Friction Force Measurements and Modeling in Hard Disk Drives

Modeling Sliding Contact of Rough Surfaces with Molecularly Thin Lubricants

“…In addition to the contact and friction forces, the finite element-based model of Kogut and Etsion (KE) includes the adhesive contributions for non-contacting as well as elastically and elastically plastically contacting asperities [32]. The SBL model's formulation of adhesion during lubricant contact was combined with the KE model in the ISBL model [4], but does not account for the variation of surface energy with lubricant penetration that was recently observed in experimental measurements [5]. Hence, we introduce a variable surface energy into the adhesion formulation according to the following equation:…”

“…Figure 8 shows the total surface energy as a function of the total lubricant thickness [5]. The exponential form of Eq.…”

“…This model is coupled with an existing rough surface dynamic contact model with friction [3,4] that has been extended to include variable lubricant surface energy according to recent experimental measurements [5,6]. Customarily, MTL contact has been neglected in rough surface contact models by assuming that the lubricant is readily displaced upon contact.…”

“…In the presence of MTL layers, adhesion was successfully accounted for in models such as the Sub-boundary lubrication (SBL) model [13], where meniscus formation is deemed energetically unfavorable due to the thinness of the lubricant film and the adhesive force was calculated based on the Lennard-Jones surface potential [14]. Experimental work showed that the surface energy of MTL layers on solid substrates is not constant but varies with penetration into the lubricant layer [5]. Hence, an adhesion formulation for non-contacting and lubricant contacting asperities-in the context of a Greenwood-Williamson (GW) formulation of roughnessis presented in this work that accounts for variations in the surface energy.…”

“…Hence, an adhesion formulation for non-contacting and lubricant contacting asperities-in the context of a Greenwood-Williamson (GW) formulation of roughnessis presented in this work that accounts for variations in the surface energy. MTL layer contact with variable surface energy is combined with the ISBL contact model with friction [3,4] into the proposed MTL dynamic contact model, which is discussed in correlation to available experimental data [5,6].…”