Effect of Surface Traction

Typical static friction coefficients are given in Table 1. These data demonstrate that the absolute traction values for synthetic surfaces are satisfactory in comparison with natural turf, provided that shoes with the appropriate surfaces are employed. Synthetic surfaces by virtue of their constmction are to a degree directional, a characteristic which, when substantial, can significantly affect both player performance and ball roU. This effect is evident in a measurement of shoe traction in various directions with respect to the turf—pile angle. Some traction characteristics are directiy affected by the materials. 

Foi example, nylon pile fabrics, exhibiting higher moisture regain, have different traction characteristics under wet and dry conditions than do polypropylene-based materials. Effects of artificial turf fabric constmction on shoe traction ate given in Table 2. Especially effective in aiding fabric surface uniformity is texturing of the pile ribbon, a process available for the two principal pile materials nylon and polypropylene. 

The representative volume element is a sample that a) is structurally entirely typical of the whole mixture on average and, b) contains a sufficient number of inclusions for the apparent overall moduli to be effectively independent of the surface values of traction and displacement so long as these values are macroscopically uniform . That is, they fluctuate about a mean with a wavelength small compared with the dimensions of the sample, and the effects of these fluctations become insignificant within a few wavelengths of the surface. By average over a volume Hill means the integral taken over the volume, divided by that volume. 

Interruptions in the stray current. Stray currents produced by rail traction systems are non-stationary, and thus the effect of interruptions of the current should be taken into consideration. In fact, gradients of ionic concentration in the pore solution near the steel surface, produced by the depletion of alkalinity due to the anodic reaction and increase in chloride concentration due to migration, can be mitigated during the interruption of current. Therefore, interruptions in the stray current may have a beneficial effect, as shown in Figure 9.6 where results of tests with continuous appHcation of the current are compared with tests with circulation of current at alternated hours (lon-loff). The periodical interruption of current had a beneficial effect, since it increased the charge required for initiation of corrosion. This effect was remarkable in cement pastes with chloride contents lower than 0.4 % by mass of cement... 

Marangoni effect is a general terra for surface flow phenomena resulting from the appearance in the interface of an interfacial tension gradient. These phenomena produce traction on the adjoining sublayers and lead to two distinct and separate effects the flux-intensive surface renewal phenomena and the area-intensive thin-film phenomena. The first phenomena predominate when the depth of the liquid is much larger than the depth of penetration of surface movement and the second are important when the two depths are comparable. In the first case the affected process parameter is the mass transfer coefficient and in the second case the interfacial area. 

Suppose that, in its reference configuration, an elastic material has a nominally flat surface that is free of applied traction. If the solid is then stressed, is the flat surface shape stable under perturbations in shape These perturbations are changes in the reference configuration both the material that are achieved by rearrangement of mass, and are not a consequence of deformation of the material. The question is addressed in this section for the case of periodic perturbation of surface shape. Perturbations of very small amplitude are considered first, and this discussion is followed by consideration of higher order effects and substrate stiffness. Cases of nonperiodic surface perturbations are considered in the following section. 

Finally, the studies summarized above address the spatial effect of the ECM on the extent of cell distortion and tension in a two-dimensional ceU culture system. With few exceptions, the mechanical interaction between a ceU and the ECM occurs around the whole cell surface in a true physiological setting. While there is not yet a direct measurement method to correlate tractions and the spatial distribution of ECM ligands in a three-dimensional system, it is likely that the correlation is similar to that in a planar culture system. 

Note that in Eqs. (16)-(23) is related to the inertia effect of the void, to the elasticity of the matrix, and to the viscous effect of the matrix is the traction acting on the inner boundary of the void due to thermal expansion and surface tension is the traction action on the outer boundary of the void... 

Incorporating the effect of adhesion in Hertzian contaet, Johnson et aL formulated a theory of adhesive contact using a balance between the stored elastic energy and the loss in surface energy, which is now renowned as the JKR theory [12], In this model, adhesion works only inside the contact area and the net traction p(r) acting on the eontact area is given by the sum of Hertzian repulsion pi and adhesive traction p, that is,... 

Young, in a celebrated work published in 1805, used the principle of tension to explain a great number of capillary phenomena. He does not fall into the same error as Segner, that is to say that he considers at the same time the effects of the two perpendicular curvatures the tension determines, at each point of the hquid surface, a pressure or a normal traction proportional to the sum of these two curvatures, and from this are bom the phenomena in a capillary tube, for example, when the hquid is raised and has thus a concave surface, normal tractions due to the tension support the weight of the column, and when the liquid is depressed, its surface being then convex, the normal pressures produced by the tension balance the hydrostatic pressure of the surrounding liquid, which tends to raise the column. 

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