Stratification constrains future heat and carbon uptake in the Southern Ocean between 30°S and 55°S

The Southern Ocean between 30°S and 55°S is a major sink of excess heat and anthropogenic carbon, but model projections of these sinks remain highly uncertain. Reducing such uncertainties is required to effectively guide the development of climate mitigation policies for meeting the ambitious climate targets of the Paris Agreement. Here, we show that the large spread in the projections of future excess heat uptake efficiency and cumulative anthropogenic carbon uptake in this region are strongly linked to the models’ contemporary stratification. This relationship is robust across two generations of Earth system models and is used to reduce the uncertainty of future estimates of the cumulative anthropogenic carbon uptake by up to 53% and the excess heat uptake efficiency by 28%. Our results highlight that, for this region, an improved representation of stratification in Earth system models is key to constrain future carbon budgets and climate change projections.publishedVersio

Cyclic loading effects on NITI alloys under biaxial conditions

In this work, the influence of the direction and the history of thermomechanical loading of NiTi shape memory alloys on the overall material behavior is experimentally investigated. In the first part, cyclic biaxial mechanical loading has been applied to cross-shaped specimens under constant temperature. The residual strains of selected points from the sample surface are extracted and analyzed. The second part of the study concerns thermomechanical testing of textured samples cut from a laminated plate under complex cyclic loading at different temperature levels. The evolution of residual strains and the transformation threshold are correlated to the history of loading and the amplitude of transformation strain. Anisotropic effects are studied by performing those same experiments on different directions according to the rolling direction of the laminated plate

Determination of the characteristic parameters of tension-compression asymmetry of Shape Memory Alloys using full-field measurements

In this work, a method for the identification of the transformation surface of Shape Memory Alloys based on full field measurements is presented. An inverse method coupled with a gradient-based algorithm has been developed to determine the characteristic parameters of the transformation surface. The constitutive equations of the chosen model that capture the macroscopic behavior of Shape Memory Alloys are first presented. The material parameters, to be identified, that are characteristic of the tension-compression asymmetry of the alloy are detailed. The identification algorithm, based on full field measurements obtained by Digital Image Correlation (DIC) and numerical simulation by Finite Element Analysis are introduced. The identification algorithm is validated using a numerically generated strain field on a Meuwissen-type specimen

Distributed Pneumatic MEMS for Fast Conveyance of Fragile Objects

International audienceIn this paper we present a distributed and modular system to convey small and fragile objects. This is done by attaching similar modular blocks together to form a larger conveyance surface. Similar to other networked control systems, each block is composed of several sensors, actuators and communication infrastructure. Control of a levitating object should be done distributed and real-time. We emphasize on realistic simulations in multiple domains such as asynchronous control and communication. Simulations with two strategies on object motion show that we can meet all the real-time requirements for a successful conveyance

Parameter identification of a thermodynamic model for superelastic shape memory alloys using analytical calculation of the sensitivity matrix

IThis paper presents an identification procedure for the parameters of a thermodynamically based constitutive model for Shape memory Alloys (SMAs). The proposed approach is a gradient-based method and utilizes an analytical computation of the sensitivity matrix. For several loading cases, including superelasticity, that are commonly utilized for the model parameters identification of such a constitutive model, a closed-form of the total infinitesimal strain is derived. The partial derivatives of this state variable are developed to find the components of the sensitivity matrix. A LevenbergeMarquardt algorithm is utilized to solve the inverse problem and find the best set of model parameters for specific SMA materials. Moreover, a pre-identification method, based on the second derivative of the total strain components is proposed. This provides a suitable initial set of model parameters, which increases the efficiency of the inverse method. The proposed approach is applied for the simultaneous identification of the non-linear constitutive parameters for two superelastic SMAs. The comparison between experimental and numerical curves obtained for different temperatures shows the capabilities of the developed identification approach. The robustness and the efficiency of the developed approach are then experimentally validatedIIME

Analysis of the deformation paths and thermomechanical parameter identification of a shape memory alloy using digital image correlation over heterogeneous tests

