A study of soil thrust exerted by a tracked vehicle

This paper deals with soil thrust exerted by a tracked vehicle. Measurements of the ground pressure beneath the tracks of a tracked vehicle were carried out and it was shown that the ground pressure distribution is approximately represented by discontinuous triangles which have their maxima under the roadwheels. The relationship between soil shear curve (shear stress or force-deformation curve) obtained from shear test and thrust curve (soil thrust-slip ratio curve) of the tracked vehicle is analyzed by using the above mentioned ground pressure distribution, and it is shown that there is a transformation law between both curves. Namely, the thrust curve due to soil shear under any wheel portion is given as a function of soil and vehicle parameters. Further, the reliability of the above method is confirmed experimentally.     

External motion resistance caused by rut sinkage of a tracked vehicle

This paper deals with the external motion resistance of a tracked vehicle caused by rut formation (sinkage) or compression of soil under the tracks. It is shown that the relationship between the applied load and the sinkage for a loading test using a plate is represented by a hyperbola. Based on the above relationship, the external motion resistance caused by the rut formation of a tracked vehicle is estimated by considering the work done by overcoming the ground pressure and the resistance. Further, measurements of the external motion resistance were carried out by using a tracked vehicle and the experimental results are compared with the theoretical ones, and the reliability of the above method is confirmed experimentally.     

Modeling track-terrain interaction for transient robotic vehicle maneuvers

This article describes integration of a realistic and efficient track-terrain interaction model with a multibody dynamics model of a robotic tracked vehicle. The track-terrain interface continuum is approximated by discretized and parameterizable force elements. Of particular note is a kinematic model used to estimate dynamic shear displacement, taking the form of a partial differential equation. This equation is approximated by a series of ordinary differential equations, making it compatible with multibody dynamics model formulations. Comparisons between simulated results and those obtained from field testing with a remotely-operated unmanned tracked vehicle are made to evaluate the effectiveness of this approach and to validate the use of nominal parameter data from the literature. The test vehicle was subjected to four different types of maneuvers (go-and-stop, j-turn, double lane change, and zero radius turn) on asphalt and dry sand. Simulated results using both the dynamic and steady-state track-terrain interaction models match very well with those obtained from the tests, except for the zero radius turning maneuver in sand. In this case, bulldozing effects must be incorporated to improve prediction of lateral forces.     

A simplified method for the estimation of soil thrust exerted by a tracked vehicle

A simplified method for estimating the soil thrust exerted by a tracked vehicle is proposed. The relationship between the soil shear torque curve (shear torque-deformation curve) obtained from ring shear test and the thrust curve (soil thrust-slip ratio curve) of a tracked vehicle is analyzed and it is shown that there is a transformation law between these curves. A simplified analytical method for estimating the soil thrust exerted by a tracked vehicle is developed by using the above-mentioned transformation law. Soil thrust can be estimated by using the soil shear torque curve, shear ring and vehicle parameters. It is experimentally confirmed that the soil thrust can be easily estimated by using the proposed method.     

Tractive and braking performance of a flexible tracked tractor moving up and down weak sloped terrain

The objective of this study is to analyse the tractive and braking performance of a tractor travelling up and down a weak silty loam sloped terrain. The effects of track belt size on terrain-track system parameters were investigated experimentally, and the force and energy balances were clarified for the actual flexible tracked vehicle. The flexibility of the track belt has been precisely analysed as a function of track tension, loading and reloading properties of terrain, and contact pressure distributions. The results show that the optimum effective driving (or braking) force decreases with the increase of slope angle due to the decreasing vehicle weight component, while the thrust (or drag) decreases and the compaction resistance increases. The contact pressure distribution under the flexible track belt shows a triangular wavy pattern having peak values under each track roller. The shear resistance distribution has positive and negative peak values for the driving and braking states, respectively.     

