A unified fracture mechanics approach to fretting fatigue crack growth

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2001.Includes bibliographical references (p. 142-154).The purpose of this work is to demonstrate the adequacy of a modeling approach of fretting fatigue for a sphere-on-flat geometry entirely based on fracture mechanics. All stages of damage evolution, from initiation to failure, are encompassed within the framework of fracture mechanics, in contrast with the general use of stress based criteria to predict crack initiation. A comparison with the classical approaches show how this methodology allows to circumvent the problem of the length scale for initiation by using the crack analogue methodology of contact of Giannakopoulos, Venkatesh, Lindley and Suresh. On the other hand, another length scale, identified as the region of dominance of the singular adhesive stresses, is introduced by the model, and experimental methods to validate it are suggested. The comparison of simulations with three sets of experiments performed on a titanium alloy, with a good control of the normal, tangential and axial loads, shows that the qualitative trends are captured. Good quantitative agreement is also obtained for some of them, depending on the details of the crack growth law. Experimentally, results on the same material after shot peening are reported and used to evaluate the ability of the approach to cope with residual stresses. A good qualitative explanation of the fretting fatigue resistance of the shot peened material is demonstrated. These experiments also serve to illustrate possible testing methods and observations which could yield more useful information than the "classical" fretting fatigue test to failure, and to emphasize the need for a careful stress analysis to avoid plastification under certain material and experimental conditions.by Laurent Chambon.S.M

Antiquité tardive en région Centre-Val de Loire (AnTaRec)

Marie-Pierre Chambon, Laurent Fournier et Édith Rivoire (Inrap), porte sur l’étude de l’Antiquité tardive en région Centre. La fourchette chronologique retenue est large puisqu’elle couvre la période allant de la seconde moitié du iiie s. apr. J.-C. à la première moitié du vie s. apr. J.-C. La zone géographique étudiée est la région Centre-Val de Loire dans ses limites administratives actuelles. L’objectif de ce PCR est de regrouper l’ensemble des chercheurs intéressés par cette période quel ..

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Evaluation probabiliste de la durée de vie de structures

Cette communication présente l'intégration dans un cadre probabiliste d'un critère de fatigue multiaxial robuste. La propagation de la variabilité à travers le modèle de fatigue est initialement réalisée à l'aide d'une méthode de Monte-Carlo. Une surface de réponse probabiliste est ensuite proposée. Les capacités prédictives du modèle sont alors évaluées à l'aide d'une base de données de fatigue sur un alliage d'aluminium réalisée au centre de recherche d'EADS France et au laboratoire CROMeP. En particulier, la dispersion prévue par le modèle est comparable aux dispersions trouvées expérimentalement

Control of turbulent flow in vertical slot fishways for the migration of small fish species

The improvement of devices that allow the upstream migration of fishes through engineering constructions or natural obstructions in rivers is now a real priority to maintain the biodiversity. Vertical slot fishways are commonly used and are very effective in ensuring unhindered passage of the species of large size fishes

MRI investigation of granular interface rheology using a new cylinder shear apparatus

The rheology of granular materials near an interface is investigated through proton magnetic resonance imaging. A new cylinder shear apparatus has been inserted in the MRI device, which allows the control of the radial confining pressure exerted by the outer wall on the grains and the measurement of the torque on the inner shearing cylinder. A multi-layer velocimetry sequence has been developed for the simultaneous measurement of velocity profiles in different sample zones, while the measurement of the solid fraction profile is based on static imaging of the sample. This study describes the influence of the roughness of the shearing interface and of the transverse confining walls on the granular interface rheology

Synthesis and stability evaluation of novel peptidomimetic Caspase-1 inhibitors for topical application

International audienceDuring our search for topically-active Caspase-1 inhibitors, we identified a novel class of potent in-hibitors based on a 1,3,5-trisubstituted uracil motif equipped with an L-aspartate semi-aldehyde derived warhead. In the literature, the majority of Caspase-1 inhibitors possessing the same warhead have been designed and evaluated for oral administration as the ethyl acetal pro-drug form. For our topical program , the pro-drug acetal form was not fully hydrolysed in the skin and was unstable in many of our standard topical excipients, therefore, we were obliged to focus on the actual hemiacetal drug form of the molecule during our drug discovery program. Our work focuses on both the synthesis and achiral and chiral stability of the final drug molecules in topical excipients