User Program study with H. Choo and W. C. Woo of University of Tennessee
| While waiting for
NRSF2 commissioning, a study of friction-stir welding (FSW) led by
Joint Faculty member Hahn Choo, graduate student Wanchuck Woo and
ORNL’s Zhili Feng and Stan David was conducted at Los Alamos National
Laboratory. FSW is a solid-state joining process that makes a strong
metallurgical bonding through (1) the frictional heat generated from
the pressing shoulder and (2) severe plastic deformation caused by the
rotation of a stirring pin. Current and future applications of FSW in
the transportation industry include automotive engine support frames;
tanks hulls, decks, and internal structures for high speed ferries and
LPG storage vessels for the shipbuilding industry; and airframes, fuel
tanks, and cryogenic tanks for space launch in the aerospace industry. It is known that the heat and deformation necessary for the joining are also the major sources of residual stresses in the welds, which are detrimental to the integrity of the joined component. However, quantitative correlation between various welding parameters and residual stresses is not available to date. Three different weld specimens were prepared from 6061Al-T6 plates: Case 1: a plate processed with both the stirring pin and pressing shoulder (i.e., a regular friction-stir weld); Case 2: a plate processed only with the pressing shoulder; and Case 3: a plate processed only with the pin. The longitudinal, transverse, and through-thickness strain components were measured across the weld line using neutron diffraction (See Fig. 5-19). The comparison of the longitudinal strains (strain parallel to the weld bead) among three different cases shows distinctly different residual-strain profiles, clearly revealing for the first time deconvoluted effects from the different welding parameters (i.e., deformation, heat, or the combination. |
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This is the beginning of a
multiple-year investigation of the
relationships between the welding parameters, residual stresses, and
mechanical properties of components joined by FSW. The results will
provide an experimental basis for more accurate computational
simulation of the FSW process, which will lead to an optimization of
the processing parameters and tool design. |
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Acknowledgments
URL: http://www.html.ornl.gov/duc/tisic.html