The primary focus of the proposed work is a combination of in-situ transmission electron microscopy studies of sliding surfaces and materials-science based modelling of the nanoscale processes taking place in the triboactive region using primarily dislocation-based analytic models. The main focus of the experimental work will be to directly resolve in real time the processes taking place, ranging from the motion of dislocations and sliding of interfaces to tribologically induced chemical or structural transitions. This will exploit all the different modes of electron microscope imaging ranging from conventional low-resolution imaging through electron-energy loss spectroscopy to atomic scale imaging. The thrust of the analytical component will be to marry conventional materials science ideas such as the effect of barriers on dislocation motion with what is taking place in the triboactive layer, to develop parameter-free analytic models which have predictive power so can be used in the future to estimate what will be taking place in new tribological problems or systems.
If successful, the work will establish a solid materials science foundation for tribological processes taking place at the nanoscale in the triboactive region. In addition, the theoretical models and the predictive analytical models can be then used to estimate issues in real engineering situations, leading to rational designs to reduce frictional energy losses and improve the reliability of mechanical systems at the nanoscale. In terms of education, the research will help support both local outreach to high-school students as part of the existing programs with Chute and Nichols Middle Schools and the HANDS program in Evanston, as well as more international outreach efforts involving efforts to run schools and workshops on electron crystallography in places such as Mongolia, Qatar and South Africa via the International Union of Crystallography.
Friction is a pervasive phenomenon; by some estimates it represents 2% to 6% of the GDP of developed countries, and in passenger cars, one-third of the fuel energy is used to overcome friction in the engine, transmission, tires, and brakes. Similar to the potential savings due to reduction in the thermal losses of buildings or improving the efficiency of light sources, reducing frictional losses would go a long way to mitigate the looming energy crisis. Beyond energy, friction and wear are important for orthopedic devices. A variety of conditions, most notably osteoarthritis, may result in a patient’s need for prosthetic joint implants of the hips and knees. Every year, as the "baby boom" generation ages and patients live longer and more active lives the demand for hip replacements rises. The number of total hip arthroplasties performed annually in the U.S. is expected to grow 174% from 2005 to 572,000 by 2030. Friction, wear and corrosion play major roles in clinical conditions associated with implants. Reducing the failure rate and increasing the long-term survivorship of permanent orthopaedic implants will not only lessen the morbidity associated with a failed implant, but also substantively reduce the costs associated with revision surgery which runs into billions of dollars per year. While friction has been appreciated as of critical importance dating back at least as far as the ancient Egyptians, for instance the carving on the tomb of Saqqara 2400 BC showing a man pouring a lubricating liquid to help move a statue of Ti, in many respects our current understanding of tribology, which includes the sources of friction as well as wear and chemical changes associated with sliding is comparatively limited. This project focused upon improving the understanding of frictional processes at the nanoscale, and has contributed to a better understanding of how tribological issues contribute to the medical issues involved in implants. During the project we were able to obtain images of a number of fundamental processes involved in tribology for which there had not previously been any direct observations. In addition to processes that were somewhat predictable, we also found some which were surprises. As we did this experimentally we were able to improve our models of what is taking place so we can model them better. In some cases the samples we used were chosen to make the experiments more exact, but in a number of cases we used materials important for orthopedic implants so we could explore some of the issues related to their use in human beings.
