Effects of low-to-medium slip, lug spacing and moisture content on lug forces

The effects of low-to-medium slip, lug spacing and moisture content on lug forces in clay soil were investigated in a laboratory soil bin with the help of two model lugs. Perpendicular and radial soil reactions on the lug were measured and they were converted to lug pull and lift forces. The lug slip was varied from 5 to 10, 15, 20 and 25%. The measurements were conducted in clay soils with 6.3, 27.4 and 51% soil moisture contents. The lug spacing was varied from 20° to 30° and 40°. The perpendicular, pull and lift forces increased after lug entry into the soil and, after attaining a certain peak value, they decreased and reached a zero value at lug exit. The increase in lug slip from 5 to 25% caused an increase in lug forces on both lugs. The increase in the soil moisture content from 6.3 to 27.6% caused increase in lug forces on both lugs, but further increase in moisture content to 51% decreased the lug forces. Lug spacing showed a significant effect on lug forces produced by the succeeding lug. The increase in lug slip increased the lug forces at any given lug spacing and moisture content.     

Experimental analysis of soil reaction on a lug of a movable lug wheel

A movable lug wheel was tested in a soil bin test apparatus to determine its traction performance and to measure the soil reaction forces on its lugs. Similar tests were also conducted using a fixed lug wheel. The effects of the lug motion pattern, lug spacing and horizontal load on pull and lift forces were studied. From the experiments it is confirmed that the movable action of the lug plate could generate superior pull and lift forces in comparison with the fixed lug wheel. Among the test wheels, lug motion pattern-2 generated the highest pull and lift forces. Within the range of the test conditions, there was no significant difference in pull and lift forces of the lug plate between the test lug wheels with 12 lugs and 15 lugs at the same level of horizontal and vertical loads. The increase of horizontal load up to 200 N generally increased the pull force and generated smaller rolling resistance before the lug left the soil, but did not increase the lift force significantly. The patterns of pull force, lift force and drawbar pull generated under a constant slip were slightly different from those under a constant horizontal load. Finally, the results were also elucidated by their actual lug trajectories in soil.     

Improvement of a power tiller cage wheel for use in swampy peat soils

This study was aimed at investigating traction performance of a cage wheel for use in swampy peat soils in Indonesia. The tests were conducted in a soil bin filled with peat soil taken from the swampy areas. A set up was developed to measure tractive performance of a single cage wheel. Deep sinkage and high wheel slip were identified as the major problems of using the existing cage wheel design in swampy peat soils. The results revealed that increasing the lug angle from 15 to 35° and the length of lug improved the tractive performance of the cage wheel significantly, while increasing the number of lugs from 14 to 18 and width of lug did not improve the tractive performance significantly. A cage wheel with lug size 325×80 mm, 35° lug angle, 14 lugs (26° lug spacing), with 2 circumferential flat rings installed on the inner side of the lugs, out performed the other settings for use with power tillers in swampy peat soils.     

Technology showcase applications of enamel coating in agriculture

Recently various experiments were conducted at the Asian Institute of Technology, Bangkok, to study the effect of enamel coating on the performance of some agricultural equipment. In order to reduce soil adhesion on cage wheel lugs, nine different coating materials were tried and enamel coating was found to be the best among these materials. It reduced soil adhesion on cage wheel lugs considerably to avoid cage wheel blocking. To investigate effect of coating on lug forces detailed lab studies were undertaken to measure the lug forces. The effects of lug slip, soil moisture content and sinkage were investigated. It was observed that enamel coating did not affect the lug forces. The pull and lift forces generated by the enamel coated and uncoated lugs were almost the same. When enamel coated bolt-on plates were mounted on the power tiller cage wheel lugs and trials were conducted in actual field conditions, it was observed that in actual field conditions enamel coated bolt-on plates on cage wheel lugs improved the performance of a power tiller. Studies about coating effects on the drag force required to pull floats on soil surface were also conducted. It was observed that enamel coating on floats reduced the drag force significantly. It also greatly improved the scouring of a mouldboard plough used in a wet, sticky clay soil.     

