46,但超过一定制动速度时摩擦系数迅速下降,材料磨损量在制动速度为3000r/min时最小,低速和高速制动时磨损量相对较大;制动速度一定时,随制动压力增大,材料的摩擦系数减小,压力增大到一定值时摩擦系数趋于稳定,制动压力对材料磨损量的影响较小;该材料低速制动下的磨损机理主要为疲劳磨损,高速制动时主要为磨粒磨损和氧化磨损.     

三维针刺C/SiC刹车材料的摩擦磨损性能

通过化学气相渗透法(CVI)结合反应熔体浸渗法(RMI)制备了三维针刺,C/SiC刹车材料 , 利用 MM21000型摩擦磨损试验机系统研究了C/SiC刹车材料的摩擦磨损性能,采用光学显微镜和扫描电子显微镜分别对摩擦表面和磨屑形貌进行了观察。结果表明:干态刹车条件下,当初始刹车速度相同时,摩擦系数随着刹车压力的升高而逐渐降低;当刹车压力相同时,摩擦系数随着初始刹车速度的增加先升高后降低。湿态摩擦性能衰减小(衰减约8 %) 、恢复快;静态摩擦系数高(为0. 56～0. 61),摩擦系数随着初始刹车温度的升高而显著降低。当刹车压力相同时,磨损率随着初始刹车速度的增加而增大;当初始刹车速度大于20 m/s时,刹车压力的增大使磨损率显著增加。      

45CrNi摩擦磨损性能研究

利用销盘摩擦磨损试验机,考察了干滑动摩擦条件下滑动速度、接触压力对45CrNi摩擦副摩擦磨损性能的影响.研究结果表明:在相同的试验条件下,530 ℃回火销的磨损率、摩擦系数较大;磨损率与硬度并不成绝对的反比关系.材料的磨损率随着接触压力、滑动速度的增加而增大;摩擦系数随着接触压力的增大而减小.     

汽车用合金化热镀锌钢板摩擦特性研究

采用平板滑动摩擦实验研究了接触压力、滑动速度、润滑油黏度和温度对合金化热镀锌钢板摩擦系数的影响,基于粘着理论深入分析了合金化热镀锌钢板摩擦系数变化的原因,并利用扫描电镜对比分析了不同摩擦条件下的镀层磨损,进一步验证了合金化热镀锌板摩擦系数的变化规律.研究表明:镀锌板摩擦系数随着接触压力、滑动速度和润滑油黏度升高均有不同程度降低;摩擦系数随着温度的增加而快速升高.摩擦系数与接触压力的1-n次方成反比;在接触压力恒定的情况下,摩擦系数的大小由模具和镀层直接接触部分占总接触面积百分比α决定;α随接触压力、温度的增加而升高,随滑动速度、润滑油黏度的增加而降低.     

电铸制备铜-石墨复合材料的研究

在酸性硫酸铜溶液中采用电铸技术制备了铜-石墨复合材料.表面活性剂、微粒浓度、电流密度和搅拌速度等工艺条件对微粒含量具有不同的影响.非离子表面活性剂对微粒共沉积具有较好的效果;随着微粒浓度增大,微粒含量也逐渐增大,最后趋于稳定值;电流密度增大使微粒含量降低;搅拌速度增大时微粒含量存在最大值.铜-石墨复合材料的硬度和摩擦系数随着微粒含量增大而减小,但是磨损量先是减小而后增大.摩擦过程中纯铜发生粘着磨损,铜-石墨复合材料却表现为剥层磨损.     

滑动速度对碳纳米管-银-石墨复合材料电磨损性能的影响

采用粉末冶金法制备了碳纳米管-银-石墨复合材料,研究了圆周速度对复合材料摩擦系数、磨损量的影响。结果表明,当压力一定时,随着速度的加快,机械磨损的摩擦系数减小,而电磨损的摩擦系数增大;复合材料的电磨损量远远大于机械磨损的磨损量,电磨损时磨损量在V=10m/s处出现最小值,而机械磨损的磨损量随速度的加快而减小。     

水环境下两种不锈钢静、动摩擦系数的试验研究

目前,有关摩擦系数特别是静摩擦系数的研究是比较薄弱的领域。研发出线接触方式下的静摩擦系数测试装置,研究了F6NM马氏体不锈钢与SA-336 Type304H不锈钢摩擦副在不同温度、应力、粗糙度水环境下的静摩擦系数和动摩擦系数。研究发现:随着温度的升高,静、动摩擦系数均增大;静摩擦系数随着应力的增大而增大,而动摩擦系数随着应力的增大有所波动。粗糙度对静、动摩擦系数的影响与压力与静、动摩擦系数的影响相同。     

