|Proposed Statement of Research
Rebecca B. Fagan
Texas Tech University
Several industries have used friction welding for many years. Aerospace has taken advantage of this process due to their high tolerance requirements and extreme conditions requirements. The process produces very high-integrity welds. Friction welding is a solid-state process. The work pieces are rotated relative to one another. As compressive forces are added heat is produced and the material is plastically displaced at the weld interface to produce a coalescence of material. Under normal conditions the weld surfaces do not melt. Most metallic engineering materials which are forgeable can be welded by the friction process. In addition, powder metals, metal matrix composites are weldable by friction welding. However, more important to the aerospace industry is the fact that many dissimilar metal combinations can be joined together by friction welding; such as, copper-to-aluminum, titanium-to-copper, and nickel alloys to steel. Limited success has also been shown in the welding of some ceramics to aluminum.
Due to the very nature of the process, it presents itself to be enhanced by the tribologists. To incorporate all aspects of moving surfaces and energy dissipation, the word "Tribology was introduced by a British committee in 1966. This word came from the word "tribos" which means "rubbing" in classic Greek. Tribology was defined as:
"The science and technology of interacting surfaces in relative motion and of related subjects and practices."
Friction is a common resistance to motion. If the movement is between two solid bodies, friction can be accompanied by wear. Wear is the progressive loss of substance from the operating surface of a body occurring as a result of relative motion at the surface. Adhesion is the ability of contacting bodies to withstand tensile forces after being pressed together. In the past, friction was confined to engineering and physics. Wear was a part of metallurgy. Lubrication studies, the substances affecting wear and friction, were relegated to the chemists. Adhesion belonged to any others.
With the invention of the electron microscope it became possible to study the molecular array of crystalline bodies, the dislocations, and the imperfections of this array. It was now possible to relate friction with plastic deformation and dislocation behavior. Nam P. Suh developed a delamination theory of wear using dislocation theory. Gane and Skinner determined that dislocation behavior alone cannot adequately account for all of the energy dissipated during the sliding process; that molecular theories of friction may best describe the surface interaction and that atomic interactions may be responsible for the plastic deformation and account for the frictional energy.
Could friction welding and wear studies be combined to produce a better weld. Could what we have learned from wear studies on various materials allow the combination of a greater variety of dissimilar materials. Could the parameters used in weld production be enhanced with better models. Attempting to bring the knowledge from the two camps together may be very successful to aerospace and tribology.
Wednesday, 26-Mar-2003 22:07:27 CST
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