Advanced Materials Research Vols. 299-300

Abstract: To ensure the carrying safety and long-term durability of nuclear waste, using orthogonal mix proportion design and incorporating steel, polypropylene hybrid fiber, fly ash or steel fiber solely in the concrete, then flexural properties and impermeability tests are carried out respectively in normal temperature and after being heated to 150°C. By the gradation and variance analysis, the quantification of effects which the different kinds of admixtures and their incorporation had toughness and impermeability of concrete had been done: The bond force of steel fiber A which is more longer and with the type of sheared thread and concrete is better, the effect of crack-resistance and toughening is all better when pre-and post heated; As the addition of the fiber mixing amount, the bending property basically present the tendency enhanced for hybrid steel fiber A and B; The factors play a strengthened role in impermeability height of concrete with the increase of fiber’s content, for the order of effect: A> C> D> B. When the time for heating is longer than 17 days, the impermeability of steel fiber concrete SP-10 is stronger than high-strength concrete SP-13, therefore, the hybrid steel fiber (A , B) concrete is fit for container for nuclear waste.

Abstract: Porous Al₂O₃ ceramic/Al₂O₃ ultrafine particle/epoxy new composites were fabricated using the ordered Al₂O₃ porous ceramic as the frame. The effects of three-dimension interpenetrated Al₂O₃ ceramic, load, and sliding velocity on friction coefficient and wear rate of the composites were studied. The results showed the new composites had better wear resistance compared with Al₂O₃ ultrafine particle/epoxy composites. The friction coefficient and wear rate of new composites with the porous Al₂O₃ ceramic frame of 16.8% were 0.32 and 0.76×10^-6 mm³/N^-1m^-1, respectively. The new composites had stable friction coefficient and low wear rate with the change of load and sliding velocity, which is due to the porous Al₂O₃ ceramic frame as undertaker of load during friction process.

Abstract: Polypropylene(PP)/carbon nanotube(CNTs) nanocomposites with different CNTs fraction were prepared by the melting blend method. The effects of CNTs content on the wear properties and mechanical properties were mainly investigated. The results show that the friction coefficient of the nanocomposites decreased as the concentration of CNTs is increased. With increasing CNTs content, tensile strength, ultimate strain, compact strength and Young’s modules increase firstly and then decrease. For the composite with an effective CNTs content of 3 wt, its tensile strength, ultimate strain, compact strength and Young's modules were improved by 72, 44.4,88 and 37 %, respectively, as compared to PP.

Abstract: In this work, the carbon nanotubes(CNTs) were reinforced with polypropylene(PP)matrix resins to improve the electrical and thermal properties of PP/ CNTs composites in different contents of 0,1, 3,and 5 wt.%. The surface, volume resistivity and crystallization type of the composites were investigated. As a result, the maximum degradation rate temperature of the composite is improved 30 °C, the surface resistivity and volume resistivity of composite are 5 ×10⁶, 7 ×10⁵,respectively, for the optimum composition of composite (CNTs 3 wt.%). The integrated XRD pattern of the composites shows the typical α-form PP crystals.

Abstract: Large cross-section composite rectangular steel tubes with ceramics inner liner, which can be used directly, and also cut into the ceramics clad plate, were made by a new effective way. The material type, shape and size parameters of cores were determined and thickness and hardness of the ceramic coating were measured. The bond stress between steel substrate and alumina ceramics were analyzed and the bond modes also were checked. The dimension parameters of hemming plate used in the experiment were determined and the bond strength between the coating and tube substrate in normal and tangential direction was examined. The results show that the ceramics coating surface is glossy, which thickness is among 1.5-3.5 mm, the hardness of alumina ceramics inner liner is above HV1100. Metallurgical bonding between steel substrate and ceramics coating could not come into being and the mechanical bonding with lower bonding force is the mainly joint mode.

Abstract: The large sandwich structure composed of thin-walled aluminum alloy panels, and variable thickness of honeycomb or Polymethacrylimide (PMI) foam core is usually manufactured by pre-bonded forming process, that is pre-forming panels and sandwich core, and then curing adhesive them to be sandwich structure. Welding process of large thin-walled panel causes the panel surface to be irregular and have greater errors relative to the design surface. Simply CNC machining the sandwich core according to the design surface cannot guarantee an exact match sandwich core consistent with the panels. The actual topography of the panels must be scanned. It is proposed that the use of a new hand-held laser scanner, Handyscan to scan large thin-walled curved surface parts, of Geomagic software to handle the acquired point clouds and construct the surface model.

Abstract: Composite sandwich structures are extensively used in the aerospace, wind power, sports equipment, shipbuilding, automotive and train locomotive industries in order to improve structure rigidity and reduce weight. The molding process of sandwich structure using glass cloth and fibre materials as panels has been reported in many literatures. However, few researches are found relative to the molding process of large scale sandwich structure with the characteristics of thin-walled aluminum alloy panels and variable thickness of Polymethacrylimide (PMI) foam cores. This paper describes a preformed molding process that consists of thermoforming foam core blocks, assembling blocks into a whole sandwich core, CNC machining the sandwich core according to surface models of the thin-walled aluminum alloy panels, and finally, bonding and curing panels and sandwich cores.

Abstract: To develop a high density brake pad for low duty application, a P/M route based on ‘Hot Powder Preform Forging’ was developed, which is not possible by sintering route. The mechanical properties of these materials were characterized using ASTM standards. The limitations of the conventional technique i.e. Compacting and Sintering for the manufacture of brake pads were tried to remove by adopting this technology. It offers better opportunity for pore free materials with better bonding between metallic and non-metallic constituents. Fade and Recovery test were done by using a Krauss Tester. μ_fade , μ_recovery and μ_performance lie within the range of friction materials used for low duty applications.

Abstract: Nanocrystalline CuCr50 alloys were fabricated by means of mechanical alloying and spark plasma sintering. The influence of milling time on the as-milled powders and properties of sintered compacts were investigated. The results show that crystallite size of powders decreases gradually with increase of milling time, while the micro-strain increases firstly then decreases correspondingly. The crystallite size is 22 nm at milling 100h.The micro-hardness of the compacts improves greatly with the increase of milling time, reaching 363HV at 150h which is about 3 times as high as that of the industrial standard (120HV), while the electrical conductivity improves gradually decline. The bulk nanocrystalline CuCr50 alloys sintered at 900^°C for 5min exhibit high relative density of 96% and uniform microstructure: nanoparticles Cr with size of about 120nm are uniformly dispersed in the matrix.

Abstract: Considering the very large direct starting current of three-phase asynchronous motor, this paper presents a design method of asynchronous motor soft starter based on a intelligent control- fuzzy adaptive PID control. The simulation model of the soft starting control system is established with the power system blockset in MATLAB/SIMULINK software. The simulation results show that the fuzzy adaptive PID control method can effectively limit the motor starting current and it is better than the control effect of traditional PID control. Therefore, the fuzzy adaptive PID control scheme presented in this paper is correct and feasible.