碱性腐蚀环境下接触载荷对钢丝微动疲劳行为的影响

以矿用钢丝为研究对象,在自制的钢丝微动疲劳试验机上开展钢丝在碱性腐蚀环境下的微动疲劳试验,考察钢丝在应变比为0.8时不同接触载荷下钢丝的微动运行特性,并用光学显微镜和扫描电子显微镜观察钢丝的磨痕和断口形貌,分析其微动磨损和疲劳断裂机理.结果表明:不同接触载荷下钢丝的摩擦系数具有相同的变化趋势,均可以分为4个阶段:跑合期、上升期、下降期和稳定期;4种不同接触载荷下钢丝摩擦副均运行于滑移状态,磨损机制以腐蚀磨损、磨粒磨损、疲劳磨损和塑性变形为主;钢丝疲劳寿命与磨损量成反比,疲劳断口可分为3个区:疲劳源区、扩展区和瞬断区.     

钢丝的微动磨损及其对疲劳断裂行为的影响研究

采用自制的钢丝微动磨损试验机考察了钢丝的微动摩擦磨损性能，随后将经过一定时间微动磨损试验后的钢丝试样在液压伺服疲劳试验机上进行拉一拉疲劳试验，进而探讨了微动摩擦系数和微动磨损深度随微动磨损试验时间和接触载荷的变化关系；并利用扫描电子显微镜分析了试样磨痕和磨屑的表面形貌．结果表明，在较大的微动振幅下，钢丝的微动摩擦系数变化幅度不大，微动磨损深度随微动磨损试验时间和接触载荷的增加而增大；微动磨损试验后钢丝试样的疲劳寿命同磨损深度成反比关系；可以将疲劳断口划分为4个区域，其同钢丝试样的疲劳断裂过程相对应．     

绳股结构对螺旋接触钢丝间微动摩擦磨损特性影响

钢丝间微动磨损会加剧提升钢丝绳的疲劳损伤,降低钢丝绳的使用寿命,严重威胁矿井提升安全.为了研究绳股结构对螺旋接触钢丝间微动摩擦磨损特性的影响,在自制试验台上开展了拉伸-扭转耦合力作用下钢丝微动磨损试验.结果显示：随着接触力增加,相同直径接触对下钢丝间摩擦系数从0.748减小到0.646,而不同直径接触对下钢丝间摩擦系数从0.941减小到0.911;相比于凹接触对,凸接触对下钢丝表面磨损更加严重,并且不同直径钢丝间磨损深度和磨损系数明显大于相同直径钢丝间磨损深度和磨损系数;钢丝间主要磨损机理为磨粒磨损、黏着磨损和疲劳磨损,并且不同直径接触对下钢丝表面疲劳磨损特征更加严重;钢丝疲劳断口的瞬断区存在大量二次裂纹和韧窝形貌,钢丝疲劳断裂失效机理主要为韧性断裂.     

