Interfacial friction

Kumacheva E 1998 Interfacial friction measurements in surface force apparatus Prog. Surf. Sc/. 58 75... 

Yoshizawa FI and Israelaohvili J N 1993 Fundamental mechanisms of interfacial friction. 2. Stick-slip friction of spherical and chain molecules J. Phys. Chem. 97 11 300-13... 

Lubricants are added to lower interfacial frictional forces between individual particles and/or between particles and fonning die surfaces to improve compaction and ejection (i.e. extraction of the pressed compact from the fonning die). Individual particle surfaces can be lubricated by an adsorbed film that produces a smoother surface and/or decreases interiDarticle attraction. Fonning (die) surfaces can be lubricated by coating with a film of low-viscosity liquid such as water or oil. 

The dependence of release force on the flexibility of the release layers is noted in systems other than silicones. Recent work in olefin release shows that release is a strong function of the density or crystallinity of the layer [44], At a density above 0.9 g/cm release for an acrylate PSA is greater than 270 g/cm. However, when the density of PE is dropped to 0.865 g/cm-, the release force of the same adhesive construction drops to 35 g/cm. An investigation of interfacial friction and slip in these systems has not yet been reported, but again the manipulation of release rheology greatly impacts the measured peel force. 

Homola, A. M., and Israelachvili, J. N., Fundamental Studies in Tribology The Transition from Interfacial Friction of Undamaged Molecularly Smooth Surfaces to Normal Friction with Wear, Proceedings of the 5th International Congress on Tribology, Finland, 1989, pp. 28 9. 

Attractive or repulsive interaction between two solid surfaces should play an important role in the interfacial frictional behavior [87,92-95]. From previous theoretical [89] and experimental investigations [87, 95], it was known that the attractive interaction result in a high friction and repulsive interaction results in low friction force. To characterize the interfacial molecular structure between two solids under electrostatic interaction is also important to elucidate the frictional properties of two solids. 

Campbell, S. D. and Hdber, A. C. (1999) Nanometer-scale probing of potential-dependent electrostatic forces, adhesion, and interfacial friction at the electrode/ electrolyte interface. Langmuir, 15, 891-899. 

Eisenthal and coworkers have also measured interfacial friction via the rotational dynamics of probe molecules at the interface. In their first study, Eisenthal and coworkers probed the rotational dynamics of rhodamine 6G (R6G, structure shown in Fig. 2) at the... 

Using the Ergun (1952) equation for the interfacial friction factor, Wen and Yu (1966) derived the following general equation to estimate the minimum fluidization superficial velocity Umf for spherical particles ... 

Tj is the slip relaxation time, or sliptime, which is the relaxation time for the monolayer slip velocity as it decays. For a rigidly bound monolayer, the velocity will decay very rapidly, at a rate comparable to the relaxation of the surface itself and will be near zero, yielding large interfacial friction and no slip. However, if the surface-monolayer bonds are highly dissipative, the time constant will be large and appreciable slip will occur. Reauanging Eq. (10) and equating to Eq. (14), we arrive at... 

Although this treatment does not explicitly involve interactions at a solid-liquid interface, the application of Green s function to find the stochastic friction force may be an excellent opportunity for modeling interfacial friction and coupling, in the presence of liquid. An interesting note made by the authors is that the stochastic friction mechanism is proportional to the square of the frequency. This will likely be the case for interfacial friction as well. 

Shafry, N., Brandon, D.G. and Terasaki, M. (1989). Interfacial friction and debond strength of aligned ceramic matrix composites, Euro-Ceramics, VoL 3, Engineering Ceramics (G. de With, R.A. Terpstra and R. Metselaar eds.), Elsevier, London, pp. 453-457. 

Hsueh, C.H. (1990b), Interfacial friction analysis for fiber-reinforced composites during fiber push-down (indentation). J. Mater. Sci. 25, 818-828. 

Shetty, D.K. (1988). Shear-lag analysis of fiber push-out (indentation) tests for estimating interfacial friction stress in ceramic-matrix composites. J. Am. Ceram. Soc. 71, C.107-109,... 

B12), and by Gazley (Gl), using air-water. It was shown that when a gas-liquid interface is smooth, energy transfer from gas to liquid is entirely dissipated in surface friction, but when a liquid surface is hydrodynamically rough, energy transfer from gas to liquid may amount to twice that to be expected on the basis of interfacial friction (Gl). Presumably this excess energy is dissipated in the formation and maintenance of surface waves. 

In particulate-filled thermoplastics, the matrix is the load-bearing component and all deformation processes take place in the matrix. Particulate fillers are, in most cases, not capable of carrying any substantial portion of the load due to the absence of interfacial friction as the means of stress transfer. This is evidenced by the lack of broken particles on the surfaces of fractured filled thermoplastics. Hence, it seems appropriate to start this volume with a brief overview of the basic structural levels and manifestation of these levels in governing the mechanical properties of semicrystaUine thermoplastics used in compounding. 

Fig. 18. The simple shear geometry used to characterise the interfacial friction the fluid thickness is e. The top plate limiting the sample is translated at the velocity and transmits this velocity to the fluid. The bottom plate is immobile, and the local velocity of the fluid at the bottom interface is Vs. The fluid is submitted to a simple shear, with a shear rate y = (Vt-VsYe. The velocity profile extrapolates to zero at a distance b below the interface, with...

Fig. 2.15 The interfacial frictional stress versus temperature for a Nicalon/SiC composite.75...

Cho et al.52 developed an analytical model that relates the temperature rise during fatigue to the interfacial frictional sliding stress, as elaborated later. Holmes and Cho12 used the model to show that in SiCf/CAS-II, the interfacial shear stress, r, decreases from a value of around 15 MPa to 5 MPa within the first 25 000 fatigue cycles (Fig. 6.13). The approach used to determine r from temperature rise data is described in greater detail in the following section. 

As will be explained later, it is considered that the surface of such a film normally consists of a thin layer of fully-ordered crystalline material with the basal planes oriented parallel to the plane of the substrate surface. Conformal contact between two such films will then be similar to the contact between two adjacent lamellae within a crystal. As a first approximation it might therefore be assumed that interfacial slip will resemble intracrystalline slip. However each surface may be degraded by the presence of contaminants, surface defects, and deviations from planarity, and it cannot be assumed that interfacial friction will be completely governed by the same considerations as intracrystalline friction. 

If this interpretation is correct, then the figure provides strong support for the argument that interfacial friction between molybdenum disulphide films and intracrystalline friction are both determined by the same factors. This is because at the point of intersection between the horizontal and decreasing portions of the curve, where interfacial friction changes to intracrystalline friction, there is no discontinuity, and the same friction value is given for both types of slip. 

Pauchon and Banerjee (1988), in their analysis of bubbly flows, have shown that the kinematic wave velocity based on a constant interfacial friction is weakly stable. They have also obtained a functional dependence of the interfacial friction factor on the void fraction by assuming the kinetic wave velocity equal to the characteristic velocity (kinetic waves are neutrally stable). They have assumed that turbulence provides the stabilizing mechanism through axial dispersion of the void fraction. 

A schematic of the flow pattern used to represent annular flow is shown in Figure 10. A preliminary model for pressure drops in the annular flow regime for the circular tubes under consideration here was reported in Garimella et al. [27], followed by the more detailed model [28] described below. For the development of this model the following assumptions were made steady flow, equal pressure gradients in the liquid and gas core at any cross section, uniform thickness of the liquid film and no entrainment of the liquid in the gas core. The measured pressure drops were used to compute the Darcy form of the interfacial friction factor to represent the interfacial shear stress as follows ... 

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