Applied Mechanics and Materials Vols. 121-126

Abstract: The fatigue parameters of welded joints made of FV520B were obtained considering the real operating situations. The fatigue fracture types were divided into two groups. The scanning electron microscope (SEM) was applied to carefully study the fatigue fracture surfaces so as to investigate the fatigue failure mechanisms. The microstructures of the base metal and the weld seam were studied by the metallographic microscope (MM), SEM and TEM in support of the dissimilar mechanical property analysis. The present paper concluded that the fatigue microcracks mainly initiated from the surface near the weld toe and inclusions in the weld seam, the heat-affected zone (HAZ) disappeared due to the postweld heat-treatment processes, and that the fatigue resistance of the base metal was better than the weld seam.

Abstract: The machining characteristics of SiC/Al composite using wire electro discharge machining (WEDM) were investigated in this study. Material cutting speed and surface roughness value were adopted to evaluate the machinability. Peak current, pulse on time, pulse duration and working voltage were selected as the input variables to investigate the machining performance. Effects of input variables on the cutting speed and surface roughness were experimentally tested. Peak current, pulse on time and working voltage were confirmed to have positive effects on cutting speed and surface roughness value. Whereas the cutting speed and surface roughness value decrease with the increase of pulse duration.

Abstract: In the present study binary Mg-xCa (x=0.5 and 1.25wt.%) and ternary Mg-1Ca-xZn (x=0.5 and 1.5wt.%) alloys are produced by casting the molten metal in a metal die at a temperature of 740°C. The microstructure analysis of the Mg-Ca and Mg-Ca-Zn alloys were studied by OM, SEM and EDX. The corrosion behavior of alloys was evaluated via potentiodynamic polarization test in Kokubo solution. The result exhibited that the grain size decrease with rising Ca content in Mg-Ca alloys and degree of grain size reduction further decreased by adding Zn to Mg-1Ca-Zn alloys. The microstructure of Mg-Ca alloys were constituted of primary Mg and lamellar eutectic (α-Mg+Mg2Ca) phase, Whilst Mg–1Ca-Zn alloys were composed of primary Mg and eutectic (α-Mg+Mg2Ca+Ca2Mg6Zn3) phases. In addition with increasing Ca and Zn the amount of Mg2Ca and Ca2Mg6Zn3 increased respectively in grain boundaries. Electrochemical test shows that the addition of Zn leads to improve corrosion resistance of the Mg–1Ca-Zn alloys as a result of the formation of Ca2Mg6Zn3 phase, whilst the addition of more than 0.5 wt% Ca to Mg-Ca alloys result in decrease corrosion resistance due to the formation Mg2Ca.

Abstract: The application of the alkaline pectinase and sodium percarbonate in the degumming of ramie was studied in this paper. According to the tests such as the fiber fineness, the single fiber tenacity and the fiber surface properties, alkaline pectinase and sodium percarbonate on the properties of degummed ramie fiber was discussed. The results showed that the effect of the degumming of ramie was associated with temperature, concentration of alkaline pectinase, time and pH value. When the temperature is 60°C, the time is 3 hours, the concentration of alkaline pectinase is 3g/L and pH 8.5, the tenacity of fiber is the highest, the fineness is the finest. Due to the application of sodium percarbonate in the inactivation process, the properties of degummed ramie fiber have been further improved and the gum of the fiber surface has been further reduced.

Abstract: This paper studies the modern design methods of hydraulic machinery by the use of Computational Fluid Dynamic (CFD), the design method not only makes up the shortcomings of the traditional design method, but also can be compared on the computer which can save a lot of trial and testing costs in new product development. Form the velocity distribution and pressure distribution of turbine, the example shows, the simulated flow field using CFD software is in agreement with the actual condition and it basically meets the requirements of design.

Abstract: Corrosion is a major concern for the durability of concrete structures under marine environment. In this paper three series of concrete was immerged in sea water to reseaech its development of compressive strength, microstructure and corrsosion production. The results showed that compressive strength of controlled concrete was decreased but it can further increased added fly ash and silicon fume after immerged in sea water. It can be observation by SEM and EDS that a number of complex salt was produced on the surface and AFt was produced inside controlled concrete. It can produce expand and lead to cracks. As result of fly ash and silicon fume added, the crystals of Mg(OH)2 was formed on the surface and no crystal and cracks was produced internal concrete. The compressive strength can still increase after immerged in sea water.