Prediction of the tractive performance of a flexible tracked vehicle

In this study, we describe a mathematical model designed to allow for the determination of the mechanical relationship existing between soil characteristics and the primary design factors of a tracked vehicle, and to predict the tractive performance of this tracked vehicle on soft terrain. On the basis of the mathematical model, a computer simulation program (Tractive Performance Prediction Model for Tracked Vehicles; TPPMTV) was developed in this study. This model took into account the characteristics of the terrain, including the pressure-sinkage, the shearing characteristics, and the response to the repetitive loading, as well as the primary design parameters of the tracked vehicle. The efficacy of the developed model was then confirmed via comparison of the drawbar pulls of tracked vehicles predicted using the simulation program TPPMTV, with those determined as the result of traction tests. The results indicated that the predicted drawbar pulls, with the change in slip, were quite consistent with the ones measured in the traction test, for the changes in the weight of the vehicle, the initial track tension, and the number of roadwheels within the entire slip range. Thus, we concluded that the simulation program developed in this study, named TPPMTV, proved useful in the prediction of the tractive performance of a tracked vehicle, and that this system might be applicable to the design of a vehicle, possibly enabling a significant improvement in its functions.     

Effects of vertical exciting force of a tracked vehicle on the dynamic compaction of a high lifted decomposed granite

The main purpose of this paper is to evaluate the effects of a jumping action of a tracked vehicle mounted with a vertical oscillator on vibro-compaction of a high lifted decomposed granite. A vibro-compaction test was executed using a model tracked vehicle of 4.9 kN weight under a condition of frequency of 16 Hz and load ratio of maximum vertical exciting force to vehicle weight of 0.2–2.0. As a result, it was observed that both the amount of sinkage of terrain surface and the dry density of soil increased hyperbolically with increment of the load ratio and the dry density distribution with depth became uniform for the whole depth of the soil stratum. It was confirmed that the volume shrinkage of soil was succeeded by the propagation of acceleration to deep stratum due to the jumping action and the dilatancy phenomenon due to an alternative shear stress. The optimum load ratio obtaining a maximum dry density at the frequency of 16 Hz was judged to be 2.0 within this experiment. In the application of these test results to an actual prototype tracked vehicle of 39.2 kN weight, it was estimated that the degree of compaction of a high lifted soil stratum of 90 cm became over 90% at the load ratio of 2.0.     

Effects of a roller and a tracked vehicle on the compaction of a high lifted decomposed granite sandy soil

The aim of this research was to innovate a new compaction machinery by comparing experimentally the effects of a two-axle, two wheel road roller and a tracked vehicle on the compaction of a decomposed granite sandy soil with a high spreading lift. By measuring the amount of sinkage of the terrain surface, the dry density distribution versus depth using a cone penetrometer, the normal earth pressure distribution versus depth using a stress state transducer (SST), the effects of the road roller and the tracked vehicle on the increment of the soil dry density were considered theoretically. It was observed that the tracked vehicle showed a larger amount of sinkage and a larger dry density distribution versus depth than the roller. The ratio of shear stress to normal stress was still large enough at the deep stratum, so that an optimal shear strain was developed on the whole range of the high lifted stratum and it increased the soil compaction density due to the dilatancy effect.     

A new contact & slip model for tracked vehicle transient dynamics on hard ground

This study presents a new general transient contact and slip model for tracked vehicles on hard ground which is simple, accurate, and in agreement with the test results to a satisfactory level. Simulating zero track speed instances become possible with the new contact/shear model which is the major proposed improvement in addition to more accurate results for transient steering and tractive inputs. The model represents a general tracked vehicle having rear or front sprockets, with parameters for center of gravity, wheel positions, number of wheels, and track-pretention. To calculate longitudinal and lateral forces, a transient shear model is used. Shear stress under each track pad is assumed to be a function of shear displacement. The contact time formulation used in shear displacement calculation is improved to gain accuracy for transient and zero track speed conditions.The model is implemented on the Matlab/Simulink platform and verified with a comprehensive program of road tests composed of transient steering and tractive/braking scenarios. The results of the simulations and the road tests are satisfactorily similar for both constant and transient input maneuvers. Moreover, sensitivity simulations for vehicle parameters are conducted to show that the model responses are inline with the expected vehicle dynamics behaviours.     

