Han Zhiwu

Erosion resistance of bionic functional surfaces inspired from desert scorpions.

In this paper, a bionic method is presented to improve the erosion resistance of machine components. Desert scorpion (Androctonus australis) is a typical animal living in sandy deserts, and may face erosive action of blowing sand at a high speed. Based on the idea of bionics and biologic experimental techniques, the mechanisms of the sand erosion resistance of desert scorpion were investigated. Results showed that the desert scorpions used special microtextures such as bumps and grooves to construct the functional surfaces to achieve the erosion resistance. In order to understand the erosion resistance mechanisms of such functional surfaces, the combination of computational and experimental research were carried out in this paper. The Computational Fluid Dynamics (CFD) method was applied to predict the erosion performance of the bionic functional surfaces. The result demonstrated that the microtextured surfaces exhibited better erosion resistance than the smooth surfaces. The further erosion tests indicated that the groove surfaces exhibited better erosion performance at 30° injection angle. In order to determine the effect of the groove dimensions on the erosion resistance, regression analysis of orthogonal multinomials was also performed under a certain erosion condition, and the regression equation between the erosion rate and groove distance, width, and height was established.

Investigation of Micro-wear and Micro-friction Properties for Bionic Non-smooth Concave Components

Five kinds of 45# steel samples with concave features on the surface were manufactured using Laser Texturing Technology (LTT). Optimum design theory was used to design the experiment, and a two-level orthogonal table — L16 (215) design was adopted. Micro-wear and micro-friction experienced by samples with concave surface features and samples with smooth surfaces were compared experimentally. The wear resistance of samples with concave surface features was increased most, and different surface morphologies had different effects on friction and wear properties.

Bionic function surface inspired by thepreventing moisture property mechanism of Ephemera pictiventris mcLachlan compound eyes

The fogging phenomenon affects light transmittance on the surface of a transparent substrate, and what’s more, the substrate surface will therefore become wet, which leads to some secondary problems such as corrosion and deterioration etc. There are two ways to solve the antifogging problem. One is hydrophilic and the other is hydrophobic. However, hydrophilic antifogging method cannot change the “wet” nature. The anti-moisture function on Ephemera pictiventris mcLachlan compound eyes surface was studied in this paper, and the compound eyes structure was characterized via Scanning Electron Microscope (SEM) and Laser Scanning Confocal Microscope (LSCM). Then anti-moisture mechanism was explained by Cassie model based on above structure data. Next artificial Ephemera pictiventris mcLachlan compound eyes surfaces were prepared by direct three-beam Laser Interference Lithography (LIL) and Colloidal Lithography (CL) respectively, and further wettability was also discussed. Results show that the compound eyes surface of Ephemera pictiventris mcLachlan exhibits striking hydrophobic anti-moisture property. The compound eyes are composed of hundreds of micron-scale ommatidia closely arranged on ellipsoidal surface. The morphology of each ommatidium is almost uniform and made up of two parts. The upper part is spherical and the lower is frustum of a cone with the upper spherical diameter of about 20 μ m and the overall height of about 11 μ m. There is no more tiny nanostructure on the ommatidia surface. The morphology and dimension of bionic convex array surface that is artificial compound eyes surface are close to the parameters of true compound eyes surface. The water contact angle (WCA) value of this surface can reach 123°, showing a strong hydrophobic property, after etched 2 min by HF with the concentration of 5%. The mechanism analysis results show that the calculated apparent WCA value is 119.2°, in agreement with the experimental value. Also the apparent WCA value increases with the increase of intrinsic WCA value. The smaller the ratio of ommatidia radius, the greater the apparent WCA value. When the ratio is less than or equal to 0.4, the apparent WCA value is up to 150° or more. The static WCA value and water sliding angle (WSA) value of artificial optimized Ephemera pictiventris mcLachlan compound eyes surface with the feature size of 350 nm are 160°±5° and 2°, respectively, showing excellent superhydrophobic and self-cleaning functions. The result indicates that Ephemera pictiventris mcLachlan compound eyes is dry-style antifogging function structure surface. The synthesis of proper size, compact arrangement of ommatidia and arc shape of the compound eyes is one of the origins of hydrophobic antifogging function. Artificial optimized compound eyes surface shows excellent superhydrophobic and self-cleaning functions.

Numerical simulation of roll forming for channel section with outer edge

The finite strip method in structural analysis has been extended, and elastic-plastic large deformation spline finite strip method based on the Updated-Lagrange method (U. L. method) was established to simulate roll forming process of channel section with outer edge. The deformation characteristics of strip was analyzed, and the three-dimensional displacement field, strain field and stress field of deformed strip were got. The calculation example proves that the peak transverse pressing membrane strain is on the corner part of the deformed strip, and the peak longitudinal stretching strain is on the outer edge part of the deformed strip in front of rolls. In addition, the transverse deformation of the deformed strip is principal, and the longitudinal deformation is small.