Sensitivity analysis of tire-ice friction coefficient as affected by tire rubber compound properties

Previous studies show that the material properties of the rubber are among the most important factors when designing a tire. In this study, we investigated the effects of different rubber properties on tire performance on ice. A theoretical model that incorporates these tire material properties was developed. The model was used to estimate the height of the water film generated due to friction and the friction coefficient for both, dry and wet regions at the tire-ice contact patch. After validating the results using experimentally collected data, the model was used to perform a sensitivity analysis on the tire performance with respect to six material properties of the tread rubber: thermal conductivity, rubber density, Young’s modulus, specific heat, roughness parameter of the rubber, and radii of spherical asperities of the rubber. To study the effect of each parameter, the desired material property was varied within a specific range while the other parameters were kept constant. The results from this study show the sensitivity of the magnitude of the friction coefficient to the rubber material properties. The friction coefficient has a direct relationship with the density of the rubber and has an inverse relationship with Young’s modulus, specific heat, and roughness parameter.     

A tire–ice model (TIM) for traction estimation

Increased traffic safety levels are of highest importance, especially when driving on icy roads. Experimental investigations for a detailed understanding of pneumatic tire performance on ice are expensive and time consuming. The changing ambient and ice conditions make it challenging to maintain repeatable test conditions during a test program. This paper presents a tire–ice contact model (TIM) to simulate the friction levels between the tire and the ice surface. The main goal of this model is to predict the tire–ice friction based on the temperature rise in the contact patch. The temperature rise prediction in the contact patch is based on the pressure distribution in the contact patch and on the thermal properties of the tread compound and of the ice surface. The contact patch is next classified into wet and dry regions based on the ice surface temperature and temperature rise simulations. The principle of thermal balance is then applied to compute the friction level in the contact patch. The tire–ice contact model is validated by comparing friction levels from simulations and experimental findings. Friction levels at different conditions of load, inflation pressure, and ice temperatures have been simulated using the tire–ice contact model and compared to experimental findings.     

Determination of adhesive parameters characterizing the interaction of pneumatic tires and concrete pavement from pull-slip curves

The author has applied traction-slip curves obtained from drawbar pull tests to determine values of the adhesive parameters controlling the peripheral forces of rubber tires rolling on concrete. The method is based on an analogy with soil shear strength characterized by cohesion, the angle of internal friction, and the tangent modulus of the derived shear-deformation curve. The peripheral force generated by a tire rolling on concrete is the total force required to shear the interlocking elementary particles in the contact patch. The adhesive parameters derived using this method are average values expressing the effect of all factors which contribute to producing the peripheral force.     

Towards a real-time pneumatic tire performance prediction using an advanced tire-ice interface model

Icy road conditions and tire operational parameters play a vital role in determining the overall performance of a vehicle. This study builds on prior work in the researchers’ group. The Advanced Tire-Ice Interface Model (ATIIM) simulates the temperature rise in the contact patch based on the measured pressure distribution and the thermal properties of the tread compound and of the ice surface. It has the capability to simulate the height of the thin water film created from the melted ice, to predict the tractive performance, and to estimate the viscous friction due to the water layer and the influence of braking operations, including the locked wheel condition. The experimental investigation included measuring the bulk temperature distribution in the contact patch to validate the temperature rise simulations of the ATIIM. As shown by the simulations and the test data, a rise in temperature was observed from the leading edge to the trailing edge of the contact patch. As the wheel load increases, the difference in temperature rise increases, as also reflected in the experimental study. When the temperature difference was significant, a thin water film was observed that resulted in a reduction of friction, which was simulated using the ATIIM.     

弹簧-金属丝网橡胶组合减振器迟滞力学模型及实验研究

金属丝网橡胶材料是一种完全由金属丝编织成的多孔复合材料,与传统螺旋卷制金属橡胶材料相比,其改进了成型工艺,剔除了制备过程中大量的手工工艺干扰,提高机械化程度,重合度更高,拥有更稳定的力学性能.由于金属丝网橡胶材料具有承载能力高、阻尼大、耐高温、耐低温、耐老化、抗油抗腐蚀等优良特性,在很多方面强于传统橡胶,多用于航空航天、船舶、军事武器等军工工业.弹簧$\!$-$\!$-$\!$金属丝网橡胶组合减振器具有可设计刚度和较高承载能力,但因其具有复杂的非线性迟滞特性,目前相关材料的本构模型还难以准确描述其力学特性.本文在弹簧$\!$-$\!$-$\!$金属丝网橡胶组合减振器静态迟滞力学性能实验的基础上,结合其干摩擦阻尼迟滞特性,提出了一种迟滞力学性能理论模型.根据减振器迟滞实验恢复力$\!$-$\!$-$\!$位移曲线特点,利用参数分离的方法将迟滞曲线分解为弹性恢复力和干摩擦阻尼力,分别建模求解等效刚度和干摩擦阻尼系数,以此建立了组合减振器理论模型,并与实验结果进行对比及进行误差分析,验证了理论模型的准确性.      

