Applied Mechanics and Materials Vols. 752-753

Abstract: N-octadecyltrichlorosilane [OTS, CH₃(CH₂)₁₇SiC_l3] self-assembled monolayer (SAM) coatings were deposited on Si micromolds by dip-coating. Chemical composition, surface roughness, friction coefficient, thermal stability and surface energy of coatings were investigated. OTS coated silicon (Si) micromolds were used to fabricate PMMA microfluidic devices by hot-embossed process. All OTS coatings were thermally stable up to 180 °C, which is higher than hot-embossing temperature of PMMA. OTS coated micromolds had low friction coefficient, adhesion and superior molding efficiency, which improved lifetime of a uncoated Si micromold from 3 to 27 times.

Abstract: Graphene film on silicon carbide is considered to be promising material for high-frequency vacuum nanoelectronics. However, the possibility of graphene application in this area is still poorly understood. We have carried out the simulation of the electric field distribution in interelectrode gap of the anode-cathode system pointed field emission cathode based on silicon carbide with graphene film on its surface subject to the rounding-off radius of the top, interelectrode gap, height and cathode forming half-angle of the cone opening by the finite element method. The influence of constructional parameters on the electric field strength in the test structure was analyzed. It is shown that the values of rounding-off radius of the cone point and interelectrode distance has the biggest influence on the electric field in the investigated structure. Changing of the height and cathode forming half-angle of the cone opening does not lead to a significant increase or decrease of the electric field value.

Abstract: During the last years the carmakers interest is focused on polymer manufacturers to develop breakthrough solutions addressing the key drivers of reducing weight and cost. The use of polypropylene (PP) and other thermoplastic olefins is growing because of their low cost and good properties. Unfortunately, some of the same properties that make these plastics attractive to designers, also make them difficult to bond with adhesives or varnish. Non-polar character of PP results in poor surface properties and low wettability. Several methods of surface pretreatments have been used to improve its wettability, but all involves cost extending additional processing. Based on lessons from nature, one of the ways how to increase wettability is surface structuring. Injection mold insert designing and manufacturing process inspired by hydrophilic structure of the moss is presented. Due to cost reducing demands were used conventional processing methods.

Abstract: It is proposed to use for synthesis of superhard and fracture tough nanocomposite coatings on dielectric products with deep cavities a source of metal atoms accompanied by pulsed beams of high-energy neutral gas molecules. Slow and fast particles are produced by one and the same plasma emitter of ions and trajectories of their movement from a common emissive grid to the product surface coincide.

Abstract: Injection is one of the most commonly used methods for delivering drugs or vaccines into human bodies. It is rapid, low-cost and compatible with almost any drugs. However, the major drawbacks of the injection by hypodermic needles are the pain associated with the injection and the disposal of used needles. Microneedles have then received wide attention since they can overcome such drawbacks, especially dissolving microneedles. Recently, silk fibroin has been used to fabricate dissolving silk microneedles for transdermal drug delivery at low temperature. In the fabrication process, the quality of the silk microneedles relies on the solidification of silk fibroin solution. This research aims to study the role of silk fibroin concentration (silk film thickness) in the formation of silk microneedles. In the experiment, silk microneedles were fabricated using various concentrations of silk fibroin solution from 3 to 7% while the volume of the silk fibroin solution was fixed. According to the experimental resuls, it was found that the concentrations of 4-5% were suitable for producing silk microneedles (silk film thickness of 470 μm) while the concentrations of 6-7% caused wrinkles on microneedle patch due to mismatch of upper and lower layers of microneedles. Furthermore, the concentration of 3% had a problem with the demolding step of microneedles since it caused mold damage due to strong adhesion force between microneedles and mold.

Abstract: Fine grained mortar (FGM) offers a new innovative technology binder system. The innovative technique is achieved by using a small maximum grain size of 600μm for the mortars. Most of the previous studies have focused on the FA to be replaced in the FGM. There is still lacking of research of using other pozzolanas in making FGM. This paper presents a study of the strength of FGM with partially replacement of ordinary Portland cement (OPC) with fine fly ash (FA) and ground rice husk ash (RHA). Flexural and compressive strength of FGM were tested. The results show that the use of FA and RHA produces FGM with improved strength with the replacement up to 20% than that of the control FGM. The use of FA and RHA is very effective in enhancing strength at the later age of FGM.

