The results of recent ultrasonic studies are presented on the microstructure of high temperature composites. The acoustic sensors consist of an acoustic emission (AE) detector, an ultrasonic generator/receiver and a scanning acoustic microscope (SAM). With the aid of high temperature waveguides some of these sensors are shown to detect the in-situ changes in some of the key properties of plates of Carbon/Carbon during pyrolysis in the range of temperatures from 25 'C to 900 °C. In particular, changes in stiffness as a result of microcracking and decomposition are readily detected and are shown as useful to guide/revise the time-temperature profile of the carbonization heat treatment. The acoustic data show a variety of features giving insight into the microstructural changes as the heat treatment proceeds. Among these are: the observation of a minimum in the temperature dependent modulus and a maximum in the AE counts at about 650 °C. Microcracking is shown to be significantly influenced by the relative roles of the reinforcing materials vis-a-vis the matrix. The results point the way towards the use of sensors toward process monitoring, understanding and control in a manufacturing environment.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Mechanics of Materials
- Mechanical Engineering
- Physics and Astronomy(all)