A Deterministic Stress-Activated Model for Tribo-Film Growth and Wear Simulation

Abstract

A new model was developed for the simulation of growth and wear of tribo-chemical films by combining a boundary element method-based contact model and a stress-activated Arrhenius tribo-film growth equation. Using this methodology, it is possible to predict the evolution and steady-state thickness of the tribo-film (selflimitation) at various operating conditions. The model was validated using two cases for which experimental data were available in the literature. The first case is a single microscopic contact consisting of a DLC-coated AFM tip and an iron-coated substrate. The second case is a macroscale contact between a bearing steel ball and disk. Subsequently, mild wear (wear after running-in) was modeled by assuming diffusion of the substrate atoms into the tribofilm.

Stress-augmented thermal activation: Tribology feels the force

“…The above experimental work has inspired models that predict tribofilm growth, removal, and consequent friction and wear in rough surface contacts by numerical modeling, with tribofilm formation governed by the local temperature and stress in a time-evolving system [133,134]. The current main limitation of such models is that while film formation rates can be modelled now with reasonable confidence, the processes and equations that describe film removal are not yet at all well understood or reliable.…”

Nano and microscale contact characteristics of tribofilms derived from fully formulated engine oil

“…The mechanical and thermal energy present in the contact can be shown to produce an appreciable tribofilm growth rate. Akchurin and Bosman [42] showed that the Arrhenius equation with an additional shear activation energy term can be used to describe the rate limiting step, controlling the growth of the tribofilm as:…”

“…where, is shear stress [Pa], is Boltzmann constant [J/K] and is absolute temperature [K]. The typical values for the factor Γ, activation energy, and activation volume, Δ for growth of a ZDDP film are 0.01 / , 1.12 × 10 −19 and 3.80 × 10 −29 3 respectively [41,42]. For new surface pairs (such as those in the current experiments) some of the asperities deform plastically through running-in conditions.…”

Running-in of metal-to-metal seals and its influence on sealing ability with application to the design of biodegradable thread compounds

“…The running-in and wear models discussed earlier (Section 2.8) can be combined with a model of tribofilm formation to come to a tribochemical model describing the growth and removal of tribofilms which can predict when equilibrium between growth and removal or the steady state regime is reached [154,[176][177][178][179].…”

“…This part is missing in the running-in model and should be added to come to a realistic prediction of the transition to severe wear. This can for instance be implemented by following the approaches of [154,[176][177][178][179].…”