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81.
Journal of Elasticity - In this work, we study the transversal vibration of thin periodic elastic plates through asymptotic homogenization. In particular, we consider soft inclusions and rigid... 相似文献
82.
Randy W. Purves Allison R. Ozog Stephen J. Ambrose Satendra Prasad Michael Belford Jean-Jacques Dunyach 《Journal of the American Society for Mass Spectrometry》2014,25(7):1274-1284
Recent reports describing enhanced performance when using gas additives in a DMS device (planar electrodes) have indicated that comparable benefits are not attainable using FAIMS (cylindrical electrodes), owing to the non-homogeneous electric fields within the analyzer region. In this study, a FAIMS system (having cylindrical electrodes) was modified to allow for controlled delivery of gas additives. An experiment was carried out that illustrates the important distinction between gas modifiers present as unregulated contaminants and modifiers added in a controlled manner. The effect of contamination was simulated by adjusting the ESI needle position to promote incomplete desolvation, thereby permitting ESI solvent vapor into the FAIMS analyzer region, causing signal instability and irreproducible CV values. However, by actively controlling the delivery of the gas modifier, reproducible CV spectra were obtained. The effects of adding different gas modifiers were examined using 15 positive ions having mass-to-charge (m/z) values between 90 and 734. Significant improvements in peak capacity and increases in ion transmission were readily attained by adding acetonitrile vapor, even at trace levels (≤0.1%). Increases in signal intensity were greatest for the low m/z ions; for the six lowest molecular weight species, signal intensities increased by ~10- to over 100-fold compared with using nitrogen without gas additives, resulting in equivalent or better signal intensities compared with ESI without FAIMS. These results confirm that analytical benefits derived from the addition of gas modifiers reported with a uniform electric field (DMS) also are observed using a non-homogenous electric field (FAIMS) in the analyser region. Figure
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83.
J. Gmez-Mancilla Jean-Jacques Sinou V.R. Nosov F. Thouverez A. Zambrano 《Comptes Rendus Mecanique》2004,332(12):955-962
Vibration peaks occurring at rational fractions of the fundamental rotating critical speed, here named Local Resonances, facilitate cracked shaft detection during machine shut-down. A modified Jeffcott-rotor on journal bearings accounting for gravity effects and oscillating around nontrivial equilibrium points is employed. Modal parameter selection allows this linear model to represent first mode characteristics of real machines. Orbit evolution and vibration patterns are analyzed, yielding useful results. Crack detection results indicate that, instead of 1x and 2x components, analysis of the remaining local resonances should have priority; this is due to crack-residual imbalance interaction and to 2x multiple induced origins. Therefore, local resonances and orbital evolution around 1/2, 1/3 and 1/4 of the critical speed are emphasized for various crack-imbalance orientations. To cite this article: J. Gómez-Mancilla et al., C. R. Mecanique 332 (2004).
Résumé
Les pics de vibration apparaissant au passage des fractions de la vitesse de critique de rotation des systèmes tournants, appelées résonances locales, facilitent la détection de fissures sur les machines. Dans cette étude, un modèle de rotor Jeffcott modifié avec une fissure tournante, comportant des coussinets et prenant en compte les effets de pesanteur et de balourd est présenté. Le choix modal des paramètres permet de représenter les caractéristiques liées au premier mode des machines tournantes usuelles. Les évolutions des vibrations et des orbites du système comportant une fissure sont analysées et permettent d'obtenir des résultats utiles pour la détection des fissures sur les machines tournantes. Ainsi, ces résultats indiquent que, en plus des composants 1x et 2x, l'analyse des autres résonances locales restantes doivent être regardées avec attention du fait de l'interaction possible entre les différentes orientations de la fissure et du balourd, et des origines multiples pouvant engendrer la présence des résonances 2x. Par conséquent les résonances et l'évolution des orbites obtenus autour de 1/2, 1/3 et 1/4 de la vitesse critique sont étudiées pour différentes variations d'angle entre le balourd et l'orientation de la fissure. Pour citer cet article : J. Gómez-Mancilla et al., C. R. Mecanique 332 (2004). 相似文献84.
