1 / 23

Tribology Lecture I

Tribology Lecture I. Tribology. From:  = rubbing. Friction Wear Lubrication. Tribology deals with all aspects of. interacting surfaces in relative motion. - bearings. Friction. Loss of energy due to rubbing. Energy is converted to heat

mbray
Download Presentation

Tribology Lecture I

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. TribologyLecture I

  2. Tribology From:  = rubbing • Friction • Wear • Lubrication Tribology deals with all aspects of interacting surfaces in relative motion - bearings

  3. Friction • Loss of energy due to rubbing. Energy is converted to heat • Extra energy and force required to overcome friction • Causes wear and failure

  4. Friction: Amonton’s Law W Ffriction A V

  5. Origin of Friction • Surface Roughness • Solid to solid contact • Adhesion • Deformation

  6. Lubrication Replace Solid to solid contact Fluid Layer with a fluid layer - i.e. a lubricant

  7. Lubrication Solid rubbing replaced by Fluid Layer viscous shearing

  8. To be useful must support some load W Fluid Layer

  9. To be useful must support some load W

  10. To be useful must support some load W Fluid Layer p Need pressure in the fluid to support the load

  11. Hydrodynamic Lubrication W Fluid Layer p Pressure is generated by motion and geometry of the the bearing in concert with the viscosity of the lubricant

  12. 1-D Reynolds Equation W z h(x) ho x U

  13. z h h0 p t Infinitesimal element U p x 0 B

  14. Force balance Viscosity equation Combine:

  15. Integrate wrt z Apply BC’s: No-slip: ux = U at z = 0, ux = 0 at z = h yields Volumetric flow rate (per unit width) Incompressible flow, q = const. Evaluate at dp/dx = 0: Solve for dp/dx

  16. 1-D Reynolds Equation wn z h(x) ho x U Reynold’s Equation • Integrate over x to get p(x) • Integrate over x again to get Wn • Result gives hoin terms of U, , Wn

  17. U Example Exponential h B wn z h(x) ho x integrate wrt x; apply BC’s p = 0 at x = 0 and at x = -B solve for p(x), integrate to get Wn/L, then solve for h0

  18. U P(x) 2-D Reynolds Equation w Sphere R z Fluid Layer hc x For sphere Exact solution

  19. U Hydrodynamic LubricationPoint Contact W Sphere R Fluid Layer hc

  20. Hydrodynamic Lubrication(Refinement: Both surfaces moving) W Sphere R U1 Fluid Layer hc U2 “Entrainment” or “Rolling Velocity”

  21. Hydrodynamic Lubrication(Refinement: two spheres) W R1 U1 hc U2 Where R is now “reduced” radius R2 1

  22. Hydrodynamic Lubrication W R1 U1 Nice theory but as a rule it greatly under estimates hc hc U2 • Pressure is very high near contact • P >>1000atm ( 108 Pa) • Pressure Dependence of  • Elastic Deformation of Sphere R2

  23. Hydrodynamic Lubrication Elasto-Hydrodynamic Lubrication

More Related