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1. The potential of large mammalian herbivores to shift plant communities between nitrogen (N) and phosphorus (P) limitation has received little attention so far. However, herbivores can influence the cycling of these growth‐limiting nutrients, and thereby affect plant nutrient limitation and productivity. Tundra ecosystems are nutrient‐poor and commonly grazed by large herbivores like reindeer and may thus be responsive to such changes. 2. Here, we examined the effect of long‐term light and heavy reindeer grazing on nutrient limitation of plant growth in a Scandinavian arctic tundra. We are the first to conduct a factorial N and P fertilization experiment across the two grazing regimes in two functionally contrasting vegetation types: heath and meadow. 3. Annual primary productivity (APP) showed contrasting responses to our fertilization treatments under light and heavy grazing. Under light grazing, APP increased in response to N + P additions in both the heath and meadow. Under heavy grazing, APP increased in response to N in the heath, with an additional positive effect of N + P combined, while APP increased in response to P and N + P additions in the meadow. 4. These results clearly show that an increase in the grazing intensity of reindeer facilitated a shift towards more P‐limited conditions in Scandinavian arctic tundra, by increasing N cycling without having a corresponding positive effect on P cycling. In the N‐poor heath, reindeer increased soil N availability at least partly due to a shift towards more N‐rich graminoids, while in the meadow, reindeer decreased soil P availability. The mechanisms behind this decrease remain unclear, but reindeer may simply export more P from the system than N due to their large P demand for the production of their antlers. 5. Synthesis. We conclude that heavy and long‐term reindeer grazing promoted a more P‐limited tundra, thus experimentally confirming the potential of large mammalian herbivores to influence nutrient limitation of plant growth.

Building on a summary of how turbulence influences biological systems, we reviewed key phytoplankton-turbulence laboratory experiments (after Peters and Redondo in Scientia Marina: Lectures on plankton and turbulence, International Centre for Coastal Resources, Barcelona, 1997) and Peters and Marrasé (Marine Ecology Progress Series 205:291–306, 2000) to provide a current overview of artificial turbulence generation methods and quantification techniques. This review found that most phytoplankton studies using artificial turbulence feature some form of quantification of turbulence; it is recommended to use turbulent dissipation rates (ε) for consistency with physical oceanographic and limnological observations. Grid-generated turbulence is the dominant method used to generate artificial turbulence with most experiments providing quantified ε values. Couette cylinders are also commonly used due to the ease of quantification, albeit as shear rates not ε. Dinoflagellates were the primary phytoplanktonic group studied due to their propensity for forming harmful algal blooms (HAB) as well as their apparent sensitivity to turbulence. This study found that a majority of experimental setups are made from acrylate plastics that could emit toxins as these materials degrade under UV light. Furthermore, most cosm systems studied were not sufficiently large to accommodate the full range of turbulent length scales, omitting larger vertical overturns. Recognising that phytoplankton-turbulence interactions are extremely complex, the continued promotion of more interdisciplinary studies is recommended.

The mineralization of nitrogen (N) and especially the regeneration of ammonium are critical processes performed by bacteria in aquatic ecosystems. Quantifying these processes is complicated because bacteria simultaneously consume and produce ammonium. Here we use experimental data on the effects of the molecular composition of the supplied substrates, combined with a classical stoichiometric model of ammonium regeneration, to demonstrate how the quantification of these processes can be improved. We manipulated a batch culture experiment with an isolated bacterial community by adding three different types of N substrates: dissolved inorganic nitrogen (DIN, nitrate), dissolved organic nitrogen (DON, amino acid) and a mixture of DIN and DON. With such experiment set-up, the ammonium regeneration per se could be easily tracked without using complicated methods (e.g. isotope dilution). We compared the experimental data with the predictions of Goldman et al’ model (1987) as well as with a revised version, using the measured consumption carbon:nitrogen ratio (C:N ratio), rather than an estimated consumption ratio. We found that, for all substrates, and in particular, mixed substrates where C and N are partially dissociated between different molecules, estimates of ammonium regeneration rates can be improved by measuring the actual consumption C: N ratio.ImportanceMeasuring bacterial ammonium regeneration in natural aquatic ecosystem is difficult because bacteria in the field simultaneously consume and produce ammonium. In our experimental design, we used nitrate as the inorganic nitrogen substrate. This way, we could measure separately the uptake and excretion of inorganic nitrogen by bacteria without incorporating cumbersome methods such as isotope dilution. Our experiment allowed us to evaluate the accuracy of various stoichiometric models for the estimation of net bacterial nitrogen regeneration. We found that:The exact distribution of C and N among the various molecules that make the bulk of DOM is a crucial factor to consider for bacterial net nitrogen regeneration.For all substrates, and in particular, mixed substrates where C and N are partially dissociated between different molecules, estimates of net nitrogen regeneration rates can be improved by measuring the actual C: N ratio of bacterial consumption.

