Research Experience For Undergraduates at
Colorado State University
Summer 2003
Made possible by financial contributions from the National Science Foundation and the Army Research Office
Introduction
My name is Chris Ryan. I am a junior undergraduate studying physics, applied mathematics, and computer science at Colorado State University. I spent 8 weeks at Colorado State University as part of an undergraduate research program in sound and vibration. I was assigned to the physics department, where I conducted studies of condensed matter via resonant ultrasound spectroscopy under the supervision of Dr. Robert G. Leisure and his graduate students, Dennis Agosta and Jennifer Atteberry.
Overview
Resonant ultrasound spectroscopy (RUS) is a relatively new means of materials analysis, making significant advances in the last 20 years. The essential idea is to use ultrasonic transducers to excite the eigenmodes of a sample (typically on the order of mm) over a range of temperatures, yielding a series of resonance frequencies. From this resonance data, we are able to apply a nonlinear inversion technique developed by Migliori to determine the elastic constants of the material, and consequently, derive such valuable information as Poisson's ratio, as well as bulk, shear and Young's moduli.
Specifics
During my eight weeks at CSU, I completed the temperature profile for LaNi5-xAlx, working specifically to complete the data collection for LaNi4Al in the temperature range of 70K-300K. LaNi alloys are of research interest due to their hydrogen retention properties in batteries and fuel cells. The essential study consists of determining how the material behaves as the concentration of Sn or Al is varied. Data had previously been collected on the material from 3K-70K and 300K-418K. I used a cryostat with a LiNbO3 transducer assembly to collect this data. In addition, I studied the elastic properties of Terfenol-D, a (nonlinear) magnetically tunable vibration absorber with a wide range of applications.
Results
Presented below are the bulk and shear moduli for LaNi5-xAlx. My data completed the middle temperature range for LaNi4Al. The trend in the data is clear - the moduli are inveresly proportional to both temperature and aluminum concentration.
For Terfenol-D, a material I found very difficult to analyze (at least at room temperature) there is an interesting trend seen in both the frequency shift and attenuation plots. There appear to be local minima and maxima (respectively). Clearly, more data is required to quantify this observation. One speculation posed by Dr. Leisure is that there may exist a potential coupling between the ultrasonic stress and magnetization of the material via the magnetostrictive properties of the material. Further studies will likely be carried out by the RUS group.
Ultrasonic attenuation and frequency shift data of Terfenol-D