Mechanics of surface damage: A new look at the old problem of wear

Transcription

1 Material resistance to extreme conditions June 2017, Kiev for future energy systems Mechanics of surface damage: A new look at the old problem of wear Ramin Aghababaei École Polytechnique Fédérale de Lausanne (EPFL), Switzerland Aarhus University, Denmark (from September) Sliding Contact Fatigue Friction Adhesion Debris particle Ploughing Fracture Subsurface cracks Plasticity Sliding Collaborators: J.-F. Molinary (EPFL) and D.W. Warner (Cornell)

2 Wear is Extreme The process of surface damage and eventual material degradation Wear in a shaft bearing Surface damage Wear debris 100 μm 10 μm Farias et al (2007) Wear, Kotzalas and Doll (2010) Phil. Trans. R. Soc. A 2

3 Wear is Extreme The process of surface damage and eventual material degradation Wear in a shaft bearing Surface damage Wear debris 10 μm 100 μm Extreme Mechanics Temperature Environment Velocity 2

4 Wear importance in energy systems A major source of materials and energy loss with serious economic, environmental and industrial impacts. 3

5 Wear importance in energy systems A major source of materials and energy loss with serious economic, environmental and industrial impacts. Vestas Wind Turbine Collapse Hornslet, Denmark (2008) Cause: wear in brake system 3

6 Archard s wear law (1953) N S V=K H N Wear coefficient: ( ) The probability of particle detachment J.F. Archard (1953) JAP 4

7 Archard s wear law (1953) N S V=K H N Wear coefficient: ( ) The probability of particle detachment J.F. Archard (1953) JAP Year

8 Archard s wear law (1953) N S V=K H N Wear coefficient: ( ) The probability of particle detachment J.F. Archard (1953) JAP Sliding Contact Fatigue Friction Adhesion Debris particle Ploughing Fracture Plasticity Subsurface cracks Sliding Year

9 Archard s wear law (1953) N S V=K H N Wear coefficient: ( ) The probability of particle detachment J.F. Archard (1953) JAP How and when do wear particles arise? Archard (1953) JAP, Archard and Hirst (1957) 4

10 Experiments Wear Experiments vs. Simulations Gradual plastic smoothing Si 10 nm Bhaskaran et al., (2010) Nat. Nanotech Vahdat et al., (2013) ACS Nano Fracture-induced debris DLC 200 nm Si Fracture of the apex Liu et al.,(2010) ACS Nano Irregular surface due to fraction 500 nm Chung and Kim, (2014) Tri. Let. 5

11 Experiments Wear Experiments vs. Simulations Gradual plastic smoothing Fracture-induced debris Si DLC 10 nm 200 nm Fracture of the apex Liu et al.,(2010) ACS Nano Irregular surface due to fraction 500 nm Chung and Kim, (2014) Tri. Let. Contact Wear ic st i ty Fr ac tu re a Pl Simulations Bhaskaran et al., (2010) Nat. Nanotech Vahdat et al., (2013) ACS Nano Si Too complex for continuum approach 5

12 Experiments Wear Experiments vs. Simulations Gradual plastic smoothing Fracture-induced debris Si DLC 10 nm Si Fracture of the apex 200 nm Bhaskaran et al., (2010) Nat. Nanotech Vahdat et al., (2013) ACS Nano Liu et al.,(2010) ACS Nano Irregular surface due to fracture 500 nm Chung and Kim, (2014) Tri. Let. Gradual plastic smoothing Contact DLC Wear W DLC Sha, J. et al., (2013) APL ic st i ty Fr ac tu re a Pl Simulations Stoyanov, et al., (2014) Acta Mat. Too complex for continuum approach Si Kim and Falk (2010) PRB 5

13 Fracture at the atomic scale 2 rp K c Plastic zone size, Rice (1972) r p =β 2 πσy 6

14 Fracture at the atomic scale 2 rp K c Plastic zone size, Rice (1972) r p =β 2 πσy 100 mm 10 mm 1 mm Ashby Map 100 um 10 um Metals 1 um Steels Ni alloys Cu alloys Ti alloys 100 nm BMGs Al alloys Mg alloys 10 nm W alloys Polymers HDPE PMMA Ceramics PVC Ps LDPE Nylons ZrO2 Al2O3 SiC MgO Si3N4 C 1 nm? 1A Model Materials Glasses Rocks Foams 6

15 Model inter-atomic potential Identical lattice structure Identical elastic properties Tunable inelastic properties Brittle Hard Ductile Soft Fracture Toughness P6 (cleavage cracking) Contact pressure (ε/r o3 ) P1 (crack blunting) Hardness F A Indentation Depth (r o) Aghababaei et al., (2016) Nat. Comm. 7

16 Idealized wear simulation Constant pressure Displacement Rigid atoms Thermostat region lx Surface spacing Asperity size Thermostat region Fixed region 8

17 Idealized wear simulation Ductile potential Gradual plastic smoothing 9

18 Idealized wear simulation Ductile potential Gradual plastic smoothing Brittle potential Fracture-induced debris 9

19 Idealized wear simulation Ductile potential Brittle potential? Gradual plastic smoothing Fracture-induced debris 9

20 Energy balance criterion Gradual plastic smoothing Fracture-induced debris 10

21 Energy balance criterion Energy E ad d 2 d E el d 3 11

22 Energy balance criterion Wear transition occurs when: Critical junction size Energy E ad d 2 d Idealized case (α=β=1) in 2D E el d 3 in 3D 11

23 Model vs. Simulations Fracture-induced debris Junction size, d 1.5 Gradual plastic smoothing Characteristic length scale, Δ w σ2j /G 12

24 3D simulations d < d* Gradual plastic smoothing d > d* Fracture-induced debris ~ 4 Million atoms ~ 10 Millions time-steps ~ 2 weeks of calculation on 240 processors 13

25 Model vs. Experiments Asperity tip size (nm) Fracture-induced debris Gradual plastic smoothing SiNx Si Au Ag Critical junction size (nm) 14

26 New mechanistic look at wear A critical length scale controls wear mechanisms at the asperity level Bulk properties Surface roughness G Δ w d =λ 2 σj * d >d * d <d * Interface properties Empirical fitting Aghababaei et al., (2016) Nat. Comm. Mechanics of interfaces 15

27 Summary and outlook A new methodology to simulate wear phenomena A critical length scale controls adhesive wear mechanisms at the asperity level Revising empirical wear laws at different scale Develop new physics-based wear models R. Aghababaei et al, (2016) Critical length scale controls adhesive wear mechanisms, Nature Communications, 7, R. Aghababaei et al, (2017) On the debris-level origins of adhesive wear: Did Archard get it right?, appears in PNAS Frérot (2017) Emergence of wear law: from single-asperity to multi-asperity, Submitted.