Advanced Materials Research Vols. 189-193

Abstract: The two-dimensional thermoelastic sliding frictional contact of the functionally graded materials (FGMs) coated half-plane under plain strain-state deformation is investigated in this paper. A rigid cylindrical punch is sliding over the surface of the FGM coating with the constant velocity, which is small compared with the Rayleigh wave velocity of the medium. Frictional heating is generated at the interface between the punch and FGM coating with its value proportional to contact pressure, friction coefficient and sliding velocity. The material properties of the coating change exponentially along the thickness direction. It is assumed that the area outside the contact region is both thermally insulated and traction-free. The Fourier integral transform method is employed to convert the problem into the Cauchy singular integral equations, which is then solved numerically to obtain the unknown contact pressure and the in-plane component of the surface stress. The effects of the gradient index, Peclet number, and friction coefficient on the thermoelastic contact characteristics are discussed in detail. Numerical results show that the change of the gradient index, Peclet number and friction coefficient can influence the distributions of the surface contact stress.

Abstract: The stress and motion state of droplet in MIG welding with alternating longitudinal magnetic field were analyzed, and the impact of alternating longitudinal magnetic field on the droplet transfer were studied by high-speed video camera. The results show that the droplet is spherical approximately and transfer to molten pool along the welding wire axis without external longitudinal magnetic field. When alternating longitudinal magnetic field was introduced into welding process, the droplet rotate around the welding wire clockwise and counter-clockwise alternately. Shape of droplet became flat and direction of transfer deviated from the welding wire axis under the action of magnetic field. As the exciting current increased, extent of deviation from the wire axis increases. When the exciting current is too large (I >20A), extent of deviation is too large and droplet are disintegrated into several small droplet during the transition. So droplet can not transfer into molten pool successfully and the bead can’t be formed.

Abstract: Operating principle and motion characteristics of an eccentric crank slide-block mechanism are analyzed. A virtual prototype model of the eccentric crank slide-block mechanism is set up based on ADAMS,a simulation software. The kinematics analysis of the eccentric crank slide-block mechanism,it is given.Under the premise of meeting the requirements of slide stroke and travel velocity-ratio coefficient, based on ADAMS, each component size of the eccentric crank slide-block mechanism with best pressure angle (α max ) min can be easily obtained. The equations and the calculations can be used in engineering practice.

Abstract: In a solution containing 10g/L NaOH and 12g/L phytic acid, anodic coatings were obtained by micro arc oxidation (MAO) on AZ91HP magnesium alloy. The morphology, structure and composition of anodic coatings were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive X-ray (EDX). The corrosion resistance of magnesium alloy before and after MAO treatment was evaluated by immersion test and potentiodynamic polarization testing in 3.5wt. % NaCl solution. The coatings were evenly formed on the substrate and mainly composed of MgO. EDX analyses showed that phytic acid took part in the coating formation. Compared with the substrate, the corrosion resistance of magnesium alloy after MAO treatment was improved considerably.

Abstract: In order to assess the cleaning effect of cleaning cloths for LCD screen according to their properties, several properties indices were extracted, they are flexural rigidity, the height of water transmission, hairiness fall off, electrical surface resistance, dust caught, and so on. Based on the measurement of these properties indices of ten typical microfiber cleaning cloths, an integrated index to evaluate their cleaning effect objectively was obtained by principal component analysis, which shows good agreement with the actual cleaning result of computer screen.

Abstract: A frequent cause of failure of portable and hand-held devices is an accidental drop to the ground. The effect of electromigration on the mechanical properties of solder joints was discussed in this paper. Without current stressing, the samples were broken in the bulk of solder or at the interface of Al interconnect and solder. If the Al-solder interfacial mechanical strength was improved by changed the interfacial structure or optimized the jointing process, the flip chip devices would show the lonely ductile fracture in the bulk of solder. After electromigration the samples were broken abruptly at the interface near the chip side while the bulk of the solder joints maintained the original shape. Due to the interfacial reaction and the polarity effect of electromigration on the interfaces, a ductile solder joint can become a brittle solder joint. The ductile-to-brittle transition is very sensitive to a high speed shear stress applied to the joints. Because solder alloys are ductile by nature, it is of interest to understand how electromigration can influence the mechanical properties of solder joints’ interfaces and change their ductile nature. Owing to the polarity effect of electromigration, vacancies will accumulate to form voids at the cathode interface of solder joints. Besides, much more intermetallic compound formation at the joint interfaces also caused the ductile-to-brittle transition. Thus the interfaces become more and more brittle with time due to IMC formation or vacancy accumulation from electromigration.

Abstract: A new technology for manufacturing large area coating, named explosive compaction- coating (ECC), was proposed in this paper, and its concrete process was described in detail. The ECC for Cu plate- Cu powder was experimented, by variety height of burst and heat treatment of Cu plate four groups divided into, and uniform coating thickness beyond 300 um was obtained. Research shows that the optimal impact velocity is 900 m/s. Annealing treatment of Cu plate has not impact on coating. ECC can manufacture large area metal or nonmetal coating and nano or amorphous coating.

Abstract: Superfine coatings have been attempted to prepare by Electro-spark deposition (ESD) on cast steel substrate. The microstructures and properties of the coating were investigated by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and microhardness tester. The results show that ultra-fine particles prevail in the coating. The primary phases of the coating contain Fe₃W₃C, Co₃W₃C, Si₂W and W₂C. Its average microhardness reaches 1511.75 HV. The results of abrasive test demonstrated that the coating had an excellent sliding wear resistance because the superfine particles distributed dispersedly in the coating increased the resistance to micro-cutting and plowing during the wear test, which effectively improves the surface performance of cast steel substrate.

Abstract: Iron oxide red is one of the important iron oxide pigments. Domestic iron oxide red will be shading and darkening when calcination temperature is above 800°C. In addition to it possess strong absorption of ultraviolet and can not be resistant to strong acids. In order to improve the above disadvantages, the α-Fe₂O₃/SiO₂ core–shell particles were synthesized with hydrolysis of sodium silicate as silica source by the way of heterogeneous phase coring precipitation in the Fe₂O₃ suspending liquid. The surface structure of these composite particles was characterized by means of IR, XRD and TG-DTA. The heat resistance, acid resistance and anti-UV absorption capacity of Fe₂O₃ particles before and after modification were analyzed via X-rite color difference meter and Ultraviolet Spectrometer. Results showed that the heat resistance, acid resistance and anti-UV absorption capacity are improved significantly because of SiO₂ coat.

Abstract: The changeable, atrocious environment of stratosphere affects the capability and performance of the structure. An effective and economical approach used to analyze thermal state of stratospheric aerostat was investigated in this study. A simplified thermal model was built in environmental experiment which simulates stratosphere and takes radiation of the sun, air and earth. This model solved a coupling problem of heat conduction, heat convection and radiant heat transfer and obtained a pleasant result through numerical simulations of Fluent. The whole process makes great effect to further analysis and study of stratospheric structure.