KY Space Grant GF-21-030: Multiscale Mechanical Evaluation of the Deformation Pathways in Porous Materials

Multiscale Mechanical Evaluation of the Deformation Pathways in Porous Materials Porous materials describe a wide range of materials for which 5% to 50% of the overall volume is a solid phase with the rest comprised by either isolated or interconnected porosity. These materials tend to possess exceptionally low thermal conductivity and density, positioning them to be attractive for a wide range of aerospace activities. ‘Lightweighting’ efforts have sought to reduce the density of parts without sacrificing reliability or performance. Additionally, thermal protection systems (TPS) rely on porous materials that are efficient at shielding delicate electronics and sensors from the high temperatures that are imposed by high velocity travel and atmospheric ingress. To realize the promise of their excellent functional properties (e.g. density and thermal conductivity), however, it is necessary that these porous materials be mechanically robust, as they experience high stresses and vibrational fatigue. In addition, materials for on-orbit use must maintain mechanical and thermal integrity even after high-rate impacts from micrometeoroid and orbital debris. Testing porous materials under service conditions is—when even possible—expensive and time-consuming, and therefore, accurate constitutive models that predict the mechanical and fatigue performance of porous materials are essential. The exact structure of porous materials varies greatly depending on material and processing method, but common to all are micro- and mesoscale heterogeneity and stochasticity not found in fully dense materials. To capture the influence of these effects, a blended experimental and computational approach that extends across relevant length scales is required. Recent NASA-supported efforts have focused on developing a stochastic meso-scale modeling approach for predicting expected properties and distributions of local properties of complex and/or randomly structured materials. Validation of this modeling approach for porous materials requires high-throughput mechanical characterization that bridges length scales and directly characterizes intrinsic variability in local properties at length scales similar to structural feature sizes. Under this project, porous Fiber Form material will be mechanically tested in two modalities to probe its mechanical response across relevant length scales. Ex situ mechanical compression of millimeter sized specimens coupled with digital image correlation strain measurement will provide ‘part average’ properties along with detailed analysis of the localization and propagation of deformation in strained parts. In situ nanoindentation will measure the local mechanical response and directly observe the attendant deformation of the material and its dependence on the stochastic heterogeneities at the nanoscale. Together, these results will inform and validate a modeling approach able to accurately predict the reliability of porous parts in service.