Traction and Agricultural Tractor Tire Selection Studies.

A machine was built to study non-rolling tire stiffness and damping coefficients of agricultural tractor tires in the vertical direction. Static deflection on a rigid surface was measured as a function of vertical load. During dynamic experiments, a sinusoidal forcing function was imposed on the test tire to determine dynamic stiffness and damping coefficient from load and deflection measurements. The experimental setup and methodology are described. Ten tires were tested. Both static and dynamic stiffnesses appeared linearly related to inflation pressure. No correlation was found between dynamic properties and excitation frequency. Comparisons among stiffness and damping coefficient values were made according to section width, carcass construction, and between tires of the same size. Traction tests were made at the National Soil Dynamics Laboratory, Auburn, Alabama. Four tires (14.9-30, 14.9R30, 18.4-38 and 18.4R38) were tested on Norfolk Sandy Loam after measuring their rolling radius on concrete under self-propelled condition, at three levels of inflation pressure, and under varying load. Traction experiments were made at three levels of inflation pressure, two levels of longitudinal slip (7.5 and 15%) and under varying dynamic load for each tire. Slip, carcass construction and inflation pressure significantly affected the pull ratios. A mathematical model is proposed that accounts for effects of tire inflation pressure and dynamic load on rolling radius

Analytical and finite element modelling of the dynamic interaction between off-road tyres and deformable terrains

Automotive tyres are one of the main components of a vehicle and have an extremely complex structure consisting of several types of steel reinforcing layers embedded in hyperelastic rubber materials. They serve to support, drive – accelerate and decelerate – and steer the vehicle, and to reduce transmitted road vibrations. However, driving is associated with certain types of pollution due to CO2 emissions, various particles due to tyre wear, as well as noise. The main source of CO2 emissions is the tyre rolling resistance, which accounts for roughly 30% of the fuel consumed by cars. The phenomenon becomes more pronounced in off-road conditions, where truck vehicles are responsible for about a quarter of the total CO2 emissions. Appropriate legislation has been introduced, to control all of these pollution aspects. Therefore, tyre simulation (especially in off-road conditions) is essential in order to achieve a feasible design of a vehicle, in terms of economy and safety. [Continues.

Analysis of Off-Road Tire-Soil Interaction through Analytical and Finite Element Methods

Tire-soil interaction is important for the performance of off-road vehicles and the soil compaction in the agricultural field. With an analytical model, which is integrated in multibody-simulation software, and a Finite Element model, the forces and moments generated on the tire-soil contact patch were studied to analyze the tire performance. Simulations with these two models for different tire operating conditions were performed to evaluate the mechanical behaviors of an excavator tire. For the FE model validation a single wheel tester connected to an excavator arm was designed. Field tests were carried out to examine the tire vertical stiffness, the contact pressure on the tire – hard ground interface, the longitudinal/vertical force and the compaction of the sandy clay from the test field under specified operating conditions. The simulation and experimental results were compared to evaluate the model quality. The Magic Formula was used to fit the curves of longitudinal and lateral forces. A simplified tire-soil interaction model based on the fitted Magic Formula could be established and further applied to the simulation of vehicle-soil interaction.Die Reifen-Boden-Interaktion ist wichtig für die Leistungsfähigkeit von Geländefahrzeugen und die Bodenverdichtung landwirtschaftlicher Nutzflächen. Mit Hilfe einen analytischen Models, das in eine Mehrkörpersimulation Software integriert wird, und der Finite Elemente (FE) Modell, werden die Kräfte und Drehmomente für die Analyse des Reifenverhaltens ermittelt. Es wurden Simulationen bei unterschiedlichen Betriebszuständen eines Baggerreifens durchgeführt und das mechanische Verhalten ausgewertet. Um das FE-Modell zu validieren, wurde ein Einzelrad-Tester entwickelt, welcher an einen Baggerarm angekuppelt wurde. In Feldversuchen wurden die Reifensteifigkeit, die Spannung in der Reifen-Hartboden-Kontaktfläche, sowie die longitudinalen und vertikalen Kräfte und die Verdichtung des Sandigen Lehmbodens in Abhängigkeit von vorgegeben Reifenbetriebszuständen untersucht. Für die Bewertung der Modellqualität werden die Ergebnisse von Simulationen und Experimenten verglichen. Das Magic Formula wurde heraufgezogen, um die Kurven der longitudinalen und queren Kräfte anzupassen. Mittels die Magic-Formula-Funktion wird ein Modell der vereinfachtes Reifen-Boden-Interaktion zur Verfügung steht, mit dem könnte die Fahrzeug-Boden-Interaktion simuliert werden kann

