Session: 03-09-02: Materials for Extreme Environments

Paper Number: 190225

190225 - A Comparative Study on the Mechanical Property of Rayon and Lyocell-Based Fiberforms 

A key aspect of spacecraft design is to ensure that the craft can withstand extreme aerothermodynamic conditions during atmospheric re-entry. The Thermal Protection System (TPS) protects the spacecraft from atmospheric adversity through ablation. Over three decades, NASA has developed various TPS materials for its missions, and the Phenolic-Impregnated Carbon Ablator (PICA), created in the 1990s, is one of the lightest ablative TPS materials. PICA is manufactured by compressing and carbonizing a Rayon-based fibrous preform, called FiberForm, followed by phenolic resin infusion. PICA has seen widespread use, but shortages of Rayon raw material have prompted the development of a new substitute, PICA-D. PICA-D is manufactured in the same way as PICA, but uses Lyocell-based FiberForm. Properties of FiberForm dictate the overall properties of PICA and PICA-D, and hence, it is necessary to understand how the properties of FiberForm, such as mechanical stiffness, influence its mechanical performance. However, FiberForm is porous and heterogeneous, which makes experimental determination of mechanical properties costly and challenging. More importantly, even for computational modeling and simulation, the extremely high temperature gradient across the thickness of the TPS during re-entry makes the properties homogenized based on the representative volume element (RVE) invalid for the smallest elements used in the macroscale modeling and simulation. As a result, effective properties based on a range of small microstructure sizes are needed and there exists a large variation in the effective properties for small microstructures.

In this presentation, a comparative study on the mechanical properties of both Rayon-based and Lyocell-based FiberForms will be presented. The Standard Mechanics Approach (SMA) implemented via Finite Element Analysis (FEA) is used to determine the effective mechanical properties. Microstructures obtained using X-ray Computed Tomography (XRCT) of five different side lengths of 100, 200, 300, 400, and 500 microns are generated to account for microstructure-sensitivity of effective mechanical properties. Distributions of effective properties are obtained using statistical analysis. Comparisons between both FiberForms are conducted, and conclusions and discussions are made at the end.

Presenting Author: Khaleda Akter Maya University of Kentucky

Presenting Author Biography: The author, Khaleda Akter Maya, is a third-year doctoral student in the Department of Mechanical and Aerospace Engineering at the University of Kentucky. Currently, she is conducting her research under the supervision of Dr. Hailong Chen in the 'Computational Mechanics and Methods Group' of the same university. Her current work focuses on computational modeling of Thermal Protection System (TPS) materials to investigate their mechanical and thermal behavior across multiple length scales, from microstructural to macroscopic. Her research interests in Computational Mechanics include Isotropic and Anisotropic Elastic Properties of Heterogeneous Fibrous Materials, Meshfree Methods Modeling, and Fracture Modeling Under Impact Loading.