Date of Award

3-23-2018

Document Type

Thesis

Degree Name

Master of Science in Materials Science

Department

Department of Aeronautics and Astronautics

First Advisor

Marina B. Ruggles-Wrenn, PhD.

Abstract

The tensile stress-strain and tension-tension fatigue of geopolymer matrix composites reinforced with 0/90 carbon fibers was investigated at 23 and 300°C in laboratory air. Geopolymers are inorganic polymeric materials composed of alumina, silica, and alkali metal oxides. Because geopolymers are synthesized as a fluid mixture or particles and liquid, they can be cast into a desired shape, and cured at only slightly elevated temperatures. The relative ease of synthesis and low processing temperatures make geopolymers an attractive choice as a matrix material for composite materials. Geopolymers also offer resistance to heat and oxidizing environments. Currently, geopolymer matrix composites are being considered as possible replacements for ceramic matrix composites and high-temperature polymer matrix composites. In this work composites with two different types of geopolymer matrix were evaluated: (1) composite with a sodium-based geopolymer matrix (NaGP) and (2) composite with a potassium-based geopolymer matrix (KGP). Experimental results revealed a degrading effect of elevated temperature on tensile stress-strain behavior and tensile properties. Tension-tension fatigue tests were conducted at 300°C. Fatigue run-out was set to 2x105 cycles. Fatigue run-out was only achieved at a low maximum stress of 30% UTS. Test specimens were examined before and after testing using an optical microscope. Examinations revealed severe degradation of the geopolymer matrix due to elevated temperature as well as due to mechanical loading. Profuse cracking and comminution of the geopolymer matrix occurred early in all tests. As a result further mechanical response of the composite was governed by the carbon fibers. The best mechanical performance was obtained for a panel of the KGP-matrix composite. Further development of the KGP-matrix composites can build on the synthesis method used to fabricate this particular panel.

AFIT Designator

AFIT-ENY-MS-18-M-304

DTIC Accession Number

AD1056638

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