盘形制动系统颤振临界速度的计算及分析

建立干摩擦的单自由度盘形制动系统动力学模型,基于微分包含理论建立其数学模型,采用数值方法计算系统发生颤振运动的临界速度,并讨论阻尼比、动摩擦因数以及最大静摩擦因数与动摩擦因数之差对临界速度的影响。结果表明:系统发生颤振的临界速度随着阻尼比的增大而减小;随动摩擦因数的增大而增大;在动摩擦因数确定的情况下,随最大静摩擦因数与动摩擦因数之差增大而增大,但最终趋于恒定,在阻尼比ζ=0.001情况下最大静摩擦因数为动摩擦因数1.115倍左右时临界速度不再发生变化。     

链传动爬行仿真及试验分析

对链传动设备上所出现的爬行现象进行理论及试验分析,根据系统运动特点进行模型简化,建立数学方程,讨论不同阻尼系数、传动系统刚度、驱动速度以及动摩擦因数对负载运动的影响,并结合数值及ADAMS仿真结果进行试验验证,得到通过合理设计传动机构来提高系统刚度或采用滚动摩擦及液体摩擦等方式来减小摩擦因数可有效提高负载运动的平稳性的结论。     

水下结构物二次就位计算分析

由于轧机的水平振动对板带质量影响很大,为减小水平振动、提高板带质量,文中通过四辊冷轧机的工作机构模型,建立了新的水平非线性动力学模型;根据多尺度法,求得系统的频响方程,并通过MATLAB对其进行了仿真。仿真结果表明:主共振振幅随着工作辊水平方向的线性阻尼和垂直方向激振力波动值的增大而增大,非线性阻尼、线性刚度、非线性刚度和垂直方向激振力均值的增大而减小;工作辊和支承辊之间的偏心距越大,共振区越大,共振峰值越小。     

四辊冷轧机水平非线性主共振分析

由于轧机的水平振动对板带质量影响很大,为减小水平振动、提高板带质量,文中通过四辊冷轧机的工作机构模型,建立了新的水平非线性动力学模型;根据多尺度法,求得系统的频响方程,并通过MATLAB对其进行了仿真。仿真结果表明:主共振振幅随着工作辊水平方向的线性阻尼和垂直方向激振力波动值的增大而增大,非线性阻尼、线性刚度、非线性刚度和垂直方向激振力均值的增大而减小;工作辊和支承辊之间的偏心距越大,共振区越大,共振峰值越小。     

机床导轨爬行问题的双质体模型的仿真分析

爬行是机床中一种常见的不利于机床工作的现象，会直接影响机床的加工精度与品质，为了解决机床导轨的爬行问题，以提高机床的加工精度与品质，对影响机床导轨爬行问题的各类因素进行了研究。首先，在单质体爬行模型的基础上，选用了双质体传输带系统模型；然后，通过ADAMS对其进行了建模仿真；最后，对该仿真结果进行了数据处理，遵循控制变量的原则，通过逐一改变参数，得到了不同条件下物体的速度时间曲线；选择速度波动量、最大速度误差、纹波率作为爬行的评价指标，绘制了速度误差随时间的变化曲线；并计算了纹波率，进而对物体的爬行程度进行了比较分析。研究结果表明：为了有效抑制机床的爬行，可以采取减小系统质量、增加阻尼、选择最佳刚度值、增加驱动速度、减小动摩擦因数与静摩擦因数之差等方法。     

液压缸低速爬行动力学研究

分别建立了横、垂向液压缸的低速爬行动力学模型，研究了不同要素对横、垂向液压缸低速特性的影响规律，并提出提高液压缸低速控制精度的方法。研究结果表明，减小液压缸活塞倾斜角度、静动摩擦因数差、摩擦降落系数、活塞质量，增大液压油阻尼系数、排除油液中的空气时可以改善液压缸低速爬行特性。     

机床切削系统摩擦颤振影响因素分析

建立舍干摩擦的单自由度机床一刀具系统的动力学模型,列写运动方程,确定系统发生颤振的临界驱动速度,给出计算临界驱动速度的计算流程图,采用理论分析和数值仿真方法讨论驱动速度、动摩擦因数、系统阻尼比对系统颤振的影响。结果表明,发生颤振后,驱动速度对于颤振的影响较为显著,动摩擦因数主要影响颤振的平衡位置,系统阻尼比对颤振的影响较为微弱,最后给出降低颤振的几项措施。     