Measurement of soil reaction forces on a single movable lug

In order to clarify characteristics of a new mechanism called a movable lug, a model of a single movable lug equipped with an L-shaped force transducer has been developed. The soil reaction forces (normal and tangential) on a flat single movable lug, a curved single movable lug and a fixed lug were measured on wet sandy loam soil in the laboratory soil bin test. These measured forces then were converted to lug pull and lift forces. The pull and lift forces obtained by the flat movable lug with 45° lug inclination angle and the curved movable lug were higher than those of the fixed lug. It was observed that the lift force of the fixed lug achieved its peak and dropped earlier than those of the movable lugs. However, the peaks of pull and lift forces of the flat and curved movable lugs were almost the same. The flat movable lug with 45° lug inclination angle generated a slightly higher peak of pull force than those with 30° and 60° lug inclination angles. However, the higher lug inclination angle produced, the lower peak of lift force. It was observed that the pull and lift forces increased as the sinkage increased. In contrast to the flat movable lug with 45° lug inclination angle, the curved movable lug produced greater lift force especially at high sinkage. The increase in lug slip from 5% to 25 and 50% caused an increase in the peaks of pull and lift forces. The soil moisture content affected the lug forces significantly.     

Cyclic-stress reduction within pin-loaded lugs resulting from optimum interference fits

Results of photoelastic tests have e been projected into a technique for evaluating optimum levels of interference within pin-loaded lugs. Based upon the measurements of the variation of maximum stress with load at various levels of interference and for several lug configurations, an analysis shows that interference fits can be used to combat fatigue within pin-loaded lugs by reducing cyclic-stress levels at the critical regions.     

Characteristics of normal and tangential forces acting on a single lug during translational motion in sandy soil

Lugs (i.e., grousers) are routinely attached to the surfaces of wheels/tracks of mobile robots to enhance their ability to traverse loose sandy terrain. Much previous work has focused on how lug shape, e.g., height, affects performance; however, the goal of this study is to experimentally confirm the effects of lug motion on lug–soil forces. We measured normal and tangential forces acting on a single lug as functions of inclination angle, moving direction angle, sinkage length, horizontal displacement, and traveling speed. The experimental results were mathematically fitted by using least square method to facilitate quantitative analyses on effects of changes in these motion parameters. Moreover, we compared the measured tangential forces to values calculated from a conventional tangential force model to evaluate the effects of the lug-tip surface, which is generally ignored in existing terramechanics models. The conclusions from this study would be useful for estimating the traveling performance of locomotive mechanisms equipped with lugs, modeling interaction mechanics between lugged wheels and soil, etc.     

Development of a data acquisition system for measuring the characteristics of real time forces by cage wheels

A new data acquisition system was introduced that could be used to monitor the real time wheel forces to solve the limitations of obtaining precise performance characteristics of actual cage wheels. Contrary to previous methods, in which the cage wheel forces were obtained by summing up the individual lug forces. The new method enables measurement of the components of lug force in three orthogonal directions simultaneously. A single unit dynamometer system, with two extended octagonal rings was designed and fabricated using a solid mild steel block, was able to measure force up to 5 kN in each direction. It was used in a soil-bin test rig to determine the characteristics of the forces produced by a cage wheel with opposing circumferential lugs. The characteristics of the pull and lift forces agreed with measured drawbar pull and calculated wheel forces respectively. The force signals fluctuated periodically with rotation angle and the corresponding period approximately equal to the interval of angular lug spacing. The side force fluctuated between positive and negative values and the average was closer to zero due to the balancing effect of opposing lugs. The new system showed better output compared to the previous attempts, confirming its applicability for accurate measurement of real time wheel forces.     

Estimation of a three-dimensional tyre footprint using dynamic soil–tyre contact pressures

A method for estimating the three-dimensional (3D) footprint of a 16.9R38 pneumatic tyre was developed. The method was based on measured values of contact pressure at the soil–tyre interface and wheel contact length determined from the contact pressures and the depths and widths of ruts formed in the soil. The 3D footprint was investigated in an area of the field where the pressure sensors of the tyre passed in a soft clay soil. The tyre was instrumented with six miniature pressure sensors, three on the lug face and the remaining three on the under-tread region between two lugs. The instrumented tyre was run at a constant forward speed of 0.27 m/s and 23% slip on a soft soil, 0.48 MPa cone index, 25.6% d.b. moisture content for four wheel load and tyre pressure combination treatments. The 3D footprint assessment derived from soil–tyre interface stress used in this research is a unique methodology, which could precisely relate the trend profile of the 3D footprint to the measured rut depth. The tyre–soil interface contact pressure distributions results showed that as inflation pressure increased the soil strength increased significantly near the centre of the tyre as a compaction increase sensed with the cone penetrometer.     

