带有微动磨损缺口钢丝的疲劳特性

在自制的微动磨损试验机上进行钢丝的微动磨损试验,将微动磨损后的钢丝试样在液压伺服疲劳试验机上进行不同应力比和不同应力幅下的疲劳试验。结果表明,钢丝的微动磨损深度随微动时间和接触载荷的增加而增加,磨损缺口处的应力集中使其成为了裂纹萌生源,也使钢丝试样的疲劳寿命大大降低,微动磨损后钢丝试样的疲劳寿命和磨损深度呈反比关系。通过钢丝疲劳断口的SEM形貌分析了其疲劳断裂机制,断口对应不同的疲劳阶段,可分为裂纹萌生区、裂纹扩展区和裂纹瞬断区。     

钢丝微动疲劳裂纹萌生寿命预测研究*

钢丝微动疲劳过程中,钢丝裂纹萌生特性直接影响其裂纹扩展特性,进而制约钢丝微动疲劳寿命,因此开展钢丝微动疲劳裂纹萌生寿命预测研究具有重要意义。基于有限元法、摩擦学理论和断裂力学理论,运用Smith-Watson-Topper（SWT）多轴疲劳寿命准则建立考虑磨损的钢丝微动疲劳裂纹萌生寿命预测模型,基于多种不同的钢丝疲劳参数估算方法对钢丝的微动疲劳裂纹萌生寿命进行了预测,并探究接触载荷、疲劳载荷、交叉角度及钢丝直径等微动疲劳参数对钢丝微动疲劳裂纹萌生寿命的影响规律。结果表明：基于中值法的预测结果最接近实际值;在微动疲劳过程中,钢丝微动疲劳裂纹萌生寿命主要与接触载荷和疲劳载荷相关。通过引入微动损伤参数建立简化的适用于钢丝绳的钢丝微动疲劳裂纹萌生寿命预测模型,通过与考虑磨损的预测模型计算结果进行对比验证了该模型的准确性。     

中性腐蚀环境下钢丝的微动疲劳行为

在自制的微动疲劳试验机上开展中性腐蚀环境下单根钢丝的微动疲劳实验,考察在相同接触载荷下,不同振幅对钢丝的微动疲劳行为的影响,并用扫描电子显微镜观察疲劳钢丝的磨痕和断口形貌,研究钢丝微动疲劳断裂机制.结果表明:在较大的振幅下,钢丝的微动区均处于滑移状态,而在较小振幅下,钢丝的微动区从滑移状态逐渐转变为黏着状态;磨损机制主要为磨粒磨损、疲劳磨损、腐蚀磨损和塑性变形;钢丝疲劳寿命随着微动振幅的增大而减小;钢丝的疲劳断口可分为3个区域,即疲劳源区、裂纹扩展区及瞬间断裂区.     

40CrNi2MoA合金钢的弯曲微动疲劳特性

在不同弯曲载荷下,对40CrNi2MoA合金钢进行弯曲微动疲劳试验,建立其弯曲微动疲劳下的循环次数-应力曲线;通过对微动损伤区的微观分析,研究该合金钢的弯曲微动疲劳特性。结果表明:40CrNi2MoA钢弯曲微动疲劳应力曲线不同于常规疲劳应力曲线,呈现"C"型曲线特征;随着弯曲载荷的增加,微动依次运行于部分滑移区、混合区和滑移区;相对于另外两个区域,混合区试样的裂纹更易萌生、扩展且微动疲劳寿命最短;试样表面的磨损机制主要为磨粒磨损、氧化磨损和剥层;由于接触应力和弯曲应力的影响程度不同,弯曲微动疲劳裂纹的扩展分为三个阶段,即接触应力控制阶段、接触应力与弯曲疲劳应力共同控制阶段和完全受弯曲应力控制阶段。     

