113 research outputs found
Effect of the matrix behavior on the damage of ethyleneâpropylene glass fiber reinforced composite subjected to high strain rate tension
This study investigates the origin of the strain rate effect on the mechanical behavior of a discontinuous glass fiber reinforced ethyleneâpropylene copolymer (EPC) matrix composite. This kind of composite materials are commonly used for automotive functional and structural applications. To this aim, a multi-scale experimental approach is developed. The deformation processes and the damage mechanisms observed at the microscopic scale are related to the material mechanical properties at the macroscopic scale. Tensile tests up to failure and specific interrupted tensile tests have been optimized and performed for high strain rates up to 200 s 1 to quantify the strain rate effect at different scales. High speed tensile tests have also been performed on the pure copolymer matrix. The threshold and the kinetic of damage have been quantified at both microscopic and macroscopic scales. Experimental results show that the composite behavior is strongly strain-rate dependent. The multi-scale analysis leads to the conclusion that the strain rate effect on the damage behavior of the EPC matrix composite is mainly due to the viscous behavior of the EPC matrix. SEM observations and analysis show that a localized deformation in the interface zone around fibers occurs at high strain rates and directly affects the visco-damage behavior. It is established that when the strain rate increases, the local deformation zone around the fibers behaves like a dissipation zone. Consequently, the damage initiation is delayed and the related kinetic is reduced with respect to the quasi-static loading case
Effect of the matrix behavior on the damage of ethyleneâpropylene glass fiber reinforced composite subjected to high strain rate tension
This study investigates the origin of the strain rate effect on the mechanical behavior of a discontinuous glass fiber reinforced ethyleneâpropylene copolymer (EPC) matrix composite. This kind of composite materials are commonly used for automotive functional and structural applications. To this aim, a multi-scale experimental approach is developed. The deformation processes and the damage mechanisms observed at the microscopic scale are related to the material mechanical properties at the macroscopic scale. Tensile tests up to failure and specific interrupted tensile tests have been optimized and performed for high strain rates up to 200 s 1 to quantify the strain rate effect at different scales. High speed tensile tests have also been performed on the pure copolymer matrix. The threshold and the kinetic of damage have been quantified at both microscopic and macroscopic scales. Experimental results show that the composite behavior is strongly strain-rate dependent. The multi-scale analysis leads to the conclusion that the strain rate effect on the damage behavior of the EPC matrix composite is mainly due to the viscous behavior of the EPC matrix. SEM observations and analysis show that a localized deformation in the interface zone around fibers occurs at high strain rates and directly affects the visco-damage behavior. It is established that when the strain rate increases, the local deformation zone around the fibers behaves like a dissipation zone. Consequently, the damage initiation is delayed and the related kinetic is reduced with respect to the quasi-static loading case
On the measurement of social progress and well being: some further thoughts
Two years after the delivery of the report on The Measurement of Economic Performances and Social Progress (Stiglitz-Sen-Fitoussi),this paper provides some further reflections on the subject. Since 2008, when the work of the Commission began, the world has experienced several dramatic events which all call into question our measurement systems and the policies which were grounded on them: the financial crisis of 2007-2008, the grave events in Japan, the Sovereign debt crisis, and the revolutions in the Arabic world. In particular, the Japanese earthquake and its aftermath underlines three central shortcomings of our metrics: the measurement of the economic product,the measurement of well being, and the measurement of sustainability. For economists, these concerns are especially important, because we often rely on statistical (econometric analyses) to make inferences about what are good policies. Those inferences are only as reliable as the metrics that they are based on. Our statistical systems should tell us whether or not what we are doing is sustainable, economically, environmentally, politically, or socially and whether proposed policies will in fact enhance well-being . There would be little sense in pursuing policies aimed at increasing some widely used metric like GDP ifsuch policies lead to a decrease in well being.1- Economic indicators 2- Gross Domestic Products 3-Social indicators 4- Well being 5- Sustainability
G20 and recovery and beyond: an agenda for global governance for the twentyâfirst century.