With the design of new devices with complex geometry and to take advantage of their large recoverable strains, shape memory alloys components (SMA) are increasingly subjected to multiaxial loadings. The development process of SMA devices requires the prediction of their thermomechanical response, for which the calibration of the material parameters for the numerical model is an important step. In this work, the parameters of a phenomenological model are extracted from tests performed on specimens with non-uniform geometry, which induce heterogeneous strain fields carried out on specimens with the same thermomechanical loading history. The digital image correlation technique is employed to measure the strain fields on the surface of the specimen and to analyze the strain paths of chosen points. Finite element analysis enables the computation of numerical strain fields using a thermodynamical constitutive model for shape memory alloys previously implemented in a finite element code. The strain fields computed numerically are compared with experimental ones obtained by DIC to find the model parameters which best match experimental measurements using a newly developed parallelized mixed genetic/gradient-based optimization algorithm. These numerical simulations are carried out in parallel using a supercomputer to reduce the time necessary to identify the set of model parameters. The major features of this new algorithm is its ability to identify the material parameters which describe the thermomechanical behavior of shape memory alloys from full-field measurements for various loading conditions (different temperatures, multiaxial behavior, heterogeneous test configurations). It is demonstrated that model parameters for the simulation of SMA structures are thus obtained based on a reduced number of heterogeneous tests at different temperatures.IIME

Toward a 2D Modular and Self-Reconfigurable Robot for Conveying Microparts.

International audienceThis paper describes the design, prototyping and control of a 2D modular and self-reconfigurable robot for conveying microparts. The elementary block is designed to have a package dimension under 1cm3 and will include the actuators, the electronics and the micro-controller. Electropermanent (EP) magnets are used for both the linkage and the traveling system to avoid any power consumption during the linkage. Some prototype blocks have been realized and show a well working of the motion and a sufficient holding force. The paper presents also an algorithm, common to all blocks units, allowing to reconfigure a set blocks from a spatial configuration to another one. This algorithm is implemented in a simulator software showing in real-time the reconfiguration of the robot

A General Damage Accumulation Model for Multiaxial, Proportional High Cycle Fatigue Loadings With Sines, Crossland and Dang Van Criteria

In this paper, a key differential equation is proposed to formulate fatigue damage evolution in metallic alloys under multiaxial, multiblock, proportional loadings in high cycle fatigue (HCF) and very high cycle fatigue (VHCF) regimes. This differential equation possesses two main components: one is a stress function to accommodate the adopted fatigue criterion and the other one is a characteristic damage function that serves to capture the HCF response of alloys. Two distinct characteristic damage functions with three different multiaxial fatigue criteria, namely Sines, Crossland, and Dang Van criteria, are examined to develop six (out of many possible) variants of the presented damage accumulation model. As a validation measure, Chaboche’s HCF damage model is retrieved as a specific case of the developed formalism. For model parameters identification, an ad hoc two-level identification scheme is designed and numerically verified. It is demonstrated that endurance limit, which is determined from fully reversed HCF tests (i.e., R = −1), can be identified from fatigue tests with positive stress ratio (R > 0), thus making our development quite suitable for specimens prone to buckling under compression. Another salient feature of the devised identification scheme is its capability in extracting model parameters from noisy data

Distributed control architecture for smart surfaces.

International audienceThis paper presents a distributed control architecture to perform part recognition and closed-loop control of a distributed manipulation device. This architecture is based on decentralized cells able to communicate with their four neighbors thanks to peer-to-peer links. Various original algorithms are proposed to reconstruct, recognize and convey the object levitating on a new contactless distributed manipulation device. Experimental results show that each algorithm does a good job for itself and that all the algorithms together succeed in sorting and conveying the objects to their final destination. In the future, this architecture may be used to control MEMS-arrayed manipulation surfaces in order to develop Smart Surfaces, for conveying, fine positioning and sorting of very small parts for micro-systems assembly lines

Identification de paramètres de comportement d'un alliage à mémoire de forme

L'objectif est d'identifier les paramètres d'une loi de comportement d'un AMF-NiTi. Le modèle est phénoménologique à trois variables internes (Chemisky-Patoor, 2009) et tient compte de la transformation martensitique et du maclage. Une analyse de sensibilité du comportement thermomécanique aux paramètres du modèle a été effectuée. Elle a permis de comprendre l'influence des paramètres et de cerner leurs domaines d'intervention. Sur la base de cette analyse, les paramètres du comportement superélastique sont identifiés à partir d'essais en chargement combiné couplés à une méthode inverse