基板强度对汽车用合金化热镀锌板摩擦因数的影响

采用平板滑动摩擦实验研究不同接触压力下合金化热镀锌钢板的摩擦因数。结果表明:在相同的变形条件下,低强度基板加工硬化较强烈;在相同接触压力下,镀锌板基板强度越高,摩擦因数越低;随着接触压力增大,低强度镀锌板摩擦因数由0.154降为0.136,高强度镀锌板摩擦因数由0.140降至0.135;随着接触压力的进一步增加,摩擦因数降低的趋势变缓。基于黏着理论深入分析了基板强度影响摩擦因数的原因,得出如下结论:摩擦因数主要由α值(总的实际接触面积中模具和镀层直接接触部分百分比)和基板表面显微硬度决定;基板强度是决定基板表面显微硬度和α值的主要因素;随着接触压力增大,不同的加工硬化率会使不同强度基板的表面显微硬度逐渐接近,致使α差异减小,最终使基板强度对镀锌板摩擦因数影响减弱。     

Contact and frictional behavior of rough surfaces using molecular dynamics combined with fractal theory

The microcontact behavior of a copper asperity on a diamond plate was carried out using a molecular dynamics (MD) simulation with the parallel algorithms atom decomposition method. The results show that the dynamic frictional force had an oscillated behavior when the flat diamond plane slipped through the copper asperity. The contact load, contact area, dynamic frictional force, and dynamic frictional coefficient increased as the contact interference increased at a constant loading velocity. The dynamic frictional force and dynamic frictional coefficient increased as the sliding velocity increased. Furthermore, the microcontact behavior can be evaluated between a rigid smooth flat plane and a rigid smooth hemisphere to a deformable rough flat plane by combining the deformed behavior of the asperity obtained from MD results and the fractal and statistic parameters.     

Influence of boron doping on mechanical and tribological properties in multilayer CVD-diamond coating systems

Titanium alloy (Ti6Al4V) substrates were deposited with smooth multilayer coatings, by hot filament chemical vapour deposition technique. The effect of boron doping on lattice parameter, residual stresses, hardness and coefficient of friction in multilayer-diamond coating system was studied. The frictional behaviour of the coatings was studied using a ball-on-disc micro-tribometer by sliding the coated samples of titanium alloy (Ti6Al4V) substrates against alumina (Al₂O₃) balls, and increasing normal load from 1 to 10 N. The average friction coefficient decreased from 0.36 to 0.29 for undoped multilayer-diamond coating system and from 0.33 to 0.18 for boron- doped (BD) multilayer-diamond coating system. The average indentation depths for undoped and BD multilayer- diamond coating systems were found to be equal to ～>58 and ～65 nm, respectively, and their hardness values were 60 and 55 GPa, respectively.     

Finger pad friction and its role in grip and touch

Many aspects of both grip function and tactile perception depend on complex frictional interactions occurring in the contact zone of the finger pad, which is the subject of the current review. While it is well established that friction plays a crucial role in grip function, its exact contribution for discriminatory touch involving the sliding of a finger pad is more elusive. For texture discrimination, it is clear that vibrotaction plays an important role in the discriminatory mechanisms. Among other factors, friction impacts the nature of the vibrations generated by the relative movement of the fingertip skin against a probed object. Friction also has a major influence on the perceived tactile pleasantness of a surface. The contact mechanics of a finger pad is governed by the fingerprint ridges and the sweat that is exuded from pores located on these ridges. Counterintuitively, the coefficient of friction can increase by an order of magnitude in a period of tens of seconds when in contact with an impermeably smooth surface, such as glass. In contrast, the value will decrease for a porous surface, such as paper. The increase in friction is attributed to an occlusion mechanism and can be described by first-order kinetics. Surprisingly, the sensitivity of the coefficient of friction to the normal load and sliding velocity is comparatively of second order, yet these dependencies provide the main basis of theoretical models which, to-date, largely ignore the time evolution of the frictional dynamics. One well-known effect on taction is the possibility of inducing stick–slip if the friction decreases with increasing sliding velocity. Moreover, the initial slip of a finger pad occurs by the propagation of an annulus of failure from the perimeter of the contact zone and this phenomenon could be important in tactile perception and grip function.     

芯轴式摩擦支撑滞回能量耗散模型及热效应影响参数研究EI北大核心CSCD

针对所提出的芯轴式摩擦支撑的构造特点,建立了滑动摩擦动热转换的滞回能量耗散模型,研究了摩擦生热对芯轴式摩擦支撑性能的影响,分析了初始摩擦力、摩擦片厚度、摩擦芯轴比热容和摩擦系数等因素对芯轴式摩擦支撑的力学性能和温度场的影响规律,给出了摩擦支撑在摩擦生热影响下的摩擦力增长值理论计算公式,并通过数值分析结果进行了验证。分析结果表明芯轴式摩擦支撑在摩擦过程中温度不断上升,高温区主要集中在摩擦芯轴和摩擦片的摩擦接触面上,并且随着摩擦片厚度、初始摩擦力和摩擦系数的增加,摩擦热效应越明显,随着材料比热容的增加,摩擦热效应下降。     

Fatigue behavior of tailor (laser)-welded blanks for automotive applications

The drive towards weight reduction in the automotive industry has led to the use of tailor-welded blanks (TWBs) for structural applications. This work is aimed at evaluating the fatigue behavior of the TWBs having different thickness combinations and compositions with and without zinc coating. The results showed that TWBs made from zinc-coated/galvanized steels exhibited a lower fatigue limit as compared with the TWB combination from uncoated bare metals. This was attributed to the intergranular cracking in the galvanized TWBs caused by the presence of zinc penetrating beneath the sheet surface. The fracture surface of the uncoated TWB was basically characterized by the fatigue striations.     

