UC Santa Barbara

Ceramic matrix composites are an extreme-environment structural material poised to lightweight and improve the efficiency of next-generation aerospace and propulsion systems. As the use of CMC components continues to expand, there is a commensurate need for accurate models and ways to monitor their damage evolution. The transient ultrasonic waves generated during crack propagation, known as acoustic emission (AE), offer a powerful means of tracking the progression of damage. Among other non-destructive evaluation techniques, AE is unique in its sensitivity to damage and in its ability to temporally resolve the evolution of damage throughout the volume of a component. While frameworks to achieve this remain limited, AE has the potential to generate, in essence, a time-resolved video of evolving subsurface crack formation. Such a capability would supply CMC modeling efforts with information-rich datasets on damage evolution and establish a basis for quantifying damage during operation. To this end, this work unifies several elements from the CMC and non-destructive evaluation literature into an intuitive multimodal framework for AE-based imaging that uses waveform energy as a metric for damage, while using the content of the waveforms to determine the spatial position of the damage. We describe experiments to validate the linear relationship between cumulative energy and accumulated matrix cracking in idealized CMC specimens, both in-situ and post-mortem. Furthermore, we show proof-of-concept for an ultrasonic-based calibration methodology, illustrated through the use of pencil-lead break datasets, that would enable improved AE location resolution and depth identification in mechanical test specimens. Our work provides experimental mechanicians with a clear path for developing quantitative and translatable AE imaging capabilities in a given material system using a combined x-ray computed tomography, ultrasonics, and acoustic emission approach.