微动频率对钢丝拉扭复合微动腐蚀疲劳行为影响研究

拉扭复合微动腐蚀疲劳是深井提升钢丝绳主要失效形式之一,深井提升钢丝绳振动频率决定钢丝间微动频率,直接影响钢丝拉扭复合微动腐蚀疲劳机理和损伤程度,进而制约深井提升钢丝绳服役安全性. 本文作者通过自制钢丝拉扭复合微动腐蚀疲劳试验机开展了酸性电解质溶液中钢丝拉扭复合微动腐蚀疲劳试验,通过钢丝切向力-位移幅值和扭矩-扭转角滞后回线分析了拉扭复合微动腐蚀疲劳过程中钢丝间接触状态及轴向和扭转方向钢丝耗散能,运用扫描电子显微镜和三维白光干涉表面形貌仪考察了拉扭复合微动腐蚀疲劳过程中钢丝磨痕形貌和磨损深度轮廓特性,采用X射线三维成像系统揭示了钢丝拉扭复合微动腐蚀疲劳裂纹扩展演化规律,通过电化学分析仪分析试验后钢丝Tafel极化曲线和阻抗谱以探究钢丝电化学腐蚀倾向和耐腐蚀性,揭示了微动频率对拉扭复合微动腐蚀疲劳过程中钢丝间接触状态、钢丝耗散能、微动磨损机理、疲劳裂纹扩展演化和疲劳寿命、电化学腐蚀倾向和耐腐蚀性的影响规律. 结果表明:在拉扭复合微动腐蚀疲劳过程中,随着微动频率的增加,钢丝间由完全滑移和部分滑移混合状态变为完全滑移状态,钢丝扭矩-扭转角滞后现象削弱,钢丝切向力-位移幅值和扭矩-扭转角滞后回线对应的耗散能均总体降低,钢丝间摩擦系数和钢丝磨损深度均降低,钢丝磨损机理均为磨粒磨损、黏着磨损、疲劳磨损和腐蚀磨损,钢丝最大裂纹深度和裂纹扩展速率均降低,疲劳寿命增加,钢丝电化学腐蚀倾向下降和耐腐蚀性增强.      

轴向加载下不同捻向多股钢丝绳的力学行为研究

多股钢丝绳在工程结构中广泛应用，其中多数钢丝经过两次捻绕成为二次螺旋钢丝。基于Love弹性曲杆理论和变形前后钢丝绳结构状态分析，建立了轴向加载下考虑二次螺旋钢丝局部变形行为的多股钢丝绳弹性理论模型，并通过有限元模拟研究了钢丝绳的弹塑性力学响应。将弹性理论模型结果与有限元模拟结果、Costello模型进行了对比验证，进一步分析了不同捻向钢丝绳(顺捻、交互捻)整绳和局部钢丝的力学行为。研究发现二次螺旋钢丝的局部响应不同于单股绳一次螺旋钢丝，钢丝的弯曲和扭转变形沿钢丝绳截面周期性变化。整绳受拉伸载荷时，沿钢丝轴线的拉伸变形占主要部分，交互捻钢丝的弯曲和扭转变形均小于顺捻钢丝，且扭转变形的方向与顺捻钢丝相反。在通常弹性使用范围内，交互捻钢丝绳沿钢丝截面的最大拉伸和扭转应力均小于顺捻钢丝绳，且产生的反作用扭矩更小，因此优于顺捻钢丝绳。     

考虑微动磨损的钢丝微动疲劳裂纹扩展寿命预测研究

微动疲劳是矿井提升钢丝绳主要失效形式之一,在钢丝微动疲劳过程中,微动磨损严重影响钢丝微动疲劳裂纹扩展特性,进而制约钢丝微动疲劳断裂机制,故开展考虑微动磨损的钢丝微动疲劳裂纹扩展寿命预测研究至关重要. 运用自制钢丝微动疲劳试验机开展钢丝微动疲劳试验和拉伸断裂试验,通过高速度数码显微系统揭示微动疲劳过程中钢丝微动磨损演化、裂纹萌生和扩展及断裂特性,基于摩擦学和断裂力学理论,运用有限元法、循环迭代法和虚拟裂纹闭合技术建立了考虑微动磨损的钢丝微动疲劳裂纹扩展寿命预测模型,并进行试验验证. 结果表明:采用微动疲劳过程稳定阶段磨损系数预测钢丝微动磨损演化可保证预测正确性,微动疲劳过程中钢丝主要为I型裂纹扩展模式,考虑微动磨损的钢丝微动疲劳裂纹扩展寿命预测值和试验值吻合较好,验证了预测模型正确性.      

