A conical mandrel tube drawing test designed to assess failure criteria

International audienceCold tube drawing is a metal forming process which enables to produce tubes with high dimensional precision. It consists in reducing tube dimensions by pulling it through a die. Tube outer diameter is calibrated by a die and the tube inner diameter and thickness are calibrated by a mandrel. One of the major concern of metal forming industry is the constant improvement of productivity and product quality. In the aim of pushing the process to the limit the question is how far the material can be processed without occurrence of failure. In the present study, a long conical mandrel with a small cone angle was designed in order to carry out drawing tests up to fracture with experimental conditions very close to the industrial process. The FEM of the process was built in order to access the local stress and strain data. A specific emphasis was put on the friction characterisation. For that purpose force measurement during the conical mandrel experiments enabled to characterise a pressure dependent friction coefficient constitutive law by means of an inverse analysis. Finally, eleven failure criteria were selected to study the drawability of cobalt-chromium alloy tubes. The assessment of failure criteria based on damage variables or damage accumulation variables involved their calibration on uniaxial tensile tests. The experimental studies were completed by SEM fractography which enabled to understand the fracture locus and the propagation direction of the fracture

Etude de l'interface NiTi/silicone

National audienceLa présente étude vise à élaborer et caractériser mécaniquement un composite architecturé, constitué de Nickel-Titane (NiTi) et de silicone. Afin de pouvoir envisager l'utilisation d'un tel composite, une bonne adhésion à l'interface entre ces deux matériaux doit être assurée. L'interface entre Nickel-Titane (NiTi) et polymères a été le sujet de nombreuses études récentes. Concernant plus particulièrement les élastomères, utilisés dans le cadre de la présente application, les études sont bien plus rares. Ce travail a donc consisté à étudier l'interface entre fil de NiTi et deux silicones chargés, l'un étant biocompatible. Plusieurs méthodes d'amélioration de l'interface entre ces deux matériaux ont été testées : une désoxydation des fils, un primaire favorisant l'adhésion, et un traitement plasma. Des essais de pull-out ont été réalisés pour déterminer l'influence de ces différentes méthodes. Les résultats ont montré qu'une forte amélioration de l'adhésion était obtenue en utilisant un primaire, un traitement plasma ou encore une combinaison de ces deux traitements 1 . Dans le cadre d'applications biomédicales, une attention particulière a été portée à l'étude des paramètres du traitement plasma. Une structure composée d'un tube tricoté de NiTi enrobé de silicone a ensuite été élaborée 2 à l'aide d'un traitement plasma par argon. Des essais de traction et gonflement ont été réalisés sur ce composite architecturé

Effects of temperature on the mechanical behavior of filled and unfilled silicone rubbers

International audienceIn this contribution, the influence of the temperature on the mechanical behavior of a filled and an unfilled silicone rubber was analyzed. Firstly, the crystallization and melting temperatures were determined by differential scanning calorimetry. Secondly, mechanical tests were carried out at different temperatures above that of crystallization, up to 150°C. Results show that both silicone rubbers exhibit an entropic behavior in this temperature range. Thirdly, the temperature influence on the stress softening and mechanical hysteresis is studied and analyzed

Effects of temperature on the mechanical behavior of filled and unfilled silicone rubbers

International audienceIn this contribution, the influence of the temperature on the mechanical behavior of a filled and an unfilled silicone rubber was analyzed. Firstly, the crystallization and melting temperatures were determined by differential scanning calorimetry. Secondly, mechanical tests were carried out at different temperatures above that of crystallization, up to 150°C. Results show that both silicone rubbers exhibit an entropic behavior in this temperature range. Thirdly, the temperature influence on the stress softening and mechanical hysteresis is studied and analyzed

Modeling of hysteresis by means of a directional approach. Constitutive Models

International audienceThis paper focuses on the mechanical hysteresis in elastomers, i.e. the difference between loading and unloading paths. This property can be time-dependent as well as time-independent, depending on the physical phenomena that come into play. Similarly, mechanical hysteresis can be affected or not by material anisotropy. In this context, the present study is devoted to the modeling of time-independent hysteresis, in the framework of material anisotropy, accommodated to the Mullins effect. For this purpose, directional model is used to predict the tridimensional response of such materials. The proposed model is based on the stress decomposition into two parts. The first one represents the hyperelasticity of the macromolecular network, whereas the second part represents the friction in the network, i.e. the hysteretic part. Experiments were carried with filled silicone rubber and results show that the model predictions and experimental curves fit well

