Improved analysis and visualization of friction loop data: unraveling the energy dissipation of meso-scale stick–slip motion

In this paper we demonstrate a new method for analyzing and visualizing friction force measurements of meso-scale stick–slip motion, and introduce a method for extracting two separate dissipative energy components. Using a microelectromechanical system tribometer, we execute 2 million reciprocating sliding cycles, during which we measure the static friction force with a resolution of $ \newcommand{\vFrictionForceResolution}{0.6} \newcommand{\vfFrictionForceResolution}{{\vFrictionForceResolution}~{\rm nN}} \vfFrictionForceResolution$ and the displacement with a resolution of $ \newcommand{\vDisplacementResolution}{0.2} \newcommand{\vfDisplacementResolution}{{\vDisplacementResolution}~{\rm nm}} \vfDisplacementResolution$ . We plot the lateral force as a function of the real contact position by compensating for the values of the spring constants of the system. This allows all friction loops to be combined in a single hexagonal bin plot, which clearly shows the evolution of the friction force magnitude and its distribution across the sliding track. We identify all individual slip events in the entire experiment using a thresholding algorithm. This allows us to show the evolution of the slip event count, the static friction force, and the coefficient of friction. Crucially, it allows us to disentangle the dissipated energy into two components: the dynamically dissipated energy, which is associated with slip motions, and the semi-statically dissipated energy, which is related to small contact deformations, plastic yield and other non-elastic behavior. Our technique provides new insight into the mechanics of stick–slip motion in multi-asperity contact systems, and paves the way towards a better understanding of the physics of meso-scale friction.