Determination of the effect of humidity and relative speed on the coefficient of friction using response surface methodology

In order to clarify the influence of duration of rubbing, humidity, and relative speed and their cross influence on friction coefficient (CoF) an analytical model is developed based on experimental results to obtain friction function using response surface methodology (RSM). The CoF with the variation of the factor levels is investigated experimentally on a micro-tribometer machine. The surface conditions of the mild steel disc base plate were 'as-turned' and tested at different humidity conditions of 50, 65, and 80%, at relative speed of 0.5, 2.25, and 4 m/s and duration of rubbing of 0.5, 2.5, and 5 min. The humidity was controlled by passing a suitable combination of atmospheric air and water into a closed chamber. A standard RSM design called a central composite design (CCD) that is suited to fit a quadratic surface is utilized to study the CoF in dry contact. It is found that the CoF increased nonlinearly with the duration of rubbing at different levels of humidity and relative speed. The CoF is decreased almost linearly with humidity and relative speed at various levels of duration of rubbing.