Seismic liquefaction: 1-G model testing system and shake table tests

Thesis (Master)--Izmir Institute of Technology, Civil Engineering, Izmir, 2013Includes bibliographical references (leaves: 126-128)Text in English; Abstract: Turkish and Englishxviii, 137 leavesSoil liquefaction is a crucial, interesting and complex seismic problem. Previous earthquake records and computational modelings have given general information about liquefaction, but many questions, such as; effects of silt content on liquefaction phenomena have not been clearly answered yet. In this study, liquefaction phenomena in sands and silty sands were simulated by a large scale 1-g laminar box system. Three shake table tests were performed, where each test consisted of four shakes to analyze the initial-liquefaction and re-liquefaction phenomena. Instrumentations were used during shake table tests to measure laminate, soil response and settlement of ground. The soil deposit was prepared with different fines content using hydraulic filling method. Piezocone penetration tests (CPTu) were conducted, before and after each shake to determine the relative density of the soil model. Following results were found; Silty sands were found to possess more liquefaction resistance than uniform fine sands. Soils with rounded shapes were more susceptible to liquefaction, than angular grained soils. Required time to trigger liquefaction increased with fines content and depth of the soil sedimentation. Liquefaction resistance of each tested sand decreased from 1st to the 2nd shaking, despite increase in relative density. Relative density values increased with each shake. Despite the increase in relative density, liquefaction resistance decreased. Relative density values have decreased, when fines content increased, but despite decreased in relative density, liquefaction resistance increased. Ground settlement values after the shaking was more than during the shaking. Ground settlement values have increased with fines content of the soil model

Experimental investigations on tractor tire vibration properties

Vehicle vibrations have raised articulate awareness in agricultural industry during the last years. Especially, the legal basis with the EU directive 2002/44/EC and its implementation into national law with the corresponding ordinance have sensitized the manufacturers concerning the vibration behaviour of their vehicles accompanied with an increasing demand for ride comfort by the customers. Furthermore, vehicle components stress due to vibration and shock is also significantly dependent on the tires vibration characteristics. Only an optimized design and combination of the vehicle components can reduce vibrations and improve ride comfort and endurance strength. In this thesis mechanical vibrations in the ride comfort frequency range between 10 Hz and 80 Hz are regarded. For the investigations a new mechanical shaker device has been developed and single frequency force excitations in the mentioned frequency range can be applied to a rolling tire. From excitation and response of the system it is possible to identify the vibration modes of the rolling tire. The shaker is designed to be applied both to a flat-belt test stand and a research tractor. Additionally, uniformity and cleat tests have been conducted with the research tractor in order to compare shaker, tire and impact excitations

