Identification, design and kinematic analysis of an earthmoving mechanism

Yongjun Pan, Alfonso Callejo  Journal of Terramechanics, Volume 66, August 2016, Pages 27-39, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.03.002
http://www.sciencedirect.com/science/article/pii/S0022489816000239
Abstract:  
Earthmoving mechanisms in motor graders are critical components for earthwork, compaction and re-handling, and yet they have not received much attention by mechanical engineering research in recent times. In this paper, a comprehensive analysis, from mechanism identification and innovative design to kinematic analysis, is presented. First, the mechanism analysis and synthesis method based on multibody system dynamics is carried out through the analysis of the system topology and connectivity. We conclude that the earthmoving multibody system is a spatial hybrid mechanism, which consists of a spatial parallel mechanism and a spatial serial mechanism. Second, a number of new spatial parallel mechanisms, which are advantageous with respect to the original one under certain conditions, are generated. The kinematic characteristics of the parallel mechanism family are investigated in terms of constraint equations formulated in natural coordinates. Third and last, kinematic simulations and optimization processes are carried out to evaluate the advantages of the presented spatial parallel mechanisms. Simulation results show that these mechanisms can provide better kinematic performance.  
Keywords: Motor grader; Earthmoving mechanism; Multibody systems; 3RRPS-S mechanism; Natural coordinates

Suitability of rubber track as traction device for power tillers

Showkat Rasool, Hifjur Raheman
Journal of Terramechanics, Volume 66, August 2016, Pages 41-47, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2015.08.003
http://www.sciencedirect.com/science/article/pii/S0022489815000737
Abstract: 
Suitability of using rubber tracks as traction device in power tillers replacing pneumatic tires was studied using an experimental setup consisting of a track test rig for mounting a 0.80 m × 0.1 m rubber track and a loading device for applying different drawbar pulls. Tests were conducted in the soil bin filled with lateritic sandy clay loam soil at an average soil water content of 9% dry basis by varying the cone index from 300 to 1000 kPa. Data on torque, pull and Travel Reduction Ratio (TRR) were acquired using sensors and data acquisition system for evaluating its performance. Maximum tractive efficiency of the track was found to be in the range of 77–83% corresponding to a TRR of 0.12–0.045. The Net Traction Ratio (NTR) at maximum tractive efficiency was found to be between 0.49 and 0.36.

Using non-linear regression technique, a model for Gross Traction Ratio (GTR) was developed and it could predict the actual values with a maximum variation of 6% as compared to an average variation of 50% with Grisso’s model. Based on this model, tractive efficiency design curves were plotted to achieve optimum tractive performance of track for any given soil condition. 
Keywords: Track tester; Soil bin; Traction ratios; Travel Reduction Ratio; Tractive efficiency

Comparison of SPH simulations and cone index tests for cohesive soils

Christopher Goodin, Jody D. Priddy
Journal of Terramechanics, Volume 66, August 2016, Pages 49-57, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2015.09.002.
http://www.sciencedirect.com/science/article/pii/S0022489815000865
Abstract:

The cone penetrometer test has been used for decades to quantify the soft soil mobility performance of ground vehicles. As physics-based methods for modeling soil are developed, it is necessary to validate these simulations against databases relating Cone Index (CI) to vehicle mobility. However, in order to make this comparison, the relationship between the engineering properties of the soil (density, bulk modulus) and the cone index must be determined. To that end, in this work, simulations of cone penetrometer tests in cohesive soil using the smoothed particle hydrodynamics (SPH) method are presented. Three dimensional simulations were conducted and compared to laboratory measurements of cone index in soft soil. The SPH model is parametrized using the elastic moduli of the soil (bulk and shear modulus), the soil density, and the soil cohesion. A novel method which includes skin friction is employed to calculate the forces exerted on the cone tip by the soil. The simulations give good agreement with the measurements, with a coefficient of determination R 2 = 0.76 . These results indicate that SPH may be viable for simulating soft soil in conditions relevant for vehicle mobility considerations.
Keywords: Cone index; SPH; Mohr–Coulomb

