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Friction Laws for Dry Nanoscale Contacts Izabela Szlufarska (University of Wisconsin - Madison) DMR 0512228. How does friction force depend on applied load and contact area? Macroscopic contacts: (Amontons’ law 1699), Nanoscale contacts: Laws Unknown Approaches: - PowerPoint PPT Presentation
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Friction Laws for Dry Nanoscale ContactsIzabela Szlufarska (University of Wisconsin - Madison) DMR 0512228
How does friction force depend on applied load and contact area?
• Macroscopic contacts: (Amontons’ law 1699),
• Nanoscale contacts: Laws Unknown
Approaches:
• AFM experiments for contacts nm-µm in size. Interpreted through continuum mechanics models:
• Continuum mechanics breaks down in nanoscale contacts.
This study:
• PI performed molecular dynamics simulations of AFM experiments at realistic length scales. Highly accurate REBO potentials are used to simulate mechanical deformation and chemical reactions of diamond simultaneously.
• Models give very good agreement with experiments on H-terminated diamond interfaces. Friction coefficient ~0.05 (exp: ~0.02), shear strength ~1,000 MPA (exp: 200 - 1,000 MPa).
Discovery:
AFM tip is not smooth. It consists of multiple atomic size asperities (total area Areal). Friction force is always proportional to this area:
Atomic roughness and interfacial interactions govern friction behavior
Non-adhesive nanoscale contacts follow macroscopic laws of friction:
Adhesive contacts are well described by continuum models:
Atomic multi-asperity model is proposed to describe simulation results.
Transition from linear to non-linear friction due to increased adhesion
Non- adhesive contact
Adhesive contact
Ff L
Ff A
Ff A
Ff L2 / 3
Ff Areal
Ff L
Ff L2 / 3
Education in Computational Materials Science
Izabela Szlufarska (University of Wisconsin) DMR 0512228
Undergraduate mentoring: Paul Kamenski (Materials Science & Engineering)
• Supported by PI’s lab for 2 years
• Wrote codes to support molecular dynamics simulations of nanocrystalline materials
• Co-op at the Oak Ridge National Laboratory through PI’s collaborations
• In the Spring ‘08 won NSF Graduate Research Fellowship (GRFP)
• In the Fall ‘08 begins graduate studies in materials science at Oxford University
Interdisciplinary course: Molecular Dynamics and Monte Carlo Simulations in Materials Science
• Taken by students across different colleges and departments (materials science & engineering, mechanical engineering, chemical engineering, chemistry, nuclear engineering, engineering mechanics, geophysics). Most students come from experimental groups
• Students work on interdisciplinary teams and on individual projects
• Final project examples:
• “Reverse Monte Carlo for Amorphous Si”
• “Radiation damage in nanoparticles”
• “Investigation of solid-water interface using LAMMPS”
• “Polymer bulk erosion: Monte Carlo simulations”
• “Modeling of phonon density of states for a Si/Ge heterostructures”Graduate student Sarah Khalil presents her final class project
Undergraduate student Paul Kamenski
Ferrite (α)
BCC
a = 2.870 Å
Austenite (γ)
FCC
a = 3.515 Å
910 °C
Education in Computational Materials Science
Izabela Szlufarska (University of Wisconsin) DMR 0512228
Example of student’s work from the course: MD and MC Simulations in Materials Science
Andy Nelson (graduate student in experimental group in Nuclear Engineering):
“Modeling of Ferrite-Austenite Transition”
ASM Materials Handbook Vol. 9