Robust predictions of predator-prey interactions are fundamental for the understanding of food webs, their structure, dynamics, resistance to species loss and invasions and role in ecosystem functioning. Most current food web models are empirically based. Thus, they are sensitive to the quality of the data, and ineffective in predicting non-described and disturbed food webs. There is a need for mechanistic models that predict the occurrence of a predator-prey interaction based on the traits of organisms and the properties of their environment.Here, we present such a model that focuses on the predation act itself. We built a Newtonian, mechanical model for the processes of searching, capture and handling of a prey item by a predator. Associated with general metabolic laws, we predict the net energy gain from predation for pairs of predator and prey species depending on their body sizes.Predicted interactions match well with data from the most extensive predator-prey database, and overall model accuracy is greater than the niche model.Our model shows that it is possible to accurately predict the structure of food webs using only a few ecomechanical traits. It underlines the importance of physical constraints in structuring food webs.

1. Outbreaks of herbivorous insects can have large impacts on regional soil carbon (C) storage and nutrient cycling. In northernmost Europe, population outbreaks of several geometrid moth species r ...

For aircraft application, the mechanical assembly of composite and metallic structures using fastener (rivet, nuts and bolt) remains the preferred technology. For aeronautical structure, it is then necessary to drill a huge amount of holes both in the composite and the metallic parts. For CFRP/Ti6Al4 V stacks, the drilling remains a critical issue. Indeed the abrasive wear and the thermo-mechanical stress induced by the cutting process lead to a fast damaging phenomena on the tool. To cope with the high quality standards required on the drilled hole, it is necessary to limit the burr height, the delamination of the composite, the roughness and the diameter tolerance. One of the proposed technical solutions is the forced vibration drilling. This process makes it possible to generate segmented and easy to evacuate chip without overloading the cutting tool. This paper presents a new vibration assisted device (VAD) which allows the adjustment of the amplitude of the forced vibration. A dynamical model is developed to optimize the vibration amplitude during the drilling process. This model is based on the identification of the static and the dynamic behavior of the VAD. An experimental protocol using monitored drilling tests was developed to identify the several parameters of the dynamical model. The good correlation between the simulation and the experimental results allows the validation of the proposed methodology.

Northern ecosystems are experiencing some of the most dramatic impacts of global change on Earth. Rising temperatures, hydrological intensification, changes in atmospheric acid deposition and associated acidification recovery, and changes in vegetative cover are resulting in fundamental changes in terrestrial-aquatic biogeochemical linkages. The effects of global change are readily observed in alterations in the supply of dissolved organic matter (DOM)-the messenger between terrestrial and lake ecosystems-with potentially profound effects on the structure and function of lakes. Northern terrestrial ecosystems contain substantial stores of organic matter and filter or funnel DOM, affecting the timing and magnitude of DOM delivery to surface waters. This terrestrial DOM is processed in streams, rivers, and lakes, ultimately shifting its composition, stoichiometry, and bioavailability. Here, we explore the potential consequences of these global change-driven effects for lake food webs at northern latitudes. Notably, we provide evidence that increased allochthonous DOM supply to lakes is overwhelming increased autochthonous DOM supply that potentially results from earlier ice-out and a longer growing season. Furthermore, we assess the potential implications of this shift for the nutritional quality of autotrophs in terms of their stoichiometry, fatty acid composition, toxin production, and methylmercury concentration, and therefore, contaminant transfer through the food web. We conclude that global change in northern regions leads not only to reduced primary productivity but also to nutritionally poorer lake food webs, with discernible consequences for the trophic web to fish and humans.

