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Finite Element Analysis of Rubber Treads on Tracks to
Simulate Wear Development
Sergio G. Arias, Ph.D.
Advanced Technology Group, Camoplast Solideal Inc.
Abstract: FEA applications to conduct product development at Camoplast Solideal, Inc. have been implemented to understand better the rubber track behaviors. Numerous simulation studies have already been conducted on the rubber tracks to understand their strengths and limitations. An important study is now being pursued to the development of a tool that will help us understand better the wear mechanisms happening on the treads of our rubber tracks. The rubber tracks are normally ud for agriculture applications, and determining wear or uful lifetime properties of the treads is a difficult task. Obtaining empirical data to model the wear of the tread is difficult, as proven by our field test where ground surface interactions are difficult to characterize. This paper will describe the process of simulating the mechanism of wear that occur at the treads when a track is rolled over a surface. The
objective of this rearch is to obtain an analytical procedure, validated with field tests that will help us understand better the conditions that affect rubber erosion at the treads to develop new rubber tread designs.
Keywords: Rubber simulation, cyclic fatigue, tread design, wear, FEA, friction.
1 Introduction
Any structural component that is in motion, of affected by the motion of others, will always suffer from a performance decline due to the phenomenon of wear development. This is supported by the 1st and 2nd Laws of Thermodynamics which state that all energy is conrved in a system and that no system can be perpetually in motion. When a system is in motion, the kinetic energy ud to generate its motion will be transformed in other forms of energy. Wear is a conquence of some of this energy change, which ultimately will cau the system to fault.
The study of wear has been conducted for many years, and numerous definitions can be found in literature. In material science, wear is defined as the material degradation generated in the contact surfaces of the material as two solid bodies are sliding or rolling.
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Although this is true for most cas, wear is not limited to contact between two solid bodies. Wear, as in the form of erosion, can be found in the contact of a solid body with a moving fluid (such as water or air). Additionally, it is important to mention that corrosion or fracture of structural components is not considered a form of wear since both of the failure mechanisms can happen even if there is no relative motion between parts, and they do not require contact between two bodies to exist. Instead, they could be produced with the prence of wear. Hence, wear can be described in a more generic definition, as the progressive damage caud by the relative motion of two contact surfaces, which will generate a loss of material or produce a change in geometry, if allowed to progress without limit.闪开
1.1. Fundamentals of Mechanical Wear
The prence of wear and how it evolves varies enormously depending upon many factors. Lubrication, loading and environmental conditions, such as time, temperature and erosion agents can affect the development of wear. But among the factors, the type of material in the contact bodies will be a critical factor in the contribution of friction, and conquently the development of wear.
Wear mechanisms of a structural component can be thought in general as the failure mechanisms of its material occurring near or at the surface contact by the relative motion of other components. Most material failure mechanisms can be described in terms of brittle fracture, fatigue, plastic deformation, etc. In
general, development of wear can occur in the mechanism described in Table 1. But in practice, however, wear process tend to u more than just one mechanism. As a conquence, it is generally difficult to test wear for a specific mechanism.
Table 1. Most common wear mechanisms found in rubber-like materials
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1. Adhesion wear
2. Single-Cycle Deformation
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3. Repeated-Cycle Deformation
4. Oxidation
5. Thermal
6. Abrasion
7. Others (fretting, erosion, etc.)
For the rearch conducted in this paper, the type of wear that is of most interest to us is that of rubber-like materials. According to some rearchers, rubber wears by two main mechanism; tearing (fracture) and fatigue. In both mechanisms, they ari from high local friction effects at or near the contact surface. The areas can be characterized into two areas of interest, as en in Figure 1: the Interfacial wear zone and the cohesive wear zone. Depending upon some key material properties, such as the tensile strength of the rubber, one would obtain different mechanism and rates of wear developing at the areas.
Figure 1 - Schematic of wear zones in a typical rubber-like material
The wear development found typically in the rubber tracks of caterpillar-drive systems is that of abrasion and Repeated-Cycle Deformation. Abrasion wear is caud mainly at the cohesive wear zone by hard particles or other erosion agents.
In a repeated-cycle deformation, the wear mechanism requires repeated cycles of deformation to cau failure. This wear mechanism is too found at the cohesive wear zone. In the types of process, the plastic strain is accumulated, nucleating more and more cracks and propagating them throughout the cycles, to the point of fracture. This is symptomatic of cyclic fatigue wear. The following figure shows a schematic of this wear development.
Figure 2 - Illustration of repeated stress cycling leading to fracture
In a typical repeated-cycle wear, the wear scarring produced is varied, depending upon inherited material properties (hardness of rubber, strength, yielding etc…) and of cour, the contact pressure. In practice, no matter how small the pressure load or contact stress is, becau sufficient rolling or sliding will generate
this type of fatigue wear. This type of mechanical wear is very typical in rolling and impact wear situations and it is found in all the rubber tracks of caterpillar-drive systems.