This item has no abstract.
Shape Memory Effect and Properties Memory Effect of Polyurethane
The relationship between shape and properties memory effect, especially viscoelastic properties of polyurethane under study is the main aim of this research work. Tensile tests have been performed in order to introduce 100% of deformation in the polyurethane samples. Under this deformation, stressârelaxation experiments have been performed in order to eliminate the residual stresses. This deformation of the samples has been fixed by cooling. Recovery tests, then, were carried out at different isothermal temperatures that varied from 30 C to 60 C. Viscoelastic behavior has been studied by a biparabolic model and by using the ColeâCole method. It was shown that this model describes the behavior of the polymer at the different states of shape memory tests. The constants of this model then have been determined. This study leads to a better understanding of the mechanism of shape memory effect. The comparison between the virgin polymer and the polymer after a recovery test by DMTA (dynamic mechanical thermal analysis) and by ColeâCole method has illustrated that the polymer does not obtain its initial properties even when it was totally regained its initial shape. These results have been confirmed by three successive shape memory tests on the same sample and by comparing the mechanical characteristics of different cycles because ââshape memory effectââ and ââproperties memory effectââ do not follow the same mechanisms
Nouvelles rĂ©flexions sur la mesure du progrĂšs social et du bien-ĂȘtre
Dans la foulĂ©e du Rapport Stiglitz-Sen-Fitoussi, nous proposons ici de nouvelles rĂ©flexions sur le progrĂšs social et le bien-ĂȘtre, qui annoncent de nouveaux travaux et de nouvelles avancĂ©es. Ă partir de quelques exemples simples empruntĂ©s Ă l'actualitĂ©, nous montrons d'abord comment notre systĂšme statistique actuel, du fait Ă la fois des lacunes des indicateurs existants et de l'absence d'alternatives crĂ©dibles, peut implicitement conduire Ă des conclusions de politique publique entachĂ©es d'erreur. Ceci importe au plus haut point car ce que nous mesurons affecte ce que nous faisons. RĂ©duire le bien-ĂȘtre en vue d'augmenter quelque imparfaite mesure de la richesse matĂ©rielle que ce soit donne lieu Ă des politiques totalement erronĂ©es. Nous portons ensuite notre attention, selon cette mĂȘme perspective critique des indicateurs et instruments de mesure actuels, sur des questions essentielles du dĂ©bat Ă©conomique contemporain telles que l'effet sur le chĂŽmage de la flexibilitĂ© des marchĂ©s du travail ou encore l'impact sur la croissance du degrĂ© d'ouverture financiĂšre des Ă©conomies. Notre Ă©valuation des mesures existantes de bien-ĂȘtre nous laisse convaincus Ă cet Ă©gard que, trop souvent, elles ont conduit les pays Ă s'orienter dans de mauvaises directions, ou Ă tout le moins Ă adopter des politiques dont les bĂ©nĂ©fices sont trĂšs discutables. Nous montrons en somme qu'il existe des possibilitĂ©s considĂ©rables d'amĂ©liorer les indicateurs de bien-ĂȘtre et d'en dĂ©velopper de nouveaux pour mieux servir les buts collectifs des sociĂ©tĂ©s humaines. [Premier paragraphe
« Gn fantÎme » : les voies pour sortir de la crise en renforçant la solidarité mondiale.
