横向交变载荷作用下三种涂层螺栓的防松性能

选用二硫化钼涂层和碳化钨涂层对45钢螺栓进行表面处理,通过横向振动试验研究横向交变载荷作用下螺栓连接结构的松动行为,并与常用的电镀锌涂层螺栓进行对比分析,讨论3种涂层螺栓的防松性能。利用扫描电子显微镜和电子能谱仪分析试验后螺纹表面损伤形貌及化学成分,揭示螺纹表面的磨损机制。试验结果表明：二硫化钼涂层螺栓螺纹表面的主要磨损机制为疲劳磨损、磨粒磨损和氧化磨损,碳化钨涂层和电镀锌涂层螺栓螺纹表面的主要磨损机制为疲劳磨损和磨粒磨损;相同预紧力或等效应力条件下,二硫化钼涂层螺栓因其界面摩擦因数低,防松性能较差,碳化钨涂层螺栓因其表面耐磨性能优异,防松性能最好;相同预紧力矩条件下,二硫化钼涂层螺栓因预紧力高,防松性能最好,碳化钨涂层螺栓次之,电镀锌涂层螺栓最差。     

横向载荷作用下螺栓连接松动过程研究

针对横向载荷作用下的螺栓连接松动过程开展研究,给出了面向螺栓松动仿真的建模方法,分析了循环往复载荷作用下接触状态与残余预紧力的变化规律,并研究了载荷作用位置、幅值和频率对螺栓连接松动的影响。分析结果表明：在横向循环载荷作用下,残余预紧力出现交替的上升与下降;螺纹接触面先于螺头承压面进入滑移状态;横向载荷作用在上板或下板对松动没有影响;载荷幅值是影响松动的主要因素,载荷幅值越大松动越容易发生,而加载频率对松动影响较小。本研究分析结果与Junker试验结果一致性良好,可推广到复杂载荷条件下的应用。     

Three-dimensional finite element analysis of the mechanical properties of helical thread connection

Conventional analytical and numerical methods for the mechanical properties of helical threads are relied on many assumptions and approximations and thus hardly yield satisfied results. A parameterized 3D finite element model of bolted joints with real helical thread geometry is established and meshed with refined hexahedral elements. The Von Mises plasticity criterion, kinematic hardening rule of materials and interfacial contacts are employed to make it possible for the suggested model be able to approach real assembly conditions. Then, the mechanical properties of bolted joints with different thread pitches, thread numbers and modular ratios are investigated, including the contact pressure distribution at joint interfaces, the axial load distribution and stress concentration in screw threads during the loading and unloading process. Simulation results indicate that the load distribution in screw threads produced by the suggested model agrees well the results from CHEN’s photoelastic tests. In addition, an interesting phenomenon is found that tightening the bolt with a large preload first and then adjusting the clamping force by unloading can make the load distribution more uniform and reduce the maximum residual equivalent stress in thread roots by up to 40%. This research provides a simple and practical approach to constructing the 3D finite element model and predicting the mechanical properties of helical thread connection.     

Influence of tightening procedures and lubrication conditions on titanium screw joints for lightweight applications

In recent years, the need for lighter vehicles led to the widespread of lightweight alloys, such as titanium, also in the field of threaded fasteners. Unluckily, the replacement of steel bolts with titanium ones, usually suggested because of their favourable ratio between strength and weight, is not quite straightforward. The coefficient of friction, a key parameter in bolted joints design, changes drastically when switching from steel to titanium. Some results concerning the frictional behaviour of bolted joints involving titanium screws are here presented: friction and torque coefficients were calculated, according to ISO 16047, for joints made up of a hexagon socket head screw made of titanium alloy (Ti–6Al–4V), a bush made of aluminium alloy (EN AW 7075 T6) and a steel nut (ISO 4032). Data were collected by performing several tightening tests on ad-hoc designed specimens, which allowed the evaluation of the different tribological behaviour of the same joint under three different conditions of lubrication (dry, Teflon^® added oil, and ceramic paste). 20 repeated tightenings (re-tightenings) have been analysed in order to simulate some maintenance operations. The DOE method was applied to manage the tests, while the results were analysed by the ANOVA and P-value methods. Out of the two lubricants examined, the ceramic paste showed the best results in terms of friction coefficients constancy throughout the re-tightening operations, as well as the best protection of the thread and underhead surfaces against wear.     