Experimental investigation of pneumatic tire performance on ice: Part 1 – Indoor study

Currently, the probability of accident occurrence is much higher when driving on icy roads than on asphalt. Since the tire is the only element of the vehicle that contacts the icy road, it is crucial to thoroughly comprehend the friction mechanism at the tire–ice interface for improved tires and safety systems for icy roads. This study investigates the available friction levels at the tire–ice interface by varying operational parameters through the indoor testing program conducted at the Advanced Vehicle Dynamics Laboratory, Virginia Tech (in part I) and the outdoor testing program conducted at the Keweenaw Research Center (in part II). This two-part article presents the design of experiment, the indoor and outdoor test programs, and friction–slip ratio curves obtained from both test programs for different conditions. The effects of operational parameters and their inter-dependency for the entire slip ratio range during operation on ice is explained, as studied from the two test programs. This article (part I) details the indoor test method consisting of the ice creation procedure, pre-test procedures, the test procedure and analysis of the obtained friction–slip ratio curves. This experimental investigation performs the necessary groundwork and builds a strong foundation towards making driving on ice safe.     

Modelling the traction of a prototype track based on soil–rubber friction and adhesion

An experimental track layer tractor, based on an Allis Chalmers 8070 tractor (141 kW) was tested on bitumen covered concrete and on cultivated sandy loam at 7.8%; 13% and 21% soil water content. The two articulated beam-type tracks (500 mm wide × 2000 mm soil contact length) were constructed out of 500 mm long and 70 mm wide rubber covered steel track elements, carried by five steel cables (36 mm diameter). The tracks resisted inward deflection but allowed outward articulation between two smooth rear driving and two smooth front pneumatic truck tires (1060 mm diameter) per track. The contact pressure and the tangential force on an instrumented track element, as well as the total torque input to one track, were simultaneously recorded during the drawbar pull/slip tests.

Different possible pressure distribution profiles under the tracks were considered and compared to the recorded data. Two possible traction models are proposed, one constant pressure model for minimal inward track deflection, and a deformable track model with inward deflection and a higher contact pressure at both the front free-wheeling and rear driving tires. For both models, the traction force was generated mainly by rubber/soil friction and adhesion and limited soil shear. A close agreement between the measured and predicted contact pressures and traction force for individual track elements, based on the deformable track model, was observed. The recorded and calculated coefficient of traction based on the summation of the force for the series of track elements were comparable, but were considerably lower than the predicted values, probably due to internal track friction rather than soil sinkage. The tractive efficiency for both a hard or soft surface was also unacceptably low, probably caused by internal track friction.     

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.     

孔隙度对湿式离合器局部润滑及摩擦特性影响研究

针对湿式离合器局部润滑及摩擦特性的影响因素,建立了摩擦副微观混合润滑模型.考虑了微凸峰接触和局部温升的影响,分析了孔隙度对湿式离合器局部压强分布、油膜和微凸峰承压比、实际接触面积、局部温升的影响.同时,利用摩擦磨损试验机(UMT)进行小试样销-盘试验,分析了不同孔隙度下离合器摩擦副局部摩擦系数的变化.结果表明:在混合润滑中,随着孔隙度的增大,润滑油膜动压作用减小,局部微凸峰接触压强增大,微凸峰法向压力承载比增大,摩擦副实际接触面积增加,因此摩擦系数增大.     

Impact of reinforcing filler on the dynamic moduli of elastomer compounds under shear deformation in relation to wet sliding friction

In pursuit of a better understanding of the relationship between wet sliding friction and bulk viscoelastic properties of elastomer compounds, especially the contribution from different reinforcing fillers, the linear thermorheological behavior, the nonlinear dynamic moduli under shear deformation (for strain up to about 140%), and the wet sliding friction have been characterized in detail for crosslinked compounds of low-cis polybutadiene filled with different reinforcing fillers including carbon black, graphitized carbon black, and precipitated silica. We examine the scenario of possible extra energy dissipation via higher harmonic excitation in rubber compounds coupled with dynamic deformation consisting of components at many frequencies during sliding of rubber on a rough surface. While no straightforward explanation is identified relating the observed difference in wet sliding friction arising from different fillers to the bulk viscoelastic properties, some unexpected viscoelastic features arising from the compounds are observed.     

