Yunhai Ma

Two-Body Abrasive Wear of the Surfaces of Pangolin Scales

The Pangolin, a soil-burrowing animal, is covered with scales. These scales are often abraded by soil and rock and their surface is corrugated. The abrasive wear of the surface of the scales was examined. The scales were taken from a pangolin that had died of natural causes. The tests were run on a rotary disc abrasive wear tester. The abrasive material was quartz sand (96.5 wt.%) and bentonite (3.5 wt.%). The morphology of the abraded surfaces and the abrasion were examined by stereoscopic microscopy and scanning electron microscopy. The concepts are proposed of “Guiding-Effect” and “Rolling-Effect” on the textured surfaces under free abrasive wear conditions and the critical dimensions of the “Rolling-Effect” are discussed.

Nanomechanical Behaviours of Cuticle of Three Kinds of Beetle

The surface materials and structures of insect cuticle can provide useful information for designing anti-adhesion components material. Quantitative measurement of mechanical properties of insect cuticle will help to develop biomimetic materials suitable for industrial products. In this work, the mechanical properties, such as the reduced modulus and hardness in nano-scale, of the cuticle of beetle Geotrupes stercorarius Linnaeus, Copris ochus Motschulsky and Holotrichia sichotana Brenske, were investigated by using a nanoindenter. It was found that the reduce modulus and hardness of these three beetles are different. The main cause of the difference of the mechanical properties is probably due to their different living circumstance, lifestyle and different functions of segments.

Effects of Biomimetic Surface Designs on Furrow Opener Performance

The effects of biomimetic designs of tine furrow opener surface on equivalent pressure and pressure in the direction of motion on opener surface against soil were studied by finite element method (FEM) simulation and the effects of these designs on tool force and power requirements were examined experimentally. Geometrical structures of the cuticle surfaces of dung beetle (Copris ochus Motschulsky) were examined by stereoscopy. The structures of the cuticle surfaces and Ultra High Molecular Weight Polyethylene (UHMWPE) material were modeled on surface of tine furrow opener as biomimetic designs. Seven furrow openers were analyzed in ANSYS program (a FEM simulation software). The biomimetic furrow opener surfaces with UHMWPE structures were found to have lower equivalent pressure and pressure in the direction of motion as compared to the conventional surface and to the biomimetic surfaces with textured steel-35 structures. It was found that the tool force and power were increased with the cutting depth and operating speed and the biomimetic furrow opener with UHMWPE tubular section ridges showed the lowest resistance and power requirement against soil.

DEM Numerical Simulation of Abrasive Wear Characteristics of a Bioinspired Ridged Surface

This paper presents numerical investigations into a ridged surface whose design is inspired by the geometry of a Farrer’s scallop. The objective of the performed research is to assess if the proposed Bioinspired Ridged Surface (BRS) can potentially improve wear resistance of soil-engaging components used in agricultural machinery and to validate numerical simulations performed using software based on the Discrete Element Method (DEM). The wear performance of the BRS is experimentally determined and also compared with a conventional flat surface. Different size of soil particles and relative velocities between the abrasive sand and the testing surfaces are used. Comparative results show that the numerical simulations are in agreement with the experimental results and support the hypothesis that abrasive wear is greatly reduced by substituting a conventional flat surface with the BRS.

Effects of bamboo fibers on friction performance of friction materials

The mechanical properties of bamboo (Phyllostachys heterocycla) fiber were evaluated. The friction and wear performance of the bamboo fiber-reinforced friction materials (BFRFMs) were tested on a constant speed friction tester. The results showed that the friction coefficient of BFRFMs (reinforced with 3 wt.%, 6 wt.% and 9 wt.% bamboo fibers) was higher than those of the non-BFRFM with identical ingredients and process conditions during the temperature increasing procedure. The friction coefficient of 12 wt.% BFRFMs decreased with increasing temperature during temperature increasing procedure, but fluctuation appeared at 200°C and then it decreased again with increasing temperature. The friction coefficients of BFRFMs with 3 wt.% bamboo fiber were higher than that with other bamboo fiber contents. Specific wear rate of BFRFMs increased with the temperature increasing during temperature-increasing procedure, and the wear rates of BFRFM with 3 wt.% fiber were lower than that of others. Morphologies of wear surfaces of friction materials were analyzed using scanning electron microscopy (SEM) and the friction characteristics were discussed. The results showed that carbonized bamboo fiber can reduce the specific wear rate and the noise and provide stable friction coefficient.