1.2. Ca Study: Abnormal wear on rubber track
As mentioned earlier, wear studies are of considerable importance when parts made of rubber are directly involved in the motion of any structural asmbly, as in the ca of the caterpillar track system. There are many other factors that contribute to the failure of the parts, but unlike most of them, the wear of rubber components is generally complex to predict.
For the purpo of this rearch, the ca of the abnormal wear development in the rubber tracks of a caterpillar-type vehicle was lected. Figure 3 shows an schematic of the asmbly of a typical positive-drive rubber track agriculture vehicle.
sucreFigure 3 – Schematic of a typical positive-drive rubber track system
Field studies showed that the tracks produced localized areas of wear in the treads, even after only veral hours of u. The areas of abnormal wear, which are clearly defined as en in Figure 4, are located in the inside part of the contact area of treads with the ground surface (away from the region of pressure induced by the midrollers). The reason why this occurs is not clear, since logic dictates the treads should either wear nearly evenly or where most contact pressure occurs. The following figure shows an example of a typical wear tread on a harvest combined vehicle track.
Figure 4 - Localized tread wear
In order to obtain a better understanding in the phenomena, Camoplast Solideal, Inc. decided to conduct an experimental field test that will focus on the study of the development of this abnormal wear. The procedure of this experimental testing will be described next.
2 Experimental Testing
As mentioned earlier, an unusual localized tread wear has been found in our rubber tracks after just veral hours of u. The areas of wear diminish the performance of the track (ie. traction performance) long before the track ends its ufulness life. A significant field study was conducted to give light to the phenomena of the development of this localized tread wear.
Upon visual examination on the rubber tracks, it was clear that the areas of high wear were perfectly defined to be in the ctions away from the roller path. In other words, the high wear was located at the inside areas of the treads. The areas where the midrollers pasd by, as the vehicle rolls, showed minimal wear, and more consistent to what is expected to deteriorate the treads after hours of u.
To study more cloly this phenomenon, a camera was rigged in cage with a glassy surface such that it would record the deformations of the treads as the undercarriage system of the vehicle rolled over it. The following figure shows the tup created to conduct the experiments.
移动英语Figure 5 - Field Testing Setup to measure tread deformation
To produce a clearer visual measure of the tread behavior as the midroller pasd them by, a discretized mesh was drawn over veral treads (as en in Figure 6). This field testing tup provided us with sufficient visualization of the mechanisms of tread deformation.
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atelierFigure 6 - Field testing visual obrvation t up
3 FEA Model Description and Material Characterization
The methodology typically ud for testing carcass solicit ation is that of the “waterbug” test tup (as en in Figure 7). In this type of tup instead of simulating the entire vehicle or the undercarriage track system, the model simulates only the behavior of a ction of the track where the midrollers roll over. Since, it is believe the midrollers are the undercarriage components that carry the highest and most critical loads to the track.
Figure 7 – Abaqus model for the Waterbug simulation test tup
In order to ensure that this model depicts with authenticity the behavior of what happens in the field, certain procedures must take place. First, the ction modeled needs to have the proper track tension that will e in the field. In order to do that, the track ction is given a 0.1% elongation, which will reprent the proper tension. That is, the track is fixed in one end to have U x, U y and U z equal to zero, meanwhile the other (free) end is given a U z displacement of 0.001*Length.
The length of the track ction was taken arbitrarily. It must be long enough to accommodate the midroller asmbly and the conquent rolling over. For this simulation, the length was equal to 2,232-mm.
To have a track that simulates correctly the rigidity and flexibility of the track, the FEA track model must have all the structural components. Additionally, other main components of the undercarriage asmbly must be properly modeled. The components ud in the FEA simulations are:
1.Carcass
2.Drive Lugs
3.Treads典范英语7
4.Reinforcement layers (modeled only the 0-degree)
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5.Midrollers
6.Undercarriage (UC)
7.Ground
The undercarriage (UC) component which encompass extremely rigid members was modeled using beam-type connectors. A hinge connector was modeled as well to simulate the kinematics of the pivot point of the entire UC sub-asmbly. Then, all midrollers were linked to the UC by means of hinge and beam connectors. The Midrollers were modeled using analytically rigid regions. The rubber layer in the midrollers was assumed to cau negligible difference for this simulation ca.
All rubber parts were modeled using hybrid elements. The carcass and lugs were modeled using linear hexahedral reduced elements, C3D8RH. The carcass was portioned into veral areas to create a finer mesh
