Abstract: Based on the independently developed optical in situ linear reciprocation tribotester, sliding tests of NBR rubber are performed under different lubrication conditions. The lubricants have different wettability which is controlled by the additive ratio. The higher additive ratio means the lubricants with better spreading and wetting behavior on the solid substrates. A new theoretical model of rubber sliding friction is constructed under wet conditions, and we try to explain the decrease of sliding friction coefficient during the transition process (the contact interface changes from dry to wet) from interface wettability perspective. In addition, the influence of surface wettability on the friction property is studied and the relationship between the contact angle and friction coefficient is constructed. Results show that the viscosity effect of rubber sharply decreases when the lubricant flows into the contact interface in a short time; with the decrease of additive ratio, the contact angle of lubricant on the solid surface gradually decreases and the static friction coefficient increases. It is concluded that the contact angle of lubricant is linear with static friction coefficient (R²≈0.92), the experimental results have a great coherence with the theoretical model.

Key words: blade-casing rub-impact experimental test, casing equivalent stiffness, law of conservation of mechanical energy, representation model, rotating blade-casing rub-impact, contact interface, rubber friction, viscosity effect, wettability