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Contact Mechanics II :
Crack propagation, Wear and Rough Surfaces
1 2 2 2E. Héripré , L. Sun , S. Dubouski , J. Durand
1
Solid Mechanics Laboratory, Ecole Polytechnique ParisTech
2
Centre des Matériaux, MINES ParisTech
Paris, 23 June 2010Introduction
 Contact mechanics I : Basis of contact mechanics.
 Contact mechanics II :
 Industrial problem : Avoid wear and crack initiation and/or
propagation.
 What is going on if we change the material behaviour ?
 How is influenced wear and crack propagation by the material
behaviour?
 How could we take into account roughness in the study of
contact mechanics?
E.Héripré | Introduction 2/24Introduction
 Parameters that govern friction / wear /crack
propagation :
 The material, its cristallographic structure, its behaviour
 Surface topography(roughness), physico-chemical state of the
surface (oxidation?)
 Lubricant : Solid lubricant, liquid films, ...
 Boundary conditions : Applied load and/or displacement
 ...
E.Héripré | Introduction 3/24Introduction
 What kind of materials are in contact ? Mostly metallic
components
idlers
sprockets
bearings
Electrical
connectors
E.Héripré | Introduction 4/24Introduction
 What is a metallic material?
( Iron/Steel, Aluminum, Copper, Titanium, Nickel alloys)
E.Héripré | Introduction 5/24Introduction
 What about the strain ε = ΔL/L0 if I change the
measurement scale L0
tensile, compressive or bending test
(Raith, 5kN, 500°C)
 Microgrids -► L0
E.Héripré | Introduction 6/24Introduction
 Effect of the variation of L0 on the strain measurements
 Total surface : 300 µm x 300 µm
L0 = 2 µm
From J. Crépin, CdM, Mines ParisTech
E.Héripré | Introduction Introduction
 Have a look at the microstructure...
Rcristal
E.Héripré | Introduction 14/24Introduction
 Have a look at the microstructure ...
 Tensile test
 Zr alloy
 Macroscopic strain: 3,57%
 Image resolution: 4000x4000
pixels
0% 7%
E.Héripré | Introduction 15/24
Tensile dir.
Rolling
directionIntroduction
 Scale of contact mechanics is comparable to the material
scale...
(µm)
 Roughness profile
E.Héripré | Introduction 16/24

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