Experimental and numerical study on wear characteristics of steel surfaces involving the tribochemistry of a fully formulated oil. Part II: Computational modelling

Modelling wear characteristics involving the fully formulated oil (FFO) with its tribochemistry is challenging due to its complex chemical components. This paper developed a model to simulate the tribochemistry, wear, and sublayer stress for rough surfaces lubricated with a general FFO with similar recipes and properties or other functional surfaces. The tribochemistry model and the wear model when using FFO were developed based on the existing modelling studies of zinc dialkyldithiophosphate (ZDDP) and experimental results of FFO in Part (I) of this research series. The layered contact model was applied to simulate the sublayer stress under the influence of the real-time tribofilm growth and can expand the computational dimensions. In the wear model, by using the concept of mass conservation, the wear process can be described as follows: the mass of iron lost in the substrate is equal to the mass of iron consumed in the tribochemical reaction, which supplements the removal part of the tribofilm. Considering the different forms of iron in the tribofilm and the substrate, a method was improved to transfer the atomic percentage of iron (Fe at.%) in the tribofilm measured by X-ray photoelectron spectroscopy (XPS) to the wear coefficient in the Archard's wear equation. The simulation results are consistent with the critical tribological experimental results of FFO, such as tribofilm growth and wear evolution. The model also successfully simulates that the tribofilm formation has a buffering effect at the contact interface, and the tribofilm growth is promoted by temperature and shear.