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121.
Electrical contact resistance between stainless steel bipolar plate and carbon felt in PEFC: A comprehensive study 总被引:1,自引:0,他引:1
Johan André Laurent Antoni Jean-Pierre Petit Eric De Vito Alexandre Montani 《International Journal of Hydrogen Energy》2009
Bipolar plate represents a key component of Proton Exchange Membrane Fuel Cell (PEFC) with several essential functions, among them the electric connection of elementary cells. Usually made of graphite, this component is studied worldwide in order to develop a commercially viable alternative: different ways have been being investigated, and to date, despite corrosion issues, stainless steel (SS) appears as a good candidate material, but its Electrical Contact Resistance (ECR) can reach unacceptable values when exposed to PEFC environment. This paper offers a comprehensive study of the parameters acting on ECR when using uncoated SS in PEFC: roughness, which influences the surface contact area with carbon baking, bulk composition of the alloy, which influences only partly the nature of passive films, and the composition and structure of passive films, strongly modified by surface treatments and ageing conditions. 相似文献
122.
Crack propagation in a linear elastic material with weakly inhomogeneous failure properties is analyzed. An equation of motion for the crack is derived in the limit of slow velocity. Predictions of this equation on both the average crack growth velocity and its fluctuations are compared with recent experimental results performed on brittle heterogeneous materials (Ponson in Phys Rev Lett, 103, 055501; Måløy et al. in Phys Rev Lett, 96, 045501). They are found to reproduce quantitatively the main features of crack propagation in disordered systems. This theoretical framework provides new tools to predict life time and fracture energy of materials from their properties at the micro-scale. 相似文献
123.
Isabelle Bruant Laurent Proslier 《International Journal of Mechanics and Materials in Design》2016,12(2):173-192
Up to now, optimal location for active control studies concern principally multilayers or homogeneous structures. In the case of functionally graded materials, very few papers exist and they only concern cross section variations. In this way, this paper deals with the optimization of piezoelectric actuators locations on axially functionally graded beams for active vibration control. For this kind of structures, the free vibration problem is more complicated as the governing equations have variable coefficients. Here, the eigenproblem is solved using Fredholm integral equations. The optimal locations of actuators are determined using an optimization criterion, ensuring good controllability of each eigenmode of the structure. The linear quadratic regulator, including a state observer, is used for active control simulations. Two numerical examples are presented for two kinds of boundary conditions. 相似文献
124.
Remy Chevallier Emmanuelle Encrenaz-Tiphene Laurent Fribourg Weiwen Xu 《Formal Methods in System Design》2009,34(1):59-81
Using a variant of Clariso-Cortadella’s parametric method for verifying asynchronous circuits, we analyse some crucial timing
behaviors of the architecture of SPSMALL memory, a commercial product of STMicroelectronics. Using the model of parametric
timed automata and model checker HYTECH, we formally derive a set of linear constraints that ensure the correctness of the
response times of the memory. We are also able to infer the constraints characterizing the optimal setup timings of input
signals. We have checked, for two different implementations of this architecture, that the values given by our model match
remarkably with the values obtained by the designer through electrical simulation.
Partially supported by project MEDEA+ Blueberries.
A preliminary version appeared in the Proceedings of 4th International Conference on Formal Modelling and Analysis of Timed
Systems (FORMATS’06), Sept. 2006. 相似文献
125.
126.
Nelly Rameau Stéphane Cadot Anthony Paquet Catherine Pinel Laurent Djakovitch 《Topics in Catalysis》2014,57(17-20):1430-1437
The heterocoupling between 2-nitrobenzoic and 2,6-dimethoxybenzoic acids was studied. It was demonstrated that the [PdCl2/Cu(OH)2:0.2/0.75 equiv.] catalytic system can catalyze this reaction with significant yield. Further optimizations (i.e.: sources and loadings of copper and palladium salts, base) allowed to isolate the biaryl in 70 % yield. A catalytic cycle that accounts for the observed results is proposed. While the bi-metal catalyst has shown high yields with some substrates, it is only able to catalyze the decarboxylative coupling in high yield for some of the substrates studied. 相似文献
127.