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.     

Design and mobility evaluation of tracked lunar vehicle

Past lunar vehicles have had difficulty traveling through soft sand areas due to the thick, soft and dry regolith. This paper describes the design and evaluation results of a tracked lunar vehicle which aims at achieving greater mobility, particularly improved climbing ability on pure sand slopes, by reducing contact pressure with a crawler link. The tracked vehicle uses mesh crawler links to reduce complexity, weight and parts count. Single-crawler tests on simulated lunar soil revealed that the crawler’s slip ratio was lower than that of a rigid wheel at any slope angle, and that its power consumption was lower than that of a wheel on slopes of 10° or more. Furthermore, the crawler’s slip ratio was stable or decreasing along the traveling distance on steep slopes, contrary to the wheel. Our tracked lunar vehicle, the “Light Crawler”, is equipped with four such mesh-crawlers, each of which is independently driven and steered. It is intended to realize high climbing ability, a small turning circle, and an obstacle-crossing capability using a unique suspension system. The vehicle’s climbing and obstacle-crossing capabilities were tested on both simulated lunar soil and a rock-scattered field, and its mobility performance was successfully confirmed.     

胶新铁路砂土液化区路基沉降规律研究

地震液化常给人们带来巨大损失,而剪切振动和循环荷载作用下的动力学效应常被认为是地震液化的主要原因,人们对剪切荷载作用下饱和砂土的液化问题进行了较多的研究,而对循环荷载作用下砂土液化的动力学效应研究较少。胶新铁路在DK39+000开始为高地震烈度区,DK283+550~DK283+770分布有地震可液化层,工程修建后列车动荷载的影响将会有诱发砂土液化的可能性。为了研究通车前自然沉降特征和通车后循环荷载作用下的路基沉降变形规律,本文在具体分析了砂土液化的概念和准则判别的基础上,重点分析了砂土液化区路基沉降特征,包括测试断面竖向分层沉降变形特征分析和路基水平位移特征分析。最后在试验的基础上,从理论上给出了循环荷载下砂土的本构关系。     

常德-张家界高速公路某大桥桥基砂土液化评价

结合常德—张家界高速公路某大桥桥基工程,在DSD—160型电磁式振动三轴试验仪上,通过往返加荷三轴试验,对饱和砂土进行了液化试验研究,探讨了基于动三轴液化试验结果判断饱和砂土液化的方法。并尝试了这种室内研究—反应分析的液化可能性估计方法与地震剪应力时程相结合的综合判断方法。在该高速公路大桥桥基的饱和砂土液化评价中,采用这种综合判断方法,对大桥桥基砂土液化进行了判断。在判断场地是否液化后,对其液化危害程度进行了等级划分,给出了该工程场地在未来遭受到不同超越概率下的地震作用时发生液化的危害程度,得到了一些有工程实用意义的结果。     

Influence of age-hardening and strain-rate on confined compression and shear behaviour of snow

The problem of assessing mobility performance of tracked or wheeled vehicles over snow is addressed in terms of the capability of the snow to provide flotation and traction capabilities. To obtain input into analyses for energy transfer from the traction element to the supporting snow cover, it is necessary to describe confined compression and shear performances of the snow—recognizing that a large density increase occurs under initial attack of the vehicle traction element. This study provides experimental input and diagrams of energy surfaces describing confined compressive and shear effects related to snow age and initial density.     

垂向动载下饱和砂土液化发展的数值模拟

针对一维应变情况,建立了垂向荷载作用时饱和砂土的一维应变动力学模型,然后进行了分析。得到了在垂向荷载作用下,饱和砂土液化发展过程的特性。结果表明,渗透系数越小,骨架强度越低,扰动强度越大,液化发展越快。     

Effects of loading patterns on the pressure-sinkage relation of dry loose sand

The pressure-sinkage relation of dry loose sand is one of the main problems considered for a vehicle to drive in desert. It is affected by loading patterns. Based on plate-sinkage tests. the effects of two different loading patterns on the pressure-sinkage relation of dry loose sand are studied. One is that the plate is horizontal with the angle of load relative to the plate normal varying from 0 to 30 degrees. The other is that the load is perpendicular to the plate with the angle of the plate relative to sand surface varying from 0 to 30 degrees. The results indicate that the pressure -sinkage relations of dry loose sand in both the above mentioned cases are different from that in the horizontal plate-vertical load case and that if the sinkage-pressure relation under the horizontal plate-inclined load case is used to determine the normal stress distribution under the tire, a precise prediction of the tractive properties of a wheel can be obtained.     

