The goal of this research project is to obtain an understanding of how to fully characterize the dynamics of structures by using non-contacting ultrasonic radiation force excitation. Although modal analysis has matured significantly in the last three decades, existing empirical approaches do not effectively address the ultrasonic frequency range (above ~20kHz) which hinders quantitative validation of numerical structural models. This holds particularly true for small structures, such as engine turbine blades, that have very high, closely spaced, resonant frequencies and cannot be appropriately excited by using physical attachment. The project will address several critical needs that are required to move ultrasound radiation force excitation from being a qualitative laboratory technique into a methodology that can be widely adopted by the engineering community. One of these involves calibration and real-time monitoring of the imparted force by utilizing interferometric methods and innovative fiber-optic pressure sensors. Another major task involves correlation of resonant frequencies for structures excited in air and the same structures in water or other fluids. The combined measurement and modeling required for this task are important since the higher intensity available for the ultrasound radiation force excitation in water would allow shorter testing times, improved signal to noise ratios, and the possibility of driving structures with sufficient force to identify non-linearities for damage detection.
The research will have a broad impact in a wide range of applications since it will enable non-contact, high-frequency characterization of structural dynamics of small components that cannot be adequately characterized using conventional techniques. Ultrasound radiation force excitation techniques will aid in understanding the dynamics of turbine blades; this is of critical importance to help reduce high cycle fatigue failure, which has relevance to companies in the aviation and power generation industries. The techniques demonstrated will also be applied to hard-drive suspensions, naval propulsive components, and similar applications that would benefit from excitation without physical contact. Both graduate and undergraduate students involved in the research will be exposed to technical and nontechnical problems crucial to industry. A strong outreach effort will be implemented using planned demonstrations to motivate women, K-12 students, and underrepresented minority groups to become interested in science and engineering. Undergraduate music students, taking a general education course, will be exposed to the research results and have the opportunity to study vibrations of their instruments. The Principle Investigators will be developing a collection of videos, and corresponding curriculum guides, that will be posted on YouTube and related sites showing vibration of musical instruments, sporting equipment and other common objects. Outreach will also extend to national laboratories and companies that may benefit from understanding the new measurement approaches and analytical methods created, as well as local, regional, and national media so as to effectively capture the imagination of the general public.