Mdscs in Infectious diseases: regulation, roles, and readjustment

Many pathogens, ranging from viruses to multicellular parasites, promote expansion of MDSCs, which are myeloid cells that exhibit immunosuppressive features. The roles of MDSCs in infection depend on the class and virulence mechanisms of the pathogen, the stage of the disease, and the pathology associated with the infection. This work compiles evidence supported by functional assays on the roles of different subsets of MDSCs in acute and chronic infections, including pathogen-associated malignancies, and discusses strategies to modulate MDSC dynamics to benefit the host

Evolution of the levels of human leukocyte antigen G (HLA-G) in Beninese infant during the first year of life in a malaria endemic area: using latent class analysis

Abstract Background: HLA-G, a non-classical HLA class I antigen, is of crucial interest during pregnancy by inhibiting maternal immune response. Its role during infections is discussed, and it has been described that high levels of soluble HLA-G during childhood increase the risk of malaria. To explore more precisely interactions between soluble HLA-G and malaria, latent class analysis was used to test whether distinct sub-populations of children, each with distinctive soluble HLA-G evolutions may suggest the existence of groups presenting variable malaria susceptibility. Method: A study was conducted in Benin from 2010 to 2013 and 165 children were followed from birth to 12 months. Evolution of soluble HLA-G was studied by the latent class method. Results: Three groups of children were identified: one with consistently low levels of soluble HLA-G during follow-up, a second with very high levels and a last intermediate group. In all groups, low birth weight, high number of malaria infections and high exposure to malaria transmission were associated with high level of soluble HLA-G. Placental malaria was not. Presence of soluble HLA-G in cord blood increased the probability of belonging to the highest trajectory. Conclusion: These results, together with previous ones, confirm the important role of HLA-G in the individual susceptibility to malaria. Assaying soluble HLA-G at birth could be a good indicator of newborns more fragile and at risk of infections during childhood

Tolerogenic Function of Dimeric Forms of HLA-G Recombinant Proteins: A Comparative Study In Vivo

HLA-G is a natural tolerogenic molecule involved in the best example of tolerance to foreign tissues there is: the maternal-fetal tolerance. The further involvement of HLA-G in the tolerance of allogeneic transplants has also been demonstrated and some of its mechanisms of action have been elucidated. For these reasons, therapeutic HLA-G molecules for tolerance induction in transplantation are actively investigated. In the present study, we studied the tolerogenic functions of three different HLA-G recombinant proteins: HLA-G heavy chain fused to β2-microglobulin (B2M), HLA-G heavy chain fused to B2M and to the Fc portion of an immunoglobulin, and HLA-G alpha-1 domain either fused to the Fc part of an immunoglobulin or as a synthetic peptide. Our results demonstrate the tolerogenic function of B2M-HLA-G fusion proteins, and especially of B2M-HLA-G5, which were capable of significantly delaying allogeneic skin graft rejection in a murine in vivo transplantation model. The results from our studies suggest that HLA-G recombinant proteins are relevant candidates for tolerance induction in human transplantation

Impact of early enteral versus parenteral nutrition on mortality in patients requiring mechanical ventilation and catecholamines: study protocol for a randomized controlled trial (NUTRIREA-2)

BACKGROUND: Nutritional support is crucial to the management of patients receiving invasive mechanical ventilation (IMV) and the most commonly prescribed treatment in intensive care units (ICUs). International guidelines consistently indicate that enteral nutrition (EN) should be preferred over parenteral nutrition (PN) whenever possible and started as early as possible. However, no adequately designed study has evaluated whether a specific nutritional modality is associated with decreased mortality. The primary goal of this trial is to assess the hypothesis that early first-line EN, as compared to early first-line PN, decreases day 28 all-cause mortality in patients receiving IMV and vasoactive drugs for shock. METHODS/DESIGN: The NUTRIREA-2 study is a multicenter, open-label, parallel-group, randomized controlled trial comparing early PN versus early EN in critically ill patients requiring IMV for an expected duration of at least 48 hours, combined with vasoactive drugs, for shock. Patients will be allocated at random to first-line PN for at least 72 hours or to first-line EN. In both groups, nutritional support will be started within 24 hours after IMV initiation. Calorie targets will be 20 to 25 kcal/kg/day during the first week, then 25 to 30 kcal/kg/day thereafter. Patients receiving PN may be switched to EN after at least 72 hours in the event of shock resolution (no vasoactive drugs for 24 consecutive hours and arterial lactic acid level below 2 mmol/L). On day 7, all patients receiving PN and having no contraindications to EN will be switched to EN. In both groups, supplemental PN may be added to EN after day 7 in patients with persistent intolerance to EN and inadequate calorie intake. We plan to recruit 2,854 patients at 44 participating ICUs. DISCUSSION: The NUTRIREA-2 study is the first large randomized controlled trial designed to assess the hypothesis that early EN improves survival compared to early PN in ICU patients. Enrollment started on 22 March 2013 and is expected to end in November 2015. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT01802099 (registered 27 February 2013)