General Torsional Stiffness Matching of Off-road Vehicle

Increasing frame torsional stiffness of off-road vehicle will lead to the decrease of body torsional deformation, but the increase of torsional loads of flame and suspension system and the decrease of wheel adhesive weight. In severe case, a certain wheel will be out of contact with road surface. Appropriate matching of body, flame and suspension torsional stiffnesses is a difficult problem for off-road vehicle design. In this paper, these theoretically analytic models of the entire vehicle, body, frame and suspension torsional stiffness are constructed based on the geometry and mechanism of a light off-road vehicle's body, frame and suspension. The body and frame torsional stiffnesses can be calculated by applying body CAE method, meanwhile the suspension's rolling angle stiffness can be obtained by the bench test of the suspension's elastic elements. Through fixing the entire vehicle, using sole timber to raise wheels to simulate the road impact on a certain wheel, the entire vehicle torsional stiffness can be calculated on the geometric relation and loads of testing. Finally some appropriate matching principles of the body, frame and suspension torsional stiffness are summarized according to the test and analysis results. The conclusion can reveal the significance of the suspension torsional stiffness on off-road vehicle's torsion-absorbing capability. The results could serve as a reference for the design of other off-road vehicles.     

轮对蛇行运动的相位同步模态分析

基于单轮对蛇行运动模型,推导了考虑悬挂系统刚度和阻尼的系统特征根解析式,根据Routh-Hurwitz稳定性判据导出了轮对蛇行运动临界速度和频率公式。应用相位同步模态分析法,消除系统阻尼引起的相位差异,实现了轮对蛇行运动的非保守系统方程实模态解耦。研究表明,减小轮对质量、转动惯量及等效锥度,增大一系横向和纵向定位刚度及阻尼,增大轮径和接触点跨距能够提高蛇行临界速度,蠕滑系数降低不会降低蛇行临界速度;减小轮对质量和转动惯量,增大一系横向和纵向定位刚度,减小接触点跨距会增大临界速度对应的蛇行运动频率,悬挂系统阻尼对临界速度时的蛇行运动频率影响不大,而等效锥度、轮径和蠕滑系数对临界速度时的蛇行频率无影响。通过一系悬挂系统刚度优化可在理论上实现足够大的轮对蛇行运动临界速度。在任意运行速度时,均存在蛇行共振响应,响应幅值和频率随速度提高而增大。轮对蛇行运动中高阻尼模态在所有速度范围内均呈现过阻尼特征,轮对蛇行响应由低阻尼振动模态主导。     

Investigation of Lubricant Transfer between Slider and Disk Using Molecular Dynamics Simulation

A model for lubricant transfer from a rotating magnetic recording disk to a magnetic recording slider is developed using molecular dynamics simulation. The combined effect of disk velocity and local air-bearing pressure changes on lubricant transfer is investigated. The simulation results indicate that local pressure changes in the absence of disk circumferential velocity can cause lubricant redistribution on the disk, while local pressure changes on a moving disk can result in lubricant transfer from the disk to the slider. The amount of lubricant transferred from the disk to the slider and the lubricant buildup on the disk are a function of the local pressure change and disk velocity. The amount of lubricant transferred from the disk to the slider and the height of lubricant buildup on the disk surface decrease with an increase in the number of functional groups of the disk, a decrease in the local pressure change, and a decrease in the disk circumferential velocity.     

Identification of the Spectrum Signature of Air-Bearing Slider Dynamics

Characterization of the motion of air-bearing slider with sub-10-nm clearance is becoming a critical aspect of developing advanced head–disk interfaces (HDI) in hard disk drives to achieve higher areal data densities. In this article, the response of sub-10-nm clearance air-bearing slider induced by a bump contact is recorded using laser Doppler vibrometer (LDV). To identify system dynamics in terms of spectral decomposition, the slider response is studied using FFT, power spectrum density, spectrogram, and Hilbert instantaneous spectrum analysis. The results demonstrate that the response of air-bearing slider in instantaneous contact exhibits nonstationary and nonlinear properties which can be accurately identified using Hilbert instantaneous spectrum. The interpretation and spectrum identification based on Fourier analysis and its extension in time–frequency domain could lead to inaccurate results due to their limitation in resolution and linearity assumption.     

