Tribology Days Ö-vik 6-8 Nov 2012 Andreas Almqvist, Luleå University of Technology

Transcription

1 Tribology Days Ö-vik 6-8 Nov 2012 Andreas Almqvist, Luleå University of Technology

2 Why is modelling & simulation important? The Luleå mixed lubrication model Surface Topography Computing Flow factors Component simulation Current activities Future work 2

3 Understanding ρh 3 12η p = 1 2 U sρh + t ρh Testing new ideas η? Optimisation Ranking η 1, η 2, η 3 3

4 A complement to: Fullscale Component Model 4

5 Few commercially available packages AVL Ricardo Suite Excite Piston&Rings Lubrication Shell COMSOL Multiphysics MIT Consortium 5

6 u u PhDs 5 Lics 60+ publications 40+ Tribology 20+ Mathematics 2010 Award Delveloped by: The division of at LTU Topography representation Flow Factor computations Flow between asperities Asperity deformation I II III u Component Simulation Utilizing the Flow Factors All regimes considered Coarse grid = fast Pressure Load Friction Leakage y 2 y 1 u

7 Local scale; describing the Surface Topography Global scale; describing Geometry - Incorporating the effects of roughness through homogenization Local Global 7

8 u u+1 1. Representative roughness # of realizations / measurements Resampling, interpolation Filtering, mirroring 2. Flow factors p minv 0 p * u Contact mechanics u Material model - Linear Elastic Perfectly Plastic # Loads (=> separations) Local problems Core of the homogenization # Separations 3. Component simulation y 2 y 1 u Interpolate ff s onto global domain and solve for homogenized pressure 8

9 I Artificial surfaces measured with AFM and VSI Anomalies created from measurement technique observed Effect on tribological parameters investigated AFM VSI S a (μm) S k (μm) S pk (μm) S vk (μm) AFM VSI Paper by Andrew Spencer et al. - Trib. Int. Vol. 57 Large differences in roughness parameters for artificial surfaces Far smaller differences for real surfaces However, care must be taken with extreme surfaces, i.e. laser textured

10 10 Mirroring => Perfect periodicity

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12 Resampling 12 Matlab GUI by Dr. Fredrik Sahlin

13 II Revamped! Was Matlab COMSOL Multiphysics 3.5a Is MATLAB code only! Mini-courses / tutorial sessions on the usage of the code will be given. ( code under construction) 13

14 II Contact mechanics BEM model Local problems Homogenization How to achieve a physically acceptable result? Representative contact mechanics model Clearance measure defining direct contact Full film computation over the non-contact area only In contact Rigid point Topography rep. 14 Contact spot

15 ---> Incorrect modelling of the so called micro-bearing problems Patir and Cheng Homogenization 15 Paper by Almqvist et al. ASME Journal of Tribology, Vol. 133

16 We want to: - Include inter-asperity coupling - Have a deterministic representation of the surface p u [ m ] [mm] [mm] 16

17 Contact pressure (-) Average interfacial separation (Å) 17 Almqvist and Persson et al. Journal of the Mechanics and Physics of Solids, Vol 59.

18 Cavitation VR Asperity collision Wear modelling SSF VR, SSF, Sauer-Danfoss Piston ring - Cylinder liner lubrication SSF, Scania II 18

19 II Universal equation (Non-linear) Elrod Incompressible HL Vijayaraghavan Compressible Linear Complementarity Problem Dini - Incompressible Almqvist & Wall - Compressible g θ = A θ θ = b, Ap + B 1 θ 1, θ 1 0, θ < 1 p 1 θ = 0 = b, 19

20 II Friction contribution to deformation included FFT accelerated solution procedure Frictionless N Friction included N F f = N 20 PhD Student - Joel Furustig

21 II After the first component scale simulation, new flow factors can be computed and then incorporated to compensate for possible plastic deformations 21 PhD Students - Joel Furustig & Andrew Spencer

22 60μm 60μm II 80 μm 3 80 μm 3 Thermoelasto-plastic, time dependent simulations in LS DYNA Interference: 4 ᵟ ᵟ 2 Y 2 Y 2 2 Mesh convergence studies & Optimisation of geometries X X 1 1 have been conducted to verify the accuracy of the model. 22 PhD Student - Shaojie Kang

23 II Interference Friction Velocity Stress Plastic strain Temperature 23 PhD Student - Shaojie Kang

24 II A B C D Stress grows from zero to the maximum value, then decreases to the residual stress after collision. The distorted stress profile is due to the existence of friction. Maximum stress is observed near the surface and large plastic deformation are observed. 24 PhD Student - Shaojie Kang

25 II A B C D Maximum plastic strain is found close to the surface Wear model could be established -> plastic strain is larger than a critical value means seizure. 25 PhD Student - Shaojie Kang

26 II A B C D Maximum temperature is found at the smaller(top) asperity Max temp rise PhD Student - Shaojie Kang

27 II III 27 PhD Student - Andrew Spencer

28 II III 28 PhD Student - Andrew Spencer

29 Cavitation VR Asperity collision Wear modelling SSF VR, SSF, Sauer-Danfoss Piston ring - Cylinder liner lubrication SSF, Scania II Piston ring - Cylinder liner lubrication Power losses in hydraulic motors Lubrication of cam roller systems Energimyndigheten, Scania, Volvo VR, Hägglunds Drives Scania, Bosch, HD III 29

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31 III - Out of roundness - Ring twist & dynamics Volvo Powertrain AB Energy agency Scania - Effect of laser texture - Floating liner test rig 31 PhD Student - Markus Söderfjäll

32 III Bosch Rexroth (Hägglunds drives AB) More than 50% reduction of power losses 32 PhD Student - Patrik Isaksson

33 III Hägglunds drives AB (Bosch Rexroth), Sweden Robert Bosch GmbH, Germany Scania AB, Sweden Aim A fast and reliable tool for prediction of slippage in cam - roller contacts 33 PhD Student - Mohammad Shirzadegan

34 III Conformal contact Non-conformal contact Global Local Are the scales separable? Reaction forces? 34 PhD Student - Mohammad Shirzadegan

35 Follower System Lumped model Free body diagram k c f s f d Spring Roller f c (t) m x, x, x f c (t) m Cam The dynamic behaviour can be predicted if the physics can represented by a mathematical model: F x = mx 35

36 Inter-asperity cavitation Micro-EHL Non-Newtonian Rheology 36

37 Tribology Days Ö-vik 6-8 Nov 2012 Questions? Andreas Almqvist, Luleå University of Technology