Analyse du comportement dynamique de mousses de polyuréthane par des tests vibratoires

L’objectif de cet article est de décrire les techniques expérimentales et l’identification des propriétés dynamiques de mousses de polyuréthane. En effet, le niveau de confort d’un siège automobile est établien considérant les propriétés quasi-statiques – densité, portance et résilience – et dynamiques – transmissibilité – de la mousse flexible de polyuréthane. Notre dispositif d’essai est un système à un degré de liberté, composé d’un dispositif expérimental reposant sur le vérin d’une machine d’essai dynamique. Ce dispositif expérimental est composé d’un plateau supérieur avec une masse libre et d’un plateau inférieur solidaire de la machine d’essai, entre lesquels est placé un échantillon de mousse de dimensions100x100x50 mm3. Les vibrations transmises à travers la mousse sont mesurées pour déterminerles caractéristiques dynamiques de l’échantillon et permettent de réaliser le diagramme de Bodede la transmissibilité de l’échantillon. Cinq types de mousses de polyuréthane utilisées dans l’automobile seront comparés dans cet article

Contribution to the dynamic comfort of automobile seats from the comprehension of polyurethane foam

L'amélioration du confort dans le secteur automobile constitue actuellement un enjeu majeur. Au coeur de ces préoccupations se trouve le système d'assise, interface majeure entre l'occupant et l'environnement vibratoire du véhicule. Ce mémoire traite de l'étude du constituant principal du siège automobile : la mousse de polyuréthane.Un large panel d'échantillons de ces mousses dont les paramètres de fabrication ont été sélectionnés par l'établissement de plans d'expérience, a été testé selon divers protocoles expérimentaux afin de déterminer leurs caractéristiques physiques, mécaniques quasi-statiques et dynamiques. Un protocole et un dispositif innovant a été conçu pour caractériser la mousse soumise aux vibrations. Des analyses statistiques et des études en composantes principales ont permis de mettre en évidence les corrélations existantes entre les différentes propriétés citées.Une modélisation rhéologique, adaptée à l'application dans un contexte industriel, a été réalisée. Dans ce but, une étude comparative du comportement de différents types de modèles confrontés à certains échantillons de mousse polyuréthane, a été menée.Afin d'extrapoler les résultats obtenus sur les échantillons de mousse vers le siège complet, des essais complémentaires ont été réalisés avec différentes formulations tant en étude quasi-statique que dynamique.L'étude des paramètres de fabrication, des propriétés physiques et de ses comportements mécaniques ont permis de mettre en lumière les liens existants entre ces différentes caractéristiques. Ainsi, il devient possible de concevoir une matelassure aux propriétés prédites en amont et de minimiser le temps de conception d'un siège.The improvement of comfort in the automotive industry is a major challenge for car manufacturers and suppliers. At the heart of these concerns is the base seat system, major interface between the occupant and the vehicle vibration environment. This dissertation deals with the study of the main car seat sub-component: polyurethane foam.A wide range of polyurethane foam samples have been molded for a design of experiments according to selected process parameters. Several experimental protocols were employed to determine their physical properties, mechanical quasi-static and dynamic characteristics. A new protocol and an innovative device have been designed to characterize the foam sample submitted to vibrations. Statistical and principal components analysis helped to highlight existing correlations between those properties.A rheological model, adapted to the application in an industrial context, was carried out. For this purpose, a comparative study of the performance of different models applied to various polyurethane foam samples was conducted.To extrapolate the results on foam samples to a complete seat, additional tests have been performed with different formulations in both quasi-static and dynamic studies.The analysis of process parameters, physical properties and quasi-static and dynamic behaviors allowed highlighting of the links between these different features. Thus, it becomes possible to design a foam pad with predicted properties and minimize the time to design a car seat

Harmonic Vibration Test for the Analysis of the Dynamic Behaviour of Polyurethane Foams

International audienceThe main goal of this paper is to describe experimental techniques and identification of dynamic properties offlexible polyurethane foam. Indeed, automotive seat comfort level is established with considering quasi-static -density core, hysteresis loss and compression set - and dynamic -transmissibility and damping - properties offlexible polyurethane foams. Our dynamic system, modeled as a single degree-of-freedom system, is composedof an experimental device with a free mass on the top and a shaker on the basement. The first one, a rigid block,is mounted on a 100x100x50 mm cube sample of foam material and the second one excites the device with harmonicvibration. The steady-state response of a polyurethane foam sample – after the same number of cycles –to harmonic vibration is analyzed for different excitation amplitude level and for different initial compression level,corresponding respectively to various road surface conditions and to various apparent-mass. The transmittedvibration between the shaker and the free mass is measured to determine the damping power and the filter bandof polyurethane foam, and enables to trace the Bode magnitude and phase plots of the dynamic stiffness functionof the system. The results presented here compare 3 types of OEM foams

Characterization of Vibrational Mechanical Properties of Polyurethane Foam

International audiencePolyurethane foam (PU) is widely used in numerous comfort applications such as automotive seat cushioning and mattresses. The present paper is devoted to describe experimental techniques and identification of dynamic properties of thin flexible polyurethane foam used in automotive seats. In the experimental device, a free mass is mounted on a 0.1square meterof different foams used in car upholstery. The foam is the only flexible component. The device is excited with an electrodynamic shaker with frequencies varying between 10 and 200 Hz. The response of foam samples to sweep sine excitation is analyzed for different excitation acceleration amplitude (1 to 2,5 mm.s-2) and for different free masses.In order to answer the issue of replacement, different multilayer products and single foam samples have been characterized and comparisons have been carried out. The results of this study show interesting properties in terms of dynamic behavior of multilayer products when compared to the PU foams

Third metacarpal bone mineral density assessment in the standing horse by dual X-day absorptiometry suitability, precision and accuracy