Molecular dynamics study of dynamic contact and separation between tip and disk surface

Molecular dynamics simulations were performed to study contact and separation between tip and lubricants on disk surface. The effects of contact indentation depth, indentation velocity, separation velocity, adhesive energy, lubricant molecular structure and lubricating film thickness on interacting force were analyzed. The results indicate that the tip force exerted by lubricants is velocity-dependent. The tip force increases with increasing indentation velocity and separation force reduces with increasing separation velocity. The damping of branched molecule and thick lubricating film is high. The high adhesive energy of tip material can produce high separation force which reduces bouncing vibration.     

Probability Model for the intermolecular force with surface roughness considered

This paper studies the intermolecular force considering both the roughness of the air-bearing surface and the disk surface by simulation. A model is developed to deal with the intermolecular force, the contact force and the air-bearing force based on the probability distributions of the roughness of the surfaces. The intermolecular force is linked with the contact force when its repulsive term is stronger than its attractive term. In such a case, all the intermolecular force, the contact force and the air-bearing force can be extended to the various flying height regions. Some interesting results are observed and discussed. It is found that both the Hamaker constant and the surface roughness have significant influences on the intermolecular pressure. Compared with the intermolecular pressure with smooth surfaces, that with the surface roughness considered shows greater attractive pressure at the flying height higher than 0.7 nm approximately, but much smaller values between 0.26 and 0.7 nm approximately. A negative stiffness region exists when the minimum flying height is between −0.2 and 1.2 nm for the case studied in this paper. It shows that the Probability Model is suitable for the intermolecular force calculation with the surface roughness considered.     

Atomistic study of lateral contact stiffness in friction force microscopy

The effective stiffness of a friction force microscope tip–substrate system is an important parameter that describes the relationship between lateral force and elastic deformation. In this study, we use a multi-spring model to simplify the system, where two contributions, the tip apex stiffness and the lateral contact stiffness, are discussed in detail. Molecular dynamics simulations are used to characterize stiffness by simulating a tip apex subject to shear or sliding over a substrate surface. The results show that, although the height of the tip apex and tip–substrate orientation affect the various stiffness contributions, the contact itself dominates the overall compliance.     

Nearmiss Count Between Flying Head and Magnetic Disk by Detecting Electrical Potential of Voltage-Applied Slider

A simple in-situ measurement of flying head dynamics is developed, making use of weak conductive sliders and media as capacitance and resistance sensors. This method is confirmed to detect such abnormal functioning occurring in the head-medium interface as nearmiss, contact or crash. Flying head dynamics are quantitatively studied, using a simple and effective method wherein the slider is excited by externally pressurized air flow. Without this disturbance, the nearmiss count is almost zero, with the number tending to increase up to a resonant frequency governed by the slider inertia and air film stiffness with increasing disturbance, presenting a maximum value at a disk velocity of 3 to 5 m/s.     

The Role of Slider/Disk Roughness in 1 Tb/in.2 Magnetic Recording

To achieve 1 Tb/in.² magnetic recording areal density, the head/disk spacing, or the flying height of the slider, has become so small that both the disk surface roughness and the slider air-bearing surface roughness need to be considered. In this region, the intermolecular force and the contact force become more significant due to the roughness of the two surfaces. This article targets two points: 1) slider/disk roughness effects on intermolecular force and 2) slider/disk roughness requirement for 1 Tb/in.² areal density. A probability model is built to simulate the intermolecular force and the contact force, and these two forces are introduced into the modified compressible Reynolds equation governing the air-bearing pressure of the slider. The equation is solved by the finite volume method based on an unstructured triangle-based mesh. The simulation results show that in 1 Tb/in.² areal density magnetic recording the effects of slider/disk roughness on the intermolecular force are negligible. Smaller R _a values will have fewer effects on flying performance.     