机械结合部单元静态变形分析研究

整机是由许多通过结合部连接的构件组成的整体,而螺栓结合部是机床设计中的主要问题之一。螺栓结合部的结合状态比较复杂,研究过程和方法也相对复杂。结合面的研究首先从结合面的静态特性开始。该文首先简要介绍了影响结合部静态特性的主要因素及接触理论,并通过非线性接触表面层理论对螺栓结合部的接触变形进行了解析计算,为整机结合部的静态特性分析提供了边界条件。     

Frictional changes during repeated tightening of zinc plated threaded fasteners

Tightening a bolt to a torque value is the most popular means of controlling the preload provided by a threaded fastener. However, repeated tightening and loosening of a threaded fastener, can have a dramatic effect on the friction coefficient. These changes will, in turn, will affect the preload and can, therefore, have an adverse effect on the structural integrity of an assembly. This study investigates the effect of repeated tightening on electro-zinc plated (EZP) nuts, bolts and washers. It is found that significant wear of the contact surfaces of the bolt/nut thread and nut face occurs upon repeated tightening.     

低温BOG压缩机活塞杆运动件预紧力的研究

BOG压缩机是对LNG储罐中蒸发出的气体进行加压的设备,其主要特点是工作在低于-100℃的超低温下。在如此低温下工作,压缩机的螺纹连接件预紧力状况会和常温预紧时产生很大变化。本文以BOG压缩机活塞杆螺栓连接为研究对象,提出了一种能预测螺栓低温预紧力变化的理论公式并进行了精度修正,通过有限元模型验证了理论公式在计算活塞杆螺栓预紧力变化的有效性,结果表明,通过理论公式与有限元模型的对比,表明结构即使不完全符合理论公式的要求,理论公式与有限元计算仍然较为吻合。在螺栓连接材料为304不锈钢和SIC815合金钢组合下,常温下预紧至60%屈服应力的螺栓连接,在-125℃低温下预紧力会产生30%的松弛。此外,本文对往复活塞力以及应力集中对活塞杆螺栓应力状态的影响进行了分析,并以理论公式为基础,将应力集中、工作温度范围、外部静载等因素考虑在内,提出了针对不同状况的螺栓常温预紧力取值范围,可满足较广范围螺栓连接预紧力取值的需求。     

由振动引起的螺栓连接预紧力松脱的数学模型

引入一种数学模型以研究螺纹连接在横向振动作用下引起的松脱.此横向振动激励会引起螺纹接触面间的滑动以及螺栓头与支撑表面之间的滑动.式中包括剪切力、支撑力以及螺纹摩擦阻力矩,它们均与振动速度相关,当所施加横向振动激励足够大时,螺纹连接会出现松脱现象.本文研究了螺栓预紧力、支撑力及螺纹摩擦系数、横向振动激励以及螺栓头下部弯矩...     

Friction and wear behaviour of AISI 5140 steel under rectangular wave loading conditions

Abstract

The tribological characteristics and wear mechanisms of AISI 5140 steel at ambient temperature were investigated using a home built ball on disc tribometer under constant normal loading and rectangular wave loading respectively. The worn surface and wear debris collected from the disc were studied using scanning electron microscope. Results show that the friction coefficients under the constant normal force correspond to the traditional theory. The coefficients all exhibited increased normal loads, whereas under the rectangular wave condition, the highest coefficient appeared when the peak value of the periodically alternative load was 90?N. The different underlying wear mechanism under different loading conditions was explored. It was found that abrasive wear was the main mechanism in the constant loading, whereas severe plastic deformation and adhesive wear were the main wear mechanism in the rectangular wave loading cases. This phenomenon can be attributed to the role of debris in the ‘lubrication’ process under the rectangular wave loading conditions.     

