摩擦系数对微铣削加工的影响

运用ABAQUS有限元分析软件对TC4进行仿真,建立了基于次摆线的二维铣削模型,分析了摩擦系数的变化对铣削力、温度及残余应力的影响。分析发现:随着摩擦系数的增大,铣削力增大,温度升高;当摩擦系数增大到0.4以上时增幅降低;残余应力随着摩擦系数的增大而增大,拉应力层会缓慢增加。     

倒圆刀刃对大应变挤出切削过程的影响

在大应变挤出切削有限元模拟过程中,设定主切削刀具的刃区型式为倒圆,通过相关参数的变化,仔细观察模拟过程中等效应变、等效应变率等参数的变化规律。研究结果发现:切削过程中的等效应变、等效应变率、等效应力和温度呈带状分布;当倒圆刀刃半径由小增大时,最大等效应变先小幅度减小再大幅度增大;最大等效应变率的变化有起伏,总体趋势为减小;最大等效应力和最高温度基本不变;主切削力的增加效果不明显;进给抗力大小明显增大。     

螺栓摩擦系数对连接防松影响的有限元分析

螺栓连接受横向振动载荷一段时间后,容易出现连接松动,夹紧力衰退,夹紧失效等现象.国内鲜见钎对螺纹连接松动现象的有限元仿真,文中利用ABAQUS有限元软件建立了螺栓连接模型,对连接松动过程进行仿真.以建立的松动模型为基础,通过对比几组螺栓连接的防松特性,得到了螺栓连接摩擦系数越大其防松性能越佳的结论,该结论与螺栓连接的摩擦力矩防松机理相吻合.     

摩擦系数对非球面玻璃透镜模压成型的影响

研究了非球面透镜玻璃模压成型过程中玻璃-模具界面的摩擦行为对成型透镜质量及成型效率的影响。针对不同的摩擦系数,对玻璃模压过程进行了热-机耦合的有限元模拟。结果表明:(1)随着摩擦系数的增大,透镜表面的等效应变减小,而透镜内部的等效应变明显增大,合模时间变长;(2)随着摩擦系数的增大,透镜内的残余应力的最大值增大,残余应力向透镜表面集中;(3)摩擦系数对透镜成型后的面型偏差影响很小。因此,为了降低透镜成型后的残余应力和提高成型效率,应减小模具和透镜接触面上的摩擦系数,但无法通过改善接触面上的摩擦情况来减小面型偏差。     

应变强化技术对压力容器稳定性的影响分析

压力容器经过应变强化技术处理后,容器整体部分发生了显著的塑性变形,目前国际上现有的应变强化规范中,容器的实际变形往往达到3%-5%,而应变强化后容器的设计仍按照预应变强化前的原始尺寸进行设计,设计思路是否合理尚未得到验证。塑性变形对压力容器整体稳定的影响尚不明确,这也使得应变强化后容器的安全性存在隐患。本文分析应变强化引起的容器主体塑性变形对内压时塑性极限载荷与外压临界载荷的影响。     

摩擦圆辊直径与摩擦包角对板成形摩擦系数测量的影响

基于Duncan方法设计了一种板料成形摩擦系数测试装置,用以考察摩擦圆辊的直径和摩擦包角对摩擦系数计算的影响。正交试验分析表明:随着摩擦圆辊直径和摩擦包角的增大,由板料弯曲和包角边界造成的摩擦系数计算干扰效应将逐级减小,进而计算摩擦系数也逐步减小,并且最终趋向真实摩擦系数。基于最终试验分析结果,得出包角在90°,圆辊直径在30 mm左右时,测得的摩擦系数可以忽略弯曲效应和包角边界效应,能反映真实摩擦状态,可以用于后续的金属板料成形有限元模拟。     

梯形结构的大应变传感性能研究

以弓形曲梁式梯形结构为研究对象,首次应用单位荷载法推导了梯形结构的大应变传递灵敏度模型,推导过程简单,模型表达式明晰。建立了梯形结构的ANSYS有限元分析模型,模拟计算得到的应变传递灵敏度与推导的理论模型一致。采用光纤光栅作为结构的小应变测量元件,制作了大应变计试样。电动平移台给定待测大应变,光纤光栅监测仪测量光纤光栅的波长信号,实验结果显示:试样实际传感结果与理论分析结果相符,试样在实验中获得的正向应变范围为0～33.3%,负向应变范围为0～-16%,其线性度在1%以内,重复性和迟滞误差分别为1%和0.9%。     

基于有限元法分析高速切削时摩擦系数对高速切削的影响

为了探究高速切削时,刀具与切屑间摩擦系数对切削的影响,采用有限元通用程序ABAQUS／Explicit,对不同摩擦系数下正交切削过程进行数值模拟。据此研究了刀具摩擦系数对高速切削中切屑变形、切削力的影响。     