Cette annĂ©e, les membres du Gn se rĂ©unissent au plus fort dâune pĂ©riode critique de lâHistoire contemporaine, du moins sur le plan Ă©conomique et social : ils doivent affronter la plus grave crise des 80 derniĂšres annĂ©es. En paraphrasant Keynes on peut aller jusquâĂ affirmer que le destin du monde est entre leurs mains. Ils peuvent agir de maniĂšre telle quâil soit possible de sortir de la crise en crĂ©ant les conditions pour quâĂ lâavenir la croissance soit plus soutenable et plus favorable Ă lâenvironnement, et que ses fruits soient distribuĂ©s de maniĂšre plus Ă©quitable Ă la fois au sein de chaque pays et entre eux. Autrement, ils devront assumer lâĂ©crasante responsabilitĂ© historique dâavoir manquĂ© au mandat qui leur a Ă©tĂ© confiĂ© par leurs peuples, alors que les circonstances exceptionnelles quâils rencontrent leur offrent une marge de manoeuvre beaucoup plus grande que celle dont ils disposent en temps « normal ». Câest pourquoi un groupe « dâexperts », sans aucune autre injonction que celle qui dĂ©coule de leur condition de citoyens du monde, a dĂ©cidĂ© de se rĂ©unir pour rĂ©flĂ©chir Ă ce qui peut ĂȘtre fait, en espĂ©rant que de leur rĂ©flexion pourraient Ă©merger quelques recommandations utiles aux gouvernements du monde. Ce groupe, qui sâest auto-baptisĂ© Gn FantĂŽme, sâest constituĂ© Ă lâinitiative de Joseph Stiglitz et Jean-Paul Fitoussi. Il a bĂ©nĂ©ficiĂ© du partenariat des UniversitĂ©s Luiss de Rome et Columbia de New York qui doivent ici en ĂȘtre remerciĂ©es. Le groupe sâest rĂ©uni deux fois, la premiĂšre Ă lâUniversitĂ© de Columbia Ă New York les 4 et 5 fĂ©vrier 2009 et la seconde Ă Rome les 6-7 mai 2009.Gn. « Gn fantĂŽme ». Crise globale. Crise financiĂšre. Gouvernance globale.;
Le « Gn fantÎme »:Les voies pour sortir de la crise en renforçant la solidarité mondiale
Cette annĂ©e, les membres du Gn se rĂ©unissent au plus fort dâune pĂ©riode critique de lâHistoire contemporaine, du moins sur le plan Ă©conomique et social : ils doivent affronter la plus grave crise des 80 derniĂšres annĂ©es. En paraphrasant Keynes on peut aller jusquâĂ affirmer que le destin du monde est entre leurs mains. Ils peuvent agir de maniĂšre telle quâil soit possible de sortir de la crise en crĂ©ant les conditions pour quâĂ lâavenir la croissance soit plus soutenable et plus favorable Ă lâenvironnement, et que ses fruits soient distribuĂ©s de maniĂšre plus Ă©quitable Ă la fois au sein de chaque pays et entre eux. Autrement, ils devront assumer lâĂ©crasante responsabilitĂ© historique dâavoir manquĂ© au mandat qui leur a Ă©tĂ© confiĂ© par leurs peuples, alors que les circonstances exceptionnelles quâils rencontrent leur offrent une marge de manoeuvre beaucoup plus grande que celle dont ils disposent en temps « normal ».
Câest pourquoi un groupe « dâexperts », sans aucune autre injonction que celle qui dĂ©coule de leur condition de citoyens du monde, a dĂ©cidĂ© de se rĂ©unir pour rĂ©flĂ©chir Ă ce qui peut ĂȘtre fait, en espĂ©rant que de leur rĂ©flexion pourraient Ă©merger quelques recommandations utiles aux gouvernements du monde. Ce groupe,
qui sâest auto-baptisĂ© Gn FantĂŽme, sâest constituĂ© Ă lâinitiative de Joseph Stiglitz et Jean-Paul Fitoussi. Il a bĂ©nĂ©ficiĂ© du partenariat des UniversitĂ©s Luiss de Rome et Columbia de New York qui doivent ici en
ĂȘtre remerciĂ©es.
Le groupe sâest rĂ©uni deux fois, la premiĂšre Ă lâUniversitĂ© de Columbia Ă New York les 4 et 5 fĂ©vrier 2009 et la seconde Ă Rome les 6-7 mai 2009
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