Herbivores impact nutrient availability and cycling, and the net effect of herbivory on soil nutrients is generally assumed to be positive in nutrient-rich environments and negative in nutrient-poor ones. This is, however, far from a uniform pattern, and there is a recognized need to investigate any interactive effects of herbivory and habitat fertility (i.e., plant C/N ratios) on soil nutrient availabilities. We determined long-term effects of reindeer on soil extractable nitrogen (N) and phosphorus (P) and their net mineralization rates along a fertility gradient of plant carbon (C) to N and P ratios in arctic tundra. Our results showed that reindeer had a positive effect on soil N in the more nutrient-poor sites and a negative effect on soil P in the more nutrient-rich sites, which contrasts from the general consensus. The increase in N availability was linked to a decrease in plant and litter C/N ratios, suggesting that a shift in vegetation composition toward more graminoids favors higher N cycling. Soil P availability was not as closely linked to the vegetation and is likely regulated more by herbivore-induced changes in soil physical and chemical properties. The changes in soil extractable N and P resulted in higher soil N/P ratios, suggesting that reindeer could drive the vegetation toward P-limitation. This research highlights the importance of including both the elements N and P and conducting studies along environmental gradients in order to better understand the interactive effects of herbivory and habitat fertility on nutrient cycling and primary production.

Growth is a process fundamental to life. It implies an increase in not only energy and information but also matter content. Recent advances in ecology have demonstrated that the elemental compositi ...

Titanium alloys are generally noticed for their high specific strength and their good corrosion resistance. They are widely used in light-weight structures especially in the aerospace industry. Surface preparation of Ti6Al4V for bonding improvement is conventionally performed by chemical, electrochemical pre-treatments (chromic acid anodizing, phosphate-fluoride, sol-gel,…) and/or sandblasting in order to modify the morphology and the chemistry of the surface. However, these processes produce a large volume of hazardous chemical or abrasive waste. They require high technical efforts and are therefore economically and environmentally inefficient. Laser processes could lead to a good alternative solution in terms of eco-compatibility, repeatability and ease of manufacturing. In this paper, we report on the latest developments of the collaboration between ALPhANOV and I2M institute on the laser surface preparation for adhesive bonding improvement of Ti6Al4V. We focus our investigations on the effect of pulsed laser irradiation (fluence, scan speed and lateral overlap) with a visible (515 nm) nanosecond "rod-type fibre" laser on the surface morphology and its bonding behaviour (cohesive or adhesive failure). The penetration of the adhesive in the roughness induced by laser irradiation was characterized. For this study, the surfaces were inspected by different means as optical microscopy, 3D profilometer and scanning electron microscopy (SEM). The adhesion performance of the laser treated surface was evaluated by means of DCB tests.

Composite in aircraft structures has become increasingly important and should represent approximately 50% in mass till 2012. During the structure assembly, in aerospace centres of production there are used pneumatic positive feed units (also called automatic drilling units). They are manually positioned on specific grids to drill the panels of structure (assemblies of composite materials, aluminium and titanium). This article compares vibration-assisted drilling and non-vibratory drilling and presents the advantages of using vibrations in the process. The conclusions will show the results obtained and the developments to be carried out in an immediate future. Keywords: multi-layer material, vibration assisted drilling, Campbell diagram.

International audience; Phytoplankton communities are influenced by light availability. Therefore, one factor promoting phytoplankton species persistence is their ability to stay within the euphotic zone. This ability is determined by the interplay between species mass, buoyancy and dispersion, which are driven by physical factors. In this study, we investigate how these physical factors and light-use efficiency, all correlated with cell size, influence species persistence. Our model shows, first, that species can persist only within a size-dependent range of turbulence strength. The minimal level of turbulence required for persistence increases drastically with cell size, while all species reach similar maximal levels of turbulence. Second, the maximal water column depth allowing persistence is also size-dependent: large cells show a maximal depth at both low and high turbulence strength, while small cells show this pattern only at high turbulence strength. This study emphasizes the importance of the physical medium in ecosystems and its interplay with cell size for phytoplankton dynamics and bloom condition

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SUMMARYThis paper presents a new methodology for the joint stiffness identification of industrial serial robots and as consequence for the evaluation of both translational and rotational displacements of the robot's end-effector subject to an external wrench (force and torque). In this paper, the robot's links are supposed to be quite stiffer than the actuated joints as it is usually the case with industrial serial robots. The robustness of the identification method and the sensitivity of the results to measurement errors, and the number of experimental tests are also analyzed. The Kuka KR240-2 robot is used as an illustrative example throughout the paper.

