Tribological study of a press-fit assembling process

International audienceA particular case of press-fitting of two metal parts is studied, with high fit interference inducing high contact pressures and plastic deformation of the bushing and collar. Furthermore, the female piece is polymer-coated by cataphoresis, and the coating evolution by damage and wear during sliding promotes significant changes of friction with sliding length. These particular frictional properties impact the structural mechanics behaviour of the system during assembling

Etude expérimentale et modélisation de l'évolution couplée du frottement et de l'usure dans un contact entre une surface métallique et un revêtement polymère

International audienceDans une jonction statique, le frottement a la particularité de devoir atteindre un fort niveau en fin d'assemblage, car il représente la majeure partie de la force de résistance de la jonction en service. Ce niveau de frottement est conféré par le procédé d'assemblage. Nous nous intéressons ici aux relations entre frottement et usure pour un assemblage polymère - métal caractérisé par un contact sous haute pression (localement, plus de 500 MPa), mais à basse vitesse (quelques mm.s-1) et avec une faible longueur de glissement (inférieure à 10 mm). Pour simuler ce contact, des essais tribologiques en régime linéaire alternatif ont été mis au point, dans lequel ont été utilisés des objets les plus proche possible des pièces réelles. Le polymère est celui qui reste en contact permanent, le métal voyant, lui, défiler la zone de contact. Le frottement augmente fortement au début de l'essai, puis se stabilise. En observant les surfaces en microscopie optique et électronique, on montre qu'une forte usure du polymère se produit, et que les particules d'usure se déposent pour une grande part dans la rugosité de la surface métallique. Des essais complémentaires montrent que ce piégeage de particules d'usure est la cause principale de l'augmentation du frottement. Un paramètre essentiel est la rugosité du métal, dont l'usure et la croissance du frottement sont fonctions croissantes. La croissance du frottement est modélisée sur la base du concept de troisième corps et d'un bilan de la circulation des particules d'usure. La comparaison aux courbes expérimentales de frottement montre la pertinence de ce modèle

Etude de l'évolution couplée du frottement et de l'usure dans un contact entre une surface métallique et un revêtement polymère

National audienceDans une jonction statique, le frottement a la particularité de devoir atteindre un fort niveau car il représente la majeure partie de la force de résistance de la jonction. Ce niveau de frottement est conféré par le procédé d'assemblage. Nous nous intéressons ici aux relations entre frottement et usure pour un assemblage polymère - métal caractérisé par un contact sous haute pression (localement, plus de 500 MPa), mais à basse vitesse (quelques mm.s-1) et avec une faible longueur de glissement (inférieure à 10 mm). Pour simuler ce contact, des essais tribologiques bille - plan en régime linéaire alternatif ont été mis au point, sous deux formes duales : le revêtement " usable ", polymère, est soit en contact permanent (bille revêtue sur tôle métallique plane et rugueuse), soit en contact transitoire (bille métallique rugueuse sur tôle plane revêtue de polymère)

TGFβ promotes low IL10-producing ILC2 with profibrotic ability involved in skin fibrosis in systemic sclerosis

Objective : Innate lymphoid cells-2 (ILC2) were shown to be involved in the development of lung or hepatic fibrosis. We sought to explore the functional and phenotypic heterogeneity of ILC2 in skin fibrosis within systemic sclerosis (SSc). Methods : Blood samples and skin biopsies from healthy donor or patients with SSc were analysed by immunostaining techniques. The fibrotic role of sorted ILC2 was studied in vitro on dermal fibroblast and further explored by transcriptomic approach. Finally, the efficacy of a new treatment against fibrosis was assessed with a mouse model of SSc. Results : We found that ILC2 numbers were increased in the skin of patients with SSc and correlated with the extent of skin fibrosis. In SSc skin, KLRG1− ILC2 (natural ILC2) were dominating over KLRG1+ ILC2 (inflammatory ILC2). The cytokine transforming growth factor-β (TGFβ), whose activity is increased in SSc, favoured the expansion of KLRG1- ILC2 simultaneously decreasing their production of interleukin 10 (IL10), which regulates negatively collagen production by dermal fibroblasts. TGFβ-stimulated ILC2 also increased myofibroblast differentiation. Thus, human KLRG1- ILC2 had an enhanced profibrotic activity. In a mouse model of SSc, therapeutic intervention-combining pirfenidone with the administration of IL10 was required to reduce the numbers of skin infiltrating ILC2, enhancing their expression of KLRG1 and strongly alleviating skin fibrosis. Conclusion : Our results demonstrate a novel role for natural ILC2 and highlight their inter-relationships with TGFβ and IL10 in the development of skin fibrosis, thereby opening up new therapeutic approaches in SSc

