FSW_General_Presentation(sysweld搅拌摩擦焊操作)

Temperature Latent heat Dissipated power Strains
MetallurgyΒιβλιοθήκη Microstructure
Mechanics
The thermal and the mechanical phenomena in a fully coupled in this approach. The stress equilibrium problem, the heat transfer problem and the mass conservation are solved for the stationary step of the process. The material is assumed to be as a viscous non-Newtonian fluid. Therefore the problem can be studied in an Eulerian frame where the mechanical stress are calculated from the velocity field and the thermal dissipation can be easily deduced.
S 2. . D (5)
where D is the strain-rate tensor defined from the velocity field
T D 1 . grad v grad v (6) 2


is an effective viscosity defined as follows [5]:
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MODELING
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Strong couplings modeling
Heat Transfer
Temperature
Viscous dissipation Heat flux density temperature
•Mechanics (Norton-Hoff law):
Effective viscosity
S 2..D with K . ( 3 . D)
Viscous stress tensor Strain rate
3D modeling of thermo-fluid flow in friction stir welding including metallurgical and mechanical consequences
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Thermo-mechanical coupling with “Eulerian” scheme
Heat Transfer
Temperatures dissipated Power
Material flow
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Objectives of FSW simulation
For this process, the numerical modelling seems to be extremely valuable for the understanding of the residual stresses, the distortions and the microstructure modifications. To model these effects, the heating needs to be carefully simulated. The objectives of the simulation are, on one hand, the understanding of physics and, on the other hand, the development of a predictive tool allowing to reduce the number of experiments needed to design new tools.
•Tool rotation velocity: 1100 r. min-1
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Backing plate temperature. Perfect contact between plate and sheets
Tool rotation
Mechanics
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Equations
•Heat transfer : conservation of energy
.S:Ddiv(q) .C.v.grad() 0
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Heat Exchange with the tool
Shear Stress
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RESULTS
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m1
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Equations
The viscous stress tensor S is related to the strain-rate tensor D using a Norton-Hoff behaviour law:
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Mechanics
Final shape
Cross-section of the stirring zone
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Welding of large panels
Use of local-global methodology with Pam Assembly:
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Conclusion
Need for Industrial/Scientific collaboration Industrial:
Less than 2 hours CPU on a PC for full computation. Welding of large structures possible
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Flow
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Streamlines
Flow direction
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Further R&D:
Improvement of metallurgical models for Al alloys. Transient effects. Application to the Friction Stir Spot Welding:
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The Friction Stir Welding Process
from the TWI web site
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Geometry
Flow
Direction
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Temperature field

Al alloy 7075 (°C) :
•Tool translation velocity: 500 mm.min-1
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Influence of contact conditions
flow flow
50 MPa
rotation
60 MPa
rotation
flow
flow
70 MPa
rotation
80 MPa
rotation
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(7) K. 3. D K and m are the consistency and the sensibility of the material, and D is the equivalent strain rate:
D 2 D: D 3


m 1

The friction between the tool and the workpiece is of Neumann boundary conditions. The contact is modelled by the Norton law [6]. In this model, the friction stress depends on the differential velocity v between the tool and the workpiece: .K . v 1.v (9) where is the shear stress, and are the contact parameters.
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Friction Stir Welding Process details
Friction stir welding is a complex process including interactions between thermal, metallurgical and mechanical phenomena. The heating is provided by the mechanical dissipation due to the strains and the contact conditions between the tool and the material.