12/02/2024
By Danielle Fretwell

The Francis College of Engineering, Department of Mechanical Engineering, invites you to attend a Doctoral Dissertation defense by Michael N. Olaya on: "Multiscale process modeling of polymer matrix and polymer-derived composites for high-performance applications."

Date: Monday, Dec. 16, 2024
Time: 10 - 11:30 a.m.
Location: BAL 302

Committee:
Christopher J. Hansen (Advisor), Chair; Professor, Department of Mechanical Engineering, UMass Lowell
Gregory M. Odegard, Chair in Computational Mechanics, Dept of Mech Engineering-Engineering Mechancis, MTU
Scott E. Stapleton, Professor, Department of Mechanical Engineering, UMass Lowell
Juan Pablo Trelles, Professor, Department of Mechanical Engineering, UMass Lowell
Marianna Maiaru, Professor, Department of Mechanical Engineering, Columbia University
Trenton M. Ricks, Research Aerospace Engineer, NASA Glenn Research Center
David Mollenhauer, Principal Materials Engineer, Air Force Research Lab

Brief Abstract:
Polymer matrix and polymer-derived composites serve as fundamental components in the aerospace industry, playing a crucial role in the development of lightweight and high-performance materials for structural components and high temperature applications. Crucially, the manufacturing process has a significant influence on the final material's structural integrity, thermal-chemical-mechanical properties, and performance. Major challenges encountered during manufacturing include the complex evolution of the polymer matrix constitutive behavior, in-situ residual stress generation, and fracture. To optimize the as-manufactured properties of composites at reduced manufacturing time and cost, it is therefore essential to have a deep understanding of the underlying thermal-chemical-mechanical mechanisms present across numerous operational length scales (e.g. nanoscale, microscale) throughout each stage of processing. Through integration of physics-based modeling and experimental mechanics, this thesis studies the fundamental relationship between materials, manufacturing, and performance to establish a multiscale computational framework for predicting the generation of residual stresses that arise during manufacturing of polymer matrix and polymer-derived composites. First, a novel experimental technique for characterizing polymer material behavior during curing for two-part thermosetting resins is postulated. This method exploits the system chemical formulation to fabricate time-independent, off-stoichiometry test specimens for intermediate cure state characterization by proxy, circumventing traditional procedures that require explicit use of time-dependent partially cured material. Then, a hierarchical approach to multiscale process modeling of polymer matrix and polymer-derived composites is proposed. Characterization of effective composite behavior during processing of microstructures of arbitrary complexity is achieved through several homogenization schemes, including a high-fidelity numerical finite element (FE) approach. The numerical approach leverages computational micromechanics to provide a flexible way for virtually studying the evolution of composite behavior throughout processing, ranging from thermoset curing to pyrolysis of preceramic polymers. To demonstrate the hierarchical approach, a multiscale curing analysis is performed on a novel 3D woven composite that is a candidate thermal protection system (TPS) for atmospheric entry vehicles. Finally, the process modeling framework is extended from modeling the curing process to the polymer infiltration and pyrolysis (PIP) process. The decomposition kinetics of a preceramic polymer are integrated into the model, enabling simulation of phenomena present during pyrolysis such as char yield, densification, and volumetric shrinkage in the matrix. To address microcracking that can occur due to residual stress generation, especially in ceramic matrix composites (CMC) where temperature changes and volumetric shrinkage are large, an instantaneous damage model is introduced into the framework to enable simulation of progressive damage during processing. To illustrate the process modeling framework capabilities for polymer-derived composites, a theoretical PIP processing simulation of a ceramic matrix composite (CMC) at the microscale is performed as a case study.