Papers by Keyword: LSI

Abstract: Liquid Silicon Infiltration (LSI) is a technique to manufacture non-oxide ceramic matrix composites such as C/C-SiC or SiC/SiC. In the beginning of this three-step process, fiber preforms are shaped and impregnated with phenolic resins. After curing, the preforms are pyrolyzed to convert the polymer matrix to a porous carbon matrix. This porosity is then used to infiltrate liquid silicon by capillary forces. Simultaneously, an exothermic reaction of silicon and carbon creates a silicon carbide matrix. Generally the liquid silicon reacts with any carbon and even with SiC present in the form of fibers, fiber coatings or matrix. Therefore, especially the fibers must be protected from Si attack effectively. The morphology of silicon carbide was observed to be heavily driven by Ostwald ripening. This can be suppressed by the addition of boron to the melt. The initially formed SiC crystals in C/C-SiC composites are hereby prevented from grain coarsening, resulting in almost completely preserved C/C blocks. For the manufacture of SiC/SiC composites, the silicon boron alloys allow an effective preservation of the nanocrystalline SiC-fibers. Thus, the use of Si based B containing alloys helps effectively to moderate and control the aggressive reaction during LSI process.

Abstract: A literature evaluation method based on user interest is proposed by synthesizing self-values of literature and subjective values relative to query users in this paper. Firstly, in the process of mining user interests by hierarchical clustering, vector space model is employed for expressing the literature information that reflects users download behavior and the feature space is compressed by latent semantic indexing to reduce the space dimension. Secondly, subjective value of new literature relative to researchers is quantitatively evaluated in latent semantic space. Finally, the comprehensive evaluation model of literature reading value is constructed by the transformed E-measure index based on self-value and subjective value relative to query user. Experiments show that the proposed evaluation method by fully weigh subjective and objective factors of literature is more reasonable and effective compared with the traditional evaluation methods.

Abstract: Co-optimization of output and reserve is necessary in order to provide maximum benefit to both consumers and producers. Once renewable generation sources like wind or solar begin to make up a large proportion of the generation mix, this co-optimization becomes much more difficult since the output of renewable sources is not well-known in advance. In this paper, a uniform reliability level is used as a constraint in the process of output and reserve. The proposed model is tested on the modified 5-bus PJM system. The co-optimization is performed by sequential quadratic programming techniques. The results show that the co-optimization results are strongly related to the uncertainties of wind power, the reliability level of the system, and the reliability of generators when wind makes up a significant portion of the generation mix.

Abstract: Various technology programmes in Europe are concerned with preparing for future propulsion technologies to reduce the costs and increase the life time of components for liquid rocket engine components. One of the key roles to fulfil the future requirements and for realizing reusable and robust engine components is the use of modern and innovative materials. One of the key technologies which concern various engine manufacturers worldwide is the development of fibrereinforced ceramics – CMC's (Ceramic Matrix Composites). The advantages for the developers are obvious – the low specific weight, the high specific strength over a large temperature range, and their good damage tolerance compared to monolithic ceramics make this material class extremely interesting as a construction material. Different kind of composite materials are available and produced by EADS ST, the standard material SICARBON® (C/SiC made by Liquid Polymer Infiltration) and the new developed and qualified composite materials SICTEX® (C/SiC made by Liquid Silicon Infiltration) and CARBOTEX® (C/C made by Rapid Chemical Vapour Infiltration). The composites are based on textile techniques like weaving, braiding, stiching and sewing to produce multiaxial preforms, the SICTEX® material is densificated by the cost effective Liquid Silicon Infiltration (LSI). Over the past years, EADS Space Transportation (formerly DASA) has, together with various partners, worked intensively on developing components for airbreathing and liquid rocket engines. Since this, various prototype developments and hot firing-tests with nozzle extensions for upper and core stage engines and combustion chambers of satellite engines were conducted. MBDA France and EADS-ST have been working on the development of fuel-cooled composite structures like combustion chambers and nozzle extensions for future propulsion applications.