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Tamoxifen treatment in the neonatal period affects glucose homeostasis in adult mice in a sex-dependent manner

International audienceTamoxifen is a selective estrogen receptor modulator used to activate the CRE ERT2 recombinase, allowing tissue-specific and temporal control of the somatic mutagenesis to generate transgenic mice. Studies integrating development and metabolism require a genetic modification induced by a neonatal tamoxifen administration. Here, we investigate the effects of a neonatal tamoxifen administration on energy homeostasis in adult male and female C57BL/6J mice. C57BL/6J male and female mouse pups received a single injection of tamoxifen one day after birth (NTT) and were fed a high-fat/high-sucrose (HF/HS) diet at 6 weeks of age. We measured weight, body composition, glucose and insulin tolerance, basal metabolism and tibia length and weight in adult mice. The neonatal tamoxifen administration exerted long-term, sex-dependent effects on energy homeostasis. NTT female mice became overweight and developed impaired glucose control in comparison to vehicle-treated littermates. NTT females exhibited 60% increased fat mass, increased food intake, decreased physical activity and decreased energy expenditure, impaired glucose and insulin tolerance, and fasting hyperglycemia and hyperinsulinemia. In contrast, NTT male mice exhibited a modest amelioration of glucose and insulin tolerance, and long-term decreased lean mass linked to decreased bone weight. These results suggest that the neonatal tamoxifen administration exerted a marked and sex-dependent influence on adult energy homeostasis and bone weight, and must therefore be used with caution for the development of transgenic mouse models regarding studies on energy homeostasis and bone biology

Osteoclast‐Derived Autotaxin, a Distinguishing Factor for Inflammatory Bone Loss

International audienceOBJECTIVE : The severity of rheumatoid arthritis (RA) correlates directly with bone erosions arising from osteoclast (OC) hyperactivity. Despite the fact that inflammation may be controlled in patients with RA, those in a state of sustained clinical remission or low disease activity may continue to accrue erosions, which supports the need for treatments that would be suitable for long-lasting inhibition of OC activity without altering the physiologic function of OCs in bone remodeling. Autotaxin (ATX) contributes to inflammation, but its role in bone erosion is unknown. METHODS : ATX was targeted by inhibitory treatment with pharmacologic drugs and also by conditional inactivation of the ATX gene Ennp2 in murine OCs (ΔATXC tsk ). Arthritic and erosive diseases were studied in human tumor necrosis factor-transgenic (hTNF+/- ) mice and mice with K/BxN serum transfer-induced arthritis. Systemic bone loss was also analyzed in mice with lipopolysaccharide (LPS)-induced inflammation and estrogen deprivation. Joint inflammation and bone erosion were assessed by histology and micro-computed tomography. The role of ATX in RA was also examined in OC differentiation and activity assays. RESULTS : OCs present at sites of inflammation overexpressed ATX. Pharmacologic inhibition of ATX in hTNF+/- mice, as compared to vehicle-treated controls, significantly mitigated focal bone erosion (36% decrease; P < 0.05) and systemic bone loss (43% decrease; P < 0.05), without affecting synovial inflammation. OC-derived ATX was revealed to be instrumental in OC bone resorptive activity and was up-regulated by the inflammation elicited in the presence of TNF or LPS. Specific loss of ATX in OCs from mice subjected to ovariectomy significantly protected against the systemic bone loss and erosion that had been induced with LPS and K/BxN serum treatments (30% reversal of systemic bone loss [P < 0.01]; 55% reversal of erosion [P < 0.001]), without conferring bone-protective properties. CONCLUSION : Our results identify ATX as a novel OC factor that specifically controls inflammation-induced bone erosions and systemic bone loss. Therefore, ATX inhibition offers a novel therapeutic approach for potentially preventing bone erosion in patients with RA

Expression of the type 1 lysophosphatidic acid receptor in osteoblastic cell lineage controls both bone mineralization and osteocyte specification.

International audienceLysphosphatidic acid (LPA) is a major natural bioactive lipid mediator whose biological functions affect multiple organs. These include bone as demonstrated by global Lpar1-knockout mice (Lpar1-/-) which present a bone growth defect. LPA acts on all bone cells including osteoblasts, that are responsible for bone formation, and osteoclasts, which are specialized cells that resorb bone. LPA appears as a potential new coupling molecule during bone remodeling. LPA1 is the most ubiquitous LPA receptor among the six LPA receptor family members (LPA1-6). To better understand the specific role of LPA via its receptor LPA1 in osteoblastic cell lineage we generated osteoblast-specific Lpar1 knockout mice (Lpar1-∆Ob) by crossing Lpar1flox/flox and Osx:Cre+ mouse lines. Lpar1-∆Ob mice do not recapitulate the bone defects of Lpar1-/- mice but revealed reduced bone mineralization and decreased cortical thickness, as well as increased bone porosity associated with an augmentation in the lacunae areas of osteocyte and their apoptotic yield. In vitro, primary Lpar1-∆Ob and immortalized cl1-Ob-Lpar1-/- osteoblasts revealed a remarkable premature expression of alkaline phosphatase, reduced cell proliferation associated with decreased YAP-P nuclear accumulation, and reduced mineralization activity. Osteocyte specification is markedly impaired as demonstrated by reduced expression of early (E11) and late (DMP1, DKK1, SOST) osteocyte markers ex vivo in enriched osteocytic fractions of Lpar1-∆Ob mouse bone explants. In addition, E11 expression and dendrite formation induced by FGF2 are markedly impaired in both primary Lpar1-∆Ob and immortalized cl1-Ob-Lpar1-/- osteoblasts. Taken together these results suggest a new role for LPA in bone mass control via bone mineralization and osteocyte function