Effect of circumferential angle, lug spacing and slip on lug wheel forces

This study was conducted to investigate the effect of circumferential angle, lug spacing and wheel slip on forces produced by a cage wheel. Experiments were conducted in a laboratory soil bin having Bangkok Clay soil with 51% (d.b.) soil moisture content. Six ring-type loadcells were used to measure the soil horizontal, vertical and transverse reactions on the cage wheel lugs. The circumferential angle was varied from 0, 15, 30 to 45°. The lug spacing and wheel slip were varied from 20, 30 to 40° and 20, 35 to 50% respectively. All the force measurements were done at a constant 7 cm sinkage. The results showed that increasing circumferntial angle up to 45° can reduce variation in lug wheel forces, at the same time it had little effect on the mean pull and lift values. The side force was affected by the changes of circumferential angle. The 20° lug spacing not only gave the minimum variations but also maximum mean lug forces. The highest lug wheel forces occurred at 35% wheel slip.     

Dynamic behaviour of an open lugged wheel under paddy soil conditions

Many experimental studies of open lugged wheel-soil interaction have been conducted, mainly based on the condition of constant slip and sinkage. As a result the reaction force to lugs seemed to be equal to the soil cutting resistance to a metal surface. However, analyses based on such methods do not appear to represent the actual behaviour of lugged wheel-soil interaction, especially when the lugs are spaced widely. The actual motion the wheel axle. In this study, an experimental device for a model lugged wheel was constructed to investigate the characteristics of the interaction between a lugged wheel and soil. Experiments were conducted under several test conditions of soil including paddy soil with a hard pan. The result of both theoretical and experimental data indicated that slip and sinkage of a lugged wheel showed a fluctuation with rotation angle of which the period is equal to the angular lug spacing. In each test soil condition used, the motion of the lugged wheel and the reaction forces acting on each lug from the soil for a free sinking wheel were different from that of the condition of constant slip and sinkage. It was found that the results obtained from this study could clarify the actual behaviour of lugged wheel-soil interaction.     

The generalized advancing conformal contact problem with friction,pin loads and remote loading – Case of rigid pin

The advancing, frictional contact problem for a rigid pin indenting an infinite plate with a circular hole is considered. The formulation is general, and considers remotely applied plate-stresses in addition to pin loads. Using the theory of generalized functions, it is found that the governing equation in full sliding is a singular integro-differential equation (SIDE). Partial-slip behavior is governed by an implicit, coupled singular integral equation (SIE) pair. Numerical solutions are presented for both types of problems. It is found that the contact tractions in monotonic loading become independent of the coefficient of friction above a certain threshold value. Finally, problems involving typical ‘fretting-type’ pin loads with and without remote-stresses are also investigated, revealing remarkable effects of the degree of conformality and load path on the steady-state traction distributions.     

Influence of Tribological Processes on a Chaotic Motion of a Bush in a Cylinder-Bush System

In this work periodic and chaotic dynamics of a bush being in a contact with a rotating shaft is analysed using the classical friction and abrasive wear models with the inclusion of the frictional heat generation. First, an analytical chaos prediction using the Melnikov method (without tribologic processes) is given, and then the analytical predictions are verified numerically. Then numerical analysis of the system including tribologic processes is carried out.     

汽车发动机用窄型链的多冲磨损特性研究

为了提高国产机油泵链条的性能,满足发动机轻量化的个性需求,通过发动机总成试验,研究了一种窄型的汽车发动机机油泵链06BN-1的磨损机制,并对套筒和销轴的磨损表面进行微观分析.结果表明,汽车发动机机油泵链的主要磨损形式为疲劳磨损,销轴?套筒零件表面的裂纹生成?扩展与剥落是其主要磨损失效机制.销轴和套筒零件均发生循环软化,滚子零件发生循环硬化.微动磨损是汽车链＂散架＂失效的重要原因之一.保证滚子零件具有足够的强度与塑性,并采取合理的成形工艺,是提高滚子零件多冲抗力的有效方法     

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.     

