FELLOWSHIP FOR SAMPSON: Non-Destructive Evaluation of Refractory Composites to Enable Damage Tolerant Design

Non-Destructive Evaluation of Refractory Composites to Enable Damage Tolerant Design A main hurdle to the sustainability and practicality of next generation air and spacecraft is developing structural components that are reusable. This is challenging, as the conditions under which these materials must operate including hypersonic exoatmospheric hops create thermomechanical conditions in which damage to the structure may be incurred. If these structures are to be reused, they must be amenable to in-field x-ray characterization to ensure incurred damage falls within acceptable limits. This would require a rigorous understanding of the relationship between observable flaws and damage tolerance to ensure that they still meet materials performance requirements. While refractory composites are excellent materials for these applications due to their wide range of attractive structural and thermal properties, to date few studies have been conducted that elucidate the relationship between flaws (e.g. pores, microcracks) to damage tolerance. We propose a multiscale x-ray microCT (XCT) approach to address this. The investigation will start by characterizing the microstructure using high-resolution (~1 μm voxel size) scans at the representative volume element (RVE) size scale for pristine carbon-carbon-6 (AAC-6) composite materials. To build the foundation for standard characterization protocols for AAC-6 we will quantify the variability across XCT systems (Thermo Scientific HeliScan Mk2, NSI X-3000) and software (Avizo, NSI efX/vfX). To better approximate the resolution attainable through in-field x-ray, lower resolution scans of larger volumes encompassing the previously studied RVE regions will be obtained to determine the types of defects that can be accurately identified using in-field x-ray. Following studies will focus on nominally identical AAC-6 in various states of damage. XCT scans will be recorded in multiple resolutions with the goal of determining the character (size, shape, local environment) of defects that are most likely initiate damage in the structure. 1