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SiC/SiC composites reinforced with Hi-Nicalon S 3 rd generation SiC fibers are promising candidates for high temperature aeronautical applications and fuel cladding in nuclear reactors. An original patented process was used to produce SiC/SiC tubular samples for dimensional and tensile mechanical characterizations. The process route is described in detail to further understanding of specific features.SiC/SiC samples show a low porosity and excellent geometrical tolerance. Highly reproducible tensile mechanical behavior is observed with good mechanical failure characteristics. Some specific features were highlighted during mechanical characterizations with loading/unloading sequences. For instance, an original mechanical behavior was observed before the onset of matrix multicracking (deviation from linearity). To our knowledge, it is the first time that this kind of behavior has been detected on SiC/SiC composites, due to the processing route leading to the microstructure of specific samples. 1. Introduction Among the Ceramic Matrix Composites (CMC), SiC/SiC composites and affiliates have aroused interest for challenging high-temperature applications such as aerospace [1], aeronautics [2], defense [3] or nuclear applications [4] for their excellent mechanical properties [5] and oxidation resistance [6] at

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Abstract. The graphene is a material obtained when carbon atoms form large planar molecules. Well organized, large graphene molecules stacked ontop each other convey to graphene particularly interesting properties useful in nuclear industry. Understanding how the organization on the molecular scale influences the mechanical properties of the material is a key element in the material manufacturing process. In this scope, features like local orientation and length have already been largely explored in the literature. This paper brings a new feature evaluating the number of plans stacked ontop each other and the length of this stacking. It allows obtaing other features such as the overall rate of organization or locality and preferential orientation. These informations, synthesized in the form of histograms provides a key information in the processus the material design. Experimental results obtained on images taken by an electronic scanning microscope are presented to illustrate the proposed method.

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Proton exchange membrane (PEM) fuel cells are energy sources that have the potential to replace alkaline fuel cells for space programs. Broad power ranges, high peak-to-nominal power capabilities, low maintenance costs, and the promise of increased life are the major advantages of PEM technology in comparison to alkaline technology. The probability of PEM fuel cells replacing alkaline fuel cells for space applications will increase if the promise of increased life is verified by achieving a minimum of 10,000 hours of operating life. Durability plays an important role in the process of evaluation and selection of MEAs for Teledyne's Phase I contract with the NASA Glenn Research Center entitled "Proton Exchange Membrane Fuel cell (PEMFC) Power Plant Technology Development for 2"d Generation Reusable Launch Vehicles (RLVs)". For this contract, MEAs that are typically used for HZ/air operation were selected as potential candidates for H2 / 0 2 PEM fuel cells because their catalysts have properties suitable for 0 2 operation. They were purchased from several well-established MEA manufacturers who are world leaders in the manufacturing of diverse products and have committed extensive resources in an attempt to develop and fully commercialize MEA technology. A total of twelve MEAs used in Hz/air operation were initially identified from these manufacturers. Based on the manufacturers' specifications, nine of these were selected for evaluation.Since 10,000 hours is almost equivalent to 14 months, it was not possible to perform continuous testing with each MEA selected during Phase I of the contract. Because of the lack of time, a screening test on each MEA was performed for 400 hours under accelerated test conditions. The major criterion for an MEA pass or fail of the screening test was the gas crossover rate. If the gas crossover rate was higher than the membrane intrinsic permeability after 400 hours of testing, it was considered that the MEA had failed the test. Three types of MEAs out of the nine total membranes failed the test.The evaluation results showed that fuel cell operating conditions (current, pressure, stoichiometric flow rates) were the parameters that influenced the durability of MEAs. In addition, the durability test results indicated that the type of membrane was also an important parameter for MEA durability. At accelerated test conditions, the MEAs with casted membranes failed during the 400 hour test. However, the MEAs prepared from the casted membrane with support as well as extruded membranes, both passed the 400h durability test at accelerated operating test conditions.As a result of the MEA accelerated durability tests, four MEAs were selected for further endurance testing. These tests are being carried out with four-cell stacks under nominal fuel cell operating conditions. This is a preprint or reprint of a paper intended for presentation at a conference. Because changes may be made before formal publication, this is made available with the understanding that it will not be cited or repr...