MEMS中梯形变截面梁优化设计

MEMS器件结构设计影响传感器的性能。为了提高加速度计系统稳定性,选用梯形变截面梁减小应力集中,同时将检测方向刚度和非检测方向刚度差值最大,减小交叉灵敏度并提高工作稳定性;为使系统动态特性达到最佳,选用合适的阻尼比ξ,计算出梁检测方向理论刚度。建立梯形变截面梁的力学模型,得到梯形变截面梁刚度方程,并给出了梁的强度。梯形等截面梁和梯形变截面梁同等刚度条件下,变截面梁质量稍微增加,但危险截面处应力大幅下降。     

机床地脚低速滑动界面法向刚度分形模型及试验验证

按照一个弹性微凸体的平均接触压强构筑微凸体顶端接触变形。计及动摩擦因数计算微凸体最初屈服的临界平均压强。采用以无阻尼自然角频率为自变量的功率谱密度函数,给出识别界面分形维数、特征长度的理论和试验方法。仿真结果表明:微凸体最初屈服的临界平均压强随着动摩擦因数的增加而变小;分形区域扩展因数随着分形维数的增加而减小;微凸体最大结合面积随着分形维数的增加呈现线性减小;增加动摩擦因数、面积比和特征长度都将衰减法向接触刚度;法向接触刚度随着分形维数、接触面积的比率、法向接触载荷或微凸体最大结合面积的增加而增强。按照有限元模拟对界面法向接触参数识别结果进行证明。考虑界面参数的有限元模型得到的动柔度、法向接触刚度数据与试验数据一致。     

机床液压爬行机理及控制技术

分析了液压爬行运动的成因、机理及其危害性,从减小静动摩擦系数之差,提高传动刚度,增加阻尼比,减少移动件质量等角度提出一系列控制措施。     

Numerical analysis of stick-slip instability by a rate-dependent elastoplastic formulation for friction

In various fields of engineering, it is important to clarify friction-induced vibration, such as stick-slip motion, for a wide range of scales from microscopic elements to continental plates. In the present study, we apply a rate- and state-dependent friction model [30] (Hashiguchi and Ozaki, 2008), which can rationally describe the reciprocal transition between the static friction and the kinetic friction by a unified formulation, to the simulation of stick-slip instability for a one-degree-of-freedom spring-mass system under various conditions. It is verified that the various basic experimental findings on stick-slip motion can be pertinently described by the present approach. Moreover, the effect of the dynamic characteristics of the system, such as the mass, stiffness and driving velocity, is discussed, and parameters prescribing the rate of reciprocal transition of static-kinetic frictions and the preliminary microscopic sliding on the instability of the stick-slip motion are also discussed.     

Stick-slip algorithm in a tangential contact force model for multi-body system dynamics

Contact force of Multi-body dynamics (MBD) system can be classified two parts. First is a normal force and the other is a tangential force called friction force. And the friction force can be represented by two states such as stick and slip. The stick-slip phenomenon is simply described as a simple contact model which is a rigid body contacted on a sloped surface. If the calculated friction coefficient between the body and sloped surface is less than the static friction coefficient, the body should be stuck. If the calculated friction coefficient is greater than the static friction coefficient, the body will be sliding along the surface. The phenomenon is called as stick and slip state of friction, respectively. Usually many researchers and commercial MBD software used a coulomb friction force model which is defined with an only function of relative velocity. This kind of friction force model will be called a conventional friction force model in this paper. A big problem of the conventional model can not describe a stick state of friction phenomenon. In the case of conventional friction force model, the body will be sliding even though friction state is stick. Because, the relative velocity must have a non-zero value in order to generate the friction force. To solve this kind of problem, we propose a stick-slip friction force model including a spring like force. In the case of stick-slip friction force model, the body can be stuck on the sloped surface because the friction force will be a non-zero value, even though the relative velocity approaches zero. We defined a relative displacement variable called stiction deformation. In this paper, the stick-slip friction model is proposed and applied in the contact algorithm of MBD system. And then two friction models are compared with numerical examples. With the proposed stick-slip friction model, more realistic results are achieved.     

