Mechanisms surface roughness

In the third case, the particle radius is much greater than the dimensions of either the atomic-molecular or mechanical surface roughness the number of molecules in the zone of a single contact remains constant, but the number of contacts increases, approaching its maximum the increase in the number of contacts brings about an increase in the force of adhesion, which in this case varies directly with particle size (Section 3 in Fig. V.7). 

Simon, H. and Bulskamper, A., On the Evaluation of Reynolds Numbei and Relative Surface Roughness Effects on Centrifugal Compressor Per formance Based on Systematic Experimental Investigation, ASME 8J-C,1 118, New York American Society of Mechanical Engineers, 1983. 

McBain and Hopkins [2], in their classical scientific study, argued that the surface roughness of a porous material was the basis of mechanical adhesion , its being... 

Quantifying the effect of surface roughness or morphology is difficult, however. Surface preparations that provide different degrees of surface roughness also usually produce surfaces that have different oxide thicknesses and mechanical properties, different compositions, or different contaminant levels. The problem of separation of these variables was circumvented in a recent study [52] by using a modified microtome as a micro milling machine to produce repeatable, well-characterized micron-sized patterns on clad 2024-T3 aluminum adherends. Fig. 2 shows the sawtooth profile created by this process. 

The scale of the microscopic surface roughness is important to assure good mechanical interlocking and good durability. Although all roughness serves to increase the effective surface area of the adherend and therefore to increase the number of primary and secondary bonds with the adhesive/primer, surfaces with features on the order of tens of nanometers exhibit superior performance to those with features on the order of microns [9,14], Several factors contribute to this difference in performance. The larger-scale features are fewer in number... 

Direct bonding. In many high-volume production applications (i.e., the automotive and appliance industries), elaborate surface preparation of steel ad-herends is undesirable or impossible. Thus, there has been widespread interest in bonding directly to steel coil surfaces that contain various protective oils [55,56,113-116], Debski et al. proposed that epoxy adhesives, particularly those curing at high temperatures, could form suitable bonds to oily steel surfaces by two mechanisms (1) thermodynamic displacement of the oil from the steel surface, and (2) absorption of the oil into the bulk adhesives [55,56]. The relative importance of these two mechanisms depends on the polarity of the oil and the surface area/volume ratio of the adhesive (which can be affected by adherend surface roughness). 

The CPE model has been used152,154,270-274 and it has been found that for electrochemically polished surfaces, the surface roughness is very small compared with mechanically polished surfaces. 

It is noteworthy that several studies exhibit contradictory results for both the mechanical and thermal characteristics of the flow. This is generally due to differences in the many parameters that characterize these studies such as the geometry, shape and surface roughness of the channels, the fluid, the boundary conditions and the measuring methodology itself. These discrepancies indicate the need for extension of the experimental base to provide the necessary background to the theoretical model. 

A direct relationship is found between the hardness of a material and its ability to withstand mechanical wear, and as a rule the harder the material, the greater is its wear resistance. A related factor is that harder materials usually take a better polish and, as a result, the wear due to surface roughness mentioned above can be minimized. Choosing material combinations with a low coefficient of friction is also an important factor in reducing mechanical wear. 

The third factor affecting dispersion is turbulence. Mechanical turbulence is caused by the roughness of the Earth s surface. Away from the surface, convective turbulence (heated air rising and cooler air falling) becomes increasingly important. The amount of turbulence and the height to which it operates depends on the surface roughness, wind speed and atmospheric stability. 

The mechanism of surface-roughness formation at the limiting current has... 

A stringent requirement for PF, nearly in accordance with fluid mechanics, is that it be fully developed turbulent flow. For this, there is a minimum value of Re that depends on D and on e, surface roughness ... 

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