Date of Award

3-2025

Document Type

Thesis

Degree Name

Master of Science in Aeronautical Engineering

Department

Department of Aeronautics and Astronautics

First Advisor

Marina B. Ruggles-Wrenn, PhD

Abstract

Tension-tension fatigue behavior of an advanced melt-infiltrated (MI) silicon carbide/silicon carbide (SiC/SiC) composite was evaluated, and basic tensile properties measured, at 1200°C in laboratory air.  The composite consists of a melt-infiltrated SiC matrix reinforced with laminated Hi-Nicalon Type-S fibers woven in a 5-harness satin weave. The Hi-Nicalon-S fiber preforms were coated with a boron nitride (BN) fiber coating by chemical vapor infiltration (CVI). The melt-infiltrated matrix was consolidated by combining CVI-SiC with SiC particulate slurry and molten silicon infiltration. The finished ceramic matrix composite (CMC) had a fiber volume fraction of 33%. Additionally, the effect of multiple small holes on the fatigue behavior of the CMC was studied by testing specimens containing an array of 17 effusion holes with 0.5 mm diameter. The holes were drilled normal to the surface of the specimen using electric discharge machining (EDM). Effect of the effusion holes on tensile properties was also evaluated in a tension to failure test at 1200°C in air. Tension-tension fatigue behavior of specimens with and without holes was studied in cyclic tests at 1200⁰C with a minimum to maximum stress ratio of 0.1 and frequency of 1 Hz. Maximum stresses ranged from 124 MPa to 203 MPa. Fatigue run-out was defined as 200,000 cycles. Specimens that achieved run-out were subsequently tested in tension to failure at 1200°C in order to assess the retained tensile properties. The presence of the effusion holes lowered the fatigue runout stress and reduced fatigue lifetimes of the CMC. Strain accumulation and modulus changes with cycles were obtained in all fatigue tests in order to assess damage development. Composite microstructure, as well as damage and failure mechanisms, were investigated using scanning electron microscopy and energy dispersive spectroscopy.

AFIT Designator

AFIT-ENY-MS-25-M-137

DTIC Accession Number

AD1356384

Comments

An embargo was observed for posting this thesis.

Distribution A: Approved for Public Release, Distribution Unlimited.

PA clearance case 88ABW-2025-0361

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