Modélisation thermique de la dégradation d’un matériau composite soumis au feu

Composite materials are increasingly used in new generation aircraft structures. Mass and as a consequence fuel savings encourage aircraft manufacturers to use them optimally. However, these materials can degrade quickly when exposed to significant heat fluxes, resulting in a loss of mechanical strength. This problem can be dramatic for passenger safety as mechanical resistance of such innovative structures can not be ensured in case of fire events. Current certification methods of fire resistance of aeronautical composite materials are mainly based on experiments, that are only representative of the specific conditions under which they were carried out. The understanding of thermal, chemical and mechanical phenomena occurring during the decomposition of these materials, with the support of numerical simulations and experiments, can help improving existing methods and optimizing the future aeronautical structures from the design chain. This study deals with the development and validation of a multi-components and multi-dimensional thermo-chemical model of decomposing composite materials. It can deal with complex degradations following several decomposition reactions as well as transport of pyrolysis gases from their formation up to their ejection out of the material. The use of advanced homogenization laws isproposed to account for the chemical transformations on heat and mass transfers occurring in the material. The application of the thermo-chemical model to a laser degradation study under known but non-uniform heat flux in a controlled environment allows to confront the simulation results with experimental measurements and thus validate the multi-components approach. Finally, the numerical analysis of a decomposing composite material submitted to a flame highlights the effectof emitted decomposition gases on the exchanged parietal heat flux.L’utilisation des matériaux composites devient de plus en plus importante dans les structures aéronautiques de nouvelle génération. Le gain de masse engendré, et donc de carburant, pousse les constructeurs aéronautiques à les employer de façon optimale. Néanmoins, ces matériaux se dégradent rapidement lorsqu’ils sont soumis à des flux de chaleur importants, entraînant une perte de leur résistance mécanique. Ce problème peut être dramatique pour la sécurité des passagers car la tenue de ces nouvelles structures peut ne plus être assurée dans le cas d’un incendie. Les méthodes actuelles de certification de la tenue au feu des matériaux composites aéronautiques reposent principalement sur l’utilisation de moyens expérimentaux, dont les résultats ne sont représentatifs que des conditions particulières dans lesquelles les essais ont été réalisés. La compréhension des différents phénomènes thermiques, chimiques et mécaniques intervenantlors de la dégradation de ces matériaux, avec l’appui de simulations numériques et d’expériences, peut permettre d’améliorer les méthodes existantes et donc d’optimiser les futures structures aéronautiques dès la phase de conception.Cette étude s’est attachée à développer et valider un modèle thermo-chimique de dégradation des matériaux composites multi-dimensionnel et multi-constituants. Ce modèle permet de traiter des cinétiques de dégradation complexes suivant plusieurs réactions de décompositions et de prendre en compte le transport des gaz produits depuis leur formation jusqu’à leur évacuation hors du matériau. L’utilisation de lois d’homogénéisation avancées est proposée afin de rendre compte deseffets des transformations sur les transferts de chaleur et de masse se produisant au sein du matériau. L’application du modèle thermo-chimique à un cas de dégradation sous flux thermique connu mais non-uniforme dans un environnement contrôlé permet de confronter les résultats de simulation aux mesures expérimentales et ainsi de valider l’approche multiconstituants adoptée. Enfin, l’étude numérique de la dégradation d’un composite soumis à une flamme met en avant l’effetdes gaz de décomposition éjectés à l’interface sur le flux thermique pariétal échangé

Chronic pelvic pain: comorbidity between chronic musculoskeletal pain and vulvodynia.

Chronic pelvic pain (CPP) is a common condition that has a major impact on the quality of life of both men and women. Male CPP is usually attributable to well-defined urogenital conditions (most frequently infectious/non infectious prostatic diseases) or musculoskeletal or bowel diseases, whereas the features of female CPP are much more complex and are of particular clinical and epidemiological importance. It is a multifactorial syndrome that can be due to diseases of the urogenital, gastrointestinal, or musculoskeletal systems, or to neurological or neuropsychiatric disorders. It is not always easy to identify its predominant pathogenesis, although it often occurs as a central sensitization syndrome triggered by an initial stimulus which is no longer detectable and only manifests itself clinically through pain. In this respect, there are some very interesting relationships between vulvodynia and fibromyalgic syndrome, as identified in a preliminary study of women with chronic musculoskeletal pain in which it was demonstrated that vulvar pain plays an important role, although it is often overlooked and undiagnosed