钢丝微动磨损过程中的接触力学问题研究

钢丝间的微动磨损以及由此引起的钢丝的疲劳断裂是提升钢丝绳失效的主要原因之一.以6×19点接触式提升钢丝绳为研究对象,将钢丝绳中钢丝的微动损伤过程进行实验室模型化,在自制的钢丝微动磨损试验机上进行钢丝试样的微动磨损实验,考察接触载荷和微动时间变化对钢丝试样磨损深度的影响.结果表明,钢丝试样的微动磨损深度随着接触载荷和微动时间的增加而呈增长趋势,但由于接触面积和接触应力在微动磨损过程中随着接触载荷和微动时间的变化而变化,使磨损深度在不同磨损工况下增长趋势不同.建立的钢丝接触有限元模型表明,接触区中心的最大接触应力随着接触载荷的增加而增大,随着嵌入深度的加深而减小.其结果验证了试验过程中接触面积和接触应力对磨损深度的影响关系.     

基于微动磨损预测矿井提升钢丝绳安全系数

为预测矿井提升过程中钢丝绳动态安全系数演变,针对浅井低载荷矿井提升机,运用动力学理论和摩擦传动理论获得了距离容器不同位置处钢丝绳动张力,建立了接触钢丝总磨损系数与钢丝间接触载荷、相对滑移和交叉角的关联模型,提出了矿井提升钢丝绳的磨损演化及承载安全系数预测方法,探究不同工况参数对钢丝绳磨损及承载安全系数的影响规律。结果表明:随着提升循环次数的增加,距容器不同位置处提升钢丝绳的横截面微动磨耗面积增大、安全系数降低;钢丝绳悬垂中间位置处,提升钢丝绳承载安全系数下降较快;提升钢丝绳承载安全系数对提升工况参数存在依赖性,随着提升侧终端质量的增加和最大提升速度的减小,提升钢丝绳承载安全系数均呈降低趋势。     

30CrNiMo8合金钢的弯曲微动疲劳特性

在不同弯曲载荷水平下,对30CrNiMo8合金钢进行了系统的弯曲微动疲劳试验,建立了其微动疲劳S-N曲线,讨论了其弯曲微动疲劳特性及相关规律。结果表明:30CrNiMo8钢弯曲微动疲劳的S-N曲线明显不同于常规疲劳的,呈现"C"曲线特征;随着弯曲载荷的增加,微动依次运行于部分滑移区、混合区和滑移区;在混合区,裂纹最易萌生且微动疲劳寿命最短;微动损伤区的磨损机制主要为磨粒磨损、氧化磨损和剥层;弯曲微动疲劳裂纹的扩展表现为三个不同的阶段,第一阶段裂纹斜向扩展,以接触应力控制为主,第二阶段裂纹转向,受接触应力和弯曲应力共同控制,第三阶段裂纹扩展方向变为垂直方向,以弯曲应力控制为主。     

悬索桥主缆钢丝与鞍座材料摩擦腐蚀疲劳行为

大跨度多塔悬索桥主鞍座两侧主缆钢丝与鞍座材料间受恒载、车载、风荷载以及腐蚀环境耦合作用产生摩擦腐蚀疲劳行为,导致钢丝承载强度渐变劣化,严重影响主缆承载安全性。因此,研究主缆钢丝与鞍座材料摩擦腐蚀疲劳行为至关重要。搭建钢丝摩擦腐蚀疲劳试验台开展钢丝与鞍座材料摩擦腐蚀疲劳实验,运用超景深电子显微镜、扫描电子显微镜考察主缆钢丝磨损轮廓、磨损机理、磨损系数和横截面失效面积特性;通过万能试验机并结合损伤力学理论和有限元法,建立疲劳钢丝损伤度演化模型和钢丝承载强度劣化模型。结果表明：钢丝摩擦因数呈迅速增加-减小-增加-稳定趋势,随接触载荷增大而减小,随疲劳载荷增大而增大;磨损轮廓随疲劳次数近似线性增加,失效面积随疲劳次数近似抛物线增加,二者随接触载荷和疲劳载荷的增大均增加;磨损系数在磨损稳定期减小,随疲劳次数增加小幅度增长;磨损机理以黏着磨损、磨粒磨损、疲劳磨损和腐蚀磨损为主;钢丝损伤度与疲劳次数呈二次函数关系;接触载荷和疲劳载荷的增加,导致钢丝损伤度增大、承载强度降低。结果对悬索桥主缆损伤及承载安全性能评估具有理论指导意义。     