The dynamics of towed seeding equipment

Seed depth consistency is a critical performance metric of agricultural seeding equipment. To improve productivity, equipment manufacturers have historically focused on increasing the equipment working width of hoe-opener style seeding drills (hoe drills). However, the physical limitations of hoe drill size do present a design challenge. Increasing seeding speed to improve equipment productivity continues to be a challenge for equipment designers. Most operating conditions restrict hoe-drill seeding speeds to approximately 2.2 m/s (5 mph); depth consistency generally degrades above this speed with current hoe drill technology. This research focused on developing an understanding of why this performance degradation occurs as speed increases. The general industry hypothesis points vaguely to "excessive motion" of the components to which the soil-engaging tools connect (the row units). However, little research on the dynamics of towed agricultural implements was found in the open literature. An understanding of the mechanism(s) causing this "excessive motion" was sought during this research. A 2-D simulation tool was developed in MATLAB to provide equipment designers with the capability to conduct performance trade-off and sensitivity studies early in the prototype stage of a project. The simulation tool was compartmentalized so that changes to equipment geometry, component-soil contact models, or hydraulic systems could be modified with little or no change to other parts of the program. Operational data were also collected using a small plot drill based on a New Holland P2070 Precision Hoe Drill. Data were collected at multiple operating speed up to 4.4 m/s (10 mph) to characterize depth consistency issues present at higher speeds. Various geometric seed depth and hydraulic pressure settings were also tested. Kinematic parameters (acceleration, position), force, hydraulic pressure, and video of the instrumented row unit were recorded during steady-state the operation of the machine in typical seeding conditions. Measured data aided in calibrating aspects of the simulation tool, and the tool enabled certain performance features in the measurement data to be explored further. Frequency domain acceleration power spectra revealed that row unit acceleration power was generally concentrated at two frequencies. The terrain profile of the test field contained furrows from the previous seeding operation; this resulted in acceleration power to be concentrated at a distinct speed-dependent frequency related to the furrow spacing. While somewhat expected, this indicated the general inability of the current design to attenuate terrain inputs. The small packer wheel provided little compliance between the row unit and soil, so improving the attenuation performance of the system could improve depth consistency performance in future designs. The second major acceleration spectra feature was related to the arrangement of the hoe opener and trailing packer wheel; both rigidly connect to the row unit body. The row unit position changed when the packer wheel encountered a terrain bump or dip; this resulted in a change in the vertical position of the hoe opener located in front of the packer wheel. Immediate changes in the operating depth of the hoe opener tool resulted. Also, depth changes generally modified the terrain such that a new bump or dip was created in the soil surface preceding the packer wheel, thus creating a feedback path between the hoe opener and packer wheel. Considering the simplifications of the 2-D model, agreement between simulated and measured data was encouraging. The frequencies of the above phenomena were in reasonable agreement throughout the speed range of interest. Power spectra amplitude differences were likely due to both input terrain differences between simulation and test terrains, and simplifications made in representing soil-tire and soil-tool contact. Future work to improve these sub-models, and to further explore the observed non-linear effect of hydraulic pressure changes would improve the predictive accuracy of the model presented

Comparison of soil compaction below wheels and tracks

This study investigated the effect of high axle loads carried on self propelled wheels and tracks on soil bulk density, soil deformation, rut depth, and penetrometer resistance under controlled laboratory conditions. Furthermore pressure distribution below a three and a two idler track was measured. A brief field study was also conducted to compare the results gained under laboratory conditions. The benefit of the “Terra Trac” driving systems compared to wheel type systems was clearly shown in uniform and stratified soil conditions. Soil deformation was reduced to 50 % for the tracks compared to the wheels at an overall load of 12 t and 10.5 t, respec­tively. Penetrometer resistance showed a very high resistance close to the surface for the tracks. In uniform soil conditions there was no significant increase in penetrometer resis­tance compared to the control below 400 mm depth. Reducing the inflation pressure to half the recommended inflation pressure reduced soil deformation by 25 %. Three passes of a tire increased soil density by 20 % compared to a single pass. The three idler track showed only a 50 % increase in pressure from the front to the rear sprocket compared to a 100 % increase for the two idler track. Single peaks in pressure below each idler were less pronounced for the three idler track. Unfortunately the advan­tage in the pressure distribution for the three idler track did not lead to significant im­proved behavior concerning soil compaction. The advantage of a tracked combine compared to a wheeled combine is also shown in field measurements. The root system of oil seed rape in former track ruts is more developed than in former wheel ruts. Soil physical properties after the passage were compared to the predictions of two models. The tendency was correct, however the real values were largely offset