Abstract: The ZnO particles with mesoporous and lamellar structure were synthesized in the method of precipitation, using zinc acetate as precursor. The ZnO particles were characterized by the means of scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and N2 adsorption–desorption measurements. The photoactivity of as-prepared ZnO particles was evaluated by degradation experiment of methyl orange aqueous solution. The results showed the obtained ZnO particles were irregular polygons with lamellar structure, and the particle size was in the range of 50 nm to 300 nm. According to XRD and N2 absorption results, ZnO particles were pure and integrated crystals with high crystallinity, and adsorption-desorption isotherms correspond to the typical type IV isotherm with a hysteresis loop of type H3, which showed ZnO particles had mesoporous structure with slit pore shape. The ZnO particles had high photocatalytic activity, the maximum degradation rate of methyl orange aqueous solution can reach 99%. When reused for the fifth time, the photocatalytic activity of ZnO particles was similar with the fresh ones, and recycled for the tenth time, the degradation rate of methyl orange aqueous solution still standed by 84.7%.

Abstract: The multiphase coatings with major phases Al2O3-AlxCuy were prepared by the reactive flame spray technology. The melting and reactive behavior of the Al-CuO agglomerated particles and the forming process of the coatings were studied by means of water-quenching experiments and the methods of XRD and SEM. It was shown that during the spray distance between 60 and 150 millimeters, CuO in the agglomerated particles was heated to decompose into Cu2O, Cu and O2. During the flying course, a little of Al reacted with Cu2O and produced Al2O3 and Cu. The reduced Cu mutually dissolved with Al and formed liquid Al-Cu alloy. After the spray particles bumped into the substrate, Cu2O reacted with Al richly, then lots of Al2O3 was produced and Cu was reduced at the same time. These products were wallowed up by the liquid Al-Cu alloy soon. When the temperature of the system dropped quickly, the structure transforming process began. The intermetallics of Cu9Al4 and Al2Cu3 were deposited from the liquid Al-Cu alloy via complicated eutectic reaction and eutectoid reaction.

Abstract: Natural ventilation is the most effective measure to reduce the cooling energy consumption, but it is quite difficult to control and quantitatively assess the natural ventilation. A method was developed with coupling simulation by both software of DeST-h and computational fluid dynamics (CFD) in typical meteorological year (TMY) in Guangzhou. First, the base room temperatures with different air change (ACH) rates of natural ventilated dwelling were simulated with DeST-h. The time period in that the indoor air temperature could meet thermal comfort requirement only by natural ventilation in occupied period was analyzed, in which the wind speed and direction in TMY was obtained for the ventilation environment simulation of rooms in windows and doors switching with the PHOENICS software. The actual air change rates in different rooms in such wind speed and direction were calculated. Also the cooling loads of building in the actual air change rates were simulated with intermittent air conditioning. The air conditioning system operated when the base room temperature was higher than 29°C. Rate of cooling loads reduction was calculated by comparing the result to the baseline, which were the cooling loads of building with 1 ACH. The actual air change rates show that the energy saving effect of natural ventilation was influenced by the windows and doors switching. 61~71.37% of the natural ventilation potential was used in the rooms with windows and doors opened, and 14.06~82.54% of the natural ventilation potential was used in the rooms with windows opened and doors closed. The rate of cooling loads reduction in rooms and building were 0.34~10.50% and 6.14% respectively.

Abstract: This paper is focused on the relationship between the motivations for people to actively use air movement and indoor climates, with an aim to determine the preferred levels of air movement for the occupants of naturally ventilated buildings in hot and humid climates in China. Based on 429 questionnaires collected in a background survey, 29 college students were chosen to join in the transverse survey. Totally 247 sets of raw data in 5 weeks were obtained. Primary results show that the main motivation of opening window changed from “fresh air” to “cool room and body” as the summer coming. The proportion of wanting more air movement increased as ET* rose, and the ambient and preferred air velocity increased linearly with ET* too.