核电690合金传热管微动疲劳试验及损伤机理分析

核电蒸汽发生器传热管在微幅磨损与交变载荷的作用下形成微动疲劳,导致其表面裂纹萌生和扩展乃至破裂,从而影响反应堆的安全. 为研究径向载荷以及轴向交变应力对690合金管微动疲劳寿命的影响规律,开展690合金管管材的微动疲劳试验,获得690合金管管材的微动疲劳寿命曲线,并与相关研究数据进行对比分析,以便探讨材料在微动疲劳下的寿命模型. 对不同载荷下的690合金管试样的磨痕表面进行三维形貌和扫描电镜观测,分析磨损表面的损伤机理;对不同载荷下的690合金管试样断口的宏观与微观形貌进行表征,分析裂纹萌生、起裂过程及其失效机理. 结果表明690合金管与403不锈钢(SS)抗振条间的磨损机理为剥层及磨粒磨损;690合金管在径向载荷作用下于微动磨损处产生裂纹源,裂纹在轴向交变应力的作用下不断向内部扩展,最终导致断裂;其断裂形式为解理疲劳断裂.      

电流作用对铜镁合金弯曲微动疲劳损伤特性的影响

采用自主研制的试验装置，研究了铜镁合金在不同电流强度条件下的弯曲微动疲劳损伤演变规律. 运用红外线热成像仪测试电流条件下微动接触区温度分布情况；利用白光干涉仪、扫描电镜、电子探针、X射线光电子能谱仪对试样接触损伤区的微观形貌和化学行为进行分析. 试验结果表明:在相同循环次数下，随着电流强度的增加，铜镁合金弯曲微动疲劳寿命逐渐降低，接触区温度逐渐上升，接触损伤区尺寸增大，剥落层逐渐细化，接触损伤区氧化程度越来越严重，氧化磨屑的主要成分为CuO和Cu₂O；主要损伤机制为氧化磨损、黏着磨损和剥落.      

矿用钢丝在腐蚀介质环境下的微动行为研究

钢丝绳中钢丝的锈蚀、磨损或断裂是造成矿井用钢丝绳失效的主要形式。以6×19点接触式提升钢丝绳为研究对象,在自制的微动摩擦磨损试验机上开展钢丝在腐蚀介质环境下的微动磨损试验研究。考察钢丝在模拟矿井淋水腐蚀介质中的微动运行特性,通过磨痕测量微动磨损量,采用光学显微镜、扫描电镜和能谱仪对钢丝的微动损伤机理进行分析。结果表明：腐蚀介质影响钢丝的微动运行区域,在干摩擦和中性腐蚀介质下运行于混合区,而在酸性和碱性腐蚀介质下运行于滑移区;腐蚀介质明显降低钢丝的摩擦系数,其中酸性介质下的摩擦系数最小,约为0.36;腐蚀与磨损的交互作用显著加速了材料的流失,酸性腐蚀介质下钢丝的磨痕深度最大;钢丝在干摩擦条件下的损伤机制以材料的塑性变形、粘附涂抹和摩擦氧化为主,而在腐蚀介质环境下的损伤机制转变为磨粒磨损和化学腐蚀。     

基于SWT方法的钢绞线索微动疲劳特性分析

为得到钢绞线索丝间接触区的应力场分布并预测微动疲劳裂纹萌生位置和微动疲劳寿命，本文利用参数化方法建立了精细化的钢绞线拉索有限元模型，包括整索模型和不同层丝间接触区域的局部精细化子模型．分析了钢绞线索在两种交变荷载工况下的应力场变化情况，并基于多轴疲劳SWT(Smith-Watson-Topper)临界平面法进行了疲劳特性分析和疲劳寿命预测．主要结论如下：钢绞线索内接触区边缘处的微动幅值较大，中心处几乎没有相对滑动，微动疲劳的初始裂纹萌生点位于接触区域边缘；经不同区域子模型分析比较，在轴向循环荷载作用下，外层钢丝的接触区域比内层钢丝更易发生微动疲劳损伤；在横向位移循环荷载作用下，同层钢丝因位置角度不同而产生了较大的疲劳特性差异，且相比轴向循环拉伸，该工况下最不利单丝的微动疲劳寿命更低；与非接触区域相比，接触区的疲劳寿命大幅降低，微动现象对钢绞线索的抗疲劳性能有明显降低作用．     

