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Thermomechanical analysis of the high cycle fatigue behavior of a peek CF30 under compressive loadings
No full textInternational audienceThe assessment of the fatigue life of structures made of short-fiber reinforced thermoplastics is a complex issue due to the non-linear dissipative behavior of the matrix and the heterogeneous distribution of fiber orientations. The aim of this study is to develop an approach for the high cycle fatigue design of PolyEtherEtherKetone reinforced with 30 wt % of short carbon fibers (PEEK CF30), for compressive loadings. This includes the assessment of the ability of the heat build-up technique to predict the fatigue lifetime. To our knowledge, there are no data in the literature for this material and these loading conditions. The results obtained in compression are compared to data obtained in tension. The effects of the loading direction from the injection direction and the load ratio are studied
Registration method for the analysis of mooring chain links degraded by corrosion and wear
No full textInternational audienceThe observation of the three-dimensional geometrical evolution of mooring chain links exposed to the marine environment can be achieved by using 3D scanners. Successive surveys make it possible to precisely identify the location, shapes and quantities of material loss by corrosion or fretting in interlink contact areas. However, the comparison is only possible after an alignment of the obtained scans, because they are not expressed in the same reference marks. The usual point cloud alignment algorithms not being adapted to the expected accuracy, the carried out work implements a new algorithm based on the iterative closest point method (ICP). The developed iterative process of alignment, moves the point cloud corresponding to the aged link onto the new link, after detecting and deleting the points located in the areas of localized material losses (pitting corrosion or wear), and after adding an extra layer on the remaining surfaces, of a value corresponding to the loss of material by a generalised corrosion assumed to be constant. The tests carried out on perfect meshes from CAD constructions show a convergence of the alignment process towards a sufficient precision with regard to the work objectives
Low divergence proton beams from a laser-plasma accelerator at kHz repetition rate
No full textInternational audienceProton beams with up to 100 pC bunch charge, 0.48 MeV cutoff energy, and divergence as low as 3° were generated from solid targets at kHz repetition rate by a few-mJ femtosecond laser under controlled plasma conditions. The beam spatial profile was measured using a small aperture scanning time-of-flight detector. Detailed parametric studies were performed by varying the surface plasma scale length from 8 to 80 nm and the laser pulse duration from 4 fs to 1.5 ps. Numerical simulations are in good agreement with observations and, together with an in-depth theoretical analysis of the acceleration mechanism, indicate that high repetition rate femtosecond laser technology could be used to produce few-MeV proton beams for applications
Extending the proximal point algorithm beyond convexity
No full textInternational audienceIntroduced in the 1970's by Martinet for minimizing convex functions and extended shortly afterwards by Rockafellar towards monotone inclusion problems, the proximal point algorithm turned out to be a viable computational method for solving various classes of (structured) optimization problems even beyond the convex framework. In this talk we discuss some extensions of proximal point type algorithms beyond convexity. We propose a relaxed-inertial proximal point type algorithm for solving optimization problems consisting in minimizing strongly quasiconvex functions whose variables lie in finitely dimensional linear subspaces, that can be extended to equilibrium functions involving such functions. Computational results confirm the theoretical advances
Extending the proximal point algorithm beyond convexity
No full textInternational audienceIntroduced in the 1970's by Martinet for minimizing convex functions and extended shortly afterward by Rockafellar towards monotone inclusion problems, the proximal point algorithm turned out to be a viable computational method for solving various classes of optimization problems, in particular with nonconvex objective functions.We propose first a relaxed-inertial proximal point type algorithm for solving optimization problems consisting in minimizing strongly quasiconvex functions whose variables lie in finitely dimensional linear subspaces. The method is then extended to equilibrium problems where the involved bifunction is strongly quasiconvex in the second variable.Possible modifications of the hypotheses that would allow the algorithms to solve similar problems involving quasiconvex functions are discussed, too. Numerical experiments confirming the theoretical results, in particular that the relaxed-inertial algorithms outperform their ``pure'' proximal point counterparts \cite{ILP, LAP}, are provided, too.Then we briefly discuss another generalized convexity notion for functions we called \textit{prox-convexity} for which the proximity operator is single-valued and firmly nonexpansive, and see that the standard proximal point algorithm and Malitsky’s Golden Ratio Algorithm (originally proposed for solving convex mixed variational inequalities) remain convergent when the involved functions are taken prox-convex, too
Un éco-système mondialisé d’innovation et d’entrepreneuriat au cœur des « marchés augmentés » de l’automobile, du numérique et de l’énergie
No full textInternational audienceThree industries are at the heart of the changes taking place in our globalized economies: mobility and the automobile in particular, energy and "digital". They are creating links, across borders, between their products, technologies, processes, infrastructures and customers, to the point of creating what we call "augmented markets" where innovation and entrepreneurship play a central role. This implies responsibilities for the companies, whether multinationals or simple start-ups, that make them up, and for the public authorities that regulate them and sometimes invest alongside them in "innovation clusters" formed with research centers and universities.How can we make our innovation and entrepreneurship ecosystems virtuous, at the individual and collective levels, from the local to the global level, via the regional and national levels, in terms of development, economic growth and welfare?Trois industries sont au cœur des mutations de nos économies mondialisées : la mobilité et l’automobile en particulier, l’énergie et le « numérique ». Elles créent des liens, par-delà leurs frontières, entre leurs produits, leurs technologies, leurs procédés, leurs infrastructures, leurs clientèles, au point de faire émerger ce que nous appelons des « marchés augmentés » où l’innovation et l’entrepreneuriat jouent un rôle central. Cela implique des responsabilités pour les entreprises, multinationales ou simples start-up, qui les composent et pour les pouvoirs publics qui les régulent et parfois s’investissent à leurs côtés au sein de « clusters d’innovation » constitués avec des centres de recherche et des universités.Comment pouvons-nous rendre nos écosystèmes d’innovation et d’entreprenariat vertueux, aux niveaux individuel et collectifs, de l’échelon local à l’échelon mondial en passant par les niveaux régionaux et nationaux, tant en termes de développement que de croissance économique ou de bien-être
Regional Coherence and Clean energy Technologies.