Tire slip-angle force measurements on winter surfaces

Tire lateral force data on winter surfaces cannot be obtained with the traditional laboratory test technique of an instrumented tire on a moving belt surface. Furthermore, changing snow and ice conditions can drastically change the tire/surface interaction. In this study the Cold Regions Research and Engineering Laboratory’s (CRREL’s) Instrumented Vehicle (CIV) was used in a unique configuration to measure tire lateral force versus slip-angle data on ice and snow at various temperatures, moisture contents, depths, and densities. The vehicle is instrumented to record longitudinal, lateral, and vertical force at the tire contact patch of each wheel as well as vehicle speed, tire speed, and front tire slip angle. The tests were conducted at the Keweenaw Research Center (KRC) in northern Michigan in February 2005 and March 2006. Tests were conducted on ice, packed snow from 0.50 to 0.58 g/cc, remixed snow depths of 2.5–20.3 cm at 0.43 to 0.48 g/cc and freshly fallen snow with depths of 0.5–17 cm at 0.07 to 0.23 g/cc. Surface air temperatures during testing ranged from −14 to 1.6 °C. The data collected show that peak lateral force and the shape of the lateral force versus slip-angle curve are related to snow properties and depths.     

迷彩服织物与人体肘部皮肤摩擦特性研究

在往复摩擦模式下模拟迷彩服穿着环境,研究了5种不同迷彩服织物的表面结构、亲疏水性、接触力值以及干湿状态对皮肤摩擦特性的影响.结果表明:在法向载荷为1 N时,湿态下的环境增强了织物与皮肤间的黏着力,织物与皮肤在湿态下的摩擦系数均高于干态;当法向载荷增加到5 N时,界面间的干湿状态对织物与皮肤的摩擦系数无明显影响.在干态时,不同迷彩服织物与皮肤的摩擦性能与织物的材质和针织结构有关,纯棉材质和斜纹结构的织物与皮肤的摩擦系数较小;在湿态时,不同迷彩服织物与皮肤的摩擦性能与织物的亲疏水性有关,疏水性强的织物由于增强了皮肤的水合作用以及界面间的粘附力,因此增加了织物与皮肤的摩擦系数.质地较硬的平纹结构织物易造成摩擦后的皮肤表面粗糙,造成皮肤不同程度的角质层分离及表皮撕裂,增加了皮肤表面损伤的风险.     

Finite element modeling of interfacial forces and contact stresses of pneumatic tire on fresh snow for combined longitudinal and lateral slips

Significant challenges exist in the prediction of interaction forces generated from the interface between pneumatic tires and snow-covered terrains due to the highly non-linear nature of the properties of flexible tires, deformable snow cover and the contact mechanics at the interface of tire and snow. Operational conditions of tire-snow interaction are affected by many factors, especially interfacial slips, including longitudinal slip during braking or driving, lateral slip (slip angle) due to turning, and combined slip (longitudinal and lateral slips) due to brake-and-turn and drive-and-turn maneuvers, normal load applied on the wheel, friction coefficient at the interface and snow depth. This paper presents comprehensive three-dimensional finite element simulations of tire-snow interaction for low-strength snow under the full-range of controlled longitudinal and lateral slips for three vertical loads to gain significant mechanistic insight. The pneumatic tire was modeled using elastic, viscoelastic and hyperelastic material models; the snow was modeled using the modified Drucker-Prager Cap material model (MDPC). The traction, motion resistance, drawbar pull, tire sinkage, tire deflection, snow density, contact pressure and contact shear stresses were obtained as a function of longitudinal slip and lateral slip. Wheel states - braked, towed, driven, self-propelled, and driving - have been identified and serve as key classifiers of discernable patterns in tire-snow interaction such as zones of contact shear stresses. The predicted results can be applied to analytical deterministic and stochastic modeling of tire-snow interaction.     

石英岩表面分子沉积膜的微观摩擦性能的试验研究

利用原子力显微镜对石英岩表面单层分子沉积膜的微观摩擦特性进行了研究,发现该分子沉积膜具有一定的减摩性.通过对其表面力-位移曲线、表面形貌像、调制力像和摩擦力像的进一步分析表明,石英岩表面分子沉积膜具有减摩作用的原因在于它能够降低表面的粘着力并对表面具有微观修饰作用.     