Longevity enhancement of bolted joints for aircrafts

New designs of bolted joints with bolt countersunk heads having high longevity in comparison with the used ones were proposed. One type of joint has the bolt heads with the reduced surface taper of the bolt head and in a joined part. Two other types have a spherical head surface, which is in contact with a tapered countersink surface. The rise in the fatigue life is achieved owing to the balance of the radial tension along the contact surfaces of the head and the countersink. Designs of a washer from the direction of a nut are proposed. These washers have ring bulges of wedge-shaped cross section that form areas of plastic deformations around a bolt body during the bolt tightening and reduce the concentration of contact stresses close to an edge of the contact surfaces of the bolt and joined parts. Procedures of fatigue tests were developed. Results of tests of the proposed bolted joints supporting their high longevity are presented. Findings of experimental investigations verify the efficiency of the application of proposed types of bolted joints in the designs of aircrafts.     

楔形螺纹连接扭拉关系理论分析及拧紧特性

楔形锁紧螺母是一种应用广泛的防松结构,但是当前关于楔形螺纹连接的扭拉关系理论分析和拧紧特性因素分析的研究成果匮乏,导致楔形锁紧螺母的安装工艺一直缺少理论指导。首次建立并验证了楔形锁紧螺母拧紧过程的扭拉关系理论公式,并对其拧紧特性进行了影响因素分析。首先考虑楔形螺纹面的复杂几何形状,构建楔形斜面上任意区域的局部坐标系,通过坐标转换获得了任意楔形区域的平面方程、切向和法向矢量,在此基础上建立楔形锁紧螺母拧紧过程的扭拉关系理论公式;然后建立精确的楔形螺纹连接有限元模型,仿真了实际的拧紧过程,通过改变不同的摩擦系数、楔形角和螺距,得到拧紧扭矩-预紧力的离散数据点,通过对比理论公式所绘制的扭拉关系直线,从数值仿真角度验证了楔形螺纹连接扭拉关系理论公式的可靠性;同时,采用航空航天领域的两种典型楔形锁紧螺母作为试验对象,通过拧紧试验进一步验证理论公式的可靠性。最后系统研究了螺栓螺母材料、被压件材料、螺纹规格、螺母结构形式、拧紧次数等因素对楔形锁紧螺母扭矩系数和重复拧紧性能的影响规律。     

栓接结合部迟滞非线性建模与辨识方法

由于栓接结合部是导致结构发生复杂非线性特性的主要因素,而对栓接结合部的传统处理方法往往忽略结合部的非线性特性或采用等效线性化的数学方法来建模,造成无法准确分析和研究栓接结合部的非线性动力行为。通过实验研究结合部上微凸体间相互挤压、搓动引起的能量耗损机理,运用Iwan模型描述栓接结合部的迟滞非线性现象。在准静态条件下获得力位移实验数据,利用无约束非线性优化方法和Newton迭代法辨识出Iwan模型中的未知参数,从而获得随外载荷幅值变化下的迟滞非线性特性,并与实验结果进行比较。结果表明,利用Iwan模型能够准确反映出栓接结合部所表现出的能量迟滞机理和非线性行为。     

A two phase circular regression algorithm for quantifying wear in CV joint ball race tracks

In this paper, a two-phase circular regression algorithm is presented for extracting wear profiles from Rzeppa-type constant velocity (CV) joints and for quantifying race track wear. In ball races operating under harsh cyclic loading conditions the predominant brinelling and “false brinelling” wear mechanism result in small indentations or grooves in the race track. These are particularly difficult to measure as the reference or nominal surface is curved in two planes in three-dimensional space. The presented algorithm achieves absolute measures of ball race track wear by a two-phase surface fitting regression methodology. The wear grooves are identified in the first phase and extracted to obtain sections of “unworn” surface; in the second regression phase, these sections are used to construct the datum surface and to establish absolute measures of wear groove depth. An important property of this algorithm is that it does not require the user to input parameters specific to the particular type or size of joint. This is particularly important in automotive aftermarket applications such as in drive-line servicing and in CV joint rebuilding/recycling. Results presented for a range of different CV joints demonstrate that race profiles can be obtained quickly and efficiently and that wear groove depth can be measured accurately to a ±3σ repeatability of 2.4 μm (±0.000 093 in).     

