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Research Papers

Modeling Damage Evolution in Friction Stir Welding Process

[+] Author and Article Information
Youliang He, Paul R. Dawson, Donald E. Boyce

Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853

J. Eng. Mater. Technol 130(2), 021006 (Mar 12, 2008) (10 pages) doi:10.1115/1.2840963 History: Received July 26, 2007; Revised December 19, 2007; Published March 12, 2008

The evolution of voids (damage) in friction stir welding processes was simulated using a void growth model that incorporates viscoplastic flow and strain hardening of incompressible materials during plastic deformation. The void growth rate is expressed as a function of the void volume fraction, the effective deformation rate, and the ratio of the mean stress to the strength of the material. A steady-state Eulerian finite element formulation was employed to calculate the flow and thermal fields in three dimensions, and the evolution of the strength and damage was evaluated by integrating the evolution equations along the streamlines obtained in the Eulerian configuration. The distribution of internal voids within the material was qualitatively compared with experimental results, and a good agreement was observed in terms of the spatial location of voids. The effects of pin geometry and operational parameters such as tool rotational and travel speeds on the evolution of damage were also examined.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

The FSW process and the finite element mesh: (a) schematic of FSW and the pin shapes (a cylinder and a frustum) and (b) discretized finite element domain. The mesh consists of 8000 20-node brick elements. The origin of the coordinate system is located on the axis of the pin, halfway through the thickness of the plates.

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Figure 2

The measured temperature history of the tool during FSW of the 304L stainless steel. The rotational speed was 300rpm(31.4s−1), and the welding speed was 0.425mm∕s. (Data courtesy of Professor C. Sorensen, Brigham Young University.)

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Figure 3

Time-temperature profiles at two locations on the middle plane (thickness direction) of the plate: (a) measured and (b) computed. The monitoring points were located 4.0mm and 5.7mm away from the centerline on the advancing side. The rotational speed was 300rpm(31.4s−1), and the welding speed was 0.425mm∕s. (Experimental data courtesy of Professor C. Sorensen, Brigham Young University.)

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Figure 4

Simulation results for an unthreaded straight pin geometry: (a) streamlines around the rotating pin, (b) temperature field, (c) distribution of the mean stress over the strength (σm∕κ), and (d) contours of porosity. Note that sections perpendicular to the x axis are viewed from the −x direction, while those normal to the y axis are viewed from the +y direction. These conventions apply to all the figures that follow.

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Figure 5

The distribution of porosity using a frustum pin. The taper angle γ=5deg and the pin diameter d=6mm. The rotational speed was 350rpm(36.6s−1), and the welding speed was 0.85mm∕s.

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Figure 6

Simulation results with a threaded pin (downward): (a) streamlines near the pin on the z=0 plane compared with those obtained with a smooth pin, (b) distribution of the mean stress over the strength (σm∕κ), and (c) contours of porosity in the weld.

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Figure 7

Simulation results for a threaded frustum pin: (a) variation of temperatures along lines y=±4 on the z=0 plane plotted against the distance from the pin center for frustum and cylindrical pins; (b) distribution of porosity for a threaded frustum pin.

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Figure 8

Comparison of (a) temperature and (b) porosity distributions in the welds obtained using different rotational speeds. The sampling points for temperatures are ±4mm away from the centerline on the middle plane (z=0). The damage profiles are taken on the advancing side of the middle plane, 3mm and 4mm away from the centerline. The welding speed was 0.85mm∕s.

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Figure 9

The variations of (a) temperature and (b) porosity with distance from the centerline (y direction) on the middle plane (z=0). The sampling points are located at x=4mm from the pin center. Welding speeds of 0.85mm∕s and 1.70mm∕s are compared, with a rotational speed of 350rpm(36.6s−1).

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