微载荷含油轴承摩擦性能研究Ⅰ.摩擦试验机设计

研制了1种针对径向轴承的微载荷摩擦试验机,介绍了其工作原理及结构,即利用外加载荷抵消浮动测试架重量以施加微小载荷,并利用激光位置传感器(PSD传感器)实现无接触位移测量;同时测量了摩擦副的转动角度并计算出摩擦系数;采用摩擦转角测量法和外加力矩平衡摩擦法测量微载荷下的摩擦性能,以测量时间末端位置作为位置基准,通过极限偏载平衡进行载荷标定.结果表明:微载荷摩擦试验机可应用于径向轴承在微小载荷下的摩擦力测量;可以通过在较大范围内设置结构参数来研究径向轴承的摩擦特性;并可利用数据采集技术研究速度和载荷连续变化条件下的摩擦性能.     

Experimental analysis of vertical soil reaction and soil stress distribution under off-road tires

In this study, the vertical soil reaction acting on a driven wheel was measured by strain gages bonded to the left rear axle of a 2WD tractor driven under steady-state condition on different soil surfaces, tractor operations, and combinations of static wheel load and tire inflation pressure. In addition, the measurements of radial and tangential stresses on the soil–tire interface were made simultaneously at lug’s face and leading side near the centerline of the left rear tire using spot pressure sensors. The experimental results indicate that the proposed method of vertical soil reaction measurement is capable of monitoring the real-time vertical wheel load of a moving vehicle and provides a tool for further studies on vehicle dynamics and dynamic wheel–soil interaction. Furthermore, the measured distributions of soil stresses under tractor tire could provide more real insight into the soil–wheel interactions.     

Rolling deformation of truck tires: Measurement and analysis using a tire sensing approach

Measurements on rolling tire deformation provide deep insights into the mechanism of generating tire forces and moments. For free rolling tires, substantial attention has been given to the rolling resistance because of its significant impact on the fuel consumption and CO₂ emissions. This paper attempts to investigate the rolling resistance force through measurements of the rolling deformation of truck tires using a tire sensing approach. An optical tire sensor system is used to measure rolling tire deformation, which includes the deformed inner profile, sidewall deformation, and tread deformation. Measurements were conducted on a test truck for both new and used tires. In addition, the influences from operational factors such as wheel load and inflation pressure on tread deformation were examined and analyzed.     

考虑粗糙结合面弹塑性接触的黏滑摩擦建模

提出一种同时考虑粗糙面上微凸体弹性变形和塑性接触的切向黏滑摩擦建模方法。采用Hertz弹性理论和Mindlin解描述弹性接触微凸体的切向载荷和相对变形的关系;采用AF(Abbott-Firstone)塑性理论和Fujimoto模型描述塑性接触微凸体切向载荷和相对变形的关系。再利用GW(Greenwood-Williamson)模型统计分析方法建立粗糙表面切向载荷和相对变形之间的关系。将模型与仅考虑微凸体弹性接触情况的模型进行对比,并研究了不同塑性指数对切向载荷和相对变形关系的影响。结果表明：与完全弹性接触模型相比,本文模型引入了塑性接触理论,能够更好地描述粗糙表面切向载荷和相对变形关系,并且考虑不同接触条件下弹性变形微凸体和塑性变形微凸体对切向接触载荷的贡献,在微滑移阶段,主要由弹性接触变形影响,而在进入宏观滑移阶段之后,切向行为主要由塑性变形影响。界面切向载荷由黏着和滑移接触作用共同决定,随着切向变形的增加,滑移接触力逐渐增加,而黏着接触力先增加后减少,反映了界面由微滑移逐渐向宏滑移演化的过程。随着塑性指数的增加,粗糙面上发生塑性接触的微凸体数目逐渐增加,切向黏滑行为主要受到塑性接触特征的控制。     

基于摄像测量原理的船体垂向变形测量半实物仿真实验研究

针对船体垂向变形测量的迫切需求,以及现有方法对于垂向变形适用性差的实际情况,提出了一种利用摄像测量原理实现垂向变形测量的新方法,推导了设备垂向变形角与姿态欧拉角变化量之间的转换关系,在此基础上设计了船体垂向变形测量方案。通过在平台上的CCD像机对与垂向设备基座固连的合作标志的实时观测,解算由于变形引起的合作标志姿态变化量,再利用合作标志与设备基座固连关系计算设备的垂向变形角。在实验室条件下进行了半实物仿真实验,实验结果测量值与参考值变化趋势一致,测量误差均在10″以下,说明该方法在垂向变形测量中正确可行。     

ANALYSIS OF GROUNDING CHARACTERISTICS AND STRAIN ENERGY OF RADIAL TIRES WITH RADIAL STIFFNESS1)