Metabolic theory proposes that individual growth is governed through the mass- and temperature-dependence of metabolism, and ecological stoichiometry posits that growth is maximized at consumer-specific optima of resource elemental composition. A given consumer's optimum, the threshold elemental ratio (TER), is proportional to the ratio of its maximum elemental gross growth efficiencies (GGEs). GGE is defined by the ratio of metabolism-dependent processes such that GGEs should be independent of body mass and temperature. Understanding the metabolic-dependencies of GGEs and TERs may open the path towards a theoretical framework integrating the flow of energy and chemical elements through ecosystems. However, the mass and temperature scaling of GGEs and TERs have not been broadly evaluated. Here, we use data from 95 published studies to evaluate these metabolic-dependencies for C, N and P from unicells to vertebrates. We show that maximum GGEs commonly decline as power functions of asymptotic body mass and exponential functions of temperature. The rates of change in maximum GGEs with mass and temperature are relatively slow, however, suggesting that metabolism may not causally influence maximum GGEs. We additionally derived the theoretical expectation that the TER for C:P should not vary with body mass and this was supported empirically. A strong linear relationship between carbon and nitrogen GGEs further suggests that variation in the TER for C:N should be due to variation in consumer C:N. In general we show that GGEs may scale with metabolic rate, but it is unclear if there is a causal link between metabolism and GGEs. Further integrating stoichiometry and metabolism will provide better understanding of the processes governing the flow of energy and elements from organisms to ecosystems.

Droop's model was originally designed to describe the growth of unicellular phytoplankton species in chemostats but it is now commonly used for a variety of organisms in models of trophic interacti ...

International audience; Ecological stoichiometry postulates that differential nutrient recycling of elements such as nitrogen and phosphorus by consumers can shift the element that limits plant growth. However, this hypothesis has so far considered the effect of consumers, mostly herbivores, out of their food-web context. Microbial decomposers are important components of food webs, and might prove as important as consumers in changing the availability of elements for plants. In this theoretical study, we investigate how decomposers determine the nutrient that limits plants, both by feeding on nutrients and organic carbon released by plants and consumers, and by being fed upon by omnivorous consumers. We show that decomposers can greatly alter the relative availability of nutrients for plants. The type of limiting nutrient promoted by decomposers depends on their own elemental composition and, when applicable, on their ingestion by consumers. Our results highlight the limitations of previous stoichiometric theories of plant nutrient limitation control, which often ignored trophic levels other than plants and herbivores. They also suggest that detrital chains play an important role in determining plant nutrient limitation in many ecosystems.

International audience; The increasing part of composite materials in aeronautic multi-material structures highlights the need to develop adapted new manufacturing processes for assembly. Among the new drilling techniques, the vibration-assisted drilling (VAD) allows to improve reliability of drilling operations on multi-layer materials. Forced vibrations are added to conventional motions to create a discontinuous cutting. The back and forth movement allows to improve the evacuation of chips by breaking it. This technology introduces two new operating parameters, the frequency and the amplitude of the oscillation. To optimize the process, the choice of parameters requires first to model precisely the operation cutting and dynamics. Many works have highlighted the parameters range to obtain fragmented chip. The accuracy of current model is not sufficient to get the optimal parameters. The goal of this work is to identify the most influential phenomena generating error between model and test. In this paper, a kinematic modelling of the process is firstly proposed. The limits of the modelling are analysed through comparison between measured and simulated down-hole surfaces. From experimental test results, the model is then completed in order to take into account dynamic phenomena that may explain behaviour differences between tests and simulations. The proposed model of cutting forces considering the dynamical behaviour of the machining system allows foreseeing the operating conditions which ensure good chips breaking. This work also presents the experimental method and the test results to validate the numerical simulator.

