Materials Science Forum Vol. 686

Abstract: In order to get a soft and enclosed vesicle which can endure an instantaneous high temperature and super high pressure the soaking technology of aramid fiber with Room Temperature Vulcanization silicon rubber and liquid polyurethane was studied. Then the performance of the composites was tested. Two kinds of rubber vesicle were made, one with metal valve and another without the valve. Using three-dimension braid method, aramid fiber vesicle was made outside the rubber vesicle. Compression test results of the composite vesicle showed that no-valve rubber vesicle had a good match with the aramid one and endured a very large pressure. It can transfer the liquid pressure from inner vesicle to the outer one, which the aramid fiber has excellent mechanical performance and can endure a very large compression.

Abstract: Driven by the increasing requirements from aircraft producers, aluminium alloy matrix composites with carbon fiber reinforcement have been largely used in the modern industry. The method of traditional preparation of carbon fiber reinforced aluminum matrix composites is not only high cost and complex to produce but also difficult to apply in the civilian. The present paper focuses on exploratory study on the preparation of carbon-fiber- reinforced aluminum composites, the intensifying material is continuous long carbon fiber. In order to avoid any interfacial reactions in the carbon fiber reinforced composites, the carbon fibers were coated with copper. We made The tensile samples were made by using the mould, the tensile properties determined, the strengthening mechanism studied, and the carbon fiber in the matrix observed with the microscope.

Abstract: In order to solve the problems involved in coarse grains, macro and micro porosities initiated by low solidification rate in sand casting, an innovative counter-gravity sand casting process, Casing under Adjustable Pressure with Accelerated Solidification (CAPAS) was put forward in this paper. The hydrodynamics of mold filling for CAPAS is based on Bernoulli's principle. The mold and crucible were placed separately in the upper and lower chambers, with the feed tube connected between them. High-speed jet flow of air made negative pressure in the upper chamber. In this way, pressure differential was created between the two chambers. Thereby the molten metal in the crucible was forced to flow upward smoothly to fill the mold cavity. After mold filling, cold air was introduced into sand mold through aisles that are set within the mold, which results in strong convective heat exchange at the casting/mold interface. So solidification rate of casting increased dramatically. The microstructures of the aluminum castings were compared between CAP (Low pressure sand casting) and CAPAS by optical microscope. The results showed that the microstructure of CAPAS aluminum casting was much finer than that of CAP casting and tensile strength markedly increased.

Abstract: An investigation was conducted to determine the influence of high temperature treatment from 1600°C to 2800°C under stretching stress of 10MPa on PAN-based carbon fiber structure and physical properties. The tensile strength of fibers decreased from 4.5GPa to 2.97GPa with increasing treatment temperature up to 2800°C，while the modulus of fibers increased from 230GPa to 375GPa The texture in the longitudinal surface of fibers through heat treatment was characterized using a scanning electron microscopy. The contours of fiber surface became accidented with gaps becoming deeper as temperature increased. It has been observed that both the crystallite sizes (L_a, L_c) and the degree of preferred orientation increasd, while the crystallite interlayer spacing (d₀₀₂) decreased by X-ray diffraction analysis with increasing heat-treatment temperature. The total porosity of fibers decreased from 21.01% to 15.09% and while the density of fibers increased from 1.720g/cm^-3 to1.886 g/cm^-3 with increasing heat-treatment. In addition, the relationship between mechanical properties and structure of variants was also explored in detail.

Abstract: Catalytic graphitization of polyacrylonitrile-based carbon fiber by doping boric acid was reported in this paper. The microstructure and mechanical properties of polyacrylonitrile-based carbon fibers with and without doping boric acid after heat treatment of 1300°C,1500°C,1800°C, 2100°C,2300°C,2400°Cand 2500°Cwas investigated by X-ray diffraction (XRD) and mechanical testing. The results showed that the tensile modulus of the carbon fibers either boron modified or not, increased obviously with increasing temperatures, and that of the modified carbon fibers was much higher than the unmodified fibers at all temperatures, reaching 404Gpa when the fiber was graphitized at 2500°C. The tensile strength of the modified carbon fibers was lower than the unmodified ones after being graphitized at temperatures below 2300°C, but increased to 2.69 GPa and 2.46 GPa respectively after the fibers were treated at 2300°C and 2500°C, which were higher than that of unmodified fibers treated under the same conditions, indicatinging that the mechanism of boron catalytic graphitization changed at the temperatures higher than 2300°C. It also showed that the interlayer spacing (d₀₀₂) decreased, while the crystallite size (L_c) and the orientation increased with increasing temperatures.

Abstract: The aim of this work is to investigate characterizations of corrosion on 7A04 aluminum alloy with epoxy coating under simulated marine atmosphere with/without ultraviolet irradiation. The environment containing Cl^- and sunlight illumination was simulated by salt spray test and UV irradiation/condensation treatment. The corrosion behavior was studied by electrochemical impedance spectroscopy, and level of coating damage was evaluated through gloss measurement. Scanning electron microscope was chosen to observe surface properties of epoxy coating/7A04 aluminum alloy system. The results show that the electrochemical characters are closely related to the aging degree of epoxy coating, which could influence the penetrating process of oxygen and corrosive medium. The coating resistance decrease, while the coating capacitance and the pore rate increase as prolonging of the test time. Along with gloss loss of epoxy coating, pores appear on the surface and the blisters break, which may act as bulk defects of epoxy coating. The coating degradation and substrate corrosion were accelerated by the cooperation of UV irradiation and salt spray. UV aging significant accelerated the deterioration of coating with larger and deeper pores compared to that of non-UV irradiation coating.

Abstract: Inflatable space vehicle (ISV) has a variety of advantages of light mass, volume changeability and low cost, and becomes the hotspot in space vehicle research recently. But most researchers concentrate their efforts on applications of ISV in their dedicated domains, and the holistic viewpoint of ISV is indistinct. In this paper, the new developing space vehicle, ISV is classified into flatness, lenticula, sphere and cabin in brief due to its different structures and applications. Each type owns its special materials for folding, inflation-deployment, rigidization and resistibility in the space rigorous environment. Materials utilized in typical ISV are summarized subsequently, which can be sorted by polymer films, flexible rigidizable composites and multiple-layer laminates. Finally, the properties of ISV materials including environment endurance, mechanics, fabrication technologies and special functions are concluded, which is useful in material design and optimization.