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To provide terrain data for the development of physics-based vehicle mobility models, such as the Next Generation NATO Reference Mobility Model, there is a desire to make use of the vast amount of cone index (CI) data available. The challenge is whether the terrain parameters for physics-based vehicle mobility models can be predicted from CI data. An improved model for cone-terrain interaction has been developed that takes into account both normal pressure and shear stress distributions on the cone-terrain interface. A methodology based on Derivative-Free Optimization Algorithms (DFOA) has been developed in combination with the improved model to make use of continuously measured CI vs. sinkage data for predicting the three Bekker pressure-sinkage parameters, kc, kϕ and n, and two cone-terrain shear strength parameters, cc and ϕc. The methodology has been demonstrated on two types of soil, LETE sand and Keweenaw Research Center (KRC) soils, where continuous CI vs. sinkage measurements and continuous plate pressure vs. sinkage measurements are available. The correlations between the predicted pressure-sinkage relationships based on the parameters derived from continuous CI vs. sinkage measurements using the DFOA-based methodology and that measured were generally encouraging.

This paper reviews experimental methods for the conversion of cone index measurements to bevameter parameters in support of vehicle soil/tire/track interactions for two general soil types, sand and lean clay. The accurate prediction of traction, motion resistance, and sinkage of tire/tracks off-road requires estimates of soil strength. Equipment used in the measurement of soil strength to support predictions of off-road mobility include the bevameter and the cone penetrometer. The portability of the cone penetrometer and rapid estimates of spatial/temporal variability in all terrain conditions make it an invaluable tool. The bevameter, a less portable tool, is used for the mechanical analysis of soils. The bevameter measures parameters defining soil strength in terms of cohesive modulus of soil deformation (kc), frictional modulus of soil deformation (kφ), exponent of soil sinkage (n), cohesion (c), angle of internal friction (φ), and the plate pressure at 1 in. (2.54 cm) of penetration (K) ( Bekker, 1969 ). The field of terramechanics would greatly benefit from having the ability to convert cone penetrometer data in areas where bevameter parameters are difficult to collect. That ability to convert from cone index to bevameter parameters could be used for the large sets of existing cone index data to support determination of traction and motion resistance. This paper examines those methods for converting cone index to bevameter plate penetration parameters kc, kφ, and n.

This paper examines pressure-sinkage and shearing behavior via bevameter testing of a light-weight, granular simulant called Fillite in support of laboratory modeling of rover mobility in high-sinkage, high-slip environments typically found on Mars, the Moon, and other planetary bodies. Normal bevameter test results helped to determine parameters for the Bekker model, the New Model of Mobility (N2M) sinkage model, and the Bekker-Wong model. A case study used the Bekker-Wong model parameters to predict the possible sinkage of 84% into Fillite of a wheel on the Mars Spirit rover, a value within the observed sinkage of 50–90% of the wheel diameter of the Spirit rover on Mars. Shear bevameter testing of Fillite provided a second set of parameters to assess shear behavior, this time simulating the stresses and shear deformations imparted by rotating wheels. The results compared well to the estimated shear stresses and deformations of Martian soil caused by the wheels of the Spirit rover. When compared to other simulants (e.g. GRC-1), the results confirm that Fillite is possibly more suitable for high-sinkage and high-slip rover studies than other typical simulants derived from natural terrestrial soils and rocks.

Mechanical properties of snow related to snowmobiles or similar lightweight tracked vehicles aren't widely researched today and it is difficult to find data. One challenge is that snow properties constantly are changing due to aging, climate conditions and location. Also the measuring procedure is difficult since aged snow often contains layers with various densities and hardness. Soil is to some extent similar to snow, in the context that both are granular materials. The bevameter is a popular device for measuring soil properties, however this device needs to be scaled in order to meet criteria of target for research, i.e. in this case snowmobiles. In this paper a new type of portable bevameter is presented, which is designed and built for measuring snow properties in the field. Results from initial tests are also presented. The aim with the bevameter is to measure snow properties which can be used to simulate the interaction between a snowmobile and soft snow. The designed bevameter can be towed with one snowmobile to the field to execute measurements. One full set of test results is introduced and parameters for simulations are extracted from the result data. The parameters from the data were usable but the quality of the measurements can be improved. One problem with the data collected was noise, which was caused by the interaction between the mechanical parts and the low mass of the bevameter. Furthermore, the usability can be improved by reducing cables which can be hard and fragile during cold weather and by replacing the laser distance-sensor with a string wire potentiometer which isn't sensitive to snow dropping in the measurement area. With some improvements the constructed bevameter is a very useful tool which can be used for field measurements to determine snow properties for snowmobile-size vehicle simulations.

