Applied Mechanics and Materials Vol. 461

Abstract: A new type of biomimetic films of bilayer lipid membrane (BLM) supported by conductive hybrid film of Au nanoparticles (Au NPs) and cellulose is developed. The facile preparation method of the conductive hybrid films and the relevant micro conducting mechanism under electrochemical redox environment are revealed. The regenerated cellulose film is prepared from the cellulose/N-methylmorpholine N-oxide monohydrate solution. After the cellulose film is regenerated by deionized water, Au NPs in the colloid react with the newborn cellulose film. Rectangular pieces of dry hybrid films with one ends clamped with copper foil are used as electrodes. The lipid solution of phospholipid and cholesterol with a ratio of 3:1 is brushed onto the surface of dry hybrid films. There are only reducing currents in the cyclic voltammetry responses of biomimetic films under the aqueous electrolyte solution of 0.1 mol/L KCl, 1 mmol/L K₃[Fe (CN)₆] and 1 mmol/L K₄[Fe (CN)₆]. It means that the anions of [Fe (CN)₆]^4- are almost impossible to be oxidized into [Fe (CN)₆]^3- by the positively charged surfaces of Au NPs under voltages below 0.3 V.

Abstract: Vertically aligned carbon nanotubes (VACNT) arrays were designed to mimic natural foot-hairs of geckos in order to elucidate the adhesion mechanism. We fabricated and systematically investigated adhesive properties of the VACNT arrays with different top structures. Balancing the gas ratio and pressure used for low pressure chemical vapor deposition (CVD) processing controls the top structures of VACNT arrays which determine the strength of adhesion. Their contact behaviors were observed using a scanning electron microscope (SEM). The VACNT arrays attached the target surface by different contact behavior based on the different top structures. The different contact behavior varied adhesive properties of VACNT arrays. VACNT arrays with free top structure present higher adhesion strength due to the side contact with target surface, which indicated that the top structure is an important factor enabling generation of a strong adhesion. These results present clear implications for the role of top structures in VACNT arrays based synthetic gecko systems, which is important for fabrication of gecko-inspired dry adhesives.

Abstract: Friction material is essential for automotive braking system. Based on previous study of existing friction material problems, hybrid biological fiber-reinforced resin-based friction materials (HBRMs, from the reinforced fiber component of resin-based friction materials) were explored in this study. Bamboo fiber, jute fiber and wool fiber (all have length of 3-5 mm) were processed to make three types of HBRMs and considered as three factors of biological reinforced fiber in test using orthogonal experimental design. Each factor had three levels of 1%, 2% and 3% fiber mass fraction while the ratio of other raw materials remains unchanged. According to the orthogonal experimental design table, nine formulations (denoted as M1-M9) were determined to test the HBRMs. For comparison, non-bio-fiber reinforced friction material (NBM) was added in the test. The properties of the HBRMs tested included Rockwell hardness, impact strength and density. The friction and wear performance of the braking materials was examined by a speed friction tester. The results show that the friction coefficient of the HBRMs was slightly higher than that of the NBM, indicating biological fibers affected the friction coefficient. The friction coefficient of the HBRMs decreased firstly with the increase of temperature and had the lowest value when the temperature reached 300°C, and it increased then as temperature increased. During recovery process, the friction coefficient of the HBRMs firstly increased with the decrease of temperature and then decreased greatly when the temperature dropped to 100°C. The wear rates of the HBRMs increased with the increase of temperature and reached maximum value when temperature reached 200°C, then it decreased with the increase of temperature. The results of fuzzy comprehensive evaluation analysis on the friction coefficient and wear rate show that the best comprehensive properties were presented when the mass fraction of bamboo, jute and wool fiber were 3%, 3% and 1%，respectively.

Abstract: This paper deals with imitating a novel type of biomimetic integrated composite with porous core layer from the beetle elytra microstructures. Firstly,the microstructures of the elytron of Anoplophora Glabripennis, Anomala Corpulenta Motschulsky, Prosopocoilus Inclinatus and Melolonthidae were examined with SEM. Inspired by these structure characteristics, a biomimetic composite model was proposed, in which the two face layers were interconnected with a porous core layer, and there are continuous fibers embedded into these three layers to enhance mechanical performance of the laminated composite. Then a specimen of this laminated composite with porous core layer was made. The procedures include: weaving a piece of two layers space fabric by glass fibers as the preform of the composite,filling the mixed resin which contained 50% granular paraffin wax and 50% epoxy resin into the space of the fabric, putting it into a flat mold, keeping 36 hours, and finally heating the composite to remove the paraffin wax to form the porous core layer. The experiment showed that the model of integrated porous core laminated composite inspired by the beetle elytra structure is reasonable and this novel type of lightweight composite material was manufacturable.

Abstract: A macromoleclar polymer (Sulfonated polystyrene - Polyhydromethylsilane, SPS-PMHS) was synthesized from polystyrene by sulfonation, acylation, amination and hydrosilylation. Characterization of the hydrosilylation process was performed with attenuated total reflectance-fourier transform infrared (ATR-FTIR) spectroscopy. The SPS-PMHS was homogeneously dispersed in the Nafion matrix with doping level of 33.3 wt %. Experimental results show that the yield tip-displacement values of the polymer nanocomposite have not been enhanced, but the nonaqueous working time is 2.7 times higher than that of the virgin nafion.