Use of reciproc instruments with different motions: cyclic fatigue testing with simulation of the body temperature

Aim: To assess the influence of different motions on the cyclic fatigue resistance of Reciproc instruments simulating the temperature of the clinical conditions. Methods: The sample size was determined using statistical software set with the following parameters: \u3b1=0.05, \u3b2=0.20, \u3b4=30.0, \u3c3=28.0. The experiment required 54 Reciproc files. Brand new R25 files were randomly allocated to three groups defined by the tested motion: continuous rotation at 300 rpm (n=18), \u201cRECIPROC\u201d mode (n=18), and \u201cWAVEONE\u201d mode (n=18). The same endodontic motor was used for all groups (X-Smart IQ). All files were rotated/reciprocated until fracture inside a custom-designed artificial canal with 60\ub0 angle and 5-mm radius of curvature milled in a stainless-steel block. The testing device was electrically heated to keep its internal temperature at 35\ub11\ub0C, which was constantly monitored with a thermometer. After file separation, the time to failure was registered with a digital chronometer and the length of the fractured fragment measured with a digital calliper. The fracture surface of each file was observed at the scanning electron microscope to perform a qualitative fractographic analysis. The collected data (time to fracture and fracture length) were tested for the normality of the distribution and the equality of variances with a Shapiro-Wilk and a Levene test, respectively. The dependent variables were compared amongst groups by means of a multivariate analysis of variance and Tuckey post-hoc test (p=0.05). Results: The continuous rotation group exhibited the shortest lifespan among the considered groups (85.4\ub19.5 s to failure). Both reciprocating motions were associated with a significant improvement of fatigue resistance (p<0.001). The \u201cRECIPROC\u201d mode allowed for longer time to failure than the \u201cWAVEONE\u201d mode, with 141.6\ub119.4 s and 117.2\ub111.2 s to failure, respectively. The absence of differences among the considered groups in terms of fracture length confirmed the correct positioning of the files inside the artificial canal. The scanning electron microscopic analysis showed signs of file separation ascribable to cyclic fatigue. Conclusion: The present study preliminary demonstrated that the native \u201cRECIPROC\u201d motion use of R25 Reciproc files should be preferred over other types of motions to prevent file separation in the clinical setting

O que mudou no cenário canavieiro 30 anos após o levante de Guariba?

Em 1984, em Guariba, SP, ocorreu um grande protesto de boias-frias que resultou em mudanças das condições enfrentadas nas lavouras de cana-de-açúcar. Neste trabalho, para avaliar o que mudou nos últimos 30 anos na paisagem, na forma de manejo da cana-de-açúcar, na vida dos trabalhadores rurais e do município, mapeou-se a mudança de uso e cobertura das terras usando imagens de satélite de 1988 e 2013, que foram interpretadas usando o software ArcGis 10.1 e as ferramentas de análise do ArcToolbox. Há 30 anos, a área de cana-de-açúcar tomava 81% do município (22.037 ha) e atualmente ocupa em torno de 23 mil ha, portanto não houve mudança expressiva, qualitativa e quantitativamente, na paisagem rural. Porém, houve aumento expressivo na área urbana do município, que passou de 581 ha para 1.190 ha, provavelmente em decorrência do êxodo da população rural para a cidade e da fixação, no município, dos antigos migrantes sazonais do Nordeste, que se dedicavam à colheita manual da cana-de-açúcar. A mudança gradativa, nos últimos 30 anos, no sistema da colheita manual de cana queimada para a colheita mecanizada sem queima reduziu de 7.000 para 970 o número de boias-frias e fortaleceu o sindicalismo na região. Trinta anos depois da maior greve rural do setor canavieiro, o transporte dos trabalhadores é feito em ônibus, há equipamentos de proteção, as empresas fornecem facões e os salários melhoraram. Entretanto, novas questões trabalhistas surgiram, como terceirização e jornadas de trabalho irregulares, horas extras ilegais, ausência de intervalos de descanso e trabalho noturno