Experimental data about mechanical behaviour during compression tests for various matted fibres

A specific experimental device has been set up to test compressive mechanical behaviour of an assembly of fibres. Simple compression, as well as cyclic loading experiments and relaxation tests were performed. The experimental set up also allows to record the evolution of the mat fibre electrical resistance while testing. Experimental results are presented for a variety of fibrous materials. Despite the very different nature of each of these individual fibres, it appears that the mats exhibit a very similar mechanical behaviour. This common behaviour has been observed during monotonic single compression tests, as well as during cyclic or relaxation experiments. These experimental results are discussed in terms of different parameters such as the intrinsic mechanical properties of individual fibres and moreover the tangle intrinsic parameters (effect of fibre length, effect of geometrical position of fibres in the sample, fibre surface modifications. . .). The influence of the contact points between fibres is discussed in regard of the electric resistivity measurement

Rafting microstructure during creep of the MC2 nickel-based superalloy at very high temperature

Directional coarsening of the single-crystalline nickel-based superalloy MC2 has been investigated by means of tensile creep tests at 1100 ◦C. Two specific specimen geometries were designed in order to generate a variety of stress and strain states. Different coarsening microstructures are observed: N- and P-type classical rafting but also coarsening oriented 45◦ away from the load axis. The comparison of microstructure maps with the local mechanical state evaluated by finite element calculations shows that the 45◦ directional coarsening appears in case of very high cumulated strain values (above 10%), independent of the stress sign. Transmission electron microscopy investigations showthat the dislocation microstructure is similar in both N-type and 45◦ coarsened areas

High-temperature creep of single-crystal nickel-based superalloy : microstructural changes and effects of thermal cycling

Creep tests were performed on MC2 single crystal superalloy at 950°C/200 MPa and 1150°C/80 MPa under isothermal and thermal cycling conditions with a tensile axis along the [0 0 1] direction. It was found that the thermal cycles strongly affect the creep behavior at 1150°C but not at 950°C. This was related to the repetitive precipitation and dissolution of small γ′ rafts at the higher temperature, as revealed by quantitative characterization of the γ/γ′ microstructure. The dislocation microstructure exhibits similar trends in all the tested conditions, with a very high activity of a[1 0 0]-type dislocations climbing through the rafts. Such climbing dislocations constitute a recovery process for the deformation active system. It appears that the density of a[1 0 0] dislocations, and not their climb velocity or diffusion rate, is the key parameter for the control of creep rate. The thermal cycles, which imply the creation and subsequent dissolution of rafts, provided new dislocations, which explains the acceleration of creep observed under such conditions

Injection of vacancies at metal grain boundaries during the oxidation of nickel

Nickel foils have been oxidised at 1000 °C on one side only in laboratory air, the other side being protected from oxidation by a reducing atmosphere. After the oxidation treatment, the unoxidised face was carefully examined by using an atomic force microscope. Grain boundaries grooves were characterised and their depth were compared to the ones obtained on the same sample heat treated in the reducing atmosphere during the same time. Grain boundaries grooves are found to be much deeper in the case of the single side oxidised samples. It is shown that this additional grooving is directly linked to the growth of the oxide scale on the opposite side and that it can be explained by the diffusion of the vacancies produced at the oxide scale–metal interface, across the entire sample through grain boundaries. Moreover, the comparison between single side oxidised samples and samples oxidised on both sides points out that voids in grain boundaries are only observed in this latter case proving the vacancies condensation in the metal when the two faces are oxidised

Oxidation Assisted Intergranular Cracking in Alloy 718: Effects of Strain Rate and Temperature

Alloy 718 is the most widely used superalloy in industry due to its excellent mechanical properties, as well as its oxidation and corrosion resistance over a wide range of temperatures and solicitation modes. Nevertheless, it is a well-known fact that this alloy is sensitive to oxidation assisted intergranular cracking under loading in the temperature range encountered in service. The mechanisms resulting in such degradation are not well-understood, but it has been well established that a relation exists between a change in fracture mode and the apparition of plastic instability phenomena over a wide range of temperatures. Quantification and characterization of the damaging process provide important information leading to a better understanding of the degradation mechanisms involved in the oxidation assisted intergranular cracking of this alloy. These observations allow various domains to be defined in the strain rate - temperature plane, where the damaging process characteristics are different: a high strain rate / low temperature domain in which instabilities occur and where the fracture mode is systematically transgranular ductile, an intermediary domain where numerous intergranular crack initiations can be observed, and a slow strain rate / high temperature domain where crack propagation is enhanced. These results lead to the proposal of consistent scenarii to explain grain boundary opening due to applied intergranular normal stress and critical decohesion stress changes

