Finite element analysis of footwear and ground interaction

Military boots are designed to prevent the soft tissue and skeletal structure of the feet from damage under heavy usage. Good slip-resistant tread patterns of the outer-sole are vital to minimise the risk or severity of slipping under demanding conditions, most likely to result in accidents. However, boot design should also offer the customer flexibility, comfort, and shock absorption, be lightweight and be able to operate regardless of the ground surface texture and various weather conditions. The issue of footwear and ground interaction investigated in this study can be classified as a traditional stability problem. Solutions to these problems are often obtained using the theory of perfect plasticity. Therefore, elastic–perfectly plastic theory was adopted in this study and the Drucker-Prager (DP) material model was chosen to model the soil properties. Literature survey showed that little studies exist on the subject of interaction between foot and soft ground, in particular, using numerical modelling methods. However, there are numerous research works on some relevant domains, such as soil–tillage tool interaction, soil–wheel interaction and soil–structure interaction, etc. A three-dimensional finite-element (FE) analysis of a subsoiler cutting with pressurised air injection was performed by employing a DP harden material model without consideration of friction force by Araya and Gao [1]. Saliba [2] undertook elastic–viscoplastic FE modelling for tire/soil interaction and Mouazen and Nemenyi [3, 4] adopted a DP model for analysing soil–tillage tool interaction

Modeling of the interaction of rigid wheels with dry granular media

We analyze the capabilities of various recently developed techniques, namely 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

Design of a compliant wheel for a miniature rover to be used on Mars

The Jet Propulsion Laboratory has identified the need for a compliant wheel for a miniature martian rover vehicle. This wheel must meet requirements of minimum mass, linear radial deflection, and reliability in cryogenic conditions over a five year lifespan. Additionally, axial and tangential deflections must be no more than 10 percent of the radial value. The team designed a wheel by use of finite element and dimensionless parameter analysis. Due to the complex geometry of the wheel, a finite element model describing its behavior was constructed to investigate different wheel configurations. Axial and tangential deflections were greatly reduced but did not meet design criteria. A composite material was selected for its high strength, toughness, fatigue resistance, and damping characteristics. The team chose a Kevlar fiber filled thermoplastic composite. This report is divided into four primary sections. First, the introduction section gives background information, defines the task, and discusses the scope and limitations of the project. Second, the alternative designs section introduces alternative design solutions, addresses advantages and disadvantages of each, and identifies the parameters used to determine the best design. Third, the design solution section introduces the methods used to evaluate the alternates, and gives a description of the design process used. Finally, the conclusion and recommendations section evaluates the wheel design, and offers recommendations pertaining to improvement of the design solution

Dynamic effect of high speed railway traffic loads on the ballast track settlement

The traditional ballast track structures are still being used in high speed railways lines with success, however technical problems or performance features have led to non-ballast track solution in some cases. A considerable maintenance work is needed for ballasted tracks due to the track deterioration. Therefore it is very important to understand the mechanism of track deterioration and to predict the track settlement or track irregularity growth rate in order to reduce track maintenance costs and enable new track structures to be designed. The objective of this work is to develop the most adequate and efficient models for calculation of dynamic traffic load effects on railways track infrastructure, and then evaluate the dynamic effect on the ballast track settlement, using a ballast track settlement prediction model, which consists of the vehicle/track dynamic model previously selected and a track settlement law. The calculations are based on dynamic finite element models with direct time integration, contact between wheel and rail and interaction with railway cars. A initial irregularity profile is used in the prediction model. The track settlement law is considered to be a function of number of loading cycles and the magnitude of the loading, which represents the long-term behavior of ballast settlement. The results obtained include the track irregularity growth and the contact force in the final interaction of numerical simulatio

Evaluation of FEM modelling for stress propagation under pressure wheel of corn planter

Seeds need a certain range of pressure in the soil bed to germinate and grow ideally. Usually pressure from machinery wheels applies more pressure and prevents seed ideal germination. A finite element model (FEM) was developed to investigate stress propagation in the soil. The pressure wheel of corn planter with 4 km/h speed was chosen to analyze the stress in a sandy-loamy soil. A real corn planter tire was modeled with its mechanical characteristics and imported into ABAQUS/Explicit environment. Frictional contact (based on Mohr-coulomb theory) was used for the soil-tire interaction. The soil was considered as an elastic-perfectly plastic material. Drucker-Prager model was used for soil behavior in plastic region. To evaluate the stress under pressure wheel, FEM results were compared with the Boussinesq theoretical model. On both models, soil stresses decrease with soil depth increasing from zero depth on soil surface to 0.2 m depth. On FEM, stress distribution varied between 47.8 to 8.1 kPa in depth of 0.01 to 0.2 m. FEM and Boussinesq models showed high correlation with each other (R2=95). Our results indicate that the stress under pressure wheels can be properly predicted by using FEM, allowing the pressure simulation to reduce the negative impacts on seed germination and crop yield

