MATETPRO - Matériaux et Procédés pour des Produits Performants

Modelling of the behaviour of superconducting cables at different scales for the optimization of their electrical performances – COCASCOPE

Modelling of the behaviour of superconducting cables at different scales for the optimization of their electrical performances

Some superconducting strands, especially those made of Nb3Sn, NbTi or MgB2 alloys, show conductivity losses depending on the deformations they undergo. Project aims at examining the deformation mechanisms influencing the conductivity properties using an approach coupling mechanical tests, numerical simulation, micro-tomography and image analysis techniques.

Characterization of damage mechanisms of conductivity properties at microscopic scale as function of the loading at macroscopic scale

1. Improve electrical and mechanical properties of superconducting cables<br /><br />The dependency of electrical performances of superconducting strands on bending and tensile loadings remains to be investigated <br /><br />2. Characterization and identification of the mechanical behaviour of strands under cycling bending loading<br /><br />Cyclical bending loadings, typical of repeated magnetic loadings, may induce progressive strains which would decrease continuously electrical properties. Determining if such ratcheting effects occur under cyclical bending is a key issue. In order to be able to simulate such effects, one objective is to propose a homogenized model for the bending behavior accounting for the composite structure of strands made of elastic micro-filaments inside an elasto-plastic matrix.<br /><br />3. Modelling of the forming of superconducting cables<br /><br />The deformations of strands during the forming process for different type of cables have significant effects on their electrical performances.

1. Electrical and mechanical tests

Electrical tests aim to examine the influence of specific loadings, in particular bending and tensile loadings on the critical current.

Mechanical tests are designed to characterize the behaviour of strands under cyclical bending in order particularly to highlight possible ratcheting effects.

2. Identification of cables geometry using tomography

Identification of complex trajectories of strands within cables is needed as validation for the simulation. Statistical analysis tools will be used to characterize these complex geometries.

3. Simulation of the initial forming and of service life loadings

Mechanical simulation codes will be employed to simulate the initial forming of the cables in the scope of the study in order to predict their geometry and to evaluate the strains caused by this process.

1. New test of critical current under bending

A VAMAS test has been adapted by cutting two grooves in a circular mandrel so as to take into account bending effects.

2. Simulation of the forming of Rutherford cables

A dynamic explicit simulation code was employed to simulate the initial forming of Rutherford cables. A good correlation with geometries identified by tomography is obtained.

The characterization of strands behavior under cyclic bending should highlight possible mechanisms of degradation of conductivity properties.

Main results will be published.

As the electrical conductivity of superconducting cables depends on the local strains they undergo, an accurate modeling of their mechanical and electrical behaviours is required to be able to optimize their global electrical performances.

Superconducting cables display a multiscale internal structure. At a first level, the cable is made of an assembly of elementary strands arranged together according to more or less complex architectures, depending on their application. At a lower scale, strands appear as composite structures formed either by superconducting microfilaments embedded in a metallic matrix, or by a thin superconducting layer deposited onto a metallic substrate. Both reversible and irreversible conductivity losses are encountered for these superconducting components at microscopic scale, depending on the magnitude of local strains.

Relying on first obtained results which partially validated the proposed numerical simulation approach in the case of cable in conduit conductors, the project aims at developing the approach in order to address new issues related to the validation by a geometrical identification, the taking into account of effects induced by the initial forming process, as well as of the cyclic constitutive behaviour of strands.

Tomography techniques will be employed in order to experimentally identify geometrical configurations of conductors, and to attempt to observe the occurrence of damage at microscopic scale. Since the complexity of configurations prevents from comparing two configurations through a simple superposition, statistical tools will be specially developed in order to compare relevant geometrical measurements and to validate simulation results against these experimental identifications.

Concerning new applications, the project will focus on determining effects induced by forming processes on the electrical performances of conductors used for electric energy distribution. The new superconducting materials used there are indeed formed before the cabling process ; strains induced by the initial forming process play therefore a predominant role on their electrical characteristics.

Since the origins of conductivity losses under cyclic loading are not yet understood, the project will try to answer this question by carrying out experimental tests in order to identify the cyclic constitutive behaviour of strands subjected to combined bending and compression loadings. Meanwhile a modeling task will be carried out in order to formulate a homogenized cyclic constitutive law at the scale of a strand, taking into account its composite internal structure. These developments will be implemented in the simulation code to predict the macroscopic behaviour of the global conductor.

An experimental setup will be implemented in order to identify the electro-mechanicall behaviour of strands and small cables, at cryogenic temperature, and under magnetic field. These tests will allow characteristics of new kinds of strands to be identified, will provide input data for the electrical simulation code, and will validate the global approach by measuring the actual electrical performances of test cables.

The cluster formed by the various skills gathered in the project in relation with the different scales and features of the studied conductors, should be able to handle issues related to the different applications of superconducting cables, from their initial forming up to their in-service operation.

Project coordination

Damien DURVILLE (Laboratoire de Mécanique des Sols, Structures et Matériaux) –

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.


INSA Lyon Laboratoire MATEIS
ARMINES CMM ARMINES Centre de Morphologie Mathématique de Mines ParisTech
NEXANS Nexans France
ECP Laboratoire de Mécanique des Sols, Structures et Matériaux
CEA/IRFM Commissariat à l’Energie Atomique et aux Energies Alternatives - Institut de Recherche sur la Fusion par confinement Magnétique
CEA/Irfu Commissariat à l’Energie Atomique et aux Energies Alternatives / Institut de Recherche sur les lois Fondamentales de l’Univers

Help of the ANR 1,177,771 euros
Beginning and duration of the scientific project: December 2012 - 48 Months

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