Materials Science Forum Vols. 546-549

Abstract: Nanocomposites were prepared by embedding carbon black and silica into phenolic resin matrix, which was supported by SEM and particle size analyses. After milling stage, the obtained hybrids were applied to transparency film using K control coater. By the crosslinking procedure, homogenous surface coatings can be achievable. The electrical properties of surface coating can be tailored by variation of silica content with the amount of carbon black fixed. The conductivity of the surface coating increases steeply and then reaches a plateau with the increase of silica. When the weight ratio of silica to carbon black is around 1:2, relatively high conductivity can be desirable. Further increase in silica results in the decrease in conductivity. This can be interpreted in terms of aided or blocked dispersion effects on carbon black imposed by silica. Also, the uniformity of the film is verified by Si-mapping analysis.

Abstract: Internal friction of 2D C/SiC composites fabricated by chemical vapor infiltration (CVI) method was measured by dynamical mechanical analysis (DMA) at different frequencies from room temperature (RT) to 400°C in air atmosphere. Internal friction of 2D C/SiC composites increased gradually with increasing temperature and then decreased after damping peak appeared in the temperature range of 250°C to 300°C. Damping capacity and peak value decreased gradually with increasing frequency, accompanied with a shift of damping peak towards lower temperatures. Moreover, the effect of interphase thickness on damping behavior of 2D C/SiC composites was investigated. The results showed that damping peak of the composites increased gradually and the temperature of the peak shifted to the lower temperature with increasing PyC interphase thickness, when the interphase thickness is in the range of 90~296nm. The influence of interphase thickness on interfacial bonding strength, sliding resistance and the microstructure of SiC matrix was discussed, which was considered to be responsible for the results.

Abstract: Tensile and high cycle fatigue (HCF) property for TiC particle reinforced titanium matrix composite has been studied in this paper. The results indicated that the composite possessed favorite comprehensive properties. The tensile properties for the composite are superior to that of the common high temperature titanium alloys, e.g. IMI834, Ti-1100. Smooth axial fatigue tests were taken at a frequency of 76Hz with a load ratio R of 0.06 and –1, respectively. And HCF strength for the composite at ambient temperature is 595MPa and 494MPa, respectively.

Abstract: The aim of this paper is to present an exploratory process to characterize fabricated 2-phase aluminum metal-matrix systems (2-phase systems) by using a dynamic consolidation technique, with an arrangement of multilayer mixings in steel cylinders. Aluminum powder (~150mm) was mechanically mixed with different fractions of multi-wall carbon nano-tubes (MWCNTs, 2 and 5 percent), with ~30 nm and ~30 μm diameter SiC and Al 2 O 3 powders (in volume fractions of 2, 4, and 21 percent), then, were green compacted uniaxially to ~80 % density, to be finally explosively consolidated with ammonium nitrate-fuel oil (ANFO) and C3. After compaction, WEDM (wire electrical discharge machining) was used to prepare tensile and hardness testing samples, also TEM, light microscopy and SEM characterization samples, all by using ~25 % of the obtained material , this represents less than 10cc , preserving ~60 % of the obtained monoliths. Densities of the consolidated monoliths achieve an average of ~98 % compaction (measured by Archimedes technique). Observations and measured hardness (HRE) reveal well compacted systems with a hardness consistent along the composites. Using light microscope imaging different zones were identified showing different grain behaviors.

Abstract: High modulus carbon/epoxy composites have been attached more and more importance in the aeronautic field. Because chemical inert of high modulus carbon fiber surface and its poor impregnation for resin, it is essential to improve its polarity in order to enhance the interfacial performances of high modulus carbon/epoxy composites. In this paper, high modulus carbon fiber was treated by ozone oxidation method to modify its surfacial properties. AFM and SEM were used to observe the surface of the carbon fiber, as well as interlaminar shear strength of high modulus carbon fiber/epoxy composite was tested. The impregnation and the interfacial performances of the high modulus carbon/epoxy composites were studied. The results show that after ozone treatment, the surface impregnation of high modulus carbon fiber and the interlaminar shear strength property of high modulus carbon/epoxy composites can be improved obviously.

Abstract: Compared to the conventional constructive materials, SiC particle reinforced aluminum matrix composites have lighter weight and higher specific modulus, and are applied in the structure framework of solar battery array for space station. According to the requests of the material properties for this framework, aluminum matrix composites are specially designed and manufactured, and then deformed into components of different shapes and sizes for various uses. The composite components were of compact structure and excellent mechanical properties, and had passed all the application tests for the framework. The application of aluminum matrix composites achieves a good result that not only the framework weight was greatly reduced but also the comprehensive properties of the framework were improved greatly. Aluminum matrix composites exhibit a great potential for further application into aerospace.

Abstract: In this paper the composite fracture process has been simulated via the finite element method. A micromechanics model was developed to predict the stress-strain response of a SiO2f/ SiO2 composite explicitly accounting for the local damage mechanisms such as fiber fracture and interfacial debonding. The effects of interfacial strength and fiber volume fraction on the toughness of fiber-reinforced ceramic matrix composites were investigated. The results showed that the composite failure behaviors correlated with the interface strength, which could achieve an optimum value for the elevation of the composite toughness. The increase of fiber volume fraction can make more toughening contributions.

Abstract: AlN-BN composite Powders with the microstructure of micrometer-sized AlN particles coated with BN particles were prepared via a chemical reaction, which used a mixture of boric acid (H3BO3) and urea (CO(NH2)2) as reactants coated on the surface of the AlN particles to react in nitrogen ambient. The XRD and TEM studies showed that the coating layer (BN) was composed mostly of amorphous BN particles at the reaction temperature of 850oC ~1100oC. When the composite powders formed into pellets using cold isostatic-pressing, then, sintered at pressureless sintering, the relative density of the composites that contained 15wt% BN reached above 98%, and there was homogeneous microstructure.

Abstract: Unsymmetric composite laminates were benefit to reducing the structure weight of some aircrafts. However, the cured unsymmetric laminates showed distortion at room temperature. Therefore, predicting the deformation before using the unsymmetrical composite is very important. In this study an attempt was made to predict the shapes of some unsymmetric cross-ply laminates using the finite element analysis (FEA). The bilinear shell-element was adopted in the process. Then the simulation results were compared with the experimental data. The studies we had performed showed that the theoretical calculation agreed well with the experimental results, the predicted shapes were similar to the real laminates, and the difference between the calculated maximum deflections and the experimental data were less than 5%. Hence the FEA method was suitable for predicting the warpage of unsymmetric laminates. The error analysis showed that the simulation results were very sensitive to the lamina thickness, 2 α and (T.

Abstract: This paper is concerned about a design of a new deployable antenna actuated by 6 shape memory alloy (SMA) hinges. The antenna consists of 6 radial, tensioned, parabolic, deployable ribs connecting to a central hub. The hinge, located at each rib, is used of the Nitinol SMA material due to the ability to generate large strains and electrical resistive actuation. The elongated SMA wire is heated by an electrical current, caused to contract in response to a converse thermally-induced phase transformation. The resulting tension creates a moment, imparting rotary motion between two adjacent beams. The concept and operation of deployable antenna system are discussed in detail, and a dynamic simulation is presented. A series of experiments are performed on the SMA actuator to investigate the system behavior in the process of deployment. Results indicated that the hinge with low speed rotation and easy fabrication achieves reliable actuation for the deployment of the antenna, and the antenna demonstrates a high deployment-to-stowage volume ratio.