Based on interfacial convection in the presence of solvent evaporation, a novel method for the fabrication of a micro-structured surface is proposed to facilitate drag reduction. A mixture was coated on a substrate through a specially developed spray-painting system. Micron scale pits formed spontaneously in the coated surface because of interfacial convection and deformation driven by the gradient of the interfacial tension. Experimental results indicated that particles in the mixture played a crucial role in pit for-mation, and with a suitable selection of particle size and dosage, the characteristic parameters of the pitting could be controlled. The drag reduction experiments were first performed in a water tunnel, and the results showed that the micro-structured surface had a remarkable drag reduction performance over a great range of flow speeds.
Three-dimensional molecular dynamics simulations have been performed to investigate the effect of a void on the nanoindentation of nickel thin film.The radius and depth of the void are varied to explore how they influence the nanoindentation.The simulation results reveal that the presence of a void softens the material and allows for a larger indentation depth at a given load compared to the no void case.The radius and depth of the void have a major effect on the indentation behaviors of the thin film.It is also observed that the void will collapse during the nanoindentation of crystal with void.And when the indentation depth is sufficiently large,the void will disappear.It is found that the indentation depth needed to make the void disappear depends on the void size and location.
ZHU PengZhe,HU YuanZhong & WANG Hui State Key Laboratory of Tribology,Tsinghua University,Beijing 100084,China