利用轮胎综合试验机对径向刚度下子午线轮胎进行性能试验,采用正交试验法针对不同胎压、垂向载荷下轮胎的接地特性进行分析,结合仿真软件ABAQUS与试验进行对比。结果表明,橡胶材料Mooney-Rivli模型也具有一定的适用性,胎压增大时径向刚度发生线性变化,胎面印痕由椭圆形转变成近似矩形,印痕面积略微增大;随着胎压的不断增大,胎面印痕的面积显著减小,接触面的压力主要集中在胎肩,胎冠处也有所增加;胎压一定时,垂向载荷逐渐增大时,整个印痕面的应力呈对称分布,印痕面应力由内高外低逐渐向外高内低变化。建立数学模型与有限元软件同时对轮胎进行应变能分析,发现在低胎压150 kPa下受载荷时轮胎容易发生微小侧向位移同时发生变形,此时极易引起迟滞损失并造成应变能急剧增加。     

A finite element study of the deformations, forces, stress formations, and energy losses in sliding cylindrical contacts

This work presents the results of a finite element analysis (FEA) used to simulate two-dimensional (2D) sliding between two interfering elasto-plastic cylinders. The material for the cylinders is modeled as elastic-perfectly plastic and follows the von Mises yield criterion. The FEA provides trends in the deformations, reaction forces, stresses, and net energy losses as a function of the interference and sliding distance between the cylinders. Results are presented for both frictionless and frictional sliding and comparisons are drawn. The effects of plasticity and friction on energy loss during sliding are isolated. This work also presents empirical equations thatt relate the net energy loss due to sliding under an elasto-plastic deformation as a function of the sliding distance. Contour plots of the von Mises stresses are presented to show the formation and distribution of stresses with increasing plastic deformation as sliding progresses. This work shows that for the plastic loading cases the ratio of the horizontal force to the vertical reaction force is non-zero at the point where the cylinders are perfectly aligned about the vertical axis. In addition, a “load ratio” of the horizontal tugging force to the vertical reaction force is defined. Although this is analogous to the common definition of the coefficient of friction between sliding surfaces, it just contains the effect of energy loss in plasticity. The values of the contact half-width are obtained for different vertical interferences as sliding progresses.     

轮胎胎面橡胶-冰面摩擦试验方法研究

基于一种新开发的轮胎胎面橡胶摩擦试验机,建立了轮胎和整车与冰面间的模拟摩擦试验手段,提出了在高滑移速度段的瞬时试验法和低滑移速度段的连续采样试验法;分别在不同滑移速度、压力、温度下针对轮胎胎面胶块与冰面进行了摩擦试验,并对试验结果进行了模型拟合和分析.结果表明:作为轮胎主要组成部分的橡胶表现出很特殊的摩擦特性,其并不符合库仑摩擦定律;橡胶轮胎的机械特性在很大程度上取决于橡胶的摩擦特性,在一些极限工况下尤其如此;相关的橡胶摩擦实验研究对轮胎力学特性的研究具有重要的参考价值.     

Agricultural tire deformation in the 2D case by finite element methods

The mechanical characteristics of the rubber tire and the interaction between a tire and a rigid surface were investigated by a two-dimensional (2D) finite element (FE) model. The FE model consists of a rigid rim and a rigid contact surface which interact with the elastic tire. Four distinct sets of elastic parameters are used to represent beads, sidewall, tread and lugs. Several sets of tire loads and inflation pressures were applied to the FE model as boundary conditions, together with various displacements and friction conditions. The deformation of the tire profile, the tire displacements in the vertical and lateral directions, the normal contact pressures, the frictional forces and the stress distribution of the tire components were investigated by the 2D FE model under the above boundary conditions. The calculated tire deflections were compared with the measured data. The results show a good fit between calculated and measured data, especially at high load and inflation pressure. The comparison shows that the FE analysis is suitable to predict aspects of the tire performance like its deflection and interactions with the contact surface. Compared with the experimental methods, the FE methods show many advantages in the prediction of tire deformation, contact pressure and stress distribution.     

Tire-ice model development for the simulation of rubber compounds effect on tire performance

The material properties of the rubber compounds, which are highly dependent on temperature, have a vital role in the tire behavior. A comprehensive study on the effect of the rubber properties on tire performance, for different temperatures, as well as different road conditions is required to adequately predict the performance of tires on ice.In this study, a theoretical model has been developed for the tire-ice interaction. The temperature changes obtained from the model are used to calculate the height of the water film created by the heat generated due to the friction force. Next, the viscous friction coefficient at the contact patch is obtained. By using the thermal balance equation at the contact patch, the dry friction is obtained. Knowing the friction coefficients for the dry and wet regions, the equivalent friction coefficient is calculated. The model has been validated using experimental results for three similar tires with different rubber compounds properties. The model developed can be used to predict the temperature changes at the contact patch, the tire friction force, the areas of wet and dry regions, the height of the water film for different ice temperatures, different normal load, etc.     