Prediction of trafficability for tracked vehicle on broken soil: real size tests

Full-scale tests were carried out within the broader framework of a study of an operational mechanical mine clearance system. This system is made up of a tracked machine pushing a mine clearance plow that scarifies the soil to approximately 30 cm depth. This study examines the capacity of the tractor to move on a disturbed soil. This paper presents motion resistance tests and drawbar pull tests on four types of soil. The soils have been chosen to be scientifically representative of the broad distribution on our planet: a sand (frictional soil), a silt (cohesive soil), a silty gravel (coarse-grained soil), and a silty sand (cohesive soil). The tests are performed in two configurations: on compacted soils and on soils scarified with an experimental plow. The results of each test condition are described. The effects of the soil type, its state, and the speed of the tested vehicle are presented. Using these results and, in addition, full-scale tests of scarification, we present an operational analysis determining the mobility of a tracked vehicle on broken soil. This method makes it possible to calculate the maximum speed of a mechanical mine clearance system for the whole range of soils tested.     

Lateral slide sinkage tests for a tire and a track shoe

Previous field studies have shown the influence of turning vehicles on rut formation or sinkage. In order to further investigate the relationships, laboratory tests were conduced on a 14.5–20.3 6-PR trailer tire and an Armored Personnel Carrier (APC) track shoe in sand. Lateral displacements, and resulting lateral forces, were applied to the tire and track shoe under constant normal forces. The tire was pulled laterally and the track shoe was pulled back and forth to represent actual movement during vehicle turning. Results show that the lateral force and lateral displacement generated by turning maneuver affect sinkage severely for wheeled and tracked vehicles. The final sinkage caused by the lateral force for the tire is 3–5 times to the static sinkage. For the track shoe, the final sinkage caused by the lateral displacement is about three times to the static sinkage.     

On the implementation of a multi-surface kinematic hardening plasticity and its applications

This paper is concerned with an application of the multi-surface plasticity in solid mechanics and geotechnical problems. The model is of a von-Mises type with associated flow rule, originally proposed by Montans. The Mroz translation rule is implemented to the movements of the yield surfaces and the fully implicit scheme with radial mapping method is applied in numerical computations. Algorithmic consistent tangent modulus with numerical integration algorithm of constitutive equations is extracted. The model is developed in the class of kinematic hardening models, so the ‘Masing’ rule is preserved. The model is able to consider the plastic strain accumulation in constant axial stress state, such as ratcheting. The implementation is validated by means of a simple deformation path of combined extension and compression test, a pure shear test with pseudo-random loading, a test which demonstrates the capabilities of the model in simulation of cyclic loading and ratcheting, a cyclic shear test in saturated undrained sand and finally, the analysis of a plate with holes, which presents the shear band using the multi-surface plasticity model.     

Ambiguity of the critical load for spherical shells with shear damageability of the material

The structural-probabilistic approach to the modeling of combined crack formation and material deformation processes is used to develop a technique for solving bifurcation stability problems for thin-walled structural members made of damageable materials under single and repeated loadings. The example of a uniformly compressed spherical shell is used to show that, under repeated loading, thin-walled structural members made of shear damageable materials can lose stability under loads smaller than the upper critical loads. The ambiguity of the critical loads for various damage accumulation processes in the material of thin-walled structures depends on the level and character of loading. This phenomenon can be one possible cause of the experimental data spread and the discrepancy between theoretical and experimental results used to determine the critical loads for spherical and cylindrical shells.