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Numerical Simulation of the new generation Non-Pneumatic Tweel™ and sand
Jianfeng MaAvinash Kolla
Joshua D. SummersPaul F. Joseph
Vincent Y. BlouinSherrill Biggers
1/20
http://aid.ces.clemson.edu
3/6/2009
Objectives of the project
• To Improve the performance of tire on sand.
– In other words traction
• To develop a full computational model for tire-sand interaction with an acceptable accuracy.
• To search for novel tread concepts that can avoid slip.
http://aid.ces.clemson.edu
2/203/6/2009
Mechanics of tire-terrain interaction
• Output energy = Input energy – Energy losses(losses due to motion resistance)
• Traction forces = Drawbar-pull + Work energy/unit travel distance
Energy dissipated in the distorting the tractive element
Energy dissipated in terms of compacting the soil
Energy loss associated with slip
VInput EnergyUseful output
energy
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Modeling Techniques
• Analytical models (Bekker, 1969)
• Empirical models (Yong and Fattah, 1986)
• Computational models
– FEM (Fervers, 1996)
– DEM (Nakasimha et al., 2003)
• FEM is employed for the simulation due to less computational effort and acceptable levels of accuracy
• Soil is treated as Elasto-plastic solid. Tweel™ is treated as a deformable body.
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Segmented cylinder Tweel™
• Typical properties of pneumatic tires carried to Tweel™:
• Low contact pressure
• low stiffness
• high load carrying efficiency
• low energy loss from obstacle impact
• In addition to being non-pneumatic makes it flexible enough to withstand extreme temperatures on both terrains.
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2D Tweel™ Model
• 2-D FEM Model of tire replicating the prototype is shown in figure.
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Soil Modeling
• Soil can be modeled using four elasto plastic models:1. Drucker-Prager model (Classical, Drucker-prager/cap model)
2. Mohr-Coloumb model
3. Critical state theory
4. Lade’s single hardening model
• For the analysis, sand is represented by elastoplastic Drucker-prager/Cap model that uses the results obtained from triaxialtests and consolidation test.
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Soil properties
• By using Drucker-prager/cap plasticity constitutive law.
Properties of soil used for ABAQUS:Drucker-Prager/Cap model*
* Taken from literature for the Lebanon sand found in NH.
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Material parameters Value
Young’s modulus, E 8500 kPaPoisson’s ratio, ν 0.32
Angle of friction, β 55.8˚Material cohesion, d 10.0 kPaCap eccentricity, R 0.45
Initial value of volumetric plastic strain 0
Flow stress ratio 1
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Interaction model
• From the simulation model, soil deformation, distributions of different stresses in both sand and Tweel™ and distributions of contact pressure along the contact patch at all instances are expected.
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Numerical results (1)
• Two loading steps:
•Initial loading to deform Tweel™
•Final step for displacing the Tweel™
• Deformation in Tweel™ is more because the spokes can’t withstand compression.
Sand bed
Tweel™ model
Displacement (0.4m, -0.04m)
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Numerical results(2)
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von Mises stress distribution
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Numerical results (3)
• The deformations in sand are permanent after the Tweel™ passes by, since sand is treated as elasto- plastic solid indicating that the residual stresses are permanent.
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• This low contact pressure can cause less deformation of sand reducing the bulldozing effect.
• Long contact path accounts for low contact pressure i.e. relatively uniform contact pressure.
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Numerical results(4) 13/203/6/2009
• σ11 distribution in Tweel™ at final instant
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Numerical results (5) 14/203/6/2009
Numerical results (6)
• σ11 distribution in sand at final instant
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• σ22 distribution in sand at final instant
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Numerical results (7) 16/203/6/2009
• σ33 distribution in sand at final instant
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Numerical results (8) 17/203/6/2009
Conclusions
• FEM code-ABAQUS is used to perform the simulation.
• Soil is modeled using elasto-plastic Drucker-Prager/cap model.
• The Numerical results show that there is a relatively low contact pressure observed for this Tweel™ model.
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• The work presented will be used as a basis for improving the performance of the Tweel™ on sand.
• Several Tweel™ that can give better tractive performance will be investigated.
• Ways to induct Tweel™’s pressure profile into another wheel model needs to be explored.
• After developing tire-model that have better traction based on pressure profiles, influence of tread profiles will be studied to find ways to improve traction further.
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Future Work 19/203/6/2009
Thank you for your Attention!!
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Questions?? 20/203/6/2009