Publication news

Effects of age and wear on the stiffness and friction properties of an SUV tyre

Kraig Richard Shipley Wright, Theunis Richard Botha, Pieter Schalk Els

Journal of Terramechanics, Volume 84, 2019, Pages 21-30, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2019.04.001.

(http://www.sciencedirect.com/science/article/pii/S0022489817301623)

Abstract: Accurate tyre models are essential for all full vehicle simulation models. Tyre models are usually parameterised based on measurements on new tyres. This article performs a sensitivity analysis, based on experimental data, to determine the effects of age and wear on a 235/55R19 tyre’s stiffness characteristics as well as the effect of wear on the tyre’s longitudinal friction characteristics. A well-researched and documented method was used to artificially age the tyres. Static tests were performed periodically on the tyre to monitor the changes in stiffness characteristics. Tyres were also subjected to accelerated wear by performing repeated side force versus slip angle and longitudinal force versus slip tests on a coarse concrete surface. The results indicate that the vertical and longitudinal force versus displacement characteristics have small but convincing dependencies on the age and wear. While the aging process was a trustworthy method, the wear process created irregular lateral and circumferential wear which impacted results. Overall the effects of age and wear did not exhibit substantial enough influence on the tyre stiffness to merit a full tyre model update. However, the wear did have a significant effect, in the order of 10%, on the longitudinal friction of the tyre.

Keywords: Tyre; Age; Wear; Modelling

Influence of tire inflation pressure on the estimation of rating cone index using wheel sinkage

Jooseon Oh, Ju-Seok Nam, Suchul Kim, Young-Jun Park

Journal of Terramechanics, Volume 84, 2019, Pages 13-20, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2019.04.002.(http://www.sciencedirect.com/science/article/pii/S0022489818300855)

Abstract: This study determines the effect of tire inflation pressure on the real-time estimation of the rating cone index (RCI) of a soil using wheel sinkage. It is postulated that wheel sinkage, slip, and tire deflection change with tire inflation pressure. The effect of tire inflation pressure on soil strength estimation is verified by using the equation for RCI estimation. Experiments are conducted to measure wheel sinkage, slip, and tire deflection at different tire inflation pressures. The results show an increase in wheel sinkage and slip and a decrease in tire deflection with a change in tire inflation pressure. A statistical analysis of the experimental results is conducted to assess the influence of tire inflation pressure on RCI estimation. The test results show that the calculated the RCI changes with variations in tire inflation pressure. These results help determine the range of tire inflation pressure that indirectly estimates RCI. In addition, a modified equation is proposed to estimate the RCI irrespective of the tire inflation pressure, and its accuracy is verified through calculations. When estimating the RCI through a new equation, constant soil strength can be estimated regardless of the tire inflation pressure. The average error rate of the estimated RCI in each tire inflation pressure was 1.59%.

Keywords: Rating cone index; Tire inflation pressure; Wheel slip; Wheel sinkage; Tire deflection; Soil strength

Mobility guidance for tracked vehicles on fine-grained soil from historical full-scale test data in DROVE 2.0

James M. Williams, Farshid Vahedifard, Isaac L. Howard, Arman Borazjani, George L. Mason, Jody D. Priddy

Journal of Terramechanics, Volume 84, 2019, Pages 1-12, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2019.04.003.(http://www.sciencedirect.com/science/article/pii/S002248981830209X)

Abstract: With over 8000 field and laboratory tests, the Database for Off-Road Vehicle Environments (DROVE) provides a consolidated database of parameters for the assessment of tracked and wheeled vehicles on fine- and coarse-grained soils. This paper presents a new release of DROVE, version 2.0, which adds 294 results from the test performed by powered and unpowered tracks on fine-grained soils. Several performance parameters including drawbar pull, motion resistance, sinkage, torque, trim angle, and slip were measured alongside track geometry and loads. Soil properties were quantified via cone index testing, allowing performance parameters to be assessed in terms of their relationship to contact pressure divided by cone index. Potentially useful relationships were identified for drawbar pull, sinkage, and powered torque. The new release of DROVE dataset can be used for several applications including evaluation of existing mobility models, development of improved algorithms, and validation of numerical simulations for tracked vehicles.