不同加载方式的齿板应力应变有限元仿真

应用确定性力学方法对破碎机齿板的应力应变进行了有限元仿真研究；为满足齿板应力应变等方面的有限元分析之需要，应用模糊随机理论对颚式破碎机齿板载荷施加方法进行了初步探讨，确定了各齿面的载荷状况；给出了计算结果和有限元仿真结果；齿面载荷的隶属度函数呈钟形分布，表明齿面受力情况为中间大，两边小，反映了齿板的真实受力情况。     

电场对摩擦系数的影响的研究进展

人们很早就发现了摩擦中伴生的电现象以及外加电场或电流影响摩擦系数的事实,这引起了许多学者的兴趣,并对其作用进行了初步的研究。近来,人们又设想通过外加电场这种手段对摩擦系数进行主动控制,以达到减摩、降噪、控制阻尼及某些精密机械的运动等目的。这方面的研究结果在节约能源、提高精密机械性能等方面具有很大的意义和实用价值。     

Effect of variable friction coefficient on contact tractions

Friction coefficient plays an important role in determining the contact tractions and consequently the stresses that drive damage mechanisms in components subjected to fretting fatigue. Friction coefficient evolves to different magnitudes at different points in the contact interface. Effect of this spatial variation in friction coefficient on the shear distribution for contacts involving similar isotropic materials has been presented in this paper. Full sliding tests have been conducted to obtain friction coefficient as a function of sliding distance. Well characterized set of experiments to determine the average friction coefficient in fretted specimens is briefly discussed. Existing analysis for obtaining the shear traction for arbitrary smooth profiles has been modified to take the variation of friction coefficient from one point to another into account. Using this analysis, spatial variation of friction coefficient in fretted specimens has been obtained. It has been found that using a constant friction coefficient (equal to the slip zone friction coefficient) throughout the contact zone is a good enough approximation in most of the cases. However, in some cases, when the slip zones extend into regions where the friction coefficient has not reached the asymptotic value, actual distribution of friction coefficient gives a different shear stress distribution as compared to a constant slip zone friction coefficient.     

一种摩擦系数计算方法

通过以一定法向压力相互接触的两物体之间的接触柱,在滑动摩擦过程中的物理变化和几何关系,揭示滑动摩擦形变机理,推导和建立关于摩擦系数的计算公式,计算结果与实验法数值基本相符,说明计算公式具有一定的参考价值。     

The significance and use of the friction coefficient

The quantity known as the friction coefficient (or ‘coefficient of friction’) has long been used in science and engineering. It is easy to define, but not easy to understand on a fundamental level. Conceptually defined as the ratio of two forces acting, respectively, perpendicular and parallel to an interface between two bodies under relative motion or impending relative motion, this dimensionless quantity turns out to be convenient for depicting the relative ease with which materials slide over one another under particular circumstances. Despite the fact that both static and kinetic friction coefficients can be measured with little difficulty under laboratory conditions, the time- and condition-dependent characteristics of friction coefficients associated with both clean and lubricated surfaces have proven exceedingly difficult to predict a priori from first principles.The shaky nature of friction's fundamental underpinnings, has not prevented investigators from compiling lists of friction coefficients and publishing them for general use. Problems often arise, however, when engineers attempt to use tabulated friction coefficients to solve specific problems in mechanical design or failure analysis. The systems-dependence of frictional behavior is sometimes ignored, leading to misapplication of published data. This is particularly true for applications in nano-technology and others that differ from typical laboratory size scales. This paper will review the measurement and use of static and kinetic friction coefficients, discuss their usefulness, and describe the sources of frictional resistances in terms of shear localization.     

Determination of friction coefficient encountered in large deformation processes

A new technique, namely, the open-die backward extrusion test technique, was developed as an alternative method to the ring compression test in order to quantitatively evaluate the coefficient of friction, μ, at the die/workpiece interface. This technique relates the percentage deformation in height of the specimen to the percentage increase in extruded height of the specimen. In this study, the open-die backward extrusion tests (ODBET) were simulated for different aspect ratios, (H/D), and different die geometries, (d/D), by utilizing an elastic-plastic finite element code (ANSYS) in order to obtain the friction calibration curves (FCCs). The results indicated that the extruded height is related to the friction conditions at the die/workpiece interface. Therefore, ODBET can be used to generate FCCs to determine the coefficient of friction at the die/workpiece interface in large deformation processes.     

电梯门机系统摩擦系数的计算

电梯的绝大部分事故都出在门系统上,而门机系统的摩擦力和摩擦系数是反映门机性能的重要指标.建立了电梯门机系统的动力学模型,通过模型计算的加速度和传感器实测的加速度进行比较获得误差函数,对其优化查找最小值,与最小值对应的未知量为门的倾角力和摩擦力,进而计算出反应门机性能指标的系统摩擦系数,为研究电梯门机性能和系统智能维护打下基础.     