For a car manufacturer, reducing the weight of vehicles is an obvious aim. Replacing steel by aluminium moves towards that goal. Unfortunately, aluminium's stamping numerical simulation results are not yet as reliable as those of steel. Punch-strength and spring-back phenomena are not correctly described. This study on aluminium validates the behaviour law Hill 48 quadratic yield criterion with both isotropic and kinematic hardening. It is based on the yield surface and on associated experimental tests (uniaxial test, plane tensile test, plane compression and tensile shearing). To cite this article: J.-J. Sinou, B. Macquaire, C. R. Mecanique 331 (2003). 相似文献
85.
The drawbacks of the classical theory of brittle fracture, based on Griffith's criterion – a notion of critical energy release rate –, and a fracture toughness k, are numerous (think for instance the issue of crack initiation) and penalize its validity as a good model. Are all attempts at building a macroscopic theory of fracture doomed? The variety and complexity of micromechanical phenomena would suggest that this is indeed the case. We believe however that structural effects still preside over fracture and consequently propose to modify slightly Griffith theory without altering its fundamental components so that it becomes amenable to the widest range of situations. The examples presented here will demonstrate that a revisited energetic framework is a sound basis for a theory which can be used at the engineering level and which reconciles seemingly contradictory viewpoints. To cite this article: G. Francfort, J.-J. Marigo, C. R. Mecanique 330 (2002) 225–233. 相似文献
86.
Jean-Jacques Aubert 《辐射效应与固体损伤》2013,168(2):469-474
Abstract One of the main problems in optical materials in the growth of single crystals and the characterization of their defects in view of performances and applications. 相似文献
87.
88.
Roberto Alessi Jean-Jacques Marigo Stefano Vidoli 《Archive for Rational Mechanics and Analysis》2014,214(2):575-615
In the framework of rate-independent systems, a family of elastic-plastic-damage models is proposed through a variational formulation. Since the goal is to account for softening behaviors until the total failure, the dissipated energy contains a gradient damage term in order to limit localization effects. The resulting model owns a great flexibility in the possible coupled responses, depending on the constitutive parameters. Moreover, considering the one-dimensional quasi-static problem of a bar under simple traction and constructing solutions with localization of damage, it turns out that in general a cohesive crack appears at the center of the damage zone before the rupture. The associated cohesive law is obtained in a closed form in terms of the parameters of the model. 相似文献
89.
Un complexe tétraédrique du nickel (II) est étudié cinétiquement pour la première fois. Le solvate Ni(HMPT)4 2+, 2ClO4 - est préparé au sein du HMPT anhydre, et les temps de relaxation de 31P mesurés à deux fréquences (8 et 14 MHz), six températures (8–66°C) et plusieurs concentrations (10-3-10-2 M). On détermine ainsi: le déplacement de contact: Δωm = 41800 Hz (25°C et 14 MHz); la constante de couplage hyperfin A = 11,9 MHz; les temps de relaxation électronique, T 1e et T 2e = 1,32 et 0,69 × 10-12 s; la trace du carré du tenseur de couplage spin-spin à champ nul Δ = 3,31 cm-1 et le temps de corrélation afférent τv = 5,6 × 10-12 s (à 25°C); les paramètres cinétiques de l'échange: libre: k M (25°C) = (9,6 ± 0,60) × 105 s-1; ΔH ? = 3,6 ± 2,1 kJ mol-1; ΔS ? = -117 ± 8 J deg-1 mol-1. Le mécanisme de cet échange est associatif, et l'enthalpie d'activation associée extrêmement faible, conformément aux prévisions qualitatives de la théorie du champ cristallin. 相似文献
90.
Hammoud H Schmitt M Bihel F Antheaume C Bourguignon JJ 《The Journal of organic chemistry》2012,77(1):417-423
A modified Ullmann reaction using p-methoxybenzyl (PMB) guanidine as guanidinylation agent yielded various aryl and heteroaryl guanidines in good yields. 相似文献