黄铜/钢摩擦副接触面积对磨损的影响研究

本文对不同直径铜销与钢盘的摩擦磨损进行了研究,研究结果表明：在相同正压力条件下,不同直径销的磨损率随销直径的增大有降低趋势,并且这种降低趋势随销直径的增大逐渐趋于平缓,当接触面积增大到一定尺寸后,其磨损率不再变化,趋于恒定值,由此建立了相同正压力条件下磨损率与接触面积的变化规律数学模型。根据该模型可确定摩擦副的设计尺寸或预测摩擦副的使用寿命;在正压强和其他试验条件相同的条件下,不同直径铜销在单位时间单位面积上的磨损量随着销直径的增大有降低的趋势,并且这种降低趋势随销直径的增大逐渐趋于平缓,本文从铜销直径变化而导致的摩擦副接触表面生热和铜销表面散热等方面对这种现象进行了论述。     

Photoelastic and holographic analysis of a turbine-engine component

Isopachics obtained by holographic methods are combined with the isochromatics and isoclinics of a conventional photoelastic analysis to obtain a complete two-dimensional stress analysis of a highly critical region of a jet engine. The analysis of the disk/blade dovetail region of the third stage fan of a turbine engine shows a stress-concentration factor of 5.2 in the disk fillet and 4.8 in the blade fillet relative to the average stress in the neck section of the disk. The stress distribution along the edge of the blade fillet and on an interior line in the disk lug is also reported. Preliminary redesign of the disk fillet indicates that a 27-percent reduction in the fillet stress of existing third-stage disks is possible by remachining the relief area between the blade and disk lugs.     

Off-road tyre modelling II: effect of camber on tyre performance

The problem of off-road vehicle tyre-terrain interaction is that it is difficult to model accurately. For an off-road vehicle over medium to firm terrain, the tyre load may be entirely supported by the tips of the lugs, or with a minimum carcass contact with the terrain. In this case, the effect of the lugs should be taken into consideration. The forces at the interface between lugged tyre and the soil, including normal and shear stresses, are discussed in this paper. The multi-spoke tyre model was developed to study the effect of tyre lugs on the forces between tyre and terrain and it has been extended to predict the tyre forces and moments in the case of combined lateral and longitudinal slip for a cambered tyre. The influence of slip angle, camber angle and soil hardness on off-road tyre performance has been investigated. A computer program was developed using MATLAB software. The results were derived as tyre forces and moments in the three directions along the tyre contact length. A comparison between the results of the multi-spoke tyre model of a smooth off-road tyre and an off-road tyre with straight lugs, in the cambered case, has been made. The results indicated that slip angle, camber angle and soil characteristics have a strong effect on off-road tyre performance. The modified mathematical model results help the off-road tyre engineering designers to predict accurate values of tyre forces and moments in this complex case.     

Frictional contact problem for a rigid cylindrical stamp and an elastic layer resting on a half plane

The frictional contact problem for a layer resting on a homogeneous half plane is handled using linear elasticity theory in this study. The layer is in contact with a rigid cylindrical stamp that is on the layer and applies a concentrated force in the normal and tangential directions. Friction between the component couples of layer–stamp and layer–half plane is taken into account. The problem is reduced to a system of singular integral equations, in which the contact pressures and the contact areas are the unknowns, and it is treated using Fourier transforms and the boundary conditions for the problem. The system of singular integral equations is solved numerically using the Gauss–Jacobi integration formula with equilibrium and consistency conditions. Numerical results for the contact pressures and the contact areas are given as a solution for both the frictional and the frictionless cases. This work is the first study that investigates the effect of friction on the receding contact problem of a layer and a half plane with two contact areas.     

Full-field and point strain measurement via the inner surface of a rolling large lug tyre

Vehicle safety and performance can be dramatically improved if force or friction measurement of the tyre-terrain interface is known. Since the tyre-terrain interface is responsible for the majority of forces acting on the vehicle, this region has received a lot of attention in vehicle dynamics. Direct measurement of the tyre-terrain interface is difficult since it is hidden by the tyre and terrain. A lot of research has been conducted on the inside of tyre using accelerometers or strain gauges with research more focussed on passenger car tyres and very little work performed on agricultural tyres with larger lugs. This study performs strain measurements using point measurement, from strain gauges, and full field measurement, using a stereo camera measurement system, of the inside of an agricultural tyre on a drum test rig during vertical and lateral loading. Results show similar trends when compared to results on passenger car tyres, however the mounting of the strain gauge relative to the lug is shown to play a large role in the developed strain. Linear relationships between the applied tyre force and strain were obtained in different direction with R² values above 0.97.