Propagation of a longitudinal pulse in wire ropes under axial loads

Measurements of the velocity of propagation of longitudinal pulses in wire ropes as a function of applied tension are reported. Twelve 3/8-in.-diam cables are investigated which differ in configuration, i.e., number of wires per strand and number of strands, and in the material from which the wires and the core are fabricated. The velocity of longitudinal waves is found to increase with increasing tension, approaching the velocity in a solid steel bar as the applied load is increased toward the failure load of the wire rope. The material from which the wires are fabricated and the number of strands, rather than the number of wires in a strand or its core material, appear to significantly affect the velocity of longitudinal pulses.     

The mechanical behavior of a wire rope with an independent wire rope core

A new model for simulating the mechanical response of a wire rope with an independent wire rope core is presented. The rope is subjected to both an axial load and an axial torque. In contrast with previous models that consider the effective response of wound strands, the present model fully considers the double-helix configuration of individual wires within the wound strand. This enables to directly relate the wire level stress to the overall load applied at the rope level. The model assumes a fiber response of individual wires. Two alternative kinematics of the wires are considered, and are used to predict the elastic response of the rope. The postulated kinematics are theoretically validated and the predicted rope response is in agreement with new experimental data. The new model enables the extraction of the stress at the wire level that can be used in turn to estimate global features of the rope such as force interaction between wires, rope stiffness, strength, and fatigue life.     

Some dynamic properties of axially loaded wire ropes

Results are presented on the transverse damping, the transverse fundamental natural frequency as well as the longitudinal fundamental natural frequency for axially loaded wire ropes. Twelve different wire ropes are tested. During the test, a mass is centrally attached to the rope. The results indicate an increasing transverse damping with an increasing axial load. This damping is primarily attributed to a Coulomb damping. Although core material and construction influence the transverse damping of the wire rope, no relationships are found when comparing this damping with the structural strength, the number of wires used in the rope, the alloy composition or the heat treatment of the rope materials. The transverse and longitudinal fundamental natural frequencies of the axially loaded wire ropes with a mass centrally attached has been satisfactorily modeled.     

Neutron Diffraction Measurement of Stress Redistribution in Parallel Seven-Wire Strands after Local Fracture

We report results from neutron diffraction experiments where partitioning of applied tensile load between the inner and outer wires of seven-wire parallel and quasi-parallel wire strands were measured while 1-all wires were undergoing elastic deformation, 2-where one wire within the bundle was undergoing plastic flow and, 3-when one or more wires fractured under load. The results indicate that mechanical interference and friction mechanisms have similar contributions to the load transferred to fractured wires, and both mechanisms should be included in analytical or numerical formulations of strain partitioning in quasi-parallel wire cables.     

Analytical solutions for bending and flexure of helically reinforced cylinders

There has been a great deal of interest in the problems of modelling cables and ropes. A recent review by Cardou and Jolicoeur [Appl. Mech. Rev. 50 (1997) 1] considers the modelling of a cable which consists of a central core surrounded by one or several helically wound wire layers. One approach has been to consider the deformations of an individual helical wire and to synthesise the model of a cable by using contact conditions between the various wires. Other authors have adopted a continuum approach regarding each layer as a transversely isotropic material whose principal direction is along a helix surrounding the central axis of the cable. In each layer the helix angle is constant so that, when referred to cylindrical polar co-ordinates, the cylinder has a constant stiffness matrix in each layer. The intention in this paper is to use the continuum approach and describe the analytical solutions that govern the simple bending, flexure, or bending under a uniform load, of an anisotropic elastic cylinder consisting of a single material of this type. The extension of this work to a composite cylinder consisting of several concentric layers, surrounding a central core, which are either bonded together or make a frictionless contact, is briefly described.