Mussel aquaculture has expanded worldwide and it is important to assess its impact on the water column and the planktonic food web to determine the sustainability of farming practices. Mussel farming may affect the planktonic food web indirectly by excreting bioavailable nutrients in the water column (a short-term effect) or by increasing nutrient effluxes from bio-deposit-enriched sediments (a long-term effect). We tested both of these indirect effects in a lagoon by using plankton-enclosing benthocosms that were placed on the bottom of a shallow lagoon either inside of a mussel farm or at reference sites with no history of aquaculture. At each site, half of the benthocosms were enriched with seawater that had held mussels (excretion treatment), the other half received non-enriched seawater as a control treatment. We monitored nutrients ([PO43-] and [NH4+]), dissolved oxygen and plankton components (bacteria, the phytoplankton and the zooplankton) over 5 days. We found a significant relationship between long-term accumulation of mussel biodeposits in sediments, water-column nutrient concentrations and plankton growth. Effects of mussel excretion were not detected, too weak to be significant given the spatial and temporal variability observed in the lagoon. Effects of mussels on the water column are thus likely to be coupled to benthic processes in such semi-enclosed water bodies.

Finishing process like polishing is usually used to obtain high quality mechanical surface characteristics such as texture and roughness. These operations are mainly handmade and need highly trained operators thus limiting their repeatability and profitability. To optimize the industrialization of the polishing process, it is therefore necessary to modelize the process to built efficient parameter database. The aim of this study is to characterise the polishing of 316L stainless steel with structured abrasive belts. The geometric data of the belts are given, and we then propose a model to determine material removal. An experimental test bench is set up to test this model and characterise the polishing process in terms of forces. It produces samples for different polishing conditions. The different polished surfaces are then analyzed thanks to the roughness and the wettability. Using experimental designs, we are able to validate the proposed model and identify the parameters that influence a polishing operation.

CAD/CAM systems need technical data to quantitatively predict the performance of the milling process. The great varieties of real machining operations prevent exhaustive studies for each machining condition. The purpose of this paper is to present a generic approach of the milling forces modelling. The objective is to limit the experiment testing while providing accurate enough data for the CAD/CAM requirement. An experimental study is presented to analyse the major influent parameters (rake angle, cutting speed) on the cutting forces. Then, simulation results based on a modified Altan’s approach are compared with experimental measurement for two different steels (AISI H11 and P20) and varying insert geometries to value the predictive capability of the presented approach.

International audience; 1. We propose an alternative model to the host-shifting model of sympatric speciation in plant-insect systems. The role of competition in driving ecological adaptive radiation was evaluated in a seed predator exploiting a single host-plant species. Sympatric speciation may occur through disruptive selection on oviposition timing if this shift decreases competition among larvae feeding on seeds. 2. The globeflower fly Chiastocheta presents a unique case of adaptive radiation, with at least six sister species co-developing in fruits of Trollius europaeus. These species all feed on seeds, and differ in their oviposition timing, one species ovipositing in 1-day-old flowers (early species), while all the other species sequentially oviposit throughout the flower life span (late species). We evaluated the impact of conspecific and heterospecific larvae on larval installation success, and on larval fresh mass and area, for early and late species, in natural conditions. 3. None of the three larval traits measured was correlated with fruit size, and no fruit lost all seeds to predation, suggesting that seed availability was not a limiting factor for larval development. 4. Our results show strong intraspecific competition among early larvae for larval installation, and among late larvae for larval mass. By contrast, larval competition between species was weak. These results are consistent with the hypothesis that shifts in oviposition promoted rapid radiation in globeflower flies by lowering competition among larvae.

Background Vitamin D deficiency is associated with smaller volume of optic chiasm in older adults, indicating a possible loss of the visual axons and their cellular bodies. Our objective was to determine whether vitamin D deficiency in older adults is associated with reduced thickness of the ganglion cell complex(GCC) and of the retinal nerve fibre layer(RNFL), as measured with high-definition optical coherence tomography(HD-OCT). Methods Eighty-five French older community-dwellers without open-angle glaucoma and patent age-related macular degeneration(mean, 71.1±4.7years; 45.9%female) from the GAIT study were separated into 2 groups according to serum 25OHD level(i.e., deficient≤25nmol/L or sufficient>25nmol/L). Measurements of GCC and RNFL thickness were performed using HD-OCT. Age, gender, body mass index, number of comorbidities, dementia, functional autonomy, intracranial volume, visual acuity, serum calcium concentration and season of testing were considered as potential confounders. Results Mean serum 25OHD concentration was 58.4±26.8nmol/L. Mean logMAR visual acuity was 0.03±0.06. Mean visual field mean deviation was -1.25±2.29dB. Patients with vitamin D deficiency(n=11) had a reduced mean GCC thickness compared to those without vitamin D deficiency(72.1±7.4μm versus 77.5±7.5μm, P=0.028). There was no difference of the mean RNFL thickness in these two groups(P=0.133). After adjustment for potential confounders, vitamin D deficiency was associated with reduced GCC thickness(s=-5.12, P=0.048) but not RNFL thickness(s=-9.98, P=0.061). Specifically, vitamin D deficiency correlated with the superior medial GCC area(P=0.017) and superior temporal GCC area(P=0.010). Conclusions Vitamin D deficiency in older patients is associated with reduced mean GCC thickness, which can represent an early stage of optic nerve damage, prior to RNFL loss.

