Investigation of Friction from Nano to Macro Force Scale under Reciprocating Sliding Conditions (Studie van wrijving in heen- en weergaande glijcontacten in een normaalkrachtenbereik gaande van nano-Newtons tot Newtons)

Contents Chapter 1. Introduction 1 1.1 Objective of this study 3 1.2 Outline of the thesis 6 Bibliography 7 Chapter 2. Friction: Review & State-of-the-art 11 2.1 Surface Roughness 12 2.2 Contact Mechanical theories 14 2.3 Laboratory scale simulations of friction under bi-directional sliding 16 2.3.1 Conventional techniques 16 2.3.2 Nanotribology 19 2.3.3 Coefficient of friction at nano- and macro- force scales 28 2.3.4 Molecular dynamic simulations 30 2.4 Amontons’ law valid or not? 36 2.5 Discussion: The importance of ‘Bridging the gap’ 39 2.6 Challenges related to friction for future engineering applications and developments 41 2.6.1 Micro electro mechanical systems 41 2.6.2 Limitations of Tribological lab scale tests 46 2.6.3 Novel materials and challenges 47 2.7 Conclusions 50 Bibliography 50 Chapter 3. Test methods and Materials 57 3.1 Measurement of friction at normal force scales from nN to N............................57 3.2 Materials 64 3.3 Conclusions 72 Bibliography 73 Chapter 4. Investigation of friction and wear at asperity level under reciprocating sliding conditions 75 4.1 Friction and wear at normal forces in the range of mN 75 4.1.1 Sliding wear analysis on DLC 76 4.1.2 Sliding wear analysis on TiN 82 4.2 Evolution of friction with test duration 86 4.3 Discussion: Evolution of debris formation during sliding tests 88 4.4 Conclusions 90 Bibliography 91 Chapter 5. Roughness effects on friction at different force scales on homogeneous surfaces 93 5.1 Experimental 93 5.2 Effect of surface roughness on friction from nN to N 95 5.3 Interplay between surface roughness, adhesion, and friction 103 5.3.1 Adhesion versus surface roughness at nanoscale 103 5.3.2 Surface roughness and adhesion effects on friction 107 5.4 Significance of surface roughness at high normal force in N’s 116 5.5 Friction over a wide range of normal forces 118 5.6 Discussion: The origin of tangential force fluctuations 123 5.6.1 Geometrical flutuations 124 5.6.2 Fluctuations due to adhesion force 128 5.7 Conclusions 129 Bibliography 132 Chapter 6. Evolution of friction from nano- to macro- normal forces on heterogeneous material 135 6.1 Experimental 135 6.2 Friction mechanisms at nN, µN, mN, and N normal forces 136 6.2.1 Friction at nN normal forces using nanotester 138 6.2.2 Friction at mN and µN normal forces using mesotester 142 6.2.3 Further analysis of tangential force fluctuations at low normal forces 144 6.2.4 Friction at N normal forces with macrotester 147 6.3 Friction over a normal force range from nano to macro 149 6.3.1 Load- and adhesion- dominated friction 150 6.3.2 Dependence of the average coefficient of friction on contact pressure 152 6.3.3 Relative contact size and exposure time in contact area 154 6.4 Energy dissipation in sliding contacts at different normal forces 159 6.5 Discussion: The evolution of the coefficient of friction with normal force 162 6.6 Conclusions 165 Bibliography 167 Chapter 7. Discussion on the non-linearity of friction in the range from nano to macro Newton forces 169 7.1 Factors leading to a non-linear dependence of friction on normal force 169 7.2 Conclusions 182 Bibliography 184 Chapter 8. General conclusions and future work 187 APPENDIX 191status: publishe