Session: 21-01: Poster Session

Paper Number: 98096

98096 - Noncontact Nonlinear Resonance Ultrasound Spectroscopy for Evaluation of Thermal Damage in Carbon/carbon Composites 

The aim of this research is to evaluate the sensitivity of the nonclassical hysteretic nonlinearity parameter α to microscopic material damage in Carbon/Carbon (C/C) composite specimens using noncontact nonlinear resonance ultrasound spectroscopy (NRUS). The NRUS procedure used for this study employs an air-coupled piezoelectric transducer source and a laser doppler vibrometer receiver for entirely noncontact excitation and detection of the axial motion of a slender C/C specimen. The composite samples are exposed to elevated temperatures in oxidative environments for varying periods of time to induce oxidation at the fiber-matrix interfaces. The interfacial oxidation that occurs at such temperatures can lead to the generation of interfacial microcracks. Furthermore, the oxidation of the interfacial layer can expose fibers to oxidation, leading to a decrease in tensile strength. The changes in the quality factor (Q) and the shift in the resonant frequency with varying excitation amplitudes are calculated. From these, α_f, which describes the frequency shift, and α_Q, which describes the energy loss as a function of strain, are determined. These hysteretic nonlinearity results (α_f and α_Q) are then compared to bulk weight loss, caused due to the release of products of oxidation of the fibers, interface and matrix material resulting in microscopic changes such as delamination and debonding.

Presenting Author: Keshav Bhat Georgia Institute of Technology