Spatially heterogeneous dynamics in a thermosensitive soft suspension before and after the glass transition

The microscopic dynamics and aging of a soft thermosensitive suspension was investigated by looking at the thermal fluctuations of tracers in the suspension. Below and above the glass transition, the dense microgel particles suspension was found to develop an heterogeneous dynamics, featured by a non Gaussian Probability Distribution Function (PDF) of the probes' displacements, with an exponential tail. We show that non Gaussian shapes are a characteristic of the ensemble-averaged PDF, while local PDF remain Gaussian. This shows that the scenario behind the non Gaussian van Hove functions is a spatially heterogeneous dynamics, characterized by a spatial distribution of locally homogeneous dynamical environments through the sample, on the considered time scales. We characterize these statistical distributions of dynamical environments, in the liquid, supercooled, and glass states, and show that it can explain the observed exponential tail of the van Hove functions observed in the concentrated states. The intensity of spatial heterogeneities was found to amplify with increasing volume fraction. In the aging regime, it tends to increase as the glass gets more arrested.Comment: 19 pages, 10 figures, Soft Matter accepte

Elaboration de gradients de composition continue dans des taillants PDC

International audienceCemented carbides are composites which possess an excellent compromise between hardness and toughness. For years, to improve one property without decreasing the other one, the concept of graduated structure was widely studied. In this work, we present a process to create one-step continuous gradients of several millimetres within WCCo cermet, by the imbibition method. This process was applied on commercial drilling bit. The effects of this thermal processing are analysed in term of microhardness, cobalt concentration and grains size. The results obtained on PDC drill cutter show gradients of 540HV in WC-Co bit and 350HV in bit covered by the polycrystalline diamond layer. Such gradients have never been reported before to our knowledge

Etude des phénomènes thermiques associés à la fabrication directe de pièces en TA6V par projection laser

International audienceDirect metal deposition is an additive manufacturing process that enables to build up a component layer-by-layer by the laser melting of a metal powder on a solid substrate, using a coaxial nozzle and a powder delivery head. The heating and cooling that occur in direct laser metal deposition can generate particular thermal conditions which are responsible of the specific microstructure and grain growth and lead to specific build features in term of mechanical properties. In the present work, an experimental study concerning laser-powder interaction, process instrumentation and metallurgical properties of the built parts is exposed. Then, a thermal balance has been established from thermal data of Ti-6Al-4V

Slipping zone location in squeeze flow

the original publication is available at http://www.springerlink.com/content/f1611lmr64836780/International audienceIn squeeze flow rheometry, the main problem is the boundary condition between the squeezed material and the plates. Therefore, the crucial assumption is to know the location and the shape of the sample part where wall slip may or may not occur. This question is investigated from experimental results. For this, squeeze flow experiments are carried out to visualize the flow pattern at the walls. Influence of boundary conditions is particularly studied using different plate surface condition. As a result, with wall slipping conditions, we propose a flow modelling divided into two zones: a circular central zone of the sample sticks on the plates and, beyond that zone, the sample slips at the plates with friction

Long-term in situ observations on typhoon-triggered turbidity currents in the deep sea

This work is supported by the National Science Foundation of China (grants 91528304, 41576005, and 41530964). We thank J. Li, X. Lyu, P. Li, K. Duan, J. Ronan, Y. Wang, P. Ma, and Y. Li for cruise assistance; G. de Lange and J. Hinojosa for editing an early version of manuscript; and E. Pope and two anonymous reviewers for their reviews.Peer reviewedPublisher PD

On the optimisation of a texture analyser in squeeze flow geometry

The original contribution is available at http://www.sciencedirect.com/science/article/pii/S0263224106000327International audienceThis paper describes how the range of application of a texture analyser, used for mechanical tests of solids and liquids in the food and cosmetics industry, can be extended to reproduce squeeze flow geometry. It describes the necessary optimisation of the device to ensure parallelism and thermal regulation of the plates during tests. The error on the load cell and the instrument compliance are evaluated. The influence of these artefact measurements is investigated in terms of interpretation of rheological properties of materials

Le test de compression simple : mise en oeuvre sur un analyseur de texture et exploitation en présence de fluides viscoplastiques

National audienc

Homogenization of periodic auxetic materials

International audienceMaterials presenting a negative Poisson's ratio (auxetics) have drawn attention for the past two decades, especially in the field of lightweight composite structures and cellular materials. Studies have shown that auxeticity may result in higher shear modulus, fracture toughness and acoustic damping. In this work, three auxetic periodic lattices are considered. Elastic moduli are computed and anisotropy is investigated by the use of finite element method combined with numerical homogenization technique

Extracting Plane Graphs from Images

International audienceIn order to use structural techniques from graph-based pattern recognition, a first necessary step consists in extracting a graph in an automatic way from an image. We propose to extract plane graphs, because of algorithmic properties these graphs have for isomorphism elated problems. We also consider the problem of extracting semantically well-founded graphs as a compression issue: we get simple graphs from which can be rebuilt images similar to the initial image. The technique we introduce consists in segmenting the original image, extracting interest pixels on the segmented image, then converting these pixels into pointels, which in turn can be related by region-based triangulation. We show the feasibility and interest of this approach in a series of experiments