Tire compaction capacity rating on non-standard soil

Alexandr Grečenko
Journal of Terramechanics, Volume 66, August 2016, Pages 59-61, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.03.003.
http://www.sciencedirect.com/science/article/pii/S0022489816300015
Abstract: 
Tire Compaction Capacity rating system with its CC index was evolved to support the choice of proper tires for off-road vehicles or machines operating on crop producing land with aim to prevent harmful compaction of the ground. This system, fundamentally presented in the Journal of Terramechanics, Vol. 52/2014, is based on a great number of laboratory compaction tests in common clay–loam soil (here marked as standard soil). The presented article deals especially with more accurate application of numerical rating to sandy and clay soils (very different grain size) under the designation equivalent Compaction Capacity (eCC) index, however, is applicable to an arbitrary soil type. The features and practical use of eCC rating are explained and discussed in this technical note. 
Keywords: Soil compaction risk; Off-road tires; Tire equivalent compaction capacity index

Experimental validation of a differential variational inequality-based approach for handling friction and contact in vehicle/granular-terrain interaction

Daniel Melanz, Paramsothy Jayakumar, Dan Negrut
Journal of Terramechanics, Volume 65, June 2016, Pages 1-13, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.01.004
http://www.sciencedirect.com/science/article/pii/S0022489816000069
Abstract:  

The observation motivating this contribution was a perceived lack of expeditious deformable terrain models that can match in mobility analysis studies the level of fidelity delivered by today’s vehicle models. Typically, the deformable terrain-tire interaction has been modeled using Finite Element Method (FEM), which continues to require prohibitively long analysis times owing to the complexity of soil behavior. Recent attempts to model deformable terrain have resorted to the use of the Discrete Element Method (DEM) to capture the soil’s complex interaction with a wheeled vehicle. We assess herein a DEM approach that employs a complementarity condition to enforce non-penetration between colliding rigid bodies that make up the deformable terrain. To this end, we consider three standard terramechanics experiments: direct shear, pressure-sinkage, and single-wheel tests. We report on the validation of the complementarity form of contact dynamics with friction, assess the potential of the DEM-based exploration of fundamental phenomena in terramechanics, and identify numerical solution challenges associated with solving large-scale, quadratic optimization problems with conic constraints.  
Keywords: Terramechanics; Discrete element method; Friction and contact; Differential variational inequality; Validation; Calibration; Direct shear test; Pressure-sinkage test; Single wheel test; Deformable terrain

Agile tire slippage dynamics for radical enhancement of vehicle mobility

Jeremy P. Gray, Vladimir V. Vantsevich, Jesse Paldan
Journal of Terramechanics, Volume 65, June 2016, Pages 14-37, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.01.002
http://www.sciencedirect.com/science/article/pii/S0022489816000045
Abstract: 
There is a need to radically increase mobility of terrain vehicles through new modalities of vehicle locomotion, i.e., by establishing a new technological paradigm in vehicle dynamics and mobility. The new paradigm greatly applies to military vehicles for the radical improvement of tactical and operational mobility. This article presents a new technological paradigm of agile tire slippage dynamics that is studied as an extremely fast and exact response of the tire–soil couple to (i) the tire dynamic loading, (ii) transient changes of gripping and rolling resistance conditions on uniform stochastic terrains and (iii) rapid transient changes from one uniform terrain to a different uniform terrain. Tire longitudinal relaxation lengths are analyzed to characterize the longitudinal relaxation time constants. A set of agile characteristics is also considered to analyze agile tire slippage dynamics within a time interval that is close to the tire longitudinal relaxation time constants. The presented paradigm of agile tire slippage dynamics lays out a foundation to radically enhance vehicle terrain mobility by controlling the tire slippage in its transient phases to prevent the immobilization of a vehicle. Control development basis and requirements for implementing an agile tire slippage control are also analyzed and considered.  
Keywords: Terrain mobility; Agile tire dynamics; Agility; Mobility enhancement; Tire slippage; Tire longitudinal relaxation length; Tire relaxation time constant

