23 research outputs found
Magnetic Pulse Welding of Sheets – Process Modelling
Magnetic pulse welding involves the application of a controlled electromagnetic impulse
and consequent high velocity impact between two overlapped parts, which leads to plastic
deformation and consolidation between the parts along the interface without melting. The
key variables in magnetic pulse welding include a high magnitude discharge energy of
damped sinusoidal nature, the coil type and geometry and the materials, thicknesses and
geometry of the overlapped metallic sheets. A computer-based coupled electromagnetic
and dynamic mechanical analysis of magnetic pulse welding of sheets is presented in this
work to provide an insightful understanding of the evolution of joints, which is otherwise
intractable for monitoring due to the high speed of the process and the presence of a high
electromagnetic field. The computed results show that such a computational process model
can serve as a robust design tool for a fundamental understanding as well as for the
identification of suitable conditions for achieving a defect-free, reliable joint
Development of a maximum entropy approach for the thermomecanical modelling of the rotary friction welding process
A multi-physics modelling of rotary friction welding process based on a Maximum
Entropy approach is proposed. This approach will be able to solve coupled thermomechanical
problems. Because strains are very high locally around the welded area, the
remeshing time in a classical finite element method is very important. The use of this
meshless method should reduce simulations time and the numerical diffusion phenomena
Magnetic Pulse Spot Welding: Application to Al/Fe Joining
Magnetic pulse welding is a rapid process (takes place within few micro seconds) that
joins both homogeneous and heterogeneous materials in the solid state. The process
involves applying variable high current on an inductor to generate Lorentz forces on to the
conductive primary part (flyer). To realize the weld it is necessary to accelerate the flyer to
impact on to the secondary stationary part (base material) at a very high velocity attained
over the distance, called air gap, between the parts. It is typically possible to perform
welding of tubes and sheets provided there is an optimized air gap between the parts to
be welded. As part of our work we have developed an innovative approach (Magnetic
Pulse Spot Welding-MPSW) that eliminates the delicate task of maintaining the
aforementioned air gap between the plates. The proposed method opens better viable
perspectives for heterogeneous assembly of automotive structures or connecting batteries
in a quasi-cold state. The developed approach has been validated on the heterogeneous
assembly Al/Fe by tensile tests (quasi-static and dynamic) that attested the quality of
welds
Electrohydraulic Crimping of 316L Tube in a 316L Thick Ring
During the electrohydraulic forming process a high current, up to one hundred of kilo amperes, is discharged between two electrodes immersed in a water tank. This creates
plasma that generates a primary shock wave and secondary pressure waves. If these
pressures are applied in a tube, it is then possible to deform dynamically this tube against
a ring, leading to crimping. This process presents several advantages: it is possible to
deform internally tubes of diameters ranging from a few millimetres to several centimetres,
no lubrication is needed and because the process is dynamic, the spring back is limited and
some materials can present an improved behaviour compared to quasi-static forming.
In this paper, we present an original electrohydraulic crimping device. We successively
present the operating principle of our system, the time evolution of the crimping pressure
and the strain rate in the tube for two kinds of pulse shaper. Finally crimping tests are
done to evaluate the efficiency of the process
Material Constitutive Behavior Identification at High Strain Rates Using a Direct-Impact Hopkinson Device
Modern numerical simulation techniques allow nowadays obtaining accurate solutions of
magnetic pulse and electrohydraulic forming/welding processes. However, one major
difficulty persists: the identification of material constitutive equations behavior at levels of
high strain rates reached by these processes, and which varies between 103 and 105 s-1.
To address this challenge, a direct-impact Hopkinson system was developed at ECN.
It permits to perform dynamic tests at very high strain rates exceeding the range of the
traditional Split Hopkinson Pressure Bars and hence enable us to identify constitutive
models for a wide range of strain rates. The alloy used to test this device was Ti-6Al-4V.
Strain rates up to 2.5Ă—103 s-1 were attained
Simulation de l'écoulement des pâtes cimentaires par un modèle diphasique
La modélisation de l'écoulement des pâtes cimentaires est un problème difficile car le matériau a non seulement un comportement rhéologique complexe mais il peut également présenter des hétérogénéités induites par l'écoulement. L'apparition de ces hétérogénéités résulte de la filtration de phases fluides au travers de phases solides et peut conduire au blocage de l'écoulement. Pour modéliser l'écoulement d'un tel matériau il est nécessaire de prendre en compte la présence d'au moins deux phases. Dans notre modélisation nous considérons que les deux phases sont continues et admettent un comportement rhéologique en loi de puissance. Le couplage entre les deux phases est pris en compte au moyen d'une loi de Darcy généralisée à un fluide en loi de puissance. Le modèle est résolu par la méthode des éléments finis et validé dans le cas d'un test d'écrasement. Nous montrons que ces simulations permettent d'établir des diagrammes d'ouvrabilité des pâtes cimentaires
Un Modéle Thermodynamique de Fluide Electro-Rhéologique
none3G. NAPOLI; DROUOT R; RACINEUX GNapoli, Gaetano; Drouot, R; Racineux, G
Development of a maximum entropy approach for the thermomecanical modelling of the rotary friction welding process
A multi-physics modelling of rotary friction welding process based on a Maximum
Entropy approach is proposed. This approach will be able to solve coupled thermomechanical
problems. Because strains are very high locally around the welded area, the
remeshing time in a classical finite element method is very important. The use of this
meshless method should reduce simulations time and the numerical diffusion phenomena