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Generalization of Greenwood- Williamson Model by Extreme value Statistics

Malekan, Azadeh | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 52445 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Rouhani, Shahin
  7. Abstract:
  8. We propose a model for friction between two rough surfaces based on extreme value statistics (EVS). Different models for single-asperity contact, including adhesive and elasto-plastic contacts, were combined with EVS. The Hertzian model for contacts and Gumbel distribution for summit heights show the closest conformity with Amonton’s law. The range over which Gumbel distribution mimics Amonton’s law is wider than that of the Greenwood–Williamson (GW) model. In comparison with other EVS distribution, Gumbel distribution seems the proper choice for summit‘ s height. Interestingly, here again, elasto-plastic contact and Gumbel distribution for summits achieve the best conformity with Amontons law. Increasing the adhesion parameter makes an increase in the relative pressure of contact, which indicates that adhesion-controlled friction is dominated by load controlled friction. On the other hand, the small value of the adhesion parameter follows Amontonian regime. We also observe that adhesion increases on a surface with a lower value of roughness. We calculated the work of adhesion of the transferred charge. We also consider the effect of the fluctuations of charge density in the work of adhesion. The electrostatic work of adhesion is about 10% of the total work of adhesion and the roughness effect in the work of adhesion is negligible. We also study the superlubricity phenomemnon. Superlubricity may be because the two surfaces do not interlock. Two rough surfaces, when pressed against each other, can get into a formation where the summits of asperities one surface lock into valleys of the other surface. We simulate the contact of two rough surfaces with random Gaussian functions. Structural superlubricity is examined by the hypothesis that surfaces are very rigid and there is no deformation in asperities. The examined lattices have four-fold symmetry and rotation of the top surface shows a peak in friction every 90∘
  9. Keywords:
  10. Friction ; Adhesion ; Amonton's Law ; Extreme Value Statistics ; Superlubricity

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