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Journal of Terramechanics, Vol. 48, Issue 6

Braham Breytenbach, Pieter Schalk Els
Optimal vehicle suspension characteristics for increased structural fatigue life
Journal of Terramechanics, Volume 48, Issue 6, December 2011, Pages 397-408, ISSN 0022-4898, 10.1016/j.jterra.2011.09.004.
Abstract: Heavy off-road vehicle suspension systems face unique challenges. The ride comfort versus handling compromise in these vehicles has been frequently investigated using mathematical optimisation. Further challenges exist due to the large variations in vehicle sprung mass. A passive suspension system can only provide optimal isolation at a single payload. The designer of such a suspension system must therefore make a compromise between designing for a fully-laden or unladen payload state. This work deals with suspension optimisation for vehicle structural life. The paper mainly addresses two questions: (1) What are the suspension characteristics required to ensure optimal isolation of the vehicle structure from road loads? and (2) If such optimal suspension characteristics can be found, how sensitive are they to changes in vehicle payload? The study aims to answer these questions by examining a Land Rover Defender 110 as test vehicle. An experimentally validated non-linear seven degree-of-freedom mathematical model of the test vehicle is constructed for the use in sensitivity studies. Mathematical optimisation is performed using the model in order to find the suspension characteristics for optimal structural life for the vehicle under consideration. Sensitivity studies are conducted to determine the robustness of the optimal characteristics and their sensitivity to vehicle payload variation. Recommendations are made for suspension characteristic selection for optimal structural life. Keywords: Off-road vehicles; Structural life; Mathematical optimisation; Dynamic modelling

Seongpil Ryu, Youngjin Park, Moonsuk Suh
Ride quality analysis of a tracked vehicle suspension with a preview control
Journal of Terramechanics, Volume 48, Issue 6, December 2011, Pages 409-417, ISSN 0022-4898, 10.1016/j.jterra.2011.09.002.
Abstract: The feasibility of a preview control is examined for tracked vehicle's suspension systems to improve the performance of tracked vehicle systems. Numerical results are compared with LQ, robust H∞, reference model tracking and hybrid preview control methods. The ride quality analysis is performed based on the vertical acceleration at the driver's position. On the simulations, it is proven that the hybrid preview controller is the most efficient and practical method. Keywords: Preview control; Active suspension; Tracked vehicle system; Ride quality

Christopher Brunskill, Nildeep Patel, Thibault P. Gouache, Gregory P. Scott, Chakravarthini M. Saaj, Marcus Matthews, Liang Cui
Characterisation of martian soil simulants for the ExoMars rover testbed
Journal of Terramechanics, Volume 48, Issue 6, December 2011, Pages 419-438, ISSN 0022-4898, 10.1016/j.jterra.2011.10.001.
Abstract: The European Space Agency (ESA) ExoMars mission involves landing a rover on the surface of Mars on an exobiology mission to extend the search for life. The locomotion capabilities of the ExoMars rover will enable it to use its scientific instruments in a wide variety of locations. Before it is sent to Mars, this locomotion system must be tested and its performance limitations understood. To test the locomotion performance of the ExoMars rover, three martian regolith simulants were selected: a fine dust analogue, a fine Aeolian sand analogue, and a coarse sand analogue. To predict the performance of the ExoMars rover locomotion system in these three regolith simulants, it is necessary to measure some fundamental macroscopic properties of the materials: cohesion, friction angle, and various bearing capacity constants. This paper presents the tests conducted to determine these properties. During these tests, emphasis was placed on preparing the regolith simulants at different levels of density in order to evaluate its impact on the value of the parameters in particular. It was shown that compaction can influence the Bekker coefficients of pressure-sinkage. The shear properties are consistent with the critical state model at normal stresses similar to those of the ExoMars rover in all but one of the simulants, which showed behaviour more consistent with transitional soil behaviour. It is necessary to give due consideration to these variations to ensure a robust test regime is developed when testing the tractive ability of the ExoMars mobility system. Keywords: Mars; ExoMars; Rover; Mobility; Simulant; Soil mechanics

M. Zehsaz, M.H. Sadeghi, M.M. Ettefagh, F. Shams
Tractor cabin's passive suspension parameters optimization via experimental and numerical methods
Journal of Terramechanics, Volume 48, Issue 6, December 2011, Pages 439-450, ISSN 0022-4898, 10.1016/j.jterra.2011.09.005.
Abstract: Reduction of transmitted vibrations of tractor cabin which is caused by road roughness is the major objective of this study; consequently operator health can be achieved. This objective is carried out via experimental measurements and finite element modeling. For this purpose the vertical acceleration of the cabin as well as the rear axle of the tractor is measured in different road conditions and forward speeds. However, it should be mentioned that tests were carried out according to the ISO 2631-1985 but no measurements were done on the driver's seat. Then the finite element model of the cabin's tractor is developed and the dynamic response of the cabin interior (with the measured axle acceleration as input dynamic force) is obtained. At the third step the suspension parameters are calculated by comparing the accelerations obtained from the model and measurements. Finally the suspension parameters are optimized according to ISO 2631-1985 via iterative method. Keywords: Tractor cabin; Road roughness; Passive suspension system; Optimization; Vibration

Mohammad A. Sadek, Ying Chen, Jude Liu
Simulating shear behavior of a sandy soil under different soil conditions
Journal of Terramechanics, Volume 48, Issue 6, December 2011, Pages 451-458, ISSN 0022-4898, 10.1016/j.jterra.2011.09.006.
Abstract: Understanding of soil shear behavior is very important in the field of agricultural machinery and soil dynamics. In this study, a discrete element model was developed using a simulation tool, Particle Flow Code in Three Dimensions (PFC3D). The model simulates direct shear tests of soil and predicts soil shear behavior, in terms of shear forces and displacements. To determine and calibrate model parameters (stiffness of particles, strength and stiffness of bond between particles), laboratory direct shear tests were conducted to examine effects of soil moisture content and bulk density on shear behaviors of a sandy soil. Three soil moisture levels (0.02%, 13.0%, and 21.5%) and four bulk density levels (0.99, 1.28, 1.36, and 1.50&#xa0;Mg/m3) were used in the tests. The test results showed that in general drier and denser soil conditions produced higher shear forces. Based on the test results, the bond strengths of the model particles were determined from soil cohesion and internal friction angle. The model particle stiffness was calibrated based on the yield forces from the tests. The calibrated particle stiffness varied from 1.0&#xa0;×&#xa0;103 to 8.2&#xa0;×&#xa0;103&#xa0;N/m, depending on soil moisture and density levels. The bond stiffness calibrated was 1.0&#xa0;×&#xa0;107&#xa0;Pa/m for all soil conditions. Keywords: Sandy soil; Moisture; Bulk density; Direct shear test; PFC<sup>3D</sup>; Stiffness; Calibration

Srđan M. Bošnjak
Comments on ''Design of aluminium boom and arm for an excavator"
Journal of Terramechanics, Volume 48, Issue 6, December 2011, Pages 459-462, ISSN 0022-4898, 10.1016/j.jterra.2011.09.001.
Abstract: This paper comments on the recently published work dealingwith the problem in the design of the backhoe excavator working device. It also includes remarks on the inadequacy in the problem approach to the device weight optimization and synthesis, and highlights mistakes in the mathematical model. This work points out the demand for a much wider approach to the optimization problem of the backhoe excavator working device. Keywords: Backhoe excavator; Working device; Weight optimization