Quantification of Directionally Dependent Mechanical Properties and Damage Tolerance of FiberForm

Porous materials exhibit a variety of functional properties that are attractive for aerospace applications such as low density and low thermal conductivity. However, to realize the full potential of these materials they must also be mechanically robust and damage tolerant. Currently, it is very costly and time-consuming to test these materials under service conditions, therefore, computational models are a good path forward. Due to the inherent microstructural stochasticity of these structures, however, their behavior is difficult to effectively model without detailed experimental studies to validate and benchmark computational results. To that end, this study investigates the mechanical properties of FiberForm (a substrate for Phenolic-Impregnated Carbon Ablator [PICA]) and ties together the global macroscopic observations to the local mesoscale properties and behaviors dictated by individual fibers and fiber junctions. Results from pristine samples have revealed clear differences in compressive deformation behavior depending on the orientation of the loading axis with respect to general fiber orientation direction. Strain localization was observed through the use of digital image correlation (DIC) and tied to features within the macroscopic stress-strain plots. Continued work to quantify the impact of previous damage (e.g. cracks and through holes) on the mechanical reliability of the material was also conducted. These defects were observed to result in decreases to the macroscale mechanical properties past what would be expected given a reduced cross-sectional area. Furthermore, distinct macroscale mechanical characteristics and mesoscale deformation behaviors were observed depending on the defect type. These results provide broad experimental data to inform and validate modeling approaches to accurately predict and tailor the reliability of porous parts under service conditions.