Evaluation qualitative macroscopique et microscopique du grasset chez un modèle expérimental d'arthrose canine 90 jours après section du ligament croisé crânial

La transection du ligament croisé crânial (CCLT) est une méthode couramment admise d'induction expérimentale d'arthrose (OA) au niveau du grasset chez le chien. Le but principal de cette étude était d'évaluer qualitativement les lésions d'arthrose induites par la CCLT par macroscopie et histologie 90 jours après chez 21 jeunes femelles de race beagle. Les lèvres de la trochlée fémorale présentaient le plus haut score ostéophytique tandis que la patelle présentait le plus bas et celui du condyle fémoral médial était supérieur à celui du condyle latéral. Les lésions méniscales ont été observées uniquement sur le ménisque médial de 5 genoux opérés. Les lésions macroscopiques du cartilage (stade de fibrillation) ont été notées dans un ordre de fréquence décroissant sur les condyles tibiaux médial et latéral, le condyle fémoral latéral, la trochlée fémorale, le condyle fémoral médial et enfin la patelle. L'examen histologique a révélé que la couche superficielle du cartilage était fibrillée et discontinue. La plupart des cellules étaient rondes et disposées tangentiellement à la surface. Dans les zones transitionnelle et profonde, quelques chondrocytes étaient modérément hypertrophiques et des amas de chondrocytes ont été uniquement observés dans la couche profonde. Concernant la membrane synoviale, un épaississement du mésothélium et une importante densité de collagène ont été notés et le rapport des épaisseurs mésothélium/fibres était entre 1/0.15 et 1/0.10 sur les genoux opérés et 1/0.05 sur les genoux témoins. Les images fournies ici pourront servir de références pour des travaux ultérieurs portant notamment sur les thérapies contre l'arthrose

Influence of oxide films on primary water stress corrosion cracking initiation of alloy 600

In the present study alloy 600 was tested in simulated pressurised water reactor (PWR) primary water, at 360 °C, under an hydrogen partial pressure of 30 kPa. These testing conditions correspond to the maximum sensitivity of alloy 600 to crack initiation. The resulting oxidised structures (corrosion scale and underlying metal) were characterised. A chromium rich oxide layer was revealed, the underlying metal being chromium depleted. In addition, analysis of the chemical composition of the metal close to the oxide scale had allowed to detect oxygen under the oxide scale and particularly in a triple grain boundary. Implication of such a finding on the crack initiation of alloy 600 is discussed. Significant diminution of the crack initiation time was observed for sample oxidised before stress corrosion tests. In view of these results, a mechanism for stress corrosion crack initiation of alloy 600 in PWR primary water was proposed

Un cas de panostéite chez un Cairn Terrier

La panostéite est une affection osseuse idiopathique du chien en croissance touchant habituellement les races de grande taille. Elle atteint préférentiellement les os longs. Elle se manifeste cliniquement par une boiterie, une douleur à la palpation diaphysaire et radiologiquement par des plages d’ossification intramédullaire. L’observation chez un chiot Cairn Terrier est apparue particulièrement intéressante du fait de sa rareté

Experimental Study of the Interactions Between Oxidation and Structural Defects

A multiscale study of the high temperature oxidation effects on high purity polycrystalline nickel behaviour is presented. In situ tensile tests have been carried out at room temperature on preoxidised thin foils. The results obtained lead to a better understanding of the strengthening effect of the oxide layer. Detailed examinations of the metal microstructure are also made after high temperature oxidation treatment. Atomic Force Microscope (AFM), Secondary Ion Mass Spectroscopy (SIMS), Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) are used to characterise the microstructure. Formation of voids at grain boundaries as well as vacancy injection are then discussed

Robert Jones bandage pressure range assessment using a pressure mapping system and application to band calibration

International audienceThe Robert Jones bandage (RJ) is a widely used bandage among veterinary surgeons to maintain physiological position of the limbs. It is a 3-layer composite bandage, which realization involves the use of several types of bands in a specific arrangement to give the bandage all its properties. Its proper making is difficult and requires experience, as the bandage needs to be not too tight or not too loose. This issue is a recurrent matter with every type of compression bandage (Rimaud et al. 2014). For the realization of a RJ, various types of bands can be used, depending on the surgeon but each layer has its own function that cannot be changed.The purpose of this study is to measure the pressure under a RJ bandage with a pressure mapping system and to evaluate the properties of some commonly used bands. The final application of these results is to propose a band calibration system to apply the correct pressure as a function of the band’s deformation