The mutual interaction between tribochemistry and lubrication: Interfacial mechanics of tribofilm

Abstract

A new mechanism for the action of antiwear tribofilms is proposed. The antiwear action of ZDDP additive is believed to be mainly due to the formation of tribofilms that reduce wear by chemical action. In this study, a mixed lubrication model is developed and tribofilm growth integrated into this model to simulate the effects of tribofilms on lubrication. The dynamic evolution of the contacting surfaces due to plastic deformation, wear and tribofilm growth continuously change the lubrication characteristics inside the contact. It is observed that the growth of tribofilm roughens the contact and increase contact severity. It was found that this roughness increase also helps to entrain more lubricant, resulting in thicker lubricant films. Therefore, the plot of the evolution of film thickness ratio (h central (t)/R q (t)) shows that the lubrication regime is improved by the presence of tribofilm. Therefore, not only the chemical presence but the physical presence of the tribofilm on the surfaces also helps to improve contact performance by retaining more lubricant and improving the lubrication regime.

Towards optimum additive performance: A numerical study to understand the influence of roughness parameters on the zinc dialkyldithiophosphates tribofilm growth

“…The model of Ghanbarzadeh et al 23 was used in present work to simulate tribofilm growth due to its flexibility and ease of use. The tribofilm growth model has been validated against several experimental scenarios and has been found to give very good match against experiments 23,26,27,53‐55 and this makes the arguments presented in this study physically valid.…”

“…Recently, a study 48,49 suggested that surface textures that result in greater pressures, thicker lubricant films and greater contact area hold promise for optimal performance under tribochemically active conditions. Azam et al 27 performed a simulation study and suggested that the growth of tribofilm leads to increased lubricant entrapment. This was thought to be due to retention of deeper grooves in the roughness geometry which are representative of non-Gaussian surfaces.…”

“…Therefore, most of the tribofilm growth models that have been developed until now, make use of approximated constants that are derived from experiments or are based on experience. The current approaches to include a tribofilm growth modelling into contact mechanics simulations relies on establishing a framework that includes: a contact mechanics/lubrication model, a tribofilm growth and removal model, a tribofilm mechanics model, and a wear model 22‐27 . All these respective components are interlinked and the information travels between these sub‐models to simulate realistic tribofilm growth experiments.…”

Tribofilm Formation of Simulated Gear Contact Along the Line of Action

“…In that model, the tribofilm removal rate changes with the height of the tribofilm. Azam et al used a modified Archard wear model with a variable wear coefficient [38]. This is a logical assumption as the hardness of the tribofilm decreases by its height [39].…”

Understanding the role of surface textures in improving the performance of boundary additives, part II: Numerical simulations

“…The experimental texture values were used as input in the in-house mixed lubrication codes to enable the simulation of textured surfaces and to ensure the simulations are in line with experiments. The mixed lubrication solvers have been well tested as evidenced in our previous modelling studies [40][41][42][43] and are being extended to even more complex experimental cases [44,45]. The key parameters affecting the performance of these textures were identified and related to the experimental outcomes.…”