Influence of fretting on the fatigue strength at the vise clamp-specimen interface

Fretting fatigue is one of the most important phenomena for inducing a significant reduction of fatigue strength and consequently, leading to unexpected failure accidents of the engineering structures even at very low stresses. In the present study, both plain and fretting fatigue tests with zero mean stress were carried out on two different types of steel, low-carbon steel and martensitic stainless steel, by means of a reversed bending fatigue testing machine. The drop in the fatigue strengths through fretting at vise clamp-specimen interface were significant for both tested steels. The fretting processes produced a reduction in fatigue strength of about 27% for low-carbon steel and 16% for martensitic stainless steel.     

Finite element simulation of the mechanics of flat contact pad fretting fatigue tests

An understanding into the macro kinetic and kinematic behaviour of fretted surfaces is provided. Making use of a modified version of a previously developed in‐house two‐dimensional elastic–plastic finite element analysis numerically simulates flat contact pad fretting fatigue tests. Basic macro mechanics concepts are adopted to idealise two bodies with rough contact surfaces and loaded at two different sites with arbitrary axial loading profiles. A time scale factor is devised to recognise the earliest candidate out of the events possibly accommodated at each loading increment. The present analysis utilises a relevant experimental set up developed in the Structural Integrity Research Institute of the University of Sheffield as an application. Computational results accurate to within 1.2% and corresponding to one contact pad span and six constant normal loads acting individually with four amplitudes of two sinusoidal axial load cycles are presented. The present computations include (1) the development of the global and local normal and tangential reactions and relative sliding displacement acting along the fretting surfaces and (2) contact pad deformation, generated stress fields and plasticity development within the neighbouring region of the fretted area.     

Effect of fretting amplitudes on fretting wear behavior of steel wires in coal mines

Given that fretting wear causes failure in steel wires, we carried out tangential fretting wear tests of steel wires on a self-made fretting wear test rig under contact loads of 9 and 29 N and fretting amplitudes ranging from 5 to 180 μm. We observed morphologies of fretted steel wire surfaces on an S-3000N scanning electron microscope in order to analyze fretting wear mecha-nisms. The results show that the fretting regime of steel wires transforms from partial slip regime into mixed fretting regime and gross slip regime with an increase in fretting amplitudes under a given contact load. In partial slip regime, the friction coefficient has a relatively low value. Four stages can be defined in mixed fretting and gross slip regimes. The fretting wear of steel wires in-creases obviously with increases in fretting amplitudes. Fretting scars present a typical morphology of annularity, showing slight damage in partial slip regime. However, wear clearly increases in mixed fretting regime where wear mechanism is a combination of plastic deformation, abrasive wear and oxidative wear. In gross slip regime, more severe degradation is present than in the other regimes. The main fretting wear mechanisms of steel wires are abrasive wear, surface fatigue and friction oxidation.     

离子束增强沉积CrN膜层及其微动摩擦学性能研究

以不同氮离子辅助轰击能量制备CrN膜层．利用纳米压入仪及显微硬度计分别测试单晶Si片上膜层的硬度及断裂韧度K1C．使用XRD、XPS及EPMA分析离子轰击能量对镀层组织结构的影响。结果表明，采用能量较低的氮离子轰击得到的涂层，由于金属Cr的存在，涂层硬度虽有所降低，但断裂韧度K1C数值较高。选择较低的4keV辅助轰击能量，在M2高速钢基体上沉积CrN涂层，膜层在空气介质中表现出优异的耐磨减摩特性.但在水介质条件下，由于膜层接触区域的去钝化，再钝化使腐蚀和磨损相互加速，导致CrN膜层摩擦系数，尤其是磨损量明显高于基材。     

Comparison of tribological properties of industrial low friction coatings

MX2(M= Mo, W; X=S, Se) and DLC (a-C: H and WC/C) are the two kinds of typical low friction coatings widely used in industry. The friction and wear properties of these two kinds of coatings marked as MOVIC,MOST, MoSez/Ni, WSez, a-C: H and WC/C coatings were determined by fretting tests in ambient air of different humidity. The results show that the coefficient of friction of MXz coatings increases when the relative humidity of air increases whereas the coefficient of friction DLC coatings decreases with the increasing of relative humidity. MOVIC and WSe2 coatings have a poor friction and wear resistance because of non-basal planes (100) and ( 101 ) parallel to the surface in the MOVIC coating, or the rough and porous surface of WSe2 coatings. Among these six coatings, MoSe2/Ni and WC/C eoatinas have the highest wear resistance which seems to be unaffected by the relative humidity.     

TC4钛合金的微动疲劳行为研究

研究了TC4钛合金在柱面-平面接触条件下的微动疲劳行为.通过观察微动区的磨损特征和截面形貌,分析了微动疲劳损伤机制,探讨了磨屑的形成与演变过程及其对微动疲劳行为的影响,考察了摩擦系数随时间的变化.结果表明,TC4钛合金微动区的损伤机制以粘着磨损、磨粒磨损和接触疲劳为主,并伴有氧化磨损.磨屑是基体材料脱落、破碎、氧化形成的,磨屑中的硬质氧化物颗粒促进了合金表面的磨粒磨损,加速了疲劳失效.     

榫联接处微动摩擦的计算机仿真

对榫联接微动摩擦状态下的计算机仿真，得到了榫联接在接触区上的正压力分布和摩擦系数分布的规律，为榫联接的微动疲劳强度的分析计算提供了数据。     

评定钢丝的微动摩擦磨损参数研究

以点接触式提升钢丝绳为研究对象，在实验室建立了钢丝绳中钢丝的微动磨损模型．在自制的钢丝微动磨损试验机上进行微动磨损实验，考察了接触载荷、微动时间和振幅的变化对钢丝试样磨损深度的影响，并用综合参数pv值和pvt值评定微动磨损深度的变化．结果表明，相同微动时间下磨损深度随pv值的增加而增大，相同接触载荷下磨损深度随pv值增大而减小，磨损深度和综合参数pvt值之间基本成线性关系．同时通过微动过程中摩擦系数的变化、磨损产生的磨屑以及磨痕形貌，分析微动磨损过程中磨损机制随微动实验条件的变化规律。     

一种典型齿形紧配合面微动损伤机理研究

结合对连杆的动力学分析，对16V280ZJ型柴油机连杆齿状紧配合件结合面的损伤进行了分析研究，结果表明，齿面间复杂的微动疲劳作用加速了齿表面裂纹的萌生与扩展，是降低使用寿命的主要原因，研究结果对其它类型的柴油机连杆（如16V240）或其它类似的紧结合面损伤机理研究具有指导意义。     

渐开线花键副微动磨损疲劳寿命预估

为准确预估渐开线花键副微动磨损疲劳寿命,在假设微动磨损与微动疲劳共同作用的情况下,对某型机主减速器花键副的微动损伤机理进行研究.分析国内外现有的微动疲劳预测方法,在传统SWT法预估疲劳寿命的基础上,忽略疲劳发生的位置和方向,给出花键副的损伤累积计算方法,在给定工况下预估航空花键副微动磨损疲劳寿命.结果表明:花键副微动作用过程中,微动磨损与微动疲劳互相竞争互相抑制,最终导致花键副在两种微动模式共同作用下发生疲劳失效;花键副的疲劳寿命随着SWT值的增大而减小.提出的损伤累积模型能较准确地反映微动磨损对微动疲劳的作用,为花键副的设计和维修提供了数值参考,也为进一步研究考虑齿侧间隙时的花键副微动磨损疲劳寿命预估提供了依据.