Abstract: In the present work, compressive creep characteristics of directionally solidified MAS-YAG (MgAl₂O₄/Y₃Al₅O₁₂) were investigated at high temperature. The compressive creep strength of a crystal grown at a rate of 5 mm/min and a flow rate of 1.2 mm/min at 1500 °C under a strain rate of 1.0 × 10^-4 was only 400 MPa, which is slightly higher than that of crystals grown under different conditions. The compressive creep strength of an oxide eutectic fabricated by the directional solidification method is higher than that of a polycrystalline sintered eutectic with the same composition. The creep behavior at high temperature was studied and the mechanisms of deformation by dislocation motion were revealed by Transmission Electron Microscopy (TEM) observations.

Abstract: Rutting is a common pavement failure in road pavement. Rutting occurs mainly due to several factors including increasing of vehicles numbers, environmental conditions and also due to construction and design errors. As a consequence the service life of asphalt pavement is affected and will be decreased. Various researches reported that using different types of polymers in bitumen modification could be a solution to delay deterioration of asphalt pavement. The main purpose of the study was to investigate the effect of the NPA polymer modifier on the rutting behaviour of the asphalt mixtures through Superpave designed mixtures. . Two different types of dense graded Superpave HMA mix were developed consists of Control mix and nanopolyacrylate (NPA) mix. Results showed that all the mixes passed the Superpave volumetric properties criteria which indicate that these mixtures were good with respect to durability and flexibility. Furthermore there is a significant difference between Control mix and NPA mix in terms of rutting in which rut depth after 8000 passes for Control mix was 5.94 mm while for NPA mix was 2.98 mm. The results of this investigation indicated that the Rutting test result of NPA demonstrates 3% better resistance to rutting than those prepared using Control mix. This is due to the addition of NPA to the bitumen has certainly improved the bitumen properties significantly and hence increase the resistant to rutting of the asphalt mixture. Therefore, it can be concluded that NPA polymer is feasible to be used as asphalt modifier and has potential for improvement in the field of pavement material and construction in future.

Abstract: Dry gas seal is often used as the seal devices in centrifugal compressor and other high-speed rotating equipment, which requires seal gas clean and dry. If there is some liquid in the seal gas, the dry gas seal will rapidly fail. When the seal gas flows through the filters, valves, orifices, seal faces and so on, the gas temperature will decrease resulted from the Joule- Thomson effect. If the gas temperature is lower than the corresponding dew point, there will be liquid condensation in dry gas seal system. Wet air is taken as an example to show how to calculate the pressure and temperature relationship when it is adiabatic expansion. Dew point lines at different conditions are calculated by considering the vapor-liquid equilibrium. Liquid condensation conditions are acquired by comparing expansion lines and dew point lines, and the factors of influencing liquid condensation were analyzed. The results shows that decreasing gas humidity, increasing the gas temperature can effectively reduce the liquid condensation.

Abstract: The effect of silicon (Si) on the stability of heat-resistant ductile iron having ferrite matrix in high temperature was investigated by dilatometric test. Microstructure of heat-resistant ferritic ductile iron consists of ferrite, eutectic carbide at eutectic cell boundaries, precipitated carbide in grain and graphite. Pearlite was found around eutectic carbide in some specimens, however, all pearlite was decomposed by the annealing treatment. As Si content was increased, the number and size of carbide decreased and full ferrite matrix were obtained. The starting temperature of ferrite-austenite transformation and the coefficient of thermal expansion increased with the increase of Si content. The growth of Si 6.0wt% specimen during held at 1,000 ^oC is lower than other specimens, and it is considered that in the case of Si 6.0wt% specimen, the carbon movement is restrained due to the low solubility of carbon in matrix. In the case of annealed specimens, the contraction during ferrite-austenite transformation was not found when heating. This is because the re-distribution of the graphite was happened through the movement of carbon during annealing treatment.