Abstract: This paper experimentally investigated the friction, wear performance, density, hardness and impact performance of pelletizing friction material. The research was used partly granulation process for prepare friction material. Experiments showed that: When the proportion of partly granulation friction material and powder was mixed with 2:1, the friction coefficient was better, which compared to 1:1 and 1:2. The friction coefficient of partly granulation friction material was higher than the powder friction material, and it also increase along with the temperature rise. The best friction material was made by diameter particle mixed the powder with 2:1, of which particle in diameter of 1-10mm. Without the particle diameter of 1-3mm, the friction material wear rate was lower than when the other diameter levels particle and powder were mixed with 2:1. The wear rate of the partly granulated friction material reduced by 10.9-39.47%, which compared to ungranulated friction material. Furthermore, the friction material that was the mixture of powder and particles, the impact strength will decrease following the increasing proportion. At the same range, the impact strength was relatively large when the particles and the powder was mixed with 1:2. The minimum impact strength was 0.0984J cm2 which the particle diameter was 8-10mm and the ratio was 2:1. The friction material density first increased and then decreased as the particle size increasing. The density whose granules and powders ratio was 1:2 was greater than the density between 1:1 and 2:1 at the same level. The minimum density,which occured in 8-10mm particle friction material, was 1.101659 g/cm3. The hardness of part of the granulated friction material increases as the particles size increases, but the range is limited. The hardness value is 102HRR of the maximum hardness of the friction material, which made with 8-10mms diameter particle and powder that ratio was 2:1, The minimum hardness is 80HRR. The friction material formed by mixing particles and the powder occurred rough surface and obvious porosity and a crack after the abrasion test. When the ration was 1:1 and 1:2, the surface scratched obviously, emerged cutting and furrows. The results showed that when Granules and powder mixed with 2:1, the worn surface of the sample is relatively flat. It also showed the main wear form of the friction material was abrasive wear and fatigue wear.

Abstract: The friction materials have many species and they are being used widely, but people have higher requests to friction materials along with the development of technology. the friction material of this expermental optimization formula have the advantages of suitable and stable friction coefficient under high temperature, low wear rate, good restoration characteristics and so on. It can effcetively reduce heat fade of friction and wear under high temperature barking. fricton and wear performance of friction material with second adhesive is better than common preparation friction material , it has higher friction coefficient and lower wear rate, It was determined by physical chemical properities of tin and sulfer. while heating or wearing, the temperature of friction material reach melting temperature of tin, it will become molten state, and sulfer has strong oxidation, on the one hand, tin and sulfer occurred chemical reaction, generating sulfide, stannous (one sulfide tin),on the other hand, while the sulfer is being molten state, it will absorb some abrasive dust, at the same time of generating sulfide, abrasive dust will be adsorb and solidify to pits of friction surface, forming abrasive dust membrane, let the friction coefficient of sample become stable rapidly, reducing the wear rate of friction material.

Abstract: In order to improve the thermal performance and wear resistance of the polymer, foamed copper filled by the curable epoxy-matrix composite are developed as tribological materials. Graphite and multi-walled carbon nanotubes (MWCNTs) were incorporated the contents as friction additives. The tribological properties of the foamed-copper reinforced composites were investigated on an UMT-2 friction and wear tester. An electric field was imposed between the specimen and disc to monitor the formation of transfer film by means of contact resistance. It is found that the foamed-copper reinforced composites possess better wear resistance than homologous polymers, and the smaller is the aperture, the better the wear resistance. While the friction coefficients increase for the local direct contact between the copper and the steel disc. The copper skeletons contribute to the timely transfer of friction heat and the load-sharing. The foamed-copper unit was modeled from the foaming mechanism of the polyurethane foam. Two parameters of the surface area density of foamed copper and the area ratio of copper at the friction interface were quantized based on two kinds of typical contact models. The modeling analysis can lead to a better understand the influence of metallic skeletons on the wear performance of composite.

Abstract: The structure of corn stubble was complex and closely combined with the soil, so dig location and root-soil separation are the urgent problem of the manufacturing of corn stubble harvesting machinery. This paper mainly focuses on investigating the interaction principles of corn stubble and soil which by the UU triaxial compression tests. Compared the shear strength of three different types of corn root-soil complexes (vertical root, horizontal root, complex root) and pure soil, and analyzed three important factors affecting the root-soil complex shear strength, it was shown that the presence of corn fibrous root can enhance the soil shear strength and different with their layout types. It will provide a theoretical basis for the design of bionic agricultural tillage components for root- soil separation.

Abstract: Abstract. One of the most effective means to treat electromagnetic pollution is to develop electromagnetic interference shielding materials. Such as Foam nickel, a new lightweight porous material with large surface area, good conductivity and permeability, has drawn much expectation by virtue of its excellent electromagnetic interference shielding(EMI) performance. Recently, with the development of nanometer materials, Tremendous researches also showed that it is an efficient way to combine Foam Ni with nanometer materials for enhanced EMI performance. Herein, in this work, porous nickl/carbon nanotubes(CNT) composites were successfully prepared by a facile electrophoretic deposition method. scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and EMI tests were adopted to carefully characterize its morphology, compositions and EMI performance, respectively. The results indicated that CNT were homogeneously and tightly deposited on the surface of foam Ni by electric field force during the electrophoresis process. With the addition of CNT, the shielding behavior of the 90 PPI and 1.5 mm thick composite could be as high as 31dB in average, which is 14 dB increased compared with the pure foam Ni under same conditions around 8~12GHz frequencies. The synergistic effects of both foam Ni and CNT resulted in superior EMI performance and broad application prospects.