International audience

National audience; Ce travail vise à déterminer le rôle de la qualité des perçages sur les mécanismes de dégradation en matage des composites stratifiés sous sollicitation de fatigue. Après une description des phénomènes engendrant les défauts de perçage, le choix de critères pertinents permettant de quantifier la qualité fonctionnelle de la surface est discuté. Concernant la tenue en fatigue, le protocole expérimental repose sur des essais interrompus successivement à différents nombres de cycles pour réaliser des observations microscopiques et des mesures de profilométrie 3D. Les résultats obtenus sur des alésages de différentes qualités sont présentés et analysés.

Mainly used in aerospace industry, positive feed units are an alternative to manual drilling units and CNC machines. They have been recently assisted by vibration systems in order to improve the evacuation of chips under ribbon form while drilling. After a first introduction of the common issues while drilling multi-stacked material, a review of the different technologies of vibration systems will be presented. In a second part, a modeling of a forced–excited vibration system will be described. Experimental figures will be faced to theoretical results to evaluate the relevance of the vibration drilling strategy in terms of chip breaking. In a third part, we will introduce some ways to set up the optimal parameters of the vibration system.

Assembling composite structures requires a significant number of drillings. During machining, defects appear on the surface of the drilled hole. This paper outlines that the criterion Ra is not adapted to reliably characterize the surface quality on composites. In particular, various tests have shown significant variations of the value of Ra according to the angular position of measurement, as well as the filtering artefacts. This study puts forward a new methodology to characterize the surface quality of a composite hole. To this end, a study of sensitivity of the various criteria proposed by standard ISO4287 was conducted. Various geometries of tool are also tested in the experimental phase. The impact of cutting parameters and tool wear are analyzed based on this new methodology.

Plant stoichiometry is thought to have a major influence on how herbivores affect nutrient availability in ecosystems. Most conceptual models predict that plants with high nutrient contents increase nutrient excretion by herbivores, in turn raising nutrient availability. To test this hypothesis, we built a stoichiometrically explicit model that includes a simple but thorough description of the processes of herbivory and decomposition. Our results challenge traditional views of herbivore impacts on nutrient availability in many ways. They show that the relationship between plant nutrient content and the impact of herbivores predicted by conceptual models holds only at high plant nutrient contents. At low plant nutrient contents, the impact of herbivores is mediated by the mineralization/immobilization of nutrients by decomposers and by the type of resource limiting the growth of decomposers. Both parameters are functions of the mismatch between plant and decomposer stoichiometries. Our work provides new predictions about the impacts of herbivores on ecosystem fertility that depend on critical interactions between plant, herbivore and decomposer stoichiometries in ecosystems.

All organisms in their complexities of shapes, structures and functions use the same building blocks, elements, assembled and cemented together by energy. But only a subset of the elements available on Earth is used by the organisms in their biomass (Figure 1). Furthermore, the elements most commonly used by living beings (e.g., H, C, N, O, P, S, Na, K, Ca, Fe) are essential components of all organisms biomass. This reveals on one hand the common origin of all species and on the other hand the very specific requirements of the various life processes, to which only a subset of the elements are adapted (see Frausto da Silva & Williams 2001 for a thorough discussion of the adequacy of elements to their biological functions).