No full textInternational audienceABSTRACT As climate change become a tangible reality, providing technical solution to reduce carbon emissions become strategically important. Reach Paris climate agreement of carbon neutrality in 2050 to keep global warming under 2 degrees Celsius needs urgent reorganization of innovative systems behind this objective. Since the first COP1 in 1995 in Berlin, strategic importance of energy production in carbon emissions is well known as well as the need to invest in clean energy production to close the cost gap with carbon-based energy (Turkenburg 2000). This work attempts to measure current reorganization of European regions around clean energy innovation help by graph theory tools and regional evolutionary theory. From 1995 COP1, to 2015 COP 21, our work describes the adoption of a common technological paradigm around clean energy innovation. To do so, we localize patent inventor's data from PATSTAT at NUTS2 level to study coherence of IPC technological class combination in patents. Evolution of these "regional knowledge base" are studied over 4 periods of five-years each. Our preliminary results show a slowly increasing organization of actors around a common way to innovate in strategic technologies as renewables technologies like photovoltaic and fuel cells technologies. This innovation is largely carried by Germany and France among others western European countries
Aggregation-Scheduling Based Mechanism for Energy-Efficient Multivariate Sensor Networks
No full textInternational audienceRecently, the world has witnessed a technology revolution in many sectors and fields with the aim to enhance the quality of life and the human security. Particularly, the integration of small sensing devices into a wide range of objects has enabled the deployment of new services and applications that made our lives smarter and safety. With such sensing-based technology, we can adequately monitor, access harsh environments, understand various phenomena and make a decision accordingly. However, sensing-based applications face several challenges beginning from the data collection at the sensors themselves until the decisionmaking process at the end-user. In this study, we focus on the energy conservation as major challenge in sensor applications due to the limited sensor resources that are not always possible to be replaced or recharged. We propose an aggregation-scheduling based mechanism called as AGING for Energy-Efficient multivariate sensor networks (MSN). Mainly, AGING is based on the cluster network scheme and consists into two phases: aggregation and scheduling. The aggregation phase is applied at each node and aims to reduce the huge amount of data sent periodically to the cluster-head (CH) based on a user-defined score table and a multi-aggregation mechanism. The second phase is applied at CH and uses a new scheduling strategy to switch nodes generating similar data into sleep/active modes; the CH first converts the correlated nodes into a graph before applying a coloring-map algorithm and a scheduling strategy to select the set of active nodes in next periods. Through simulations on real sensor data, we show the relevance of our mechanism in terms of saving the node energies and prolong the network lifetime compared to other existing techniques
Influence of multiwalled carbon nanotube on progressive damage of epoxy/carbon fiber reinforced structural composite
No full textInternational audienceThe present work aims to demonstrate the effect of multiwalled carbon nanotube (MWCNT) on mechanical behavior and damage of woven carbon fiber/epoxy composites through experimental characterizations and multi-scale modeling. Tensile tests were conducted for MWCNT/epoxy nanocomposites, and carbon nanotube (CNT) reinforced laminated open hole composites with different MWCNT weight ratios. The tensile modulus in CNT/epoxy nanocomposite was enhanced by 15.0%, 37.86%, and 22.86% for MWCNT reinforcement of 0.5%, 1.0%, and 1.5% wt, respectively. The corresponding improvement of tensile modulus for woven composites was 3.45%, 10.25%, and 1.53%; whereas tensile strength was increased by 19.76%, 25.78%, and 6.70%. The enhancement of tensile modulus and strength was less for 1.5% wt MWCNT laminates due to the formation of MWCNT agglomeration. The effective elastic isotropic/orthotropic properties for nanocomposite/woven composite were estimated through Mori-Tanaka approach and numerical homogenization. The finite element simulations were performed with Hashin's damage model and extended finite element method-based crack growth study. The delaminations between layers have been demonstrated through cohesive zone modeling. Damage propagation, interface delamination, and fiber/matrix failure were demonstrated by numerical simulations in line with scanning electron microscope observations
Influence of chemistry on the steady solutions of hydrogen gaseous detonations with friction losses
No full textInternational audienceThe problem of the steady propagation of detonation waves with friction losses is revisited including detailed kinetics. The derived formulation is used to study the influence of chemical modeling on the steady solutions and reaction zone structures obtained for stoichiometric hydrogen-oxygen. Detonation velocity-friction coefficient (D − c f) curves, pressure, temperature, Mach number, thermicity and species profiles are used for that purpose. Results show that both simplified kinetic schemes considered (i.e., one-step and three-step chainbranching), fitted using standard methodologies, failed to quantitatively capture the critical c f values obtained with detailed kinetics; moreover one-step Arrhenius chemistry also exhibits qualitative differences for D/D CJ ≤ 0.55 due to an overestimation of the chemical time in this regime. An alternative fitting methodology for simplified kinetics is proposed using detailed chemistry D − c f curves as a target rather than constant volume delay times and ideal Zel'dovich-von Neumann-Döring profiles; this method is in principle more representative to study non-ideal detonation propagation. The sensitivity of the predicted critical c f value, c f,crit , to the detailed mechanisms routinely used to model hydrogen oxidation was also assessed; significant differences were found, mainly driven by the consumption/creation rate of the HO 2 radical pool at low postshock temperature