Publications on underwater drag reduction by gas have been gathered in the present study. Experimental methods, results and conclusions from the publications have been discussed and analyzed. The stable existence of gas is a requirement for underwater drag reduction induced by slippage at the water-solid interface. A superhydrophobic surface can entrap gas in surface structures at the water-solid interface. However, many experimental results have exhibited that the entrapped gas can disappear...

Disc specimens manufactured from commercial bearing rollers (AISI 52100 steel, 62?63 HRC) in initial state and after pre-treatment by pulsed magnetic field (PMF) with a magnetic field strength of 1?7 MA/m were tested with sunflower oil using pin-on-disk apparatus. According to the obtained results the treatment causes a reduction in the coefficient of friction and wear. To explain the results, nano- and microhardness tests as well as optical and atomic force microscopy were used. Reasons of t...

The platinum/ruthenium/nitrogen doped diamond-like carbon (PtRuN-DLC) thin films were deposited on Si substrates via DC magnetron sputtering by varying negative substrate bias. The tribological performance of the PtRuN-DLC films was systematically investigated using ball-on-disc microtribological test. The Raman results showed that the increased negative substrate bias significantly increased the number of sp³ bonds in the PtRuN-DLC films as a result of the increased kinetic energi...

The engraving process of a projectile rotating band is one of the most basic research aspects in interior ballistics, which has not been thoroughly understood thus far. An understanding of this process is of great importance from the viewpoints of optimal design, manufacturing, use, and maintenance of gun and projectile. In this paper, the interaction of copper and nylon rotating bands with a CrNiMo gun barrel during engraving was studied under quasi-static and dynamic loading conditions. The...

Three kinds of new conductive lubricating greases were prepared using lithium ionic liquids as the base oil and the polytetrafluoroethylene (PTFE) as the thickener. These lithium ionic liquids ([Li(PEG)X]) were obtained by blending lithium salts (LiBF₄, LiPF₆ and LiNTf₂) with poly(ethylene glycol) (PEG) because lithium salts have an extremely high solubility in PEG. The conductivities and contact resistances of the prepared lubricating greases were investigate...

A study was done to determine the effect of best stacking sequence (position and orientation) on the mechanical properties, friction and wear response of hybrid composites. The main purpose of the study was to determine the best available stacking sequence for which the physical, mechanical and three body abrasive wear rate is optimum. Test for mechanical properties (tensile strength, flexural strength, inter laminar shear strength, impact strength and hardness) was done on glass-carbon hybri...

The availability of high-strength fabrics and progress in the development of large-scale inflatable technology made possible the creation of temporary and quickly deployable structures for protection of underground infrastructure. Inflatable structures are relatively lightweight and portable, and can maintain the required rigidity while in operation. These benefits have prompted the development of inflatable structures for use in confined spaces, such as tunnels and large-diameter pipes to ac...