特性拦阻材料的台架实验装置研制

本文建立了单轮负载、平台拖动式的台架实验装置,并开展了验证实验。该装置主要包括固定框架、吊篮、活动平台、机轮夹持组件和传感器。将拦阻材料安装在活动平台上,通过牵引活动平台实现机轮对拦阻材料的碾压。该装置可以更换不同机轮、安装不同性能的拦阻材料;实验条件包括机轮胎压、机轮承重等参数;传感器可以测量实验过程中机轮受到的拦阻力、机轮压入深度等参数。该装置可以为研究机轮规格、胎压、承重、拦阻材料性能等对拦阻力的影响提供实验手段。验证实验结果表明,所建立的装置可以满足机轮与特性拦阻材料力学模型研究的需要。     

Soil displacement beneath an agricultural tractor drive tire

Soil strain transducers were used to determine strain in an initially loose sandy loam soil in a soil bin beneath the centerline of an 18.4R38 radial-ply tractor drive tire operating at 10% travel reduction. The initial depth of the midpoints of the strain transducers beneath the undisturbed soil surface was 220 mm. Strain was determined in the vertical, longitudinal, and lateral directions. Initial lengths of strain transducers were approximately 118 mm for the longitudinal and lateral transducers and 136 mm for the vertical transducer. The tire dynamic load was 25 kN and the inflation pressure was 110 kPa, which was a recommended pressure corresponding to the load. In each of four replications, as the tire approached and passed over the strain transducers, the soil first compressed in the longitudinal direction, then elongated, and then compressed again. The soil was compressed in the vertical direction and elongated in the lateral direction. Mean natural strains of the soil following the tire pass were −0.200 in the vertical direction, +0.127 in the lateral direction, and −0.027 in the longitudinal direction. The mean final volumetric natural strain from the strain transducer data was −0.099, which was only 35% of the mean change in natural volumetric strain calculated from soil core samples, −0.286. This difference likely resulted from the greater length of the lateral strain transducer relative to the 69 mm lateral dimension of the soil cores. The strain transducer data indicated the occurrence of plastic flow in the soil during one of the four replications. These results indicate the complex nature of soil movement beneath a tire during traffic and emphasize a shortcoming of soil bulk density data because soil deformation can occur during plastic flow while soil bulk density remains constant.     

Experimental study on wheel-soil interaction mechanics using in-wheel sensor and particle image velocimetry part II. Analysis and modeling of shear stress of lightweight wheeled vehicle

Wheeled vehicle mobility on loose sand is highly subject to shear deformation of sand around the wheel because the shear stress generates traction force of the wheel. The main contribution of this paper is to improve a shear stress model for a lightweight wheeled vehicle on dry sand. This work exploits two experimental approaches, an in-wheel sensor and a particle image velocimetry that precisely measure the shear stress and shear deformation generated at the interaction boundary. Further, the paper improves a shear stress model. The model proposed in this paper considers a force chain generated inside the granular media, boundary friction between the wheel surface and sand, and velocity dependency of the friction. The proposed model is experimentally validated, and its usefulness is confirmed through numerical simulation of the wheel traction force. The simulation result confirmed that the proposed model calculated the traction force with an accuracy about 70%, whereas the conventional one overestimated the force, and its accuracy was 13% at the best.     

Tire deflection and contact studies

Dimensional variations of pneumatic tires influence off-road locomotion and more particularly their aptitude for the transmission of high propulsive torques to the tire-soil contact area.Height variation of the tire when load increases is linear and allows a classification of the casings by means of the angular coefficients for the straight lines expression this relationship.Variation in the level where the enlarging of the torus is maximum is directly connected with the applied load and inversely proportional to the inflation pressure. Ply rating and inflation pressure define a stiffness coefficient for a tire, while the ratio of height to width under load specifies a deformation coefficient, a squash rate and a flattening rate. These three parameters characterize the elasticity of the tire and so are connected to the effective tire-soil contact areas.Compressive effects of the vertical stress as well as the transmitted torques are in relation with tire deformability. The study points to the need for better specification of the parameters for the choice, or for the definition of the desired characteristics for manufacturing, of tires.Experiments already done on superficial compaction effects concluded with a new type of cross section for the tire called the camel shoe.     