关于微动磨损与微动疲劳的研究

微动磨损与微动疲劳是２种主要的微动模式,造成的损伤在工业中相当普遍,并可能引发灾难性的后果。主要研究了们移幅度、压力和疲劳应力３个基本微动参数,并以获得的微动区域、微动图为基础,分析了微动磨损与微动疲劳的运行机制和破坏规律。为更好地了解微动磨损与微动疲劳之间的内在联系,进一步探讨了接触磨损与局部疲劳、局部疲劳与整体疲劳之间的竞争机制。     

TiAlZr合金微动磨损性能研究

采用高精度液压式微动磨损试验机研究了TiA lZr合金在不同微动运行区域的微动磨损行为,建立了其运行工况微动图。试验结果表明:滑移区、混合区和部分滑移区的摩擦因数随循环次数变化呈现不同的规律,其中部分滑移区摩擦因数较低,磨损体积随着位移幅值的增大而增大;滑移区、混合区磨损体积随着法向载荷的增加而增大,而部分滑移区磨损体积随着法向载荷的增加而减小;滑移区磨屑堆积于中心区域,磨损以磨粒磨损和剥层机制为主;混合区磨损机制主要表现为粘着磨损与磨粒磨损并存;部分滑移区磨损轻微。     

金属橡胶内螺旋金属丝微动磨损预测模型研究*

目前金属丝微动磨损预测模型多适用于垂直接触，而锐角交叉下的模型存在计算过程繁琐、表征不全面等不足，难以便捷有效地预测金属橡胶内部复杂无序的金属丝磨损情况。基于有限元分析，确定螺旋曲率对磨损结果的影响极小，因此将金属橡胶内部螺旋金属丝接触对微元理想化为直金属丝接触对，探究无序接触下金属丝磨损特征的演化规律。结果表明，无序接触状态下的磨损特征演化规律与金属丝接触夹角大小密切相关。依据几何学分析，得到任意锐角接触下磨损磨痕位于金属丝1/2接触夹角处的特殊位置关系，据此建立任意接触形态下的微动磨损演化预测模型，并利用已有文献中的金属丝微动磨损试验结果对预测模型进行验证。结果显示，建立的任意锐角下的磨损演化模型能够较准确地预测金属丝的磨损结果，误差均在15%以内。研究结果为预测金属橡胶内部金属丝微动磨损和使用寿命提供一定理论基础。     

Some Observations on Frictional Force During Fretting Fatigue

Frictional force behavior during fretting fatigue and its interdependence on other fretting variables are investigated. Both coefficient of static friction and the normalized frictional force (i.e., the ratio of frictional force and normal contact load) increase during the earlier part of a fretting fatigue test and then both reach to a stabilized value. The variation of temperature in the contact region and normalized frictional force with increasing cycle numbers and bulk stress show similar trend implying that normalized frictional force represents the average friction in the contact region during a fretting fatigue. An increase in bulk stress, relative slip, and hardness of pad material results in an increase of the normalized frictional force, while an increase in contact load, frequency and temperature decreases the normalized frictional force. The normalized frictional force is also affected by the contact geometry. On the other hand, coefficient of static friction increases with an increase in the hardness of mating material, temperature and roughness from shot-peening treatment, but is not affected by contact geometry and displacement rate. Further, the normalized frictional force is not affected by the contact geometry, roughness and applied bulk stress level when fretting fatigue test is conducted under slip controlled mode, however it increases with increasing applied relative slip and decreasing contact load in this case.     