冰面上轮胎摩擦牵引力的实验研究

研制开发了测试冰雪面轮胎力学特性的试验装置,该装置具有可作往复运动的平台冰槽。在不同冰基体温度下,分析了轮胎摩擦引力受侧偏角,载荷和轮胎充气压力的影响,从试验角度论证了轮胎中央充放气系统对改善冬季轮胎牵引性能的作用,该装置的建立将有利于轮胎新结构和新材料的开发,并起到完善现有轮胎力学模型的作用。     

丁腈橡胶紫外线臭氧照射亲水改性及其水润滑性能研究

以丁腈橡胶为基底,采用紫外线-臭氧照射进行亲水/超亲水表面改性,通过接触角测量仪、光学显微镜对亲水改性表面的接触角、接触角滞后和微观形貌等特性进行表征,分析了表面亲水性的改性机理,并采用MFT-5000型摩擦磨损试验机测试了丁腈橡胶亲水表面的机械耐久性和保持性. 研究结果表明:采用紫外线臭氧照射丁腈橡胶10 min,就能得到完全润湿的超亲水表面,且在紫外线臭氧照射下,丁腈橡胶与臭氧发生反应生成氧化膜,使亲水改性后的丁腈橡胶,在干摩擦和水润滑状态下均表现出较小的摩擦系数和较好的耐磨性      

Modeling and motion simulation of a three-wheeled mobile robot with front wheel driven and steered taking into account wheels�� slip

The problem of modeling of dynamics of a three-wheeled mobile robot with front wheel driven and steered is analyzed in this paper. Kinematical structure and kinematics of the robot are described. A universal methodology of analytical modeling of robot??s dynamics is applied. This methodology takes into account wheel-ground contact conditions and wheels?? slip. Its essence is the use of a contact model of deformable tire with rigid ground and division of the robot??s dynamics model into parts connected with wheels, including tire model, and with the mobile platform. The tire model used in this paper results from empirical dependencies determined during investigations of car tires. Ground geometry and type are specified in the environment model. Tire-ground interface is characterized by coefficients of friction and rolling resistance. The robot model takes into account the presence of friction in kinematical pairs. The model of servomotors is included as well. The important part of this work is simulation research performed using Matlab/Simulink package. Simulation research includes solving of the forward and inverse dynamics problems as well as the tracking control task. During simulations, the robot was moving on concrete and on a piece of ice. The simulation research enabled verification of the elaborated solutions.     

仿生柔性表面的结构设计及吸附力试验分析

模仿昆虫脚上光滑型吸附垫表面的结构设计,选用具有黏弹性的硅胶板,分别测试了光滑、带凹槽、带凹坑试样在干的和湿的玻璃表面上的水平摩擦力和垂直吸附力.结构表明在干玻璃表面非光滑结构的接触面积比光滑的要小,具有减粘降阻的作用;而在有一层厚液体膜作媒介时,摩擦力比光滑的要大.有液体时,水平摩擦力是凹槽型的最大,垂直吸附力是凹坑型的最大.有一薄层液体时的湿吸附能力比干吸附大,且液体粘性越大吸附能力越强.这些研究为仿生爬壁机器人的足掌设计提供了有价值的参考.     

EFFECT OF INTERGRANULAR FRICTION ON THE BOTTOM FORCE CHAIN OF TWO-DIMENSIONAL PARTICLE PILES WITH POINT DEFECTS1)

力链对颗粒物质的宏观与微观力学性质起着决定性的作用。在离散元法的基础上,建立二维规则排列的颗粒物质系统,分别研究无缺陷颗粒系统在集中载荷变化与有缺陷颗粒系统在缺陷区域改变时,粒间摩擦系数对颗粒系统底部接触力分布规律的影响。结果表明：在无缺陷颗粒系统中,颗粒系统底部接触力的分布形式受摩擦系数和集中载荷的大小影响。随摩擦系数的增大,底部接触力由双峰形式经平台过渡,逐渐向单峰形式转变。在有缺陷颗粒系统中,摩擦系数和缺陷尺寸对底部接触力分布均有影响。同种载荷作用下,随缺陷尺寸的增大,底部接触力峰值显著增大;底部平均力被明显削弱,力向边界的传递增强。系统中轴线上缺陷的存在使底部中间区域受力削弱,当缺陷尺寸超过2 层以上时,底部中间力随摩擦系数的变化特征由递增曲线演变为线形衰减曲线。     

Vehicle-wet snow interaction: Testing,modeling and validation

For a vehicle interacting with snow, whether dry or wet, uncertainties exist in the mechanical properties of snow, and in the interfacial properties between the tires of the vehicle and snow. For dry snow, these uncertainties have been studied recently using methods within a statistical framework employing a simple stochastic tire-snow interaction model and several validation metrics. Wet snow is more complicated and much less studied than dry snow, especially for tire-snow interaction. In this paper, the authors used a physical tire-snow interaction model and a similar statistical framework as was used to analyze dry snow, and presented results of calibration and validation of the interaction model for wet snow in conjunction with new test data based on a single test run with the assumption that it would provide needed sampling points for statistical analysis. Four local and global statistical validation metrics were used to assess the physical and statistical models with good results. Comparison between wet and dry snow, based on a single test run, shows that the former has a lower interfacial coefficient of friction, and a higher drawbar pull than the latter.