Huaping Xiao

Two-dimensional nanostructured Y2O3 particles for viscosity modification

Nanoparticle additives have been shown to improve the mechanical and transport phenomena of various liquids; however, little has been done to try and explain the rheological modifications provided from such modifications from a theoretical standpoint. Here, we report a non-Einstein-like reduction of viscosity of mineral oil with the utilization of yttrium oxide nanosheet additives. Experimental results, coupled with generalized smoothed-particle hydrodynamics simulations, provide insight into the mechanism behind this reduction of fluid shear stress. The ordered inclination of these two-dimensional nanoparticle additives markedly improves the lubricating properties of the mineral oil, ultimately reducing the friction, and providing a way in designing and understanding next generation of lubricants.

Tribological evaluation of porcine skin

This research studies the effects of external parameters on the friction of porcine skin. A tribometer was used to evaluate the frictional behavior of the same. The effects of DI water and body oil on porcine skin against steel and glass balls were evaluated in terms of coefficient of friction (COF). The COF dropped rapidly when DI water/body oil was introduced into the sliding system and remained stable when the volume of the liquid exceeded a certain value. The COF increased with increasing sliding speed under dry conditions and decreased in wet. Under an increasing normal force, the COF decreased regardless of the presence of liquid. The ratio of the real contact area to the nominal contact area of the skin with the steel/glass ball was found to increase with a power law as the applied force was increased. These results reveal basic tribological properties of the skin in contact with a hard slider. These properties could be used as reference for the design and development of artificial skin in prosthetic applications.

Silicon-oxide-assisted wear of a diamond-containing composite

A composite containing diamond in silicon carbide substrate was studied for revealing wear mechanisms. Due to the low production cost, this material is being evaluated as an alternative economical solution in industry. Tribochemical examination was conducted using a pin-on-disk configuration in both aqueous and dry environments. Characterization was conducted on worn disks and wear debris. Phase transformation from diamond carbon (sp3) to graphite, tetrahedral carbon, or amorphous carbon (sp2) in friction was confirmed by Raman spectroscopy. In addition, the Raman peak of wear debris identified a shift from crystalline Si (521 cm−1) to the mixture of amorphous silicon and silicon oxide at 510 cm−1. The surface roughness of the diamond particles was found to be greatly reduced due to wear. The smoothening of the edges was due to polishing by silicon oxide as abrasives promoting removal of weaker sp2 bonded carbon. This research proposes a tribochemical wear mechanism of diamond that has significant benefit...

Long term atmospheric corrosion in Mauritius

Abstract Carbon steel is a commonly used metal in Mauritius. Short term exposure of the metal at several sites has shown that the corrosivity of the Mauritian atmosphere lies in the C3 category according to ISO 9223. Long term atmospheric corrosion behaviour of carbon steel in the Mauritian atmosphere has never been studied, though this can be considered as essential information in the design and maintenance of steel structures. Hence, this study investigates the atmospheric corrosion of carbon steel over an 18-year period through outdoor exposures of the metal. It was observed that the atmospheric corrosion of low carbon steel in Mauritius can be divided into two time periods. An initial time period extending over 4 years involves a high corrosion rate which would probably result due to the formation of porous rust layer on the surface. In the second time period, the corrosion degradation decreases to much lower levels over time. This can be due to a change in the corrosion mechanism and the formation of a more compact rust layer. Moreover, scanning electron microscope (SEM) tests have shown that goethite has formed in the rust layer after 18 years of exposure, which is more stable, as a corrosion product.

Direct observation of oil displacement by water flowing toward an oil nanogap

A fluorescence microscope and a light microscope were employed to observe the phenomenon of water flowing toward an oil nanogap between two solid surfaces. It was found that water was able to displace hexadecane in the nanogap confinement, which contradicted previous viewpoints. An increase in water flow speed contributed to entrainment of water into the contact region, due to inadequate oil supply. Surface energy was found to be another factor that influenced the displacement phenomenon. It was easier for water to enter the contact region on the surface with a greater surface energy, since less energy is required to separate the contact of hexadecane and solid surface and to form water’s own contact.

The mechanical forces in katydid sound production

Katydids and crickets generate their characteristic calling sound by rubbing their wings together. The mechanisms of the rubbing force, however, have not been extensively studied. The change of mechanical force with external parameters (speed and applied load) in the stridulation process has not been reported. Our current study aims to investigate the mechanical forces of katydid stridulation. Four pairs of files and plectrums from a katydid, which are responsible for the katydids sound production, were examined with a specially designed experimental configuration. Due to the asymmetric nature of the wing motion in their opening and closing, the contact between the plectrum and file resembles that of a ratchet. Multiple frequencies were generated during experimental wing rubbing so that a calling-like sound was produced. Results showed that the morphology of the plectrum/file contact has significant effects on mechanical forces induced on the wings and resulting sound production. The roles of the mechani...