The effect of frequency of vibration and humidity on the coefficient of friction

Variation of friction coefficient with the variation of frequency of vibration and relative humidity is investigated experimentally on a mild steel disc. A pin-on-disc apparatus having facility of vibrating the disc at different frequency and amplitude is used for the experiment. During the experiment, normal load, speed and relative humidity were varied. The surface conditions of the mild steel base plate were ‘as-turned’ and ‘as-ground’. It is found that friction co-efficient under no vibration condition is higher than that under vibration condition, and the values of friction co-efficient decrease with the increase of frequency of vibration. Similarly, the friction co-efficient decreases with the increase of relative humidity. It is also observed that the rate of reduction of friction co-efficient has a particular relationship with the frequency of vibration and the relative humidity.     

The effect of amplitude of vibration on the coefficient of friction for different materials

This work examines how friction coefficients are affected by amplitude of normal vibration at different frequencies. Variation of friction coefficient with the amplitude of normal vibration is investigated experimentally when mild steel pin slides on different types of material such as glass fiber reinforced plastic, cloth reinforced ebonite, polytetrafluoroethylene (PTFE), rubber and mild steel. For this, a pin-on-disc apparatus having facility of vibrating the test samples at different amplitudes and frequencies of vibration was designed and fabricated. During the experiments, the effects of sliding velocity, roughness, normal load and duration of rubbing were also investigated. Studies have shown that the friction coefficient decreases with the increase of amplitude of vibration within the observed range. The observed ranges of amplitude of vibration were 10–200 μm. In this study, it is also observed that the rate of reduction of friction coefficient has a particular relationship on the amplitude and frequency of vibration. The experimental results are compared with those available in the literature and simple physical explanations are provided.     

Modeling the effect of skewness and kurtosis on the static friction coefficient of rough surfaces

Engineering surfaces possess roughnesses that exhibit asymmetrical height distributions. However, the Gaussian distribution is most often used to characterize the topography of surfaces, and is also used in models to predict contact and friction parameters. In this paper, the effects of kurtosis and skewness on different levels of surface roughness are investigated independently. This is accomplished by adopting the Pearson system of frequency curves and used in conjunction with a static friction model for rough surfaces to calculate the friction force and friction coefficient. This study is the first attempt to independently model the effect of kurtosis and skewness on the static friction and friction coefficient. It is predicted that surfaces with high kurtosis and positive skewness exhibit lower static friction coefficient compared to the Gaussian case. More importantly, it is predicted that, for high kurtosis values, the static friction coefficient decreases with decreasing external force rather than increasing as seen with increasing skewness. This is a very promising result for applications involving smooth lightly loaded contacts such as magnetic storage devices and microelectromechanical systems. The practical significance of the present model is specifically demonstrated on static friction predictions in magnetic storage head–disk interfaces. Such predictions can be used to determine the optimal characteristics of such devices prior to fabrication to achieve lower friction in terms of surface roughness, mechanical properties, apparent contact area, and operational environment.     

Effect of surface coating and tin plating on friction characteristics of P-110 tubing for different thread compounds

Design factor problems related to galling failure have become an increasing concern for deepwater offshore wells. This paper presents the results of an experimental study conducted to determine friction characteristics of P-110 tubing coated with manganese phosphate and plated with tin. Six repeated tests were run to investigate the effect of lubrication type on friction characteristics of P-110 tubing by using thread compounds of API modified Threadkote-706, Shell Type-3 and Graphite/PTFE at a rotational speed of 5 rpm. In each test the bearing load was increased monotonically to a maximum value of 625 kN. The results of this study clearly indicate the importance of tin-plating in reducing the coefficient of friction.     

Inverse calculation of the friction coefficient during the warm upsetting of molybdenum

This study focused on the variation of the friction coefficient during the upsetting process and the concept of treating the solution of unknown parameters as an inverse problem. Based on the experimental measurement data, the Levenberg–Marquardt method, a numerical optimization approach was used in conjunction with the constrained function, convergence criterion and the axial symmetry thermo-elastic-plastic finite element method to solve, inversely, the variation of friction coefficient during the upsetting process.The inverse calculation steps of the warm upsetting of the molybdenum proposed in this paper was based on the load values measured in the upsetting experiment. The inverse calculation procedures were taken to solve the variation of the friction coefficient during the warm upsetting process. The results related to stress distribution, strain distribution, temperature distribution and shape variation were then compared with those reported in other studies. The comparison further confirmed the justification of using the load to solve the friction coefficient inversely. By means of the inverse algorithm presented in this paper, physical phenomena that better approximated the reality could be obtained, and the entire upsetting forming simulation could be more complete.