Laurent Crouzeix Jean Noël Pri Francis Collombet Bernard Douchin 《Composites Part A》2009,40(11):1732-1740
In this paper, it is proposed to apply the equilibrium gap method to orthotropic composite materials to retrieve damage laws from measured displacement fields. A finite difference implementation method is first proposed. A linear system is formed, for which the unknowns are piecewise constant orthotropic rigidities, while the measured displacements are input (known) data. In this example, a cruciform specimen is considered for biaxial test. It is shown that, by referring to FE computed displacement fields a prescribed contrast map can be identified. Corrupted artificial displacement fields obtained through non-linear simulations are also used. When considering shear damage, a procedure using estimated contrast maps to identify a damage law is validated. An experimental biaxial test on a 2.5 C/C composite is finally analysed following the proposed approach. For each unloading step, a contrast map for all moduli is obtained from full-field measurements. By assuming that the shear moduli contrasts result from a damage mechanism, one subsequently obtains damage maps, and therefore, a growth law. The results are first validated by comparing measured and FE reconstructed displacement fields, and by comparing the identified damage fields with post-processed ones. 相似文献
128.
Demany Laurent; Semal Catherine; Pressnitzer Daniel 《Canadian Metallurgical Quarterly》2011,37(2):597
Listeners had to compare, with respect to pitch (frequency), a pure tone (T) to a combination of pure tones presented subsequently (C). The elements of C were either synchronous, and therefore difficult to hear out individually, or asynchronous and therefore easier to hear out individually. In the “present/absent” condition, listeners had to judge if T reappeared in C or not. In the “up/down” condition, the task was to judge if the element of C most similar to T was higher or lower than T. When the elements of C were synchronous, the up/down task was found to be easier than the present/absent task; the converse result was obtained when the elements of C were asynchronous. This provides evidence for a duality of auditory comparisons between tone frequencies: (1) implicit comparisons made by automatic and direction-sensitive “frequency-shift detectors”; (2) explicit comparisons more sensitive to the magnitude of a frequency change than to its direction. Another experiment suggests that although the frequency-shift detectors cannot compare effectively two tones separated by an interfering tone, they are largely insensitive to interfering noise bursts. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
129.
Helen Reveron Laurent Blanchard Yann Vitupier Emmanuelle Rivière Guillaume Bonnefont Gilbert Fantozzi 《Journal of the European Ceramic Society》2011,31(4):645-652
Many space systems such as satellite mirrors and their supporting structures require to be made from very low-thermal expansion materials combining both high hydrostability and relatively high mechanical properties. In this study, we have applied the “composite concept” in order to explore the possibility of fabricating near zero thermal expansion silicon nitride based ceramics. Consequently, a negative thermal expansion material belonged to the lithium aluminosilicate family (LAS powder crystallized under de β-eucryptite structure) was introduced in an alpha-silicon nitride fine powder (5 and 20 vol% of LAS) and the resulting composite system was sintered by Spark Plasma Sintering (SPS) at 1400 and 1500 °C. In the case of 20 vol% LAS compositions, relatively well-densified ceramics (94.4% of the theoretical density) were produced without adding any further sintering additive. The addition of yttria and alumina oxides allowed enhancing the densification level up to 98.2% (20 vol% LAS compositions) or from 62.3% up to 96.7% of the theoretical density in 5 vol% LAS materials. Nevertheless, it was impossible to full consolidate silicon nitride/LAS composite ceramics at temperatures lower than the temperature at which β-eucryptite melts, even by using SPS technology. Moreover, because of the relatively low temperatures involved in SPS, the α to β-Si3N4 transformation was avoided, resulting in microstructures composed of fine equiaxed α-Si3N4 grains (<200 nm) and of a glassy phase. Even if the effect of having a very large negative thermal expansion material was lost during the sintering step (because of the β-eucryptite melting), ceramics containing only 20 vol% of LAS-based phase exhibited very interesting values as regards of mechanical properties (strength, hardness, toughness, and Young's modulus), thermal conductivity and thermal expansion coefficient. We discuss in this work why we are so interested in developing dense silicon nitride/LAS ceramics sintered without any further additive addition, even though β-eucryptite is melted during the process and the transformation to the β phase is avoided. 相似文献
130.
Laurent Mezeix Christophe Bouvet Julitte Huez Dominique Poquillon 《Journal of Materials Science》2009,44(14):3652-3661
Entangled fibrous materials have been manufactured from different fibers: metallic fibers, glass fibers, and carbon fibers.
Specimens have been produced with and without cross-links between fibers. Cross-links have been achieved using epoxy spraying.
The scope of this article is to analyze the mechanical behavior of these materials and to compare it with available models.
The first part of this article deals with entangled fibrous materials without cross-link between fibers. Compression tests
are detailed and test reproducibility is checked. In the second part, compression tests were performed on materials manufactured
with cross-linked fibers. The specific mechanical behavior obtained is discussed. 相似文献