Numerical investigations in mixed friction systems
International Conference of Multiphysics
Lille, December 9th
Author: Albert Albers, Benoit Lorentz, Lukas Nowicki
IPEK – Institute of Product Development
1 KIT – University
09.12.2009
of the State of Baden-Wuerttemberg and
National Laboratory of the Helmholtz Association
www.kit.edu
Contents
Introduction
Presentation of the KIT and IPEK
Motivation, goal of the project and global procedure
Models and methods
Phenomena explanation
Model configuration
Model: boundary conditions
Results
Fluid field pressure
Separation of the friction coefficient into fluid and solid friction
Conclusion and outlook
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Prof. Albert Albers – Numerical investigations in mixed friction systems
Contents
Introduction
Presentation of the KIT and IPEK
Motivation, goal of the project and global procedure
Models and methods
Phenomena explanation
Model configuration
Model: boundary conditions
Results
Fluid field pressure
Separation of the friction coefficient into fluid and solid friction
Conclusion and outlook
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Prof. Albert Albers – Numerical investigations in mixed friction systems
Introduction: presentation of the KIT and IPEK
KIT: regroupment of Research Center of Karlsruhe (north
campus) and University of Karlsruhe (south campus)
IPEK: Institute of formale university, activities:
Methodic development
CAE/Optimization
Friction systems
Condition monitoring
Robotics
Power train technology
NVH/Drivability
Project based on tribology and using CAE tools: Mixed
lubricated systems in the micro scale
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Prof. Albert Albers – Numerical investigations in mixed friction systems
Introduction: motivation, goal of the project and global
procedure
Context
Systems submitted to mixed
lubricated conditions:
multidisc clutches,
hydrodynamic bush bearings, …
Wear due to solid friction contact
Friction behavior not mastered
Motivation
Decrease the friction energy loss
Increase friction knowledge of
mixed lubricated system
Necessity to know phenomena
at the micro scale
Not always possible to use
experimental way
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Prof. Albert Albers – Numerical investigations in mixed friction systems
Introduction: motivation, goal of the project and global
procedure
Goals
Develop a numerical micro model
Take into account surface roughness
Use FE Method to increase accuracy compared with analytical
methods
Separation of solid and fluid friction part
Global procedure
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Prof. Albert Albers – Numerical investigations in mixed friction systems
Contents
Introduction
Presentation of the KIT and IPEK
Motivation, goal of the project and global procedure
Models and methods
Phenomena presentation
Model configuration
Model: boundary conditions
Results
Fluid field pressure
Separation of the friction coefficient into fluid and solid friction
Conclusion and outlook
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09.12.2009
Prof. Albert Albers – Numerical investigations in mixed friction systems
Models and methods: phenomena presentation
Mixed lubrication: two contact ways
Solid 1
Fluid-solid
contact interface
Fluid
Solid-solid
contact interface
Solid 2
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Prof. Albert Albers – Numerical investigations in mixed friction systems
Models and methods: Model configuration
Mixed lubrication model Æ modelling methods fluidstructure-interactions
Fluid part
Eulerian mesh
Finite volume method
Newtonian fluid
No influence of pressure
No influence of temperature
Solid part
Lagrangian mesh
Finite elements method
Fully elastic behavior
Coupling method
One way method (only pressure coupling)
ALE method Æ fluid mesh
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09.12.2009
Prof. Albert Albers – Numerical investigations in mixed friction systems
Models and methods: Model configuration
Model of two grinded surfaces
Roughness: Ra= 0.8µm
Oil film thickness: 1.2µm
Plattes of 140x140µm Æ 30000 elements
Solid properties
Young’s modulus: 210000MPa
Yield stress: 900MPa
Poisson’s ratio: 0.3
Fluid properties
Density: 843kg/m3
Dynamic viscosity: 28mPa.s
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Prof. Albert Albers – Numerical investigations in mixed friction systems
Models and methods: Boundary conditions
Solid boundary conditions
Pressure load: way controlled
Fixed support
Fluid boundary conditions
Pressure
v2=0
1
Pi
2
Inlet: 100MPa
Outlet: 90MPa
Velocity
Slipping velocity: v1 = 4m/s
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Prof. Albert Albers – Numerical investigations in mixed friction systems
Po
v2=0
Vrel=v1
Models and methods: ALE method
Principle
Remesh domain
Keep good mesh quality
Advantages
Model high deformations
Precise contact interactions
Limitations
Too large deformations
Contact topology changes too much Æ domain separation
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Prof. Albert Albers – Numerical investigations in mixed friction systems
Contents
Introduction
Presentation of the KIT and IPEK
Motivation, goal of the project and global procedure
Models and Methods
Phenomena explanation
Model configuration
Model: boundary conditions
Results
Fluid field pressure
Separation of the friction coefficient into fluid and solid friction
Conclusion and outlook
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09.12.2009
Prof. Albert Albers – Numerical investigations in mixed friction systems
Results: Stress field
Stress distribution (Effective Stress in MPa)
plastic
deformation in
solid-solid contact
elastic
deformation in
solid-solid contact
elastic deformation
issuing from the
lubricant pressure
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Prof. Albert Albers – Numerical investigations in mixed friction systems
Results: Stress field
Deformation damping forces
Displacement direction
Tangential force issuing from the
plastic stress
spl,3
spl,2
spl,1
Tangential force issuing from the
elastic stress
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Prof. Albert Albers – Numerical investigations in mixed friction systems
Results: Separation of the friction coefficient into fluid
and solid friction
FT,f = FT,el + FT,pl + FT,adh
Solid friction:
Elastic friction:
μel = 0.00001
Plastic friction:
μ pl = 0.00036
Adhesion:
FT,adh = Fadh,Ham + Fadh,BoTa → μadh = 0.086
Hydrodynamic friction
FT,hd =
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09.12.2009
∑V
k
⋅ τ hd ,k
k
Vrel
⋅ Ahd → μhd = 0.00063
Prof. Albert Albers – Numerical investigations in mixed friction systems
Contents
Introduction
Presentation of the KIT and IPEK
Motivation, goal of the project and global procedure
Models and Methods
Phenomena explanation
Model configuration
Model: boundary conditions
Results
Fluid field pressure
Separation of the friction coefficient into fluid and solid friction
Conclusion and outlook
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Prof. Albert Albers – Numerical investigations in mixed friction systems
Conclusion and outlook
Abilities of the model
Combine solid and fluid contact
Measure friction coefficients
Making investigation at the micro scale
Limitations
High CPU resources are needed
Not efficient for too large contact topology changes
Outlook
Compare with Coupled Eulerian Lagrangian method
Model temperature influences
Create database used for future macro models
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Prof. Albert Albers – Numerical investigations in mixed friction systems
Thank you for your attention
Questions?
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Prof. Albert Albers – Numerical investigations in mixed friction systems