Duplex positioning method for increasing the fatigue life of threaded connections under eccentric loading

A new method, duplex positioning method DPM, to increase the fatigue lifetime of the threaded connection under eccentric loading is presented. When DPM is applied, the most damaged stud regions periodically are removed from risky positions by a change of the stud’s and nut’s mutual position in the axial direction alongside with a change of the stud’s position in respect to bending plane. The mathematical model for DPM enables us to predict its efficiency. To simulate the fatigue strength of the stud the following was used: Patterson’s and Kenny’s thread deflection factors, solutions for the distributions of the axial load and bending moment along the threads, Neuber’s method for the stress concentration factors in multiplier notches, Heywood’s formulas for the stress due to the thread flank loading and for the combined stresses, as well as the results of the photoelastic analysis of the araldite models under eccentric loading.

     

螺旋传动中酚醛树脂螺母螺牙载荷分布研究

通过有限元分析研究了螺旋传动结构中酚醛树脂螺母的受力特征,得到了它在传动受力时各部分的变形、应力分布曲线。结果表明整个螺母螺牙上载荷分布非常不均匀,螺纹出口处受力最大,但结构却最薄弱,因此此处最危险。通过优化找到了一种合理结构,此结构能够使螺母螺牙载荷分布较为合理,减小最薄弱部分承受的载荷。     

紧固件横向振动试验台的研制

详细介绍了紧固件横向振动试验台的原理、组成及各部分主要结构。该试验台具有试验周期短、可试验项目多、结构简单和成本低等优点。实践证明,该试验台能有效测试螺纹联接的防松性能。     

Improvement of tribological performance of steel by solid lubricant shot-peening in dry rolling/sliding contact wear tests

The effect of shot-peening treatment with the particulate MoS₂ solid lubricant on the wear resistance of steel in the dry rolling/sliding contact wear tests was investigated. The duplex shot-peening treatment with ceramic balls and the particulate MoS₂ solid lubricant provided excellent wear resistance under a severe loading and sliding condition because the uniform and minute surface roughness given by shot-peening treatment with ceramic balls could keep shot-peened MoS₂ particles with a low friction coefficient on the sample surface. Furthermore, the sample surface was covered with shot-peened MoS₂ particles by a MoS₂ layer formed during the rolling/sliding contact wear test.     

高温环境复合材料螺栓连接振动的防松试验

具有耐高温、轻质、高强等特点的复合材料及其连接结构可满足航空航天领域的迫切需求,已广泛应用于工程中。为比较高温振动环境下不同复合材料螺栓连接形式的防松效果,进行了常/高温条件复合材料搭接板的随机振动试验研究。以搭接结构固有频率为评判量,通过对比试件承受振动载荷作用前后的固有频率变化,研究了常/高温环境下高温胶、双螺母防松形式,以及沉头螺栓张角等因素在给定随机振动载荷下对搭接结构连接刚度的影响。研究结果表明:常温随机振动条件下双螺母防松、60°沉头螺栓的防松性能更好;高温环境下,高温胶防松、30°沉头螺栓连接形式性能较优。     

螺纹联接防松方法的评述

本文分析了紧固螺纹联接松动的原因，对常用的多种防松型式进行了性能比较，指出了螺纹防松装置的设计要点是设法阻止紧固螺纹副之间的相对转动，最后对几种新的防松型式做了简要的介绍。     

Kinetic characteristics of the transformation and failure of the surface layers of metals under dry friction

The proposed approach, based on a model of normal wear, permits separate treatment of the processes of transformation and destruction of the surface layers of metals under friction. The relevant rate constants and the corresponding quantities of cyclic loading were determined and plotted against the load per unit area and the sliding velocity for dry friction. The transformation process was found to consist in oxidation of the frictionactivated metal; it obeys a parabolic rate law, with a rate constant close to that for the formation of Fe₃O₄ at 950 °C. The destruction process is governed by fatigue mechanisms and takes place at the metal-film interface.