The tractor-mounted bevameter consists of a main frame, an instrument box which contains the hydraulic and electrical components, a leveling system that applies a safe load vertically onto the soil, sinkage plates with three different shapes to characterize the soil pressure–sinkage relationships, and a carrier supporting the bevameter unit and sinkage plates. The accuracy of the displacement and force measurements were ±0.01 mm and ±2 N, respectively. A laptop data acquisition and a software tool were used to assist in real-time measuring, recording the applied loads, and the resulting sinkage of the plate during the field sampling operation. The experiments were carried out at a penetration rate 3 cm/s for sinkage plates. Field tests of the tractor-mounted bevameter unit were conducted with three different types of the sinkage plates. Statistical analysis and graphs produced from collected data showed that the shapes of the sinkage plates had considerable influence on the soil parameters. Soil sinkage is affected by the shape of sinkage plates. The values of k c and k φ are affected by the values of p , z and b.

In field experiments conducted over a period of 6 years, seedbed preparation was carried out on four different sites with clay contents of 45, 27, 24 and 15%. Over the years soil conditions varied considerably. Seedbed preparation was conducted in the spring with implements of different designs such as drags and harrows, twin rotor, gyro- and rotaspikes. In analysing the fragmentation due to tillage, the soils could be grouped according to moisture contents and soil compaction. Soil with a moisture content greater than 0.20 kg kg −1 was classified as wet soil irrespective of the state of compactness. Soil with a lower moisture content was classified as moist soil and divided into the following compactness states: loosened, workable and compacted. Loosened soil was ploughed or chiselled just before seedbed preparation, workable soil was autumn ploughed and compacted soil was unploughed. A normalisation procedure transforming the fragmentation effect and the specific energy supply to dimensionless quantities eliminated the difference between all the unloosened soil states, i.e. states where the soil was a continuous compact material. This normalisation procedure related the increase in aggregate surface area to the initial surface area. The specific energy supply was related to the specific energy needed to fracture a clod or to fracture the soil in the ground with a bevameter. With this normalisation procedure the fragmentation effect of the three compact states—workable, compacted and wet soils—was described by the same function. Loosened soil was, however, still different and had a much lower effective fragmentation than the other states. In general, the strength of the clods determined the fragmentation in this soil state. The normalisation procedure provided a basis for an investigation of the energy efficiency of fragmentation of various tillage implements and tools. For the compact soil states, drags were superior in fragmentation compared to harrows and rotary implements ( ∗∗ P . There was no difference in fragmentation between harrows and rotary fragmentation implements. For the loosened soil state, there was no significant difference between the three implement groups. Rotary implements seemed, however, to be more effective in the conversion of energy to fragmentation.

A study of the correlation between the measured and predicted vehicle performance over undistributed and preconditioned snow using the Nepean Tracked Vehicle Performance Model, NTVPM, has been carried out. It is shown that on undisturbed snow in Fernie, British Columbia, the performance of a BV 206 predicted by NTVPM correlates very well with measured performance obtained in the field. On preconditioned snow, there is also a reasonable correlation between the measured vehicle performance and predicted one using NTVPM. It is found that predictions of vehicle performance made by NTVPM using pressure-sinkage data obtained with the Swiss Rammsonde and with the bevameter are comparable. This indicates that the pressure-sinkage data obtained using the Rammsonde can be used as input to the NTVPM for predicting tracked vehicle performance over snow. It is shown that in comparison with an earlier version, NTVPM-85, the latest version of the Nepean Tracked Vehicle Performance Model, NTVPM-86, which takes into account fully the characteristics of roadwheel suspension systems, provides improved predictions of vehicle performance over snow where track sinkage is significant. It is suggested that the computer simulation model NTVPM, using pressure-sinkage data obtained by the Rammsonde as input, could form a useful interface with cone based models, such as the NATO Reference Mobility Model, to provide them with an additional capability of predicting tracked vehicle performance over snow.

