Rapid manufacturing of high-performance fiber-reinforced polymer matrix composites

Centellas, Polette

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https://hdl.handle.net/2142/115497 Copy

Description

Title

Rapid manufacturing of high-performance fiber-reinforced polymer matrix composites

Author(s)

Centellas, Polette

Issue Date

2021-12-14

Director of Research (if dissertation) or Advisor (if thesis)

• Sottos, Nancy R
• Geubelle, Philippe H

Doctoral Committee Chair(s)

• Sottos, Nancy R
• Geubelle, Philippe H

Committee Member(s)

• Chasiotis, Ioannis
• Baur, Jeffery

Department of Study

Aerospace Engineering

Discipline

Aerospace Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Manufacturing
• Fiber-reinforced thermoset-polymer composites
• Frontal polymerization
• Multiple-front polymerization
• Vascular composites

Abstract

Lightweight fiber-reinforced thermoset-polymer composites are excellent structural materials for transportation and energy sectors. However, conventional bulk curing of composites is a costly, energy-intensive, and time-consuming process, which motivates research in more efficient alternatives that produce economically viable components. Current solutions to this problem include using rapid-cure resins and time-optimized cure profiles to significantly reduce the composite cure time from hours to minutes. These alternative approaches still require a large energy input from external sources, such as ovens, autoclaves, or heated molds, to achieve the necessary thermal conditions for curing. In contrast, frontal polymerization (FP)-based manufacturing promises both time and energy savings compared to bulk curing. FP is a rapid curing strategy sustained by the exothermic polymerization of the monomer matrix, thus eliminating the need for an external energy source. The FP reaction self-propagates through the matrix volume as a front that transforms uncured monomer into cured polymer. However, inclusion of fiber reinforcement within the matrix volume reduces the exothermic energy produced and quenches the reaction at high reinforcement loadings required for structural applications. This dissertation outlines the development of frontal curing for out-of-autoclave manufacturing of structural and multifunctional carbon-fiber-reinforced polymer (CFRP) composites. Initial studies investigate the effect of boundary conditions on sustaining frontal curing in high fiber volume fraction (Vf ) CFRP composite panels. Frontal curing is initiated in uncured laminates placed on five different tool plates with varying material properties and captured using an infrared imaging setup. A thermally insulated polyisocyanurate tooling is found to minimize conductive heat losses during curing to demonstrate, for the first time, the frontal curing of composites with ca. 50 % Vf at room temperature. Subsequent studies use these optimized boundary conditions to investigate the effect of resin-based processing parameters on composite quality and performance. CFRP composites are fabricated at room temperature using a vacuum-assisted resin-transfer molding (VARTM) technique. Elimination of solvent from the resin chemistry used for the composite matrix achieves a maximum glass transition temperature of ca. 140 °C in cured panels. The very low viscosity of the solvent-free resin results in fast infusion times (on the order of minutes) compared to conventional resins used for VARTM processing. Tuning the resin infusion time improves the impregnation of the carbon fiber reinforcement to produce quality composites with minimal voids (under 0.5 vol. %). Optimized frontal-cured panels are manufactured in ca. 5 minutes at room temperature, reducing cure time and energy consumption by two and four orders of magnitude, respectively, compared to bulk-cured panels. Frontal-cured composites also exhibit comparable tensile properties to bulk-cured composites using the same constituents and a bulk-cured aerospace-grade epoxy control. Mulitple-front polymerization is then explored to further reduce cure time and demonstrate an avenue for manufacturing large-scale components. Two polymerization fronts are initiated simultaneously and the cured components are compared to panels frontal-cured using one polymerization front (from initial studies). Localized void formation, resin accumulation, and thermal spike are measured between two merging fronts and observed to have a detrimental impact on composite performance. In a collaborative effort, numerical simulations are performed to guide the mitigation of the thermal spike by modifying the layup boundary conditions. Panels manufactured with modified boundaries successfully mitigate all adverse phenomena at the merging fronts, leading to improved composite mechanical properties. A 5-fold reduction in cure time from ca. 5 minutes for one-front panels to ca. 1 minute for two-front panels is achieved. We extend the application of frontal curing to manufacture structural CFRP composites with embedded vascular networks inspired by the circulatory systems found in biocomposites, such as wood and bone. Vascular composites are fabricated using the Vaporization of Sacrificial Components (VaSC) technique, which involves embedding a sacrificial polymer template within the uncured laminate. The chemical energy released during exothermic frontal curing of the resin matrix facilitates tandem depolymerization of the embedded sacrificial polymer with polymerization of the composite matrix. We first investigate the effect of Vf on the successful clearance and cross-sectional fidelity of microchannels by fabricating composites with an embedded 1D sacrificial fiber at varying Vf. Selection of a low-temperature sacrificial polymer (polypropylene carbonate) and additional energy input via a through-thickness polymerization front enable complete vascularization of 1D channels for 30 % to 60 % Vf. Next, we demonstrate the synchronized fabrication of a composite with undulating 2D vascular network and surface coating for potential self-healing applications. All frontal-cured vascular composites are processed at room temperature and cured in ca. 35 seconds, thereby reducing thermal energy consumption for manufacturing by several orders of magnitude compared to previous reported methods.

Graduation Semester

2022-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Polette Centellas

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