激光表面织构化对GCr15钢摩擦磨损性能的影响

本文利用Nd:YAG固体脉冲激光对GCr15钢样品表面进行了微坑织构化处理,考察了激光表面织构参数对其摩擦性能的影响,同时通过扫描电镜等对磨斑表面进行了分析.结果表明:与光滑面试样相比,经织构化处理的样品表面在干摩擦条件下虽然摩擦系数较高,但表现出了较好的抗磨性能;在贫油润滑条件下,织构面的摩擦系数与磨损均明显小于光滑面;在低载低速下较小孔径织构面摩擦系数较小,随着速度及载荷的增大,较大孔径织构面表现出更好的摩擦学性能.采用Stribeck曲线探讨了织构化表面与光滑面在贫油润滑下的润滑机理,结果表明织构面在试验条件下均保持油膜流体润滑状态.     

A Linearized Method to Measure Dynamic Friction of Microdevices

We propose and evaluate a linearized method to measure dynamic friction between micromachined surfaces. This linearized method reduces the number of data points needed to obtain dynamic friction data, minimizing the effect of wear on sliding surfaces during the measurement. We find that the coefficient of dynamic friction is lower than the coefficient of static friction, while the adhesive pressure is indistinguishable for the two measurements. Furthermore, after an initial detailed measurement is made on a device type, the number of trial runs required to take the data on subsequent devices can be reduced from 200 to approximately 20.     

Slip-based experimental studies of a vehicle interacting with natural snowy terrain

As longitudinal slip affects vehicle–pavement interactions on roads and hard surfaces, so too does it play an important role in interactions between vehicles and soft terrains, including snow. Although many slip-based models have been developed recently for tire–snow interactions (e.g., [1] and references cited therein), these models have only been partially validated, due to a lack of relevant experimental data. This paper presents comprehensive data from tests that were performed using a newly-developed test vehicle traversing natural snowy terrain, over a wide range of values for longitudinal slip, vertical load and torque via an effective accelerate/brake maneuver. Drawbar pull, motion resistance, wheel states and tire stiffness were presented as a function of slip; tire sinkage was obtained using a laser profilometer; strength and depth of snow were found using a snow micropenetrometer. The effects of the rear tire going over snow compacted by the front tire were also studied. The maximum traction force normalized by the vertical load is found to be ≈0.47, maximum motion resistance normalized by the vertical load is ≈0.4. Comparison of the trend and order-of-magnitude of test results with those from existing slip-based numerical model [1] shows good comparison in motion resistance, tire sinkage, and longitudinal stiffness, but indicates that a better traction model is needed to improve the comparison.     

爆破振动作用下顺层岩质边坡稳定性分析

基于对顺层岩质边坡的受力分析,在极限平衡理论的基础上,应用Mohr-Column准则,按照Bishop关于边坡稳定性安全系数的定义,推导出在爆破振动作用下顺层岩质边坡稳定性安全系数的计算方法。通过算例分析,证实了计算方法的可行性,说明了爆破振动拟静力系数同顺层边坡安全系数的关系。研究结果表明,垂直向下、水平指向坡外的爆破振动荷载以及两者的联合爆破荷载对边坡稳定性安全系数的影响最大;爆破荷载拟静力系数从0起每增加0.05,爆破振动水平指向坡外和垂直向下时,层裂长度为12.76 m的顺层边坡安全系数分别减少7.801%～10.665%、1.366%～1.978%,无层裂的顺层边坡安全系数分别减少7.61%～10.546%、1.473%～2.289%。同时,爆破振动产生的层裂长度、边坡长度以及联合爆破荷载的方向对边坡稳定性也有影响。     

Green functions for an incompressible linearly nonhomogeneous half-space

Summary Time-harmonic vibrations of an incompressible half-space having shear modulus linearly increasing with depth are studied. The half-space is subjected to a surface load which has vertical or hovizontal direction. The general solution of the time-harmonic, in the vertical direction nonhomogeneous problem is constructed for arbitrary angular distribution in the horizontal plane. Numerical results concerning surface displacements due to a point force are given for the case of nonzero shear modulus at the surface. These results show that nonhomogeneity can considerably increase amplitudes at large distances from the applied force.     

子午线轮胎接触变形的结构有限元分析

针对195／60R14子午线轮胎建立了三维非线性有限元模型，着重研究了额定充气压力及静载荷作用下帘线承受拉应力和剪应力的基本特征。计算结果表明，接地区域摩擦力呈斜对称分布，反映了轮胎中帘线-橡胶复合材料存在变形耦合效应；冠带层、带束层、胎体帘线应力分布较为复杂，载荷变化对其应力水平和分布影响较大；在胎肩部位应力较高，且随载荷变化局部帘线应力变化剧烈，在承受交变载荷时，易形成层间剥落。分析结果有助于预测轮胎的使用性能，可以针对性地应用于因轮胎结构设计引起的质量损坏，某些对轮胎使用性能不利的受力状态可通过结构的优化设计来克服。