Introduction of a power law formulation to quantify the contact size effects on friction and wear responses of dry oscillating sliding contacts: Application to a chromium steel interface

A major problem in tribology is the difficulty of transposing friction and wear properties extracted from small laboratory contacts to large industrial interfaces. Indeed, very little has been done to define the contact size effects on the wear rate and friction responses. To address this fundamental aspect and to provide a basic expression to extrapolate the tribological response from micro to macro contacts, a multiscale tribological approach was developed. Using a dry reference AISI 52100/AISI 52100 chromium steel interface, micro, meso and macro sphere/plane (3D) and cylinder/plane (2D) contacts subjected to various contact pressures and sliding amplitudes were examined. This analysis shows that both the coefficient of friction and Archard wear rates display an asymptotic decrease with the contact size increase until a threshold value characterizing the very large contact condition. The fretted scar analyses suggest that an increase of the contact area accentuates the influence of the third body in the interface response: The coefficient of friction and wear rate are lower when debris are trapped within the interface. A power function is introduced to define this typical behavior. The analysis concludes that if the friction response is better defined by using the contact radius variable, then the wear rate is better described by using the contact area variable. This approach is valid for micro to macro contact sizes. The introduction of this basic expression is discussed with regards to the potential interest in predicting the tribological response of industrial contacts using micro experiments.