Resonant Ultrasound Spectroscopy, as Applied to Nondestructive Evaluation and Characterization of Carbon Fiber Reinforced Epoxy Composite Materials.
Resonant ultrasound spectroscopy (RUS) can be an elegantly simple nondestructive evaluation tool. The resonance spectrum of any specimen is dependent on, and sensitive at ppm levels to, its density, geometry, elastic and thermal properties, and boundary conditions. The measurement of spectrum is fast, taking between 15 and 90 seconds with state-of-the-art instrumentation, making it appropriate for following properties as a function of temperature. Parts per million changes in specimen density, geometry, elastic moduli, temperature, and boundary conditions are detected with RUS. A novel apparatus is presented for driving and detecting the mechanical resonance of objects with major dimensions ranging from 0.1 cm to 33 cm. The noise floor of the apparatus is characterized using a high Q titanium alloy and a low Q graphite/epoxy composite. The apparatus is used to measure the amplitude/frequency resonance spectra of right rectangular parallelepiped (RRP) specimens of four different lay-ups of AS4/3501-6 carbon fiber reinforced epoxy (CFRE) composite material at room temperature and at one degree C intervals between -177^circC and 25 ^circC. It is important to know the mechanical properties of this material at low temperatures for underwater, polar, and space applications. The temperature dependence of the second order elastic moduli are calculated from the resonance spectra of the AS4/3501-6 RRPs. High power ultrasound is used to enhance the cure of AS4/3501-6 CFRE composite. Composite panels are insonified through the caul plate, by a high power ultrasonic horn, while curing. Stiffness enhancements of five percent are observed. The resonance spectrum of a steel caul plate is used to monitor the degree of cure of AS4/3501-6 CFRE composite panels in real time. Because the curing composite acts to change the boundary conditions, the resonance spectrum changes as the composite cures. RUS is used to screen a variety of high precision engineered parts for mechanical defects. The second order elastic moduli of poly-crystalline Ti6Al4V alloy and single crystal aluminum are determined using RUS.
- Pub Date:
- August 1996
- Engineering: Materials Science; Physics: Acoustics