International audience; The six axis robots are widely used in automotive industry for their good repeatability (as defined in the ISO92983) (painting, welding, mastic deposition, handling etc.). In the aerospace industry, robot starts to be used for complex applications such as drilling, riveting, fiber placement, NDT, etc. Given the positioning performance of serial robots, precision applications require usually external measurement device with complexes calibration procedure in order to reach the precision needed. New applications in the machining field of composite material (aerospace, naval, or wind turbine for example) intend to use off line programming of serial robot without the use of calibration or external measurement device. For those applications, the position, orientation and path trajectory precision of the tool center point of the robot are needed to generate the machining operation. This article presents the different conditions that currently limit the development of robots in robotic machining applications. We analyze the dynamical behavior of a robot KUKA KR240-2 (located at the University of Bordeaux 1) equipped with a HSM Spindle (42000 rpm, 18kW). This analysis is done in three stages. The first step is determining the self-excited frequencies of the robot structure for three different configurations of work. The second phase aims to analyze the dynamical vibration of the structure as the spindle is activated without cutting. The third stage consists of vibration analysis during a milling operation.

This paper presents a new methodology for joint stiffness identification of serial robots. This methodology aims at evaluating all joint stiffness values responsible for both translational and rotational displacements of the robot end-effector subject to an external wrench (force and torque). The links of the robot are supposed to be quite stiffer than the joints and not known as it is usually the case with industrial serial robots. The robustness of the identification method and the sensitivity of the results to measurement errors and number of experimental tests are also analyzed. The Kuka KR240-2 robot is used as an illustrative example through the paper.

The increasing part of multi-layer materials in the aerospace industry has created new machining problems. Indeed it is very difficult to machine these materials, particularly to drill them because they consist of materials with very different nature stacks, as strongly heterogeneous materials, such as carbon fibre composite, and materials monolithic, such as aluminium and titanium. The choice of cutting tool should be a compromise, to withstand high temperature involved during titanium drilling, as well as highly abrasive carbon fibre, while allowing the acquisition of drilling of aircraft grade.

Heterotrophic microbial decomposers, such as bacteria and fungi, immobilize or mineralize inorganic elements, depending on their elemental composition and that of their organic resource. This fact has major implications for their interactions with other consumers of inorganic elements. We combine the stoichiometric and resource-ratio approaches in a model describing the use by decomposers of an organic and an inorganic resource containing the same essential element, to study its consequences on decomposer interactions and their role in elemental cycling. Our model considers the elemental composition of organic matter and the principle of its homeostasis explicitly. New predictions emerge, in particular, (1) stoichiometric constraints generate a trade-off between the R* values of decomposers for the two resources; (2) they create favorable conditions for the coexistence of decomposers limited by different resources and with different elemental demands; (3) however, combined with conditions on species-specific equilibrium limitation, they draw decomposers toward colimitation by the organic and inorganic resources on an evolutionary time scale. Moreover, we derive the conditions under which decomposers switch from consumption to excretion of the inorganic resource. We expect our predictions to be useful in explaining the community structure of decomposers and their interactions with other consumers of inorganic resources, particularly primary producers.

Surface preparation is a critical step for applications as diverse as bonding, corrosion or fatigue resistance improvement of mechanical parts. For Ti6Al4 V bonding, sandblasting and/or chemical treatments are generally used to modify the surface topology and achieve adequate chemical conversion. Recently, laser surface preparation have been proposed as a promising alternative to the traditional methods. In this article, the surface of Ti6Al4 V plate are observed after being exposed to laser treatment. The influence of the accumulated fluence through several scan speed and overlap ratio is analyzed. The surface morphology is investigated using SEM, optical microscopy and 3D profilometer. These observations are compare with a analytical irradiation model to evaluate the resulting texture pattern according to the laser settings.

Vibrations assisted drilling is a process which ensures chip shape control in order to increase reliability during drilling operations. The adding of axial oscillation, controlled with amplitude and frequency, introduce two new parameters which must determinate according to the conventional parameters (feed and speed rotation). The optimal setting of vibrations assisted drilling is not obvious. To provide an optimization-tool of the process, a new model which take into account the “Tool-Workpiece-Machine” environment, is proposed. Drill geometry, Tool-Workpiece interactions and dynamic behavior of the Machine are incorporated in the model. Tis specificity allows adjusting behavior of the process with the case of application. An identification methodology is presented to characterize the environment. Simulation’s results and experimental results are compared to validate the model. This model thus allows predicting process behavior in order to optimize the operational parameters.; Le perçage assisté par vibrations est un procédé assurant la maîtrise dimensionnelle des copeaux pour gagner en fiabilité sur les opérations de perçage. L’ajout d’une oscillation axiale pilotée en amplitude et en fréquence introduit deux nouveaux paramètres à déterminer en adéquation avec les paramètres conventionnels que sont l’avance et la vitesse de coupe. Le paramétrage d’une telle opération n’est donc pas trivial. Afin de fournir un outil d’optimisation du paramétrage du procédé, une nouvelle modélisation prenant en compte l’environnement « Pièce-Outil-Machine » est proposée. L’intégration de la géométrie de l’outil, des spécificités des interactions entre l’Outil et la Matière, et du comportement dynamique de la Machine permet s’adapter aux conditions de mise en oeuvre du procédé. Une méthode d’identification dissociée des éléments de l’environnement « Pièce-Outil-Machine » permet de caractériser les spécificités de chacun de ces éléments. Cette modélisation est validée par une campagne d’essai. La modèle développé dans ces travaux permet donc de prédire le comportement du procédé en vue d’une optimisation des paramètres opératoires.