TC4合金微动疲劳损伤研究

研究了TC4合金在柱面-平面接触务件下的微动疲劳行为，分析了其微动疲劳损伤机制。结果表明：在试验务件下，微动区边缘的损伤特征以粘着磨损为主，而微动区中部则以磨粒磨损和接触疲劳为主。疲劳裂纹易于在微动区．特别是在蚀坑处萌生和扩展。促使微动疲劳裂纹萌生的因素：一是法向应力和切向摩擦力引起的材料表层塑性变形，二是微动磨损破坏了材料的表面完整性，造成了缺口应力集中效应。     

Oil-Lubricated Fretting Behaviors of 304 Stainless Steels under Different Fretting Strokes and Normal Loads

The influence of oil lubrication on the fretting wear behaviors of 304 stainless steel flat specimens under different fretting strokes and normal loads has been investigated. The results proved that fretting regimes and fretting wear behaviors of 304 stainless steels were closely related to the fretting conditions. In general, the increase in normal load could increase wear damage during sliding wear. However, according to the results, a significant reduction in wear volume and increase in friction coefficient was observed when the normal load was increased to critical values of 40 and 50 N at a fretting stroke of 50 μm due to the transformation of the fretting regime from a gross slip regime to partial slip regime. Only when the fretting stroke further increased to a higher value of 70 μm at 50 N, fretting could enter the gross slip regime. There was low wear volume and a high friction coefficient when fretting was in the partial slip regime, because oil penetration was poor. The wear mechanisms were fatigue damage and plastic deformation. There was high wear volume and low friction coefficient when fretting was in the gross slip regime, because the oil could penetrate into the contact surfaces. Unlike the wear mechanisms in the partial slip regime, fretting damage of 304 stainless steels was mainly caused by abrasive wear in the gross slip regime.     

Development of a test device for the evaluation of fretting in point contact

Fretting wear and fatigue may occur between any two contacting surfaces, wherever short‐amplitude reciprocating sliding is present for a large number of cycles. A test device has been developed for the evaluation of fretting fatigue and wear in partial and gross slip conditions. Three similar sphere‐on‐plane contacts run at the same time. Normal force, tangential force or displacement amplitude and constant bulk stress can be controlled and measured separately. Reciprocating tangential displacement is produced with rotational motion, the amplitude and frequency of which can be adjusted and controlled accurately by an electric shaker. The number of load cycles for crack initiation and growth is determined with strain‐gauge measurements near the fretting point of contact. The contact surfaces are measured with 3D optical profilometer before fretting measurements to determine actual contact geometry. The measurements were done with quenched and tempered steel. The initial results indicate that cracks are mostly formed in partial slip conditions, whereas fretting wear is more heavily involved in gross slip conditions. The initiation of a crack occurs near the edge of the contact in the slip direction, where the calculated cracking risk has its maximum value in partial slip conditions. The number of cracks increases as the displacement amplitude, i.e. friction force, increases in partial slip conditions. Copyright © 2008 John Wiley & Sons, Ltd.     

铝合金压印接头微动疲劳机理研究

压印连接是近年来新兴的连接方式,因其具有简单高效、低耗环保等优点,使得在应用连接方面越来越受到重视。疲劳破坏是机械构件失效的主要形式,疲劳过程中的微动磨损是造成零部件失效的主要原因之一。基于以上条件,对铝合金压印接头的疲劳性能进行了试验研究,结果显示疲劳失效部位主要集中在下板靠近压印点处,断口处发现大量微动磨屑,经能谱分析可以确定磨屑成分主要为氧化铝和金属铝;对疲劳失效断口和微动磨损区域进行了扫描电镜分析,发现压印接头的微动磨损部位主要分为两类,并对其进行了定义,一类定义为颈部微动磨损,另一类定义为环点板间微动磨损。分析发现颈部微动磨损所占比例随着外加载荷的大小而变化,且微动磨损是导致压印接头疲劳失效的重要因素。