点蚀与剥落对齿轮扭转啮合刚度影响的分析

为了模拟齿面点蚀和剥落对齿轮扭转啮合刚度的影响,提出了利用ANSYS软件对齿轮传动扭转啮合刚度有限元模型的建模和计算方法。根据扭转啮合刚度定义,分别建立了无齿面缺陷和有齿面缺陷的齿轮三维接触仿真分析模型。计算了两种运行状态下,不同接触位置上的扭转啮合刚度,并利用MATLAB比较了有点蚀剥落与无点蚀剥落齿轮的扭转啮合刚度的变化情况。模拟结果表明,点蚀和剥落的存在使齿轮的扭转啮合刚度减小,特别是在轮齿的单啮合区时,对扭转啮合刚度的影响剧烈。     

DYNAMIC CHARACTERISTIC ANALYSIS OF PRECISE LONG STROKE LINEAR MOTOR WITH AIR-BEARING IN OPTICAL LITHOGRAPHY

Dynamic characteristic is presented by identifying the model and the dynamic parameters of a precise long stroke linear motor （PLSLM） with the air-bearing in optical lithography. The PLSLM is supported by air-bearing on the stator, and is driven by on-board two large linear motors in a cross-configuration. Firstly, a model of the PLSLM is established by finite element method （FEM）. Secondly, based on the model, the natural frequencies and model shapes are discusse＆ And the contribution of each active mode is evaluated by computing the modal participation factors （MPF）, which indicates the major vibration direction. Furthermore, by the experimental modal analysis, the experimental results are in agreement with simulation results, which it is sure that the FEM is reasonable. What＇s more, comparing with the effects on the frequency due to the air-bearing stiffness, the relations of the natural frequencies with the air-bearing stiffness are found. It is found that the frequency response curve is fluctuant with the air-bearing stiffness in each direction. Finally, it is conclusion that the natural frequency of the PLSLM is largely affected by the air-bearing stiffness variety. This research is contributed to the dynamic characteristics resulted from the air-beating stiffness. Further work will include better optimization on the dynamic parameter in the controller design through the control algorithm for the precise long stroke motor.     

Tribological Behavior of Rice Bran Ceramics in a Vacuum Environment

ABSTRACT

In this study, we investigated the friction and wear of rice bran (RB) ceramics—hard porous carbon materials made from rice bran—in a vacuum environment. Sliding friction tests for RB ceramic pin–RB ceramic disk contact were performed using a pin-on-disk-type friction tester installed in a vacuum chamber. The ambient pressure was controlled at 0.02, 0.6, 30, and 10⁵ Pa (i.e., atmospheric pressure). The normal load was 0.49 or 2.94 N, the sliding velocity was 0.01 or 0.1 m/s, and the number of friction cycles was 50,000. The friction coefficient tended to decrease with decreasing ambient pressure for all combinations of normal load and sliding velocity; by contrast, the specific wear rate of the RB ceramic pin and disk specimens tended to increase with decreasing ambient pressure. The friction coefficient exhibited a low value of 0.05 or less at 0.02 Pa. The results suggested that the reduced surface roughness and graphitization of the sliding surface of the RB ceramic pin and disk due to induced friction, as well as the increased ratio between the partial pressure of water vapor and the ambient pressure, are related to the reduction in the friction of RB ceramic–RB ceramic dry sliding contact under vacuum conditions.     

图案化介质磁盘-磁头气体润滑动态特性分析

在小扰动条件下,提出应用偏导数法在复数域内求解可压缩气体润滑的动态Reynolds方程,以计算任意磁盘表面形状的磁盘-磁头气膜润滑的动态刚度和阻尼系数。以圆柱形和立方形比特图案化介质(BPM)磁盘为研究对象,研究了磁单元尺寸参数对气膜动态系数的影响,并比较了两种BPM对应的动态性能。数值结果表明,与光滑磁盘相比,图案化介质磁盘对应的气膜润滑动态刚度系数和阻尼系数大大减小,且随磁单元高度增大,动态系数逐渐减小。相比圆柱形BPM,立方形BPM对应的气膜具有较大动态刚度和阻尼系数,计算结果可为图案化介质磁盘的设计提供重要的理论依据。     

Measurement of wear of carbon coated sliders using atomic force microscopy and Raman spectroscopy

Wear of carbon coated sub-ambient pressure “pico” sliders is investigated during sweep testing as a function of interference height, slider design and sliding distance using atomic force microscopy. The wear results from atomic force microscopy measurements are compared with wear measurements of the carbon overcoat using Raman spectroscopy. The effect of interference on wear and disk burnishing is studied using acoustic emission measurements and atomic force microscopy. The results show that wear of a slider is higher for larger interference height and higher stiffness of the air-bearing.     