The weight reduction of aero structures has led to use composite materials combined to metallicparts to form multilayer materials. Stacked materials are drilled in one-shot during the assemblyprocess. The objective of this work is to find optimised parameters to drill efficiently CFRP-7175-TA6Vmaterial stack using Automatic Drilling Units (ADU). Three research areas have been explored. Thefirst one concerns drill bit optimisation. A customized functional analysis had led to several toolimprovements. The second area focuses on vibration-assisted drilling. This method consists in addinga reciprocating axial displacement. Formerly under ribbon form, the chips become well broken withthe vibrations and their evacuation gets better. At last, the self-adaptive drilling technique is studied.A new methodology for real-time material identification is proposed., L’allégement des structures aéronautiques conduit à associer par stratification les composites aux métaux : on parle alors de multi-matériaux. L’assemblage mécanique des empilages nécessite au préalable des opérations de perçage qui s’effectuent majoritairement sur Unité de Perçage Automatique (UPA). L’objectif des travaux présentés dans ce mémoire est d’optimiser les opérationsde perçage effectuées sur UPA dans des multi-matériaux CFRP-7175-TA6V. Trois axes de recherche ont ainsi été étudiés. Le premier concerne l’optimisation de l’outil. L’utilisation d’une méthode de conception adaptée a conduit vers plusieurs pistes d’améliorations de la géométrie d’un foret. Le deuxième axe traite de la modélisation du perçage vibratoire. Cette méthode consiste à ajouter un mouvement de vibration axiale, au mouvement de coupe. Le dernier axe développe la technique du perçage auto-adaptatif. Une nouvelle méthode est proposée pour identifier les différents matériaux constituants l’empilage.

Vibrations assisted drilling is a process which ensures chip shape control in order to increase reliability during drilling operations. The adding of axial oscillation, controlled with amplitude and frequency, introduce two new parameters which must determinate according to the conventional parameters (feed and speed rotation). The optimal setting of vibrations assisted drilling is not obvious. To provide an optimization-tool of the process, a new model which take into account the “Tool-Workpiece-Machine” environment, is proposed. Drill geometry, Tool-Workpiece interactions and dynamic behavior of the Machine are incorporated in the model. Tis specificity allows adjusting behavior of the process with the case of application. An identification methodology is presented to characterize the environment. Simulation’s results and experimental results are compared to validate the model. This model thus allows predicting process behavior in order to optimize the operational parameters.; Le perçage assisté par vibrations est un procédé assurant la maîtrise dimensionnelle des copeaux pour gagner en fiabilité sur les opérations de perçage. L’ajout d’une oscillation axiale pilotée en amplitude et en fréquence introduit deux nouveaux paramètres à déterminer en adéquation avec les paramètres conventionnels que sont l’avance et la vitesse de coupe. Le paramétrage d’une telle opération n’est donc pas trivial. Afin de fournir un outil d’optimisation du paramétrage du procédé, une nouvelle modélisation prenant en compte l’environnement « Pièce-Outil-Machine » est proposée. L’intégration de la géométrie de l’outil, des spécificités des interactions entre l’Outil et la Matière, et du comportement dynamique de la Machine permet s’adapter aux conditions de mise en oeuvre du procédé. Une méthode d’identification dissociée des éléments de l’environnement « Pièce-Outil-Machine » permet de caractériser les spécificités de chacun de ces éléments. Cette modélisation est validée par une campagne d’essai. La modèle développé dans ces travaux permet donc de prédire le comportement du procédé en vue d’une optimisation des paramètres opératoires.