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The concept behind this Research Topic (RT) was to collect works, in which Atomic Force Microscopy (AFM) techniques are employed to study tribological phenomena and to push the resolution of measurements towards single asperity contact. Thanks to the direct determination of sample height with sub-nanometer resolution and the possibility of measuring local friction, AFM can be employed after a tribotest to detect topography and friction changes at the nanometer scale. Recently, efforts are being expended to use AFM cantilevers as tribometers, i.e., as probes altering the volume of suitable samples, thereby measuring tip and/or sample wear and friction at the nano/microscale. Thus, single asperity contact, friction, and wear can be investigated. Since friction and wear at the macroscale are the result of asperities interactions, such experiments are of great importance for better understanding of tribological processes.
The frictional behavior at local contacts in an automotive brake system was analysed on the basis of computer simulation by movable cellular automata method. The boundary conditions of the model were adjusted to experimental observations obtained by TEM. The model proved to be adequate for simulating mechanical mixing and velocity accommodation at the pad-disc interface. Dynamics of particle interaction were visualized by showing rotation angles and velocity vectors. The model provided information on the development of plastic deformation for metal-on-metal contacts and on crack formation at graphite lamellae of cast iron disc. Results are in agreement with conventional friction theories.
Applying a high-frequency lateral vibration between the sample surface and the tip of a scanning force microscope (SFM), a harmonically modulated lateral (friction) force image can be obtained using lock-in techniques. The principles of operation are explained, in particular the dramatic decrease of image artefacts generally caused by topography cross-talk and laser beam interference. Flat interfaces between the two immiscible polymers, poly(methyl methacrylate) (PMMA) and polystyrene (PS), are prepared on a sodium chloride single crystal from the melt. These samples are used to evaluate the appropriate model for the tip-sample interaction geometry. The relationship between frictional and normal force does not follow Amonton's law. This shows that a single-asperity interaction between the tip and sample surface can be considered. Using the new technique, local measurements of shear strength and Young's modulus can be performed.