Overview of the Use of Acoustic Emission and Electrical Resistivity for Damage Detection in Ceramic and Polymer Matrix Composites

Abstract

Micro-fracture events such as matrix cracks and fiber breaks are critical phenomena to monitor for ceramic and polymer composites in order to assess the health of the material. For example, in ceramic composites, low stress matrix cracking leads to life-limiting conditions at elevated temperatures in the presence of oxygen or water vapor environments. Modal acoustic emission and electrical resistivity are two techniques which have been used to monitor matrix cracking as well as other microfracture events in ceramic and more recently polymer matrix composites which can then be incorporated into thermo-mechanical behavior models to determine residual properties and/or life-expectancy. The keys to effective use of acoustic emission, when monitoring damage in ceramic and polymer composites, are the ability to accurately locate the events and effectively quantify the waveform properties to relate waveforms to physical sources. Several location techniques have been explored with different levels of success. Waveform frequency content and energy have been used to accurately quantify sources. Finally, an example of acoustic emission and electrical resistance monitoring for a SiC/SiC composite is shown to highlight the potential for the use of electrical resistance as a health monitoring technique in this composite system.