Surface films and metallurgy related to lubrication and wear

The nature of the tribological surface is identified and characterized with respect to adhesion, friction, wear, and lubricating properties. Surface analysis is used to identify the role of environmental constituents on tribological behavior. The effect of solid to solid interactions for metals in contact with metals, ceramics, semiconductors, carbons, and polymers is discussed. The data presented indicate that the tribological surface is markedly different than an ideal solid surface. The environment is shown to affect strongly the behavior of two solids in contact. In certain instances, the environment can dominate surface characteristics. With metals in contact with metals, adhesion is found to be related to the cohesive binding energy. Strong adhesive bonding occurs for metals in contact with ceramics, semiconductors, carbons, and polymers. Bond strength at the interface is, with some exceptions, stronger than the bond strength of the cohesively weaker of the two materials. Many different surface properties of metals and alloys influence tribological performance. These include (1) surface energy, (2) crystallographic orientation, (3) amorphous versus the crystalline state, (4) grain boundaries, (5) texturing of the surface, (6) crystal structure, and (7) order-disorder transformations. At sufficiently high loads or sliding velocities, metals or alloy surfaces are shown to undergo recrystallization effecting tribological properties. The chemical valency, d-valence-bond characteristics, of metal surfaces affect adhesion, friction, and wear. The greater the percent d-bond character, the lower the friction and wear. The ideal tensile and shear strengths of simple transition metals correlate with friction coefficients. Results presented also show that small amounts of alloying elements in base metals can alter markedly adhesion, friction, and wear by segregating to the solid surface.     

Aerodynamic optimization of the flat-plate leading edge for experimental studies of laminar and transitional boundary layers

This work is concerned with the design of a leading edge for a flat-plate model used to study laminar and transitional boundary layers. For this study, the flow over the complete boundary-layer model, including leading edge, flat section, and trailing-edge flap, is modeled. The effect of important geometrical features of the leading edge on the resulting pressure distribution, starting from the well-known symmetric modified super ellipse, is investigated. A minimal pressure gradient on the measurement side of the plate is achieved using an asymmetrical configuration of modified super ellipses, with a thickness ratio of 7/24. An aerodynamic shape optimization is performed to obtain a novel leading edge shape that greatly reduces the length of the non-zero pressure gradient region and the adverse pressure gradient region compared to geometries defined by ellipses. Wind tunnel testing is used to validate the numerical solutions.     

Best constants for metric space inversion inequalities

For every metric space (X, d) and origin o ∈ X, we show the inequality I _o (x, y) ≤ 2d _o (x, y), where I _o (x, y) = d(x, y)/d(x, o)d(y, o) is the metric space inversion semimetric, d _o is a metric subordinate to I _o , and x, y ∈ X \ {o} The constant 2 is best possible.     

The use of water-soluble phthalocyanines as textile dyes in nylon/elastane fabric: fastness and antibacterial effectiveness

This work reports on dyeing of nylon/elastane fabric with water-soluble phthalocyanines ( 1-4 ) bearing quinoline 5-sulfonic acid substituents on the peripheral or nonperipheral positions and determining the antibacterial efficiency of the phthalocyanine compounds and the dyed nylon/elastane fabrics. The light, washing, water, perspiration, and rubbing fastness properties of nylon/elastane fabrics dyed with phthalocyanines were also determined. The results showed that all dyed fabrics showed very good wet fastness values. The lightfastness value of the nylon/elastane fabric dyed with phthalocyanine dye ( 1 ) showed a much better value than the others. Also, the antibacterial efficiencies of the dyed nylon fabrics and the dye compounds were investigated against a gram-negative ( Escherichia coli ) and a grampositive ( Staphylococcus aureus ) bacteria by using disc diffusion method. The results showed that the dyed nylon/elastane fabrics and the compounds exhibited antibacterial activities against both bacteria.