A calculation method of track shoe thrust on soft ground for splayed grouser

Congbin Yang, Ligang Cai, Zhifeng Liu, Yang Tian, Caixia Zhang  Journal of Terramechanics, Volume 65, June 2016, Pages 38-48, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.02.001
http://www.sciencedirect.com/science/article/pii/S0022489816000070
Abstract:  
Thrust of track shoes on soft ground is affected by soil moisture content, shear rate and structure parameters of track shoes. A lack of comprehensive consideration of these factors exists for normal calculation methods. A method to predict thrust for track shoes on soft ground with splayed grouser was established based on experimental results and theoretical derivations. Model track shoe traction experiments were conducted for verification and correction of the thrust formula. It was observed that the thrust for the track shoes decreased with the increase in moisture content of the soil. Increases in shear rate, grouser height, and grouser splayed angle resulted in greater tractions. Effect of grouser thickness and grouser draft angle on tractions was not obvious. A corrected thrust formula allowed accurate prediction of thrust for a single track shoe on soft ground.  
Keywords: Track shoe thrust; Soft ground; Splayed grouser; Shear stress; Soil strength

A comparison of ground vehicle mobility analysis based on soil moisture time series datasets from WindSat, LIS, and in situ sensors

Maria T. Stevens, George B. McKinley, Farshid Vahedifard  Journal of Terramechanics, Volume 65, June 2016, Pages 49-59, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.02.002
http://www.sciencedirect.com/science/article/pii/S0022489816000203
Abstract:  
Soil moisture is a key terrain variable in ground vehicle off-road mobility. Historically, models of the land water balance have been used to estimate soil moisture. Recently, satellites have provided another source of soil moisture estimates that can be used to estimate soil-limited vehicle mobility. In this study, we compared the off-road vehicle mobility estimates based on three soil moisture sources: WindSat (a satellite source), LIS (a computer model source), and in situ ground sensors (to represent ground truth). Mobility of six vehicles, each with different ranges of sensitivity to soil moisture, was examined in three test sites. The results demonstrated that the effect of the soil moisture error on mobility predictions is complex and may produce very significant errors in off-road mobility analysis for certain combinations of vehicles, seasons, and climates. This is because soil moisture biases vary in both direction and magnitude with season and location. Furthermore, vehicles are sensitive to different ranges of soil moistures. Modeled vehicle speeds in the dry time periods were limited by the interaction between soil traction and the vehicles’ powertrain characteristics. In the wet season, differences in soil strength resulted in more significant differences in mobility predictions.  
Keywords: Soil moisture; Off-road mobility; Soft soil trafficability; Remote sensing

Design of manned lunar rover wheels and improvement in soil mechanics formulas for elastic wheels in consideration of deformation

Wanshen Xiao, Yan Zhang
Journal of Terramechanics, Volume 65, June 2016, Pages 61-71, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2016.03.004
http://www.sciencedirect.com/science/article/pii/S0022489816300027
Abstract: 
Most of the current lunar rover vehicle wheels are inconvenient for changing broken wheels and have poor shock absorbing in driving, so they cannot be used to carry people on the moon. To meet the demands for manned lunar transportation, a new wheel possessing a woven metal wire mesh tire and using hub-rim combination slide mechanism is designed in this article. The characteristics of the new wheel is analyzed by comparing with the same-size conventional rover wheels after demonstrating the validity of FEM simulation. The new wheel possesses lighter structure and superior shock absorbing. It also provides stronger traction because the deformation of the designed wheel increases the contact area between the tire and lunar terrain. In order to establish an on-line soil parameter estimation algorithm for low cohesion soil, the stress distribution along a driven deformable wheel on off-road terrain is simplified. The basic mechanics equations of the interaction between the wheel and the lunar soil can be used for analytical analysis. Simulation results show that the soil estimation algorithm can accurately and efficiently identify key soil parameters for loose sand. 
Keywords: Manned lunar rover; Woven metal wire mesh tire; Wheel deformation; Soil parameter