Evolution of the True Contact Area of Laser Textured Tungsten Under Dry Sliding Conditions

Abstract

Despite the great importance of the real contact area, it is a parameter which, depending on the tribological system, is difficult or impossible to obtain experimentally. In this work, a combination of methods was used to estimate the development of the real contact surface, and the results were compared with the friction coefficient course. The measurements were carried out with a home-built in situ tribometer, which records a 3D image of the surface after each individual friction cycle. A tungsten sample was treated by laser interference with a line-like pattern to produce a deterministic surface. This allowed for more precise tracking of the real contact area when combined with the use of an inert corundum sphere as a counter-body. The real contact area was calculated numerically from the height information obtained using a contact application. Finally, the true contact surface was compared with the parallel-recorded friction values. After a short running-in phase, the friction behavior and the real contact surface showed comparable courses. This indicates that the changes in the real contact area could explain the friction behavior of the laser-patterned sample, and the methodology was proven to be suitable for experimentally estimating the real contact area.

Measurement of Real Contact Area for Rough Metal Surfaces and the Distinction of Contribution From Elasticity and Plasticity

“…Using a monolayer of fluorescent molecules, Weber et al [18][19] measured the real contact area in-situ and verified the linear relationship between friction force and real contact area. Through an in-situ tribometer, Lechthaler et al [20] measured the evolution of real contact area under cyclic sliding, in which the real contact area was determined numerically from height information. Using the total internal reflection method, Song et al [21] measured the real contact area between two transparent PMMA blocks, in which both optical refection and transmission were required.…”

Objective homogeneity quantification of a periodic surface using the Gini coefficient

“…Sample 1: Tungsten exhibits a very high homogeneity H MH = 0.910 with regard to the Mid-Height attribute; the deviations are primarily explained by the rough oxidized surface. A closer examination of the oxide layer for this type of sample can be found in 34 .…”

Ageing of Polymer Frictional Interfaces: The Role of Quantity and Quality of Contact

“…The area of real contact is however reduced again when the interface starts to slip because microcontacts that have aged are replaced by new, younger contacts . The friction force F f is widely assumed to be proportional to the area of real contact. , Therefore, as A is reduced, so is the friction force. − Exceptions to this behavior have also been observed, notably by Bureau et al who observed that polymer-on-glass interfaces display glassy behavior which involves a varying interfacial shear stress. More recently, lateral force microscopy experiments have demonstrated that the interfacial shear stress can also increase because of the formation of chemical bonds across a frictional interface during contact ageing. , Furthermore, recent results for polymer–glass interfaces suggest that the proportionality between the macroscopic friction force and the microscopic area of real contact may not always hold; visualization of the contact area during slide-hold-slide experiments demonstrates that the increase in the static friction coefficient with ageing time is larger than that of the area of real contact: the friction force per unit contact area increases .…”