A wear particle-based model of friction in a polymer-metal high pressure contact

International audienceSliding contact under high pressure between a more or less rough metal surface and a polymer occurs in diverse manufacturing processes. Transfer of the softer material on the harder counterpart is a common phenomenon under such conditions (high pressure) due to high level of polymer wear. The transfer of worn polymer particles on the metal surface generally has a large influence on friction. A model of wear, transfer and their consequences on friction is described. Based on the third body concept, it shares the created wear particles between the transfer film and particles escaping the contact. The model includes unknown parameters describing particles creation and movement on the one hand, and the friction-transfer relationship on the other hand. The parameters are determined experimentally on a linear reciprocating sliding tribometer, where a polymer-coated bar slides on a rough metallic cylinder in a point contact configuration, under conditions of large sliding length (10 mm) and high pressure. Abrasive wear and transfer occur, the initial friction coefficient is shown to follow Coulomb's model (no variation with the applied average pressure); it increases with sliding length (or cycle number) due to increasing coverage of the metal surface by wear particles (or transfer film average thickness). It is shown finally that the model describes quite well the evolution of friction along several cycles

Extension of paralimbic low grade gliomas: toward an anatomical classification based on white matter invasion patterns.

OBJECT: Low grade gliomas are both proliferative and diffusive tumors, as recently modelized. When proliferation is predominant, the tumor is rather bulky and its main locations are the supplementary motor area and the paralimbic system. Diffusion occurs preferentially along white matter tracts. Recent anatomo-functional studies, performed both in vitro and in vivo, have described the fiber tracts centered around the insula. We thus propose to analyze the extension of paralimbic low grade gliomas in terms of invaded subcortical pathways. METHODS: We retrospectively reviewed the MRIs of patients followed for a WHO grade II glioma at the Salp?i? Hospital between 1991 and 2003. We selected patients with tumors centered on the insula and extending in temporal and frontal lobes (Type 2b-2c-3 of Yasargil's classification). We then analyzed on FLAIR sequences the extension (tracked on successive examinations before any treatment) along two main fasciculi in that area: the uncinate and arcuate fasciculi. RESULTS: A total of 40 patients fulfilled the inclusion criteria. The uncinate fasiculus was invaded in 28 cases, the arcuate fasciculus in 9 cases, and both fasciculi in 3 cases. Longitudinal follow-up was available in 16 cases, and confirmed the preferential extension along these fasciculi. CONCLUSION: This kinetic analysis of extension of paralimbic low grade gliomas confirms that these tumors spread along distinct subcortical fasciculi. Due to the functional role of these pathways, this classification could be useful to elaborate therapeutic strategy (prognosis index, pre- and intra-operative neuropsychological testing, functional outcome)

Superior longitudinal fasciculus subserves vestibular network in humans.

Vestibular function is known to be represented in a large-scale network within the brain. Although much is known about the topography of this cortical network, the subcortical anatomo-functional connectivity has received less attention. We present three patients operated on while conscious for cerebral low-grade gliomas, in which we elicited vestibular symptoms during subcortical stimulation. Anatomo-functional correlations between postoperative imaging and intraoperative findings suggest the involvement of the superior longitudinal fasciculus in the spreading of the vestibular symptoms. We argue that this fasciculus plays a major role in the functional connectivity of the areas involved in the complex multimodal network that controls vestibular function

The insular lobe and brain plasticity: Lessons from tumor surgery.

OBJECTIVES: Despite recent literature supporting the likely role of the insula in many functions, the actual participation of this multimodal lobe in the brain functioning remains unclear, i.e. has the insula an essential or compensable role? PATIENTS AND METHODS: We surgically resected an insular low-grade glioma, using intraoperative electrical stimulation, in 42 patients who experienced seizures, but who presented no or only a slight neurological deficit. Surgery was performed under local anesthesia in patients with a lesion in the dominant hemisphere. The resection was systematically stopped according to cortico-subcortical functional boundaries. RESULTS: Intraoperative electrical mapping induced language disturbances, pain and vertigo, but no other side effects were observed. Post-operatively, the patients experienced a transient hemiparesis in 21 cases, language disorders in 10 cases, an athymhormic syndrome in 7 cases, a Foix-Chavany-Marie syndrome in 3 cases, and micturition disturbances in one case. Despite this immediate post-surgical worsening, all the patients recovered their preoperative neurological status within 3 months, except in three cases due to a deep stroke. CONCLUSION: These results show that the insula, a complex associative multimodal structure poorly studied until now, can be functionally compensated. Such a plastic potential may have important fundamental and clinical implications, in particular in the field of oncological neurosurgery