Mechanical Characterization and Constitutive Modeling of High-Temperature Fluoroelastomers
Date of Award
12-1-2023
Degree Name
M.S. in Mechanical Engineering
Department
Department of Mechanical and Aerospace Engineering.
Advisor/Chair
Advisor: Robert Lowe
Abstract
Fluoroelastomers can maintain their stretchability and elasticity at high temperatures, making them well-suited for applications that require extreme thermal resistance. Presently, there is significant interest in casting compounded fluoroelastomers to create high-temperature seals with intricate geometric features. It is not well understood, however, how these materials will perform mechanically in service as they undergo repeated heat cycling and are subjected to complex, multi-axial stress states. To address this research opportunity, a suite of commercially available compounded fluoroelastomers were thermally aged (10, 20, 50 cycles at 200 °C for 8 hours) and mechanically tested in uniaxial tension and uniaxial compression. Preliminary room-temperature uniaxial tension results displayed increases in strength and elastic modulus with modest heat cycling (20 cycles), followed by a subsequent decrease in strength at large amounts of heat cycling (50 cycles). Even at 50 cycles, however, the heat-conditioned materials still exhibited greater strength than the unconditioned materials. This mechanical response is likely due to a competition between the chemical mechanisms of polymer cross-linking and chain scission, with strength degradation at large amounts of heat cycling reflective of chain scission dominating cross-linking. From this suite of candidate materials, the compounded commercial fluoroelastomer FKM Viton A-500 RB75A5 was downselected for the desired sealant application and subsequently tested at elevated temperatures (85, 140, 200 °C) in uniaxial tension to better understand its behavior in extreme environments. Lower mechanical strength and reduced elongation were observed in the material’s elevated temperature response. This is likely because the higher temperatures result in shorter polymer chains, which corresponds to a higher entropy state and a weaker, lower-elongation material. Additional room-temperature tests were performed on Viton RB75A5 to facilitate the calibration of hyperelastic constitutive models, both parameterized (e.g., Ogden) and tabulated. Coupon-level validation tests involving inhomogeneous planar deformations were used to verify the accuracy of the constitutive models. Comparisons of principal surface strains from digital image correlation to LS-DYNA finite element simulations of the tests indicate that the tabulated (MAT 181) and parameterized Ogden models capture the inhomogeneous deformation well. These validated material models for unconditioned Viton RB75A5 can be used for simulation-aided design and optimization of seals and other elastomeric components.
Keywords
Fluoroelastomers, Viton, Dyneon, Constitutive Modeling, High-Temperature, Mechanical Characterization, Digital Image Correlation
Rights Statement
Copyright © 2023, author.
Recommended Citation
Johnson, Brent Matthew, "Mechanical Characterization and Constitutive Modeling of High-Temperature Fluoroelastomers" (2023). Graduate Theses and Dissertations. 7348.
https://ecommons.udayton.edu/graduate_theses/7348
