Publication news

Applicability of the 1g similitude law to the physical modeling of soil-track interaction

Sung-Ha Baek, Joonyoung Kim

Journal of Terramechanics, Volume 85, 2019, Pages 27-37, ISSN 0022-4898,

Abstract: This study aimed to investigate the applicability of the 1g similitude law to the physical modeling of soil-track interaction. Model track experiments were performed using four physically modeled soil-track systems with different geometric scale factors, under three different relative densities of the model ground. Based on the modeling of the model technique, the results of the physical models were compared in terms of the largest physical model scale. The soil-track interaction behaviors showed similar tendencies on the whole, but slight differences were also observed depending on the geometric scale factor. Such differences, however, were not significant compared to the differences in relation to other soil-structure interaction problems. Moreover, considering that the shearing action on the soil-track interface is a large replica of the shearing process in the direct shear tests of the soil, the differences among the physical models were attributed to the specimen size effect observed in the direct shear test of the soil, rather than to the similitude relationships. Therefore, it can be concluded that the 1g similitude law can be applied to the assessment of the soil-track interaction behavior, provided that the mechanical boundary restraint of the shearing action on the soil-track interface is properly accounted for.

Keywords: Soil-track interaction; Physical modeling; Similitude law; Modeling of the model technique; Off-road tracked vehicle

Parametric study and design guidelines for rigid wheels for planetary rovers

Hiroaki Inotsume, Scott Moreland, Krzysztof Skonieczny, David Wettergreen,

Journal of Terramechanics, Volume 85, 2019, Pages 39-57, ISSN 0022-4898,

Abstract: This paper addresses the design of rigid wheels for planetary rovers in loose, granular soil. Wheel surface features, such as grousers, are known to improve tractive capability in planetary-relevant soils. However there are no comprehensive design guidelines for these wheel features. In this research, a series of intensive and extensive parametric studies were carried out in full-scale vehicle slope experiments and single-wheel tests that assess the influence of grouser count, height, orientation, and end-cap in various longitudinal and lateral slip conditions. This work also investigates the traction process of grousers based on a soil flow imaging technique. The soil motion analysis reveals that grousers reduce forward soil flow/motion resistance and increase net traction. A grouser design formula is derived from the soil flow observation, and design guidelines of rigid wheels of planetary rovers for loose soil are proposed based on these results. The proposed guidelines are applied to the modification of grouser design of the Mars Science Laboratory rover to improve tractive performance on loose terrain.

Keywords: Planetary rover; Rigid wheel; Grouser design; Loose soil; Slope traverse

Modeling of the interaction of rigid wheels with dry granular media

Shashank Agarwal, Carmine Senatore, Tingnan Zhang, Mark Kingsbury, Karl Iagnemma, Daniel I. Goldman, Ken Kamrin

Journal of Terramechanics, Volume 85, 2019, Pages 1-14, ISSN 0022-4898

Abstract: We analyze the capabilities of various recently developed techniques, namely granular Resistive Force Theory (RFT) and continuum plasticity implemented with the Material Point Method (MPM), in capturing dynamics of wheel-dry granular media interactions. We compare results to more conventionally accepted methods of modeling wheel locomotion. While RFT is an empirical force model for arbitrarily-shaped bodies moving through granular media, MPM-based continuum modeling allows the simulation of full granular flow and stress fields. RFT allows for rapid evaluation of interaction forces on arbitrary shaped intruders based on a local surface stress formulation depending on depth, orientation, and movement of surface elements. We perform forced-slip experiments for three different wheel types and three different granular materials, and results are compared with RFT, continuum modeling, and a traditional terramechanics semi-empirical method. Results show that for the range of inputs considered, RFT can be reliably used to predict rigid wheel granular media interactions with accuracy exceeding that of traditional terramechanics methodology in several circumstances. Results also indicate that plasticity-based continuum modeling provides an accurate tool for wheel-soil interaction while providing more information to study the physical processes giving rise to resistive stresses in granular media.

Stress distributions of a grouser wheel on loose soil

Shoya Higa, Kenji Nagaoka, Kazuya Yoshida

Journal of Terramechanics, Volume 85, 2019, Pages 15-26, ISSN 0022-4898,

Abstract: Measurement of stress distribution at the contact patch is the best way to understand the wheel–soil interaction on loose soil because the wheel only interacts with the terrain at the contact patch. Grousers attached to the wheel rim upgrade the mobility performance of the wheel on loose soil; however, the stress distribution of the grouser wheel has not yet been elucidated. Understanding of the interaction between the grouser wheel and the soil contributes to the improvement in the mechanical model of the grouser wheel, and will be helpful to estimate the terrain parameters beneath the wheel. In conventional approaches, it is assumed that the traction of the grouser wheel can be expressed by merely adding bulldozing effects of the grousers into the rigid wheel model, or can be addressed as the enlargement of the wheel diameter; however, the experimental investigations are not enough. For more appropriate modeling and design of a grouser wheel, the stress distribution of a grouser wheel should be revealed. Therefore, this article addresses the experimental investigation of the stress distribution on a grouser wheel. Experimental results reveal that almost all tractive components of the grouser wheel are exerted at the grousers, unlike in the conventional model.

Keywords: Wheel–soil interaction; Stress measurement; Stress distribution; Grouser wheel; Loose soil

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

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

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

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

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,

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