Stick-Slip Motion in Boundary Lubrication

Using dynamical analysis for a pin-on-disk sliding system and the consideration of meniscus formation at the sliding interface, a wide range of experimental observations on stick-slip motion can be explained. It is shown that when the initial growth rate of the static friction force is larger than about half the product of the substrate speed and the spring constant, slick-slip motion occurs in that sliding system. The critical substrate speed or the critical spring constant, above which stick-slip motion ceases, can thus be determined. It is also shown that the saturation substrate speed, below which stick-slip motion retains its maximum stick-slip amplitude, is inversely proportional to the total growth time of the static friction force. The maximum stick-slip amplitude is proportional to the final difference between the static and kinetic friction force. For a thicker surface liquid-film, the initial growth rate and the final static friction force are larger but the total growth time is shorter, resulting in a larger critical speed, a larger stick-slip amplitude, and a larger saturation speed. For rougher contact surfaces, the initial growth rate is larger but the final static friction force and the total growth lime are smaller, resulting in a larger critical speed, a smaller stick-slip amplitude, and a larger saturation speed.     

基于非连续能量耗散的界面摩擦黏滑行为动力学研究

建立界面摩擦过程黏滑行为动力学模型,仿真分析摩擦系统内外因素对黏滑行为的影响规律.结果表明:界面摩擦过程中,黏滑行为不仅与材料本身如晶格常数、原子质量、原子间横向刚度系数有关,而且与系统外界参数如滑动速度及滑动部件的质量有关;材料的原子间横向刚度、晶格常数、原子质量、滑动机构质量愈小,黏滑行为愈显著,而相对滑动速度愈大,黏滑行为愈显著.     

离合器从动盘性能对汽车耸车的影响

为了研究离合器从动盘性能对汽车耸车振动的影响,建立了传动系统-汽车整车的11自由度非线性动力学模型。模型考虑了离合器从动盘的扭转特性、干摩擦阻尼、离合器接合黏滑特性以及变速器轮齿啮合刚度。利用建立的模型计算汽车起步过程系统动力学响应,通过实车测试验证模型的正确性,分析离合器从动盘性能参数对耸车振动的影响。结果表明:汽车的耸车现象发生在离合器完全接合之后;耸车振动频率与传动系第2阶固有频率相近;提高静摩擦因数,降低从动盘转动惯量和2级扭转刚度,可以降低汽车在起步过程中的耸车振动。本研究的建模和分析方法,可以用来计算与分析离合器从动盘结构性能参数对整车耸车振动特性的影响。     

热连轧机横向-垂向耦合振动研究

为了研究某热连轧机组的振动特性,根据轧制界面粘滑摩擦特性和轧辊轴承座-牌坊接触非线性,建立轧辊-轴承座有无间隙时的轧辊横-垂向模态耦合振动模型.分析表明,当系统刚度和外激励频率处于某区段时轧辊横向和垂向振动幅值均出现大幅波动的现象,轧制生产中应避开此范围;机座有间隙时,轧辊出现跳振,轧辊横向响应曲线有明显的削顶现象,辊系动力学性能变差.     

矿用汽车油气悬架系统建模与仿真

以WC5铰接式矿用汽车的油气悬架系统为研究对象,建立了包括刚度、阻尼、摩擦等因素的油气悬架系统非线性数学模型,并对油气悬架系统刚度特性和阻尼特性进行分析;分析表明,蓄能器初始条件直接决定着油气悬架的刚度特性,增大悬架缸的内径,减小单向阀、阻尼孔的直径则产生的阻尼力增大,这为矿用汽车油气悬架系统的设计提供了一定的参考依据。     

The generation of dislocations in metals under a sliding contact and the dissipation of frictional energy

Observations on static friction behaviour under stick-slip vibration conditions are presented. A static contact-time model of static friction does not adequately describe the observed variation in static friction; the governing variable is the rate of increase of the tangential force coefficient.     

NONLINER VIBRATION ANALYSIS OF THE PLATE WITH DRY FRICTION SUPPORT CONDITION

The rigid-interface friction model is usually used in the nonlinear vibration of the rectangular plate with dry friction support edges. The present study provides an extension by using a hysteretic spring friction model and taking account of the stick-slip motion of the plate. Results for a range of problem parameters have been obtained. The results show that the nonlinear frequency response behavior of the system can be quite different from the rigid-interface friction model. The effects of the stiffness at friction interfaces and the stick-slip motion on the nonlinear vibration of the plate are significant and hence cannot be neglected.