Rubber Adhesion and Friction: Role of Surface Energy and Contamination Films

We study the influence of the surface energy and contamination films on rubber adhesion and sliding friction. We find that there is a transfer of molecules from the rubber to the substrate which reduces the work of adhesion and makes the rubber friction insensitive to the substrate surface energy. We show that there is no simple relation between adhesion and friction: adhesion is due to (vertical) detachment processes at the edge of the contact regions (opening crack propagation), while friction in many cases is determined mainly by (tangential) stick-slip instabilities of nanosized regions, within the whole sliding contact. Thus while the pull-off force in fluids may be strongly reduced (due to a reduction of the work of adhesion), the sliding friction may be only slightly affected as the area of real contact may be dry, and the frictional shear stress in the contact area nearly unaffected by the fluid.

ADHESIVE FRICTION BEHAVIOR OF ROUGH RUBBER SURFACES SLIDING AGAINST SMOOTH RIGID SURFACES

ABSTRACT A model for the characterization and prediction of the adhesional friction experienced by a rough rubber surface sliding against a smooth rigid surface using fracture mechanics based peeling behavior is supported by experimental results. The friction is characterized by the strain energy release rate associated with the unpeeling of the asperities. This peeling energy of the rubber and rigid surface interface is used to derive a general relation for the frictional shear stress. Peeling characteristics are first found using rolling experiments, then this information is used to predict the results of sliding experiments. The velocity dependence of the friction is explained by relation to the dynamic viscoelastic properties of the rubber. The experiments compare favorably with the theoretical prediction derived using the model.

Ultrasonic Measurement of Gas Bubbles Advecting Under a Ship Bottom for Investigating Drag Reduction Performance

Bubbles injected into a turbulent boundary layer have a significant potential to reduce frictional shear stress, but this drag reduction technique has not been optimized yet because of its low and unstable performance. If monitoring and controlling of advective bubbles beneath ships are realized, these provide insight for improving the performance. In this paper, we performed experiments using a model ship with 4 m in length in a towing tank with 80 m in distance. The model ship is fully made of acrylic resin and mounts shear stress sensors and ultrasonic measurement system. The shear stress and bubble information, such as a void fraction and a thickness of liquid film above the bubbles, are obtained at three locations arranged at the front, the middle and the rear of the ship bottom plane. By analyzing these data, it is confirmed that the drag reduction occurs when a thin liquid film exists.

Frictional Effects on Gear Tooth Contact Analysis

The present paper concentrates on the investigations regarding the situations of frictional shear stress of gear teeth and the relevant frictional effects on bending stresses and transmission error in gear meshing. Sliding friction is one of the major reasons causing gear failure and vibration; the adequate consideration of frictional effects is essential for understanding gear contact behavior accurately. An analysis of tooth frictional effect on gear performance in spur gear is presented using finite element method. Nonlinear finite element model for gear tooth contact with rolling/sliding is then developed. The contact zones for multiple tooth pairs are identified and the associated integration situation is derived. The illustrated bending stress and transmission error results with static and dynamic boundary conditions indicate the significant effects due to the sliding friction between the surfaces of contacted gear teeth, and the friction effect can not be ignored. To understand the particular static and dynamic frictional effects on gear tooth contact analysis, some significant phenomena of gained results will also be discussed. The potentially significant contribution of tooth frictional shear stress is presented, particularly in the case of gear tooth contact analysis with both static and dynamic boundary conditions.