Static and Dynamic Slider Air-Bearing Behavior in Heat-Assisted Magnetic Recording Under Thermal Flying Height Control and Laser System-Induced Protrusion

The air bearing’s response to regions of elevated temperature on its bounding surfaces (the slider and disk) may be an important consideration in the head–disk interface design of heat-assisted magnetic recording (HAMR) systems. We implement the general non-isothermal molecular gas lubrication equation into an iterative static solver and dynamic air-bearing solver to evaluate the effect of localized heating of the air-bearing surface (ABS) due to the near-field transducer (NFT). The heat-dissipating components in our simplified HAMR design are the NFT, laser diode, and thermal flying height control (TFC) heater. We investigate the effect of each HAMR slider component on ABS temperature and thermal deformation and the slider’s flying height. The NFT induces a localized thermal spot and protrusion on the larger TFC bulge, and it is the location of maximum temperature. This ABS temperature profile alters the air-bearing pressure distribution, increasing the pressure at the hot NFT location compared with predictions of an isothermal air-bearing solver, so that the center of the pressure acting on the ABS is slightly closer to the trailing edge, thereby decreasing the pitch angle and increasing the minimum flying height. Other researchers have shown that the NFT’s thermal response time may be much faster than its protrusion response time (Xu et al. in IEEE Trans Magn 48:3280–3283, 2012). The slider’s dynamic response to a time-varying NFT thermal spot on the ABS while the combined TFC and NFT induced thermal protrusion remains constant is investigated with our dynamic air-bearing solver. We simulate the slider’s step response to a suddenly applied ABS temperature profile and a pulsed temperature profile that represents laser-on over data zones and laser-off over servo zones. The sudden (step) or rapid (pulse) increase in ABS temperature induces a sudden or rapid increase in pressure at the NFT location, thereby exciting the air bearing’s first pitch mode. For the slider design and simulation conditions used here, the result of the pitch mode excitation is to alter the position of the center of pressure in the slider’s length direction, thereby changing the pitch moment. In response, the pitch angle and minimum flying height change. The step response decays after approximately 0.15 ms. Because the laser duty cycle is much shorter than this response time, a periodic disturbance is predicted for the center of pressure coordinate, pitch angle, and minimum flying height. The peak-to-peak minimum flying height modulations are relatively small (only up to 0.126 nm); more significantly, the time-averaged minimum flying height increases 0.5 nm for the NFT that reached 208 °C compared to simulations of the isothermal ABS at ambient temperature.     

Suspension modeling and optimization using finite element analysis

A finite element based optimization software Altair OptiStruct is used to optimize the design of suspensions in hard disk drives. Topology optimization, topography optimization and combinations of both techniques are used to optimize a contact start-stop suspension with respect to torsion, bending and sway mode frequencies. The suspension, gimbal, slider and airbearing are modeled. The airbearing is modeled with linear springs to represent stiffness in the z-direction, pitch and roll. Modal analysis is compared to experimental resonance data to verify the model. The results show that improvements of more than 50% can be achieved with respect to increasing sway or torsional modes.     

