Publication news

Journal of Terramechanics, Vol. 48, Issue 3

Jonah H. Lee
Finite element modeling of interfacial forces and contact stresses of pneumatic tire on fresh snow for combined longitudinal and lateral slips
Journal of Terramechanics, Volume 48, Issue 3, June 2011, Pages 171-197, ISSN 0022-4898, 10.1016/j.jterra.2010.12.003.
Abstract: 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. 
Keywords: Tire; Snow; Longitudinal slip; Slip angle; Contact stresses; Interfacial forces; Drucker–Prager; Wheel state; Carpet plot

Yalda Favaedi, Alexandre Pechev, Marco Scharringhausen, Lutz Richter
Prediction of tractive response for flexible wheels with application to planetary rovers
Journal of Terramechanics, Volume 48, Issue 3, June 2011, Pages 199-213, ISSN 0022-4898, 10.1016/j.jterra.2011.02.003.
Abstract: Planetary rovers are typically developed for high-risk missions. Locomotion requires traction to provide forward thrust on the ground. In soft soils, traction is limited by the mechanical properties of the soil, therefore lack of traction and wheel slippage cause difficulties during the operation of the rover. A possible solution to increase the traction force is to increase the size of the wheel-ground contact area. Flexible wheels provide this due to the deformation of the loaded wheel and hence this decreases the ground pressure on the soil surface. This study focuses on development of an analytical model which is an extension to the Bekker theory to predict the tractive performance for a metal flexible wheel by using the geometric model of the wheel in deformation. We demonstrate that the new analytical model closely matches experimental results. Hence this model can be used in the design of robust and optimal traction control algorithms for planetary rovers and for the design and the optimisation of flexible wheels.
Keywords: Wheel–soil-model; Flexible wheels; Mobility; Traction; Rover-terrain interaction force

Andi Isra Mahyuddin, Nuhansyah Sulaiman, Djoko Suharto
Dynamic response of shallow buried structures associated with landmine clearing operations
Journal of Terramechanics, Volume 48, Issue 3, June 2011, Pages 215-224, ISSN 0022-4898, 10.1016/j.jterra.2011.02.002.
Abstract: The development of mechanical means of landmine clearing using flail machines requires a good knowledge of load transfer and tool–soil–landmine interaction. Recent research have provided a good understanding of the soil–tool interaction, but load transfer and responses of buried landmines due to loading from the flails remains undefined. Buried landmines act as unsupported buried structures and loads from the flailing motion are considered as impact loading on the soil surface. A 4 degree-of-freedom mechanical model is constructed and corresponding experiments are conducted to better understand the load transfer and dynamic responses of buried structures due to surface impact loading. The model and experiment is limited to a single impact load directly above the structure, and the buried structure is assumed to move only in the vertical direction. Experiments are conducted for various load magnitude and depth of burial for buried structure in two types of soil. The minimum surface impact forces needed to trigger a landmine in prescribed conditions for two different types of soils have been found. This information could be useful in the design optimization of a mine flail. A correction factor to account for nonlinearity in the form of the ratio of Burgers model and Kelvin stiffness and damping constants is introduced. Considering an appropriate correction factor, the response behavior of the model compares well with the experimental results. The model, while simple, is deemed adequate to represent and predict the behavior of a buried landmine in a mine clearing condition – or any other unsupported buried structure – in soil and sand medium subjected to surface impact loads.
Keywords: Impact load; Buried structure; Load transfer; Landmine clearing

U. Solomon, Chandramouli Padmanabhan
Semi-active hydro-gas suspension system for a tracked vehicle
Journal of Terramechanics, Volume 48, Issue 3, June 2011, Pages 225-239, ISSN 0022-4898, 10.1016/j.jterra.2011.01.002.
Abstract: A semi-active hydro-gas suspension is proposed for a tracked vehicle to improve ride comfort performance, without compromising the road holding and load carrying capabilities of the passive suspension. This is achieved through an active damper used in parallel with a gas spring. The suspension damper parameters are varied by a control mechanism based on sky-hook damping theory, which alters the flow characteristics. A damper prototype has been developed, tested for its flow characteristics, after which it has been integrated into an existing hydro-gas suspension system. An analytical model has been proposed from first principles rather than developing a phenomenological model based on experimental characteristics. This model is validated with experiments carried out on a suspension test rig. In order to compare the performance with the original passive system, an in-plane vehicle model is developed and the simulations clearly show that the semi-active system performance is superior to the passive system.
Keywords: Semi-active hydro-gas suspension; Sky-hook damper; Variable orifice damper