To examine the feasibility of using the pressure-sinkage data obtained with a Rammsonde as input to a proposed module for the NATO Reference Mobility Model for predicting tracked vehicle performance over snow, a series of measurements of penetration resistance of undisturbed and preconditioned snow was made using a Rammsonde, and compared with those obtained with a bevameter and Rammsonde cones driven by a bevameter. This paper describes the results of the field measurements made using the three types of device, as well as the approaches to the characterization of the pressure-sinkage data obtained. It is found that the data obtained using the Rammsonde, the bevameter and the Rammsonde cone driven by a bevameter are, in general, comparable, considering the possible variations of terrain conditions in the field. It is shown that the pressure-sinkage equations proposed by Bekker could form a common basis for characterizing the data obtained using the three different techniques. It is found that in soft, undisturbed snow (with density less than 0.2 g/cm3), the small (or standard) Rammsonde cone of 4 cm in diameter cannot be used to obtain meaningful pressure-sinkage data within a certain snow depth. Under these circumstances, the use of the large Rammsonde cone of 10 cm in diameter is recommended. Over preconditioned snow, both the small and large Rammsonde cones could provide comparable data. The size effect of the sensing element (such as the diameter of the Rammsonde cone or the bevameter sinkage plate) on the pressure-sinkage relationships was examined. It is found that in many cases, the values of the pressure-sinkage parameters derived from data obtained using a single sensing element of 10 cm in diameter are comparable to those obtained using two sizes of sensing elements of 4 and 10 cm in diameter.

The relationship between the soil parameters measured during soil testing using the bevameter system and horizontal forces acting on a simple tillage tool were investigated. Field experiments were conducted on untilled, compacted and recently tilled soil. On both soils, five sites were randomly chosen where bevameter and draft measurements were performed. The parameters measured were modulus of soil deformation, wet and dry bulk density, soil moisture content, tool operating depth, tool operating speed and horizontal draft. A statistical analysis of data indicated that a mathematical model for predicting draft should include operating depth, dry bulk density and modulus of deformation.

This paper reviews techniques for measurement of soil strength and makes recommendationsfor suitable methods for off-road vehicle performance prediction. The cone penetrometer and bevameter were found to be the most appropriate largely because they enable measurements to be made in situ. However, even though the penetrometer is the only technique that can assess variation of soil resistance with depth, neither the cone index nor its gradient with respect to depth is uniquely related to soil cohesion or density, but varies with moisture content and structural state. Furthermore, the formation of soil bodies and compaction zones ahead of the cone effectively changes its geometry and the penetration no longer reflects the original properties of the soil. On the other hand, the bevameter technique only characterizes surface soil properties. Nevertheless, the bevameter provides the closest simulation of vehicle-terrain interaction among all the currently available techniques. The main criticism of the bevameter and also of the penetrometer is that the sizes of the penetration and grouser plates and the cones, respectively, are too small.

The relationship between the parameters measured during soil testing using the bevameter system and the horizontal forces acting on a simple soil-cutting blade were investigated. Field experiments were conducted on untilled, compacted soil and on recently-tilled soil. On both soils, five sites were randomly chosen and bevameter and draft measurements were performed The parameters measured were modulus of soil deformation, wet and dry bulk density, soil moisture content, tool operating depth, tool operating velocity and horizontal draft. A statistical analysis of the data indicated that a mathematical model for predicting draft should contain the following variables: operating depth, dry bulk density and modulus of deformation. A linear regression analysis of draft versus modulus of deformation showed significance at the 95% confidence level on the untilled sites at all measured depths. A similar analysis of the tilled site indicated significance at the 70 mm depth only. The usefulness of the bevameter deformation modulus as an indicator of draft was found to be limited to shallow depths.

The methodology for processing load-sinkage and shear test data obtained using the bevameter is examined. A weigthed least squares technique is proposed for deriving terrain values from experimental data. To streamline data processing time, a portable automatic data processing unit for the bevameter has been developed. The basic features and functions of the unit are described. The automatic data processing unit, together with associated bevameter, has undergone extensive field trials. They have been employed to measure the properties of various types of natural terrain. The results indicate that this new system can provide a basis for the development of a reliable, convenient and standardized technique for identifying terrain properties in relation to off-road mobility.

An outline of the development of the experimental equipment capable of recording terrain strength tests carried out with a variety of soil probes. The equipment and instrumentation have been designed as a special type of bevameter, because of its capability of parametric soils strength analysis.

The apparatus described is driven hydrautically and uses oil pressure to record torque and thrust by means of an engine type indicator. The bevameter can be operated by one person and is intended for use either in the laboratory or in the field. For field use it is mounted on the back of a Land Rover and is powered by an engine driven midmounted hydraulic unit.