Keywords: Mobility; Database Records for Off-Road Vehicle Environments (DROVE); Tracked vehicle; Fine-grained soil; Drawbar pull; Motion resistance; Sinkage; Vehicle Terrain Interaction (VTI)

Rapid automated soil preparation for testing planetary rover-soil interactions aboard reduced-gravity aircraft

Krzysztof Skonieczny, Parna Niksirat, Amir Ali Forough Nassiraei

Journal of Terramechanics, Volume 83, 2019, Pages 35-44, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2019.03.001.(http://www.sciencedirect.com/science/article/pii/S0022489818301642)

Abstract: Mitigating potential hazards for planetary rovers posed by soft soils requires testing in representative environments such as with Martian soil simulants in reduced gravity. However, constraints imposed by testing aboard an aircraft performing parabolic flights make critical elements of the test procedure, such as soil preparation, challenging. This work describes the design, development, and operation of a novel rover-soil testing system that includes rapid automated soil preparation. The repeatability of the prepared soil condition is demonstrated by cone penetrometer tests in the laboratory as well as in a Falcon 20 aircraft during a parabolic flight campaign.

Keywords: Automatic test equipment; Space exploration; Planetary rovers; Robot motion; Reduced-gravity flights

Experimental verification on analytical models of lunar excavation

Banglu Xi, Mingjing Jiang, Liang Cui, Jun Liu, Huayang Lei

Volume 83, 2019, Pages 1-13, ISSN 0022-4898,

https://doi.org/10.1016/j.jterra.2019.01.002.(http://www.sciencedirect.com/science/article/pii/S0022489817301805)

Abstract: In this paper, a series of excavation tests were conducted with a carefully designed apparatus and testbed based on soil mechanics theories to obtain reliable excavation forces in Tongji-1 lunar soil simulant at first. Then the measured data were compared with the forces predicted by six typical analytical models to verify their capability of accurately capturing the effects of cutting depth, rake angle, blade width and cutting speed. The results show that for the horizontal excavation forces, the Zeng model, the Kobayashi model, the Mckyes model and the Swick and Perumpral model can capture the effects of cutting depth, and the Lockheed-Martin/Viking model could capture the effects of the cutting depth, blade width and rake angle. For the vertical excavation forces, the Swick and Perumpral model and the Mckyes model can capture the effects of the cutting depth, blade width and rake angle. The overall assessment of excavation force predictions shows that the Lockheed-Martin/Viking model, the Zeng model, the Swick and Perumpral model and the Mckyes model are recommended for predicting the horizontal excavation force, and the Swick and Perumpral model and the Mckyes model are recommended for predicting the vertical excavation force.

Keywords: Testbed; Boundary effect; Soil-tool interaction; Lunar excavation

Study on applicability of RFT to traveling analysis of wheel with grousers: Comparison with DEM analysis as a virtual test

Hirotaka Suzuki, Kota Katsushima, Shingo Ozaki

Journal of Terramechanics, Volume 83, 2019, Pages 15-24, ISSN 0022-4898,

https://doi.org/10.1016/j.jterra.2019.01.001

(http://www.sciencedirect.com/science/article/pii/S0022489818300569)

Abstract: We studied a method to calculate the traveling characteristics of small and lightweight rovers at low cost. Specifically, discrete element method (DEM) was considered as a high-cost and high-accuracy virtual test, and plate tests and traveling analyses of the wheel with grousers were performed. Meanwhile, we adopted resistive force theory (RFT) as a low-cost analysis method and confirmed its applicability to the traveling of wheels with grousers by comparing it with the results obtained by DEM analysis of a loose frictional soil. First, we determined the scale factor necessary for RFT calculation by DEM analysis of the plate penetration test. Then, DEM wheel models with three types of grouser were prepared, and we compared the drawbar-pull under several levels of slippage with the results obtained by RFT. Although RFT cannot sufficiently consider the influences of the shearing of the soil and of distance between grousers, it found that the effects of grousers can be examined at low cost by RFT.