三维编织碳/环氧复合材料的摩擦磨损性能研究

采用RTM工艺制备了不同纤维体积比的三维编织碳／环氧（C3D／EP）复合材料。采用MM－200摩擦磨损试验机对其摩擦磨损特性进行了研究,并对C3D／EP复合材料的磨损机理进行了分析。结果表明,纤维体积比载荷和滑动速度对复合材料的摩擦系数和磨痕宽度均有明显的影响;C3D／EP复合材料的磨损机理主要为疲劳磨损和粘着磨损,当载荷或速度较小时,以疲劳磨损为主,反之则以粘着磨损为主。     

平流层飞艇气动阻力的参数分析

为了研究环境参数及外形布局对平流层飞艇气动阻力的影响,在验证CFD数值模拟方法的基础上,从气动阻力包括压差阻力与摩擦阻力的角度探讨了风速、动力粘度系数、空气密度、Re数、长细比及尾翼对飞艇气动阻力的影响规律及机理。结果表明：气动阻力系数随风速与空气密度的增加而减小,随动力粘度系数的增加而增加;气动阻力系数随Re数减小的趋势,取决于摩擦阻力系数随Re数的减小趋势;随长细比的增加,摩擦阻力系数呈现增加趋势,但气动阻力系数呈现先减小后增加的趋势;尾翼对气动阻力系数的影响主要体现在压差阻力系数的改变。     

Normal and sliding contact experiments on gneiss

The development of reliable discrete element models to simulate the mechanics of granular media requires knowledge of the grain-to-grain contact laws of the material in question. We have conducted a series of normal and sliding contact experiments on material used in laboratory triaxial experiments to obtain such contact laws for DEM simulations of the experiments. The contact experiments employed segments of 14.72 mm-diameter spherical grains from the triaxial specimens and flat specimens of the same material. The spherical grains had a uniform diameter with a smooth surface finish. Monotonic and cyclic loading paths were applied in both the normal and sliding modes, and both sphere-sphere and sphere-flat contact behavior were examined. Force-displacement behavior and frictional loss were measured in all cases. The behavior was generally Hertzian in the normal contact experiments, which involved forces up to approximately 100 N. The normal contact stiffness increased from ≈2 to 15MN m⁻¹ over the range of normal force examined. The sliding experiments employed several normal forces up to approximately 25 N, and produced a value of the coefficient of static friction of 0.28. The shear stiffness of the sliding contact increased with normal force, and ranged from 0.8 to 1.2MN m⁻¹ under normal loads ranging from ≈1 to 7.5 N, respectively, for virgin contacts. The shear stiffness observed for the sphere-flat contact decreased with wear. Surface roughness measurements were obtained on both tested and untested regions of the spheres and flat specimens. The average roughness (Ra) for untested regions of the sphere and flat specimens were 270 and 230 nm, respectively. Repeated testing in the sliding mode reduced these values by 29–45% for the flat surfaces, and by 20% for the spherical contact. Frictional losses were observed in both the normal and sliding modes. In the sliding mode, frictional loss decreased with increasing normal load. We observed stable sliding (associated with significant contact movement under an increasing shear force) at forces that were below the macroscopic frictional limit and resulted in permanent displacement of the contact. There was generally a distinct threshold in shear force for this permanent sliding. The extent of sliding increased significantly with wear for the sphere-flat contact and was accompanied by a substantial drop in shear stiffness.     

Friction and wear studies of bulk polyetherimide

Polyetherimide, ULTEM 1000, was studied as a neat resin for investigating its friction and wear behaviour while sliding against mild steel, under unlubricated conditions on a pin on disc machine. Experimental parameters selected were different loads, sliding distances and counterface roughness. It was observed that unlike other semicrystalline highly linear thermoplastics and some thermoplastic thermosetting polyimides, this polyimide does not transfer a film on the counterface under the conditions of the study. It seems that it wears mainly by fatigue mechanism but crack propagation could not be observed in SEM micrographs of pin surfaces. The frictional coefficient was low as compared with other polyimides and varied with contact pressure from 0.4 to 0.22, although the initial value was high. The cycles required to initiate wear particles were around 90 kcycles at 13 N cm^–2 contact pressure. Once the wear started, the specific wear rate was high (K ₀=10^–13m³N^–1 m^–1).