Anthony P. Reynolds - US grants

Optimization of and broadening of applications for the friction stir welding (FSW) process will be greatly accelerated by the development of flexible and accurate process models which can be used to predict the effects of varying FSW process parameters on porosity, mechanical properties of the weld, and, ultimately, final weld microstructure. The intent of the research effort described herein is to take a large step down the path toward development of such models. A hierarchical approach is proposed in which first, a fluid mechanics based model describing the thermal history of material in the weld and the material transport in the weld is used to enhance the understanding of the physics of friction stir welding. Next, using the knowledge and experience obtained from development of the CFD model, a solid mechanics model will be developed. Both models will be developed in combination with a comprehensive, experimental characterization of the friction stir welding process. At every step of the model development, the experimental program will verify assumptions and results and conversely, modeling results will suggest critical experiments to be performed. Initial modeling attempts will be as simple as is consonant with accurately capturing the physical phenomena. As understanding of the process increases, so will the complexity, the fidelity, and utility of the models which follow. The ultimate goal is to create a solid mechanics based model which provides a complete description of the thermal, stress/strain, time history of all the material in a friction stir weld. Experimental tasks to be undertaken include: (1) Temperature measurement during the friction stir welding process. A digital IR camera will measure surface temperatures while embedded thermocouples measure subsurface temperatures. (2) Measurement of energy input to the weld by the friction stir-welding machine (via conversion of electrical energy to mechanical). (3) Determination of material transport in the weld by mapping the movement of marker materials via destructive post weld examination. (4) Post-weld microstructural evaluation. (5) Mechanical testing of weldments and fractographic examination. Each of these experimental tasks will either help to establish proper boundary conditions for the proposed models or will aid in verification of the models or both. Details of the experimental program may be amended as needed to fully support the model development. Critical tasks for the modeling efforts include: (1) Determination of an appropriate model geometry that captures the essence of the physical process without unduly complicating the analysis. (2) Deriving appropriate thermal and mechanical boundary conditions from experimental data that are compatible with the chosen model geometry. (3) Selection of an appropriate material constitutive law for characterizing the behavior of the material in the weld zone. (4) Incorporating the constitutive law into computational fluid/therma/solid analysis packages chosen for the model.

If all of the pieces outlined above come together, the result will be a predictive model which can be used to guide friction stir welding process parameter optimization and give guidance in the development of process modifications which can broaden the application of FSW.

This award is for a planning grant for the establishment of a new multi-institutional Industry/University Cooperative Research Center (I/UCRC) for Friction Stir Processing. Nationally and internationally recognized leaders in the research and development of this novel metals joining and processing technology are located at the South Dakota School of Mines and Technology, Brigham Young University, the University of Missouri-Rolla and the University of South Carolina, bringing together these institutions to establish the Friction Stir Processing I/UCRC.

The proposed Friction Stir Processing I/UCRC will focus on furthering developments in the following fields of study for Friction Stir Processing/Friction Stir Joining of ferrous, non-ferrous, and metal matrix composite alloys: Friction Stir Joining; Friction Stir Microstructural Modification; Friction Stir Post-Processing; Friction Stir Structural Designs and Applications; Friction Stir Intelligent Controllers and Efficient Tooling; Friction Stir Cost Benefit Analysis.

Center for Friction Stir Processing (CFSP)

IIP-034383
South Dakota School of Mines and Technology (SDSMT)
Arbegast

IIP-0934319
University of South Carolina (USC)
Reynolds

IIP-0934377
Brigham Young University (BYU)
Nelson

This award id funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

The proposal requests a five rear renewal of NSF funding for the SDSMT, USC and BYU sites of the Center for Friction Stir Processing (CFSP). The Center, comprised of these three sites, was established in 2204; and currently has two additional sites (Wichita State University and Missouri University of Science and Technology) who joined later. The lead institution is SDSMT. The main vision of CFSP is to provide the forum for industry/university cooperative research on the development, validation, and industrial implementation of the emerging solid-state materials joining and processing technologies known as Friction Stir Welding and Friction Stir Processing.

CFSP continues to perform basic and applied research programs that address the implementation needs of the Center's industrial and government sponsors. The specific research areas include: Friction Sir Joining (FSJ), Friction Stir Processing (FSP), friction Stir Spot Welding (FSSW), Friction Stir Post-Processing, Friction Stir Structural Designs and Analysis, Friction Stir Intelligent Controllers and Efficient Tooling, and Friction Stir Cost Benefits Analysis. The Center has numerous publications in archival journals and conference proceedings, and notable commercial successes have also resulted from the Center.

The broader impacts on the community are strongly built into the proposal through university, local, regional, national and international participation in the center activities. The membership of the Center is derived at a national and international level. In addition several teaming arrangements have already been established between the participating universities and local (Native American) colleges and community technical schools for the purpose of technology transfer and collaborative educational opportunities. Each CFSP site has supported outside activities to promote educational opportunities and to increase awareness of FSW in the world.

This grant provides funding for the development of the friction extrusion process and associated equipment to enable direct production of high-value materials (such as titanium wires) from low-cost precursors (such as powders or machining chips) with reduced energy consumption. Friction extrusion die and process chamber design will be studied. Experiments and numerical simulations will be carried out to develop an in-depth understanding of the scientific principles and physical mechanisms operating in the friction extrusion process. Friction extrusion experiments will be carried out to gain a physical understanding of the process and equipment, such as the effect of extrusion die and chamber design on power consumption and quality of the produced wire. Computational models will be created to simulate the extrusion process in order to investigate issues (e.g. full-field material flow pattern and thermal history) not approachable experimentally. Validation and visualization experiments will be designed and performed to provide measurements of material position, velocity and temperature for validating simulation model predictions, so that computational models can be utilized reliably for process design and optimization purposes.

If successful, the results of this research can be used to enable the design, optimization and utilization of the friction extrusion process for the energy-efficient production of high-value materials from low-cost precursors and for recycling machining wastes (chips). The friction extrusion process has the potential to greatly reduce energy requirements for the production of titanium wire feedstock by eliminating costly vacuum melting and billet casting. Wires produced from this process could be used as feedstock for additive manufacturing processes or as filler wires for niche welding applications.