Keywords: RFT; Wheel-soil interaction; Grouser; Trafficability; Slippage

Design optimization of deep-seabed pilot miner system with coupled relations between constraints

Su-gil Cho, Sanghyun Park, Jaewon Oh, Cheonhong Min, Hyungwoo Kim, Sup Hong, Junyoung Jang, Tae Hee Lee

Journal of Terramechanics, Volume 83, 2019, Pages 25-34, ISSN 0022-4898,

https://doi.org/10.1016/j.jterra.2019.01.003

(http://www.sciencedirect.com/science/article/pii/S0022489817301271)

Abstract: In the pilot miner system, the hydraulic type collector is sensitive to the traffic ability of moving on cohesive soil. Therefore, the traffic ability needs to be simultaneously considered with collector performances in the design process. This means that the system has coupled disciplines and constraints, which can reduce the size of the feasible region, rendering it difficult to use the current optimization techniques to search the optimum satisfying all of the constraints. In this study, a new technique which stochastically explores the optimum point with the highest probability, improving the objective and satisfying the constraints, is applied to the design of a deep-seabed pilot miner system.

Keywords: Coanda effect; Cohesive soil; Constraint global optimization; Coupled discipline; Deep-seabed pilot miner system; Kriging surrogate model; Ocean mining system

Real time rut profile measurement in varying terrain types using digital image correlation

Theunis Botha, Devin Johnson, Schalk Els, Sally Shoop,

Journal of Terramechanics, Volume 82, 2019, Pages 53-61, ISSN 0022-4898,

https://doi.org/10.1016/j.jterra.2018.12.003.(http://www.sciencedirect.com/science/article/pii/S0022489818301241)

Abstract: An important parameter in terramechanics is the rut depth produced when a vehicle traverses deformable soil. The rut depth provides a measure of vehicle tractability as well as the impact on the environment. Rut depth is not uniform on natural terrain and typically only a few manual points are measured. Synchronizing rut depth with other measurements is also problematic. This paper investigates the feasibility of using cameras to measure 3D terrain profiles from which a single rut depth measurement is obtained. Tests were performed on different vehicles, for various dynamic vehicle manoeuvres, over varying terrains including sand, mud, grassland, snow and ice. Results were validated using the traditional stick ruler method. Measurement frequencies of 58 Hz were obtained using affordable commercially off the shelf computational hardware and dedicated software. Determining whether a vehicle can traverse a terrain can significantly improve the vehicle mobility. Therefore, real time measurements of rut depth can be used to determine the mobility of vehicles in off-road conditions that can change rapidly due to environmental conditions e.g. rain or snow. The techniques described can assist in gathering terrain and vehicle mobility data that can be used directly to assist the driver in making safety related decisions.

Keywords: Real time; Rut depth; Stereo; Terrain measurement

An in-wheel sensor for monitoring tire-terrain interaction: Development and laboratory testing

Raul G. Longoria, Robert Brushaber, Andrew Simms

Journal of Terramechanics, Volume 82, 2019, Pages 43-52, ISSN 0022-4898,

https://doi.org/10.1016/j.jterra.2018.12.004.(http://www.sciencedirect.com/science/article/pii/S0022489818301320)

Abstract: An in-wheel sensor system was developed to monitor the deflection and shape of a tire that it is operating on and interacting with terrain. Three ultrasonic sensors were mounted to rotate with the wheel rim to measure radial distance to the inner tire surface at the mid-plane and at two equidistant lateral planes of the tire. This study describes evaluation of the sensor system using a laboratory drum-test machine which drives the tire over a wide range of speeds at different normal tire loads and inflation pressures. Signal processing methods are described for extracting characteristic measures of the tire contact and shape geometry which can be determined from measurements of inner tire surface deflection. The measurement of contact length compared well with results measured using other methods and reported in the literature. Additional tire shape metrics are defined that may be useful for informing how automated adjustments can be made to inflation pressure by central tire inflation pressure systems. In most of the test cases, the three sensors showed no significant lateral variation in measured deflections, as expected for testing on a rigid drum.

Keywords: Tire-terrain contact measurement; Tire contact area sensor; Contact length