Papers by Author: Zhi Wu Han

Abstract: Sand erosion is a phenomenon that solid particles impinging to a wall cause serious mechanical damages to its surface. It's tough to be a machine in the desert: particles of dirt and sand work their way into moving parts, where they abrade helicopter propellers, airplane rotor blades, pipes and other equipments. However, the desert scorpion (Androctonus australis) live their entire lives subjected to blowing sand, yet they never appear to be eroded. In this study, the anti–erosion characteristic rules of the scorpion surfaces under aerodynamics effect of gas/solid mixed media were studied. Biomimetic linear–cutted surfaces consisting of an array of three types of grooves, square–type, V–type and U–type, were designed and investigated to quantify their erosion wear resistance properties. A smooth surface sample was fabricated for comparison. The ANSYS-Fluent simulation of biomimetic models showed that the V-type groove sample, inspired by the desert organism's surface with different morphologies, exhibited the best erosion resistance. It also indicated the anti-erosion property of biomimetic samples could be attributed to the rotating flow in the grooves that reduces the impact speed of particles. The synchronized erosion test confirmed the conclusions. Furthermore, an application exploring of bionic blades on a centrifugal fan was conducted. The blades with optimum parameters could effectively improve anti-erosion property by 29%. We envision that more opportunities for biomimetic application in improving the anti–erosion performance of parts that work under dirt and sand particle environment will be proposed.

Abstract: CSCNT is a new type carbon nanotube, which has better physical and mechanical properties than the traditional materials. In this study, the effect of the dispersion and concentration of cup-stacked carbon nanotubes on mechanical properties of the CSCNTs/epoxy nanocomposites were investigated. The epoxy resin system used in this study was a two component (resin and harder) Prime 20. The CSCNTs were dispersed into the Prime 20 by ultrasonic agitation and mechanical mixing together. And the morphologies of the fracture surface of CSCNTs/Prime 20 nanocomposites were observed by scanning electron microscope (SEM); damping behaviors of the nanocomposites were studied by DMA at frequency domain.

Abstract: Commercially available magnesium alloy is extensively used in structural engineering components although, like many magnesium-based materials, it suffers from poor corrosion resistance, particularly in moist environments, which limit wider application. Previously, by reducing the contact area of metal substrate with surrounding water environment and decreasing the risk of corrosion is shown to improve the corrosion resistance of magnesium alloy in humid environments and in the presence of chloride-containing aqueous environments. The objective of this study, without the low-surface-energy materials modification, is to fabricate the superhydrophobic surfaces by wet-chemical methods and to understand how the microstructure influences the surface wettability of unstable materials such as magnesium alloy. The influence of the variety of experiment conditions on the wettability of the substrates was investigated by a contact angle goniometry with water as a probe liquid. Scanning electron microscopy and energy dispersive spectroscopy were used to study the surface chemistry and microstructure at various stages of the multi-wet-chemical process.

Abstract: The metal and nano-ceramic nanocomposite coatings were prepared on gray cast iron surface by electrodepositon. The nickel and cobalt were used as metal matrix of coating, and the nano-Al2O3 was chosen as second-phase particulates, which had good chemical stability, high microhardness and good wear resistance. The morphology of composite coatings was flatter and microstructure was denser than pure nickel and cobalt coatings. The composite coatings were fabricated by different dispersion methods such as high speed mechanical stir, ultrasonic vibration and ultrasonic vibration together with mechanical stir. The result indicated the nano-Al2O3/Ni+Co composite coating with fine and compact microstructure are obtained compared with pure Ni-Co coating. The nanoparticles were dispersion evenly when dispersion style was ultrasonic vibration together with mechanical stir according to composite coatings SEM images of different dispersion style. The concentration of nanoparticulates reached a maximum value when the dispersion style was ultrasonic vibration together with mechanical stir, at the same time the mechanical property such as microhardness reached a maximum value also. The reason was that nano-Al2O3 caused dispersive strengthening and grain refining.

Abstract: Carbon nanotubes have better physical and mechanical behaviors than the traditional materials, in this study cups-stacked carbon nanotubes (CSCNTs) were filled into epoxy nancomposites to fabricate CSCNTs/epoxy nanocomposites. RTM6 was used by epoxy resin system. The cups-stacked carbon nanotubes (CSCNTs) were dispersed into the RTM6 matrix. In this study, damping properties of the CSCNTs/RTM6 were measured; effect of different weight percentages of the CSCNTs was investigated. And the morphologies of fracture surface of CSCNTs/epoxy nanocomposites were observed by scanning electron microscope (SEM); damping behaviors of the nanocomposites were studied by DMA tester at frequency domain.

Abstract: Biologically structural colors have been attracting more and more researcher’s attention and many bionics theoretical achievements of this kind may be used for surface decorating and product anti-counterfeiting. But further application has been restricted for the bottleneck problem in specimen manufacture, because of the complexity and nano-dimention of the biological structure. In this work, based on the optimized structure parameters of butterfly scales which have structural color, the specimen was manufactured using the ‘two-photon polymerization method’. Using a femto-second laser system and the photoreswast SU8 of polymer monosomic material, specimen of bionic structural color were prepared. The sample was 30×30μm. The manufacture parameters included that the laser intensity was 5.5-7mw, the distance of the adjacent points was 100nm, the exposure time was 0.6ms, and the numerical aperture of the objective lens was 1.4. The optical effects of the replication structure had been calculated with 1D photonic ‘crystal band gap’ theory. The results of the calculation showed a great consistency with natural butterfly structural color. This work is a meaningful exploration for replication of butterfly or other bionic specimens.