轮胎稳态运动学与六分力预报Ⅰ:理论与方法

提出一种新的轮胎运动学描述和六分力预报理论。滚动接触是汽车轮胎力学、轮轨动力学的核心问题,由于涉及刚体转动与有限变形,滚动接触运动学与动力学的描述与求解非常困难。用拉格朗日—欧拉混合描述法分析大变形滚动接触结构的速度场、加速度场和接触变形。以车轮定位角为卡尔丹角,用拉格朗日描述,得到了包含刚体转动和弹性变形的轮胎速度场。而接触区域的变形和受力用欧拉描述,通过欧拉网格和拉格朗日网格的信息传递,完成滚动结构动力学分析。所提出的理论可以退化到Fiala模型,并可以从理论上解释子午线轮胎的伪侧偏和伪侧倾现象。基于所建立的运动学理论和非线性有限元,建立轮胎六分力预报方法。针对某轿车子午线轮胎,分析轮胎接地面滑移速度、接地面积、接地压力、侧向剪力分布等随着侧偏角的变化规律,并研究该轮胎侧偏力和回正力矩随着胎面刚度和摩擦因数的参数敏感性。结果表明轮胎侧偏刚度和回正刚度主要受结构刚度控制,而峰值侧偏力和峰值回正力矩主要受摩擦因数控制。将利用所建立的方法和试验,探讨带束层结构对大规格子午线轮胎侧偏特性的影响规律,进一步验证所提出的理论和方法的正确性。所提出的理论和方法开辟了直接从轮胎设计预报轮胎六分力的新途径。     

中子应力谱仪样品承重台回转支承载荷分析

针对中子应力谱仪样品承重台(简称“中子谱仪样品台”)旋转运动机构用三排圆柱滚子回转支承的特殊结构和受载情况,基于Hertz理论,实现了力学分析模型的建立和求解,在此基础上通过有限元法分析了中子谱仪样品台极限工况下滚子与滚道之间的接触特性,然后分析了轴向载荷、径向载荷、滚子数量对回转支承刚度的影响。研究结果表明：在中子谱仪样品台极限工况下,上排滚子与滚道的接触区域等效应力最大,为76.98MPa,外圈滚道的最大等效应力为14.82MPa,内圈滚道最大等效应力为11.26MPa;刚度分别随轴向载荷、径向载荷和滚子数目的增大而增大,且均成非线性关系,当轴向载荷增至1200kN、径向载荷增至300kN时,轴向刚度和径向刚度增长趋势明显减慢,当上排与下排滚子数量增至170时,轴向刚度的增大趋势明显加快。研究结果为中子谱仪样品台旋转运动机构的设计提供了参考。     

钢玄武岩纤维树脂混凝土结合面法向接触刚度数值计算研究

为解决分形接触理论中最大接触面积难以准确计算导致结合面实际接触面积难以有效获取的问题,基于离散化数值计算方法建立了一种结合面实际接触面积的计算方法,并将该方法与结合面接触刚度理论模型相结合,建立了一种新的钢玄武岩纤维树脂混凝土(BFPC)结合面接触刚度计算方法.通过模态实验对五种预载荷下的钢BFPC结合面组件的接触刚度...     

Adhesion and Friction Evaluation of Textured Slider Surfaces in Ultra-Low Flying Head-Disk Interfaces

To achieve extremely high-density magnetic recording of 1Tbit per square inch using conventional technologies, the distance between the recording slider and the rotating disk needs to be less than 5nm. For successful operation, disk and slider surfaces must also be extremely smooth with root-mean-square roughness values of few angstroms. However, ultra-low flying super smooth head-disk interfaces may be exposed to a significant amount of intermittent contact, adhesion, stiction and friction that can cause the interface to collapse. In order to circumvent such problems, many novel techniques have been proposed, such as laser zone texturing, contact pads and surface microtexturing. A reliable method to reduce adhesion and friction in ultra-low flying head-disk interfaces is to control the area of contact and roughen the interface, which allows the slider to fly at sub-5nm with minimal contact. A technique known as preferential texturing provides a unique roughening of the air-bearing surface, where parts of the surface are removed, i.e., subtractive texturing process. In this paper, the effect of preferential texturing (roughening) of slider air-bearing surfaces on the adhesion and friction forces are investigated using quasi-dynamic models. The simulation results show that surface texturing reduces adhesion and friction by reducing the effective area of contact between the slider and media surfaces and by preferentially roughening the interface. The simulation results of friction compare favorably with experimental data.