Biomimetic Anti-Abrasion Surfaces of a Cone Form Component Against Soil

The geometrical surfaces of soil-burrowing animals were imitated and modeled on a cone component, the measuring tip part of a soil cone penetrometer. These biomimetic surfaces are concave dimples, convex domes and two wavy forms. The conventional cone surface and the biomimetic cone surfaces were analyzed in ANSYS 11.0 program to estimate cone equivalent stress and soil equivalent stress. Results show that biomimetic surfaces with the geometrical structures have lower cone equivalent stresses and soil equivalent stresses than that with conventional (smooth) surface. The least maximum cone equivalent stress and least maximum soil equivalent stress were recorded for biomimetic surfaces with concave dimples and wavy form-2 respectively. The two-body abrasive wear of biomimetic cone surfaces and conventional (smooth) cone surface were run on a rotary disk type of abrasive wear testing machine. The biomimetic cone surfaces were found to have lower abrasive wear than the conventional surface. It was found that and biomimetic cone surface with concave dimples has the lowest abrasive wear among the all tested surfaces.

Tribological and mechanical properties of pine needle fiber reinforced friction composites under dry sliding conditions

Pine needle fibers were pretreated with alkali, and then mixed with other raw materials to fabricate pine needle fiber reinforced friction composites through compression moulding. The effects of pine needle fiber content on the tribological properties of the friction composites were tested using a friction material tester at constant speed. Experimental results showed that the friction coefficient of the pine needle fiber reinforced friction composites was very stable and markedly fade was not obvious compared with specimen FC0 (containing 0 wt% pine needle fibers); the wear rates of the friction composites generally increased with the increase of temperature and were significantly influenced by the test temperature. The wear rate of specimen FC7 (containing 7 wt% of pine needle fibres) was the lowest compared with that of other specimens at each temperature, except for that when the temperatures were about 200 °C. Morphologies of wear surfaces of pine needle fiber reinforced friction composites were observed using scanning electron microscopy (SEM) and the friction characteristics were analyzed. The results showed that the worn surface of specimen FC7 was smoother compared with that of specimen FC0.

Evaluation of Wear Resistance of Friction Materials Prepared by Granulation

The tribological properties of friction materials prepared by hot-pressing pellets of different sizes were experimentally investigated. Friction and wear tests of the specimens were performed and morphological analysis was carried out by investigating images acquired with both scanning electron and confocal laser microscopes. The highest friction coefficient of friction materials was obtained with pellets having 1-5 mm size. The lowest wear rate was obtained with pellets having 8-10 mm size. Specimens processed by mixing pellets of different sizes had the highest density and the lowest roughness and were the least expensive to fabricate. The results show that granulation generally enabled increasing the friction coefficient, decreasing the wear rate, and reducing the number of defects on the surface of friction materials.

Friction and wear behaviour of steel with bionic non-smooth surfaces during sliding

Steels with and without bionic non-smooth surfaces were prepared and then their friction and wear properties under dry/lubricant wear conditions were evaluated. The average friction coefficients of the specimens with non-smooth surfaces were relatively low under dry wear condition. Moreover, the specimens with or without bionic non-smooth surfaces had lower friction coefficients under the load of 200 N compared with the load of 300 N. The worn morphologies of the specimens after the friction tests were observed using the scanning electron microscope for analysing the worn characteristics. The energy-dispersive spectrometer) was implemented to analyse the wear mechanism. The results showed that the bionic surfaces of testing samples had better wear resistance and provided stable friction coefficient to some extent.

Investigation of the Potential and Mechanism of Clove for Mitigating Airborne Particulate Matter Emission from Stationary Sources

Vegetative Barriers (VB) have the potential to mitigate air pollutants emitted from area sources, including concentrated Animal Feeding Operations (AFOs). However, the mechanism has not been fully investigated, thereby limiting the application of vegetation systems in practice. An experimental method with repeatable and controllable conditions was developed to measure the change of Particulate Matter (PM) concentrations at upwind and downwind of VB in the wind tunnel and observe accumulated PM on leaves with Scanning Electron Microscope (SEM), thus evaluating the ability of VB in mitigating PM emitted from AFOs. Branch-scale vegetation, clove (syzygium aromaticum) was selected because its leaves are one of the major factors affecting PM dispersion. The results show that the branch-scale barriers, as porous medium have the ability to interfere with airflow and reduce PM, which could be influenced by wind speed, particle size fraction and surface area density of clove. Moreover, clove elements could adjust to the wind and the micro structure of clove (such as the hierarchical structures of leaves) affected on the PM deposition. These results indicate that the methods developed in this study may be used to evaluate the potential of vegetation in mitigating PM from stationary sources, and some characteristics of vegetation can be further studied as bionic prototype for exploring engineering application of reducing particulates.