DEVELOPMENT OF A FINITE ELEMENT MODEL TO PREDICT THE BEHAVIOR OF A PROTOTYPE WHEEL ON LUNAR SOIL

The All-Terrain Hex-Limbed Extra-Terrestrial Explorer (ATHLETE) is a mobile lunar lander under development by the National Aeronautics and Space Administration\u27s Lunar Architecture Team. While previous lunar missions have lasted only a few days, the ATHLETE is designed to last for 10 years, which will enable a sustained U.S. presence on the moon and exploration of the more treacherous regions which are not suitable for landing. Because the ATHLETE will carry entire astronaut habitats, its six wheels must be carefully designed to support a large load on soft lunar soil efficiently. The purpose of this thesis is to develop a finite element model that will allow designers to examine how the tractive performance of the lunar wheel is affected by changes in the wheel geometry through numerical analysis. It has been shown in the literature that a wheel rolling on soil is not suited to a plane strain analysis. Two different three-dimensional deformable wheel models are explored, a single-part shell model and a multi-part solid-shell model. For the purposes of this research, the shell model offers sufficient detail with less computational expense. The key to obtaining a smooth pressure distribution is in careful selection of the contact stiffness. For the soil model, a set of parameters to represent a pressure-dependent elasto-plastic cap hardening lunar soil was assembled. Two different methods of selecting an appropriate soil bed size are compared. A holistic method that determines all dimensions at once was found to be quick and reliable. Finally, the wheel and soil models were integrated into one finite element model in the commercial code, AbaqusTM, and three small studies were conducted to demonstrate the utility of the model in predicting changes in traction dues to change in wheel design and operation. For example, the model can help determine how quickly the wheel can accelerate without significant slippage. The model can also inform design decisions. The pilot tests suggested that softening the cylinders and/or the spokes could improve traction, but softening the cylinders too much can lead to structural failure

Lunar soil properties and soil mechanics

The long-range objectives were to develop methods of experimentation and analysis for the determination of the physical properties and engineering behavior of lunar surface materials under in situ environmental conditions. Data for this purpose were obtained from on-site manned investigations, orbiting and softlanded spacecraft, and terrestrial simulation studies. Knowledge of lunar surface material properties are reported for the development of models for several types of lunar studies and for the investigation of lunar processes. The results have direct engineering application for manned missions to the moon

Lunar surface engineering properties experiment definition Quarterly report, 1 Oct. - 31 Dec. 1968

Mechanical properties of simulated lunar soil

Dynamic response of rigid wheels on deformable terrains

Off-road vehicle performance, such as vehicle mobility, maneuverability, and traction performance is generally affected by the pneumatic tire-off-road terrain interaction. Modeling of such cases is usually based on empirical and semi-empirical solutions, which have limited applicability in real situations due to their inherent weaknesses. In this study, numerical simulation of the dynamic mobility of a rigid wheel on a deformable terrain is performed through a series of transient nonlinear dynamic finite element analyses with the use of the finite element code ABAQUS (v. 6.13). The dynamic interaction of a rigid wheel with the underlying soil during off-road vehicle travel is simulated. The effects of the vertical load carried by the wheel, the tread pattern, the longitudinal and lateral tread parameters, and the slip ratio of the wheel on the wheel performance are investigated and useful results are extracted. The numerical results reveal that the effects of the tread pattern particularly tread depth and the terrain constitutive properties, such as soil cohesion can be of high importance for the general wheel response

Dynamic response of rigid wheels on deformable terrains

Off-road vehicle performance, such as vehicle mobility, maneuverability, and traction performance is generally affected by the pneumatic tyre-off-road terrain interaction. Modelling of such cases is usually based on empirical and semi-empirical solutions, which have limited applicability in real situations due to their inherent weaknesses. In this study, numerical simulation of the dynamic mobility of a rigid wheel on a deformable terrain is performed through a series of transient nonlinear dynamic finite element analyses with the use of the finite element code ABAQUS (v. 6.13). The dynamic interaction of a rigid wheel with the underlying soil during off-road vehicle travel is simulated. The effects of the vertical load carried by the wheel, the tread pattern, the longitudinal and lateral tread parameters, and the slip ratio of the wheel on the wheel performance are investigated and useful results are extracted. The numerical results reveal that the effects of the tread pattern, particularly tread depth and the terrain constitutive properties, such as soil cohesion can be of high importance for the general wheel response