Author

Colton Corley

Date of Award

Fall 2021

Document Type

Open Access Thesis

Department

Mechanical Engineering

First Advisor

Xinyu Huang

Abstract

Silicon carbide fiber reinforced silicon carbide matrix composite is one of the candidate materials for accident tolerant nuclear fuel cladding concepts. In a Nuclear power plant, the reactions between the fuel, cladding, and coolant in a potential loss of coolant accident(LOCA) are of utmost importance to ensure safety in the accident tolerance of such plants. It is for this reason that SiC(silicon carbide) composite tubes have been selected as a possible alternative to the older Zirconium based cladding methods currently used in the industry, which were a partial cause of the Fukushima 2011 meltdown. To serve as fuel cladding, a material must be able to withstand certain stresses and strains in high temperature environments, and the use of SiC composite is due to its low reactivity with steam and it’s capability or maintaining high strength at high temperature. In studying the SiC composite to ensure its safety in actual usage, many different techniques are being employed to create a full knowledge of the material. The goal of this study is to better understand the mechanical behavior of SiC composite tubing, particularly its mechanical strength under uniaxial and multi-axial loading situations.

This will be accomplished by compiling testing results for multiple uniaxial and multiaxial testing scenarios. These include, burst testing, axial testing, torsion testing, torsion-burst testing, and tension-torsion testing. By encapsulating all 5 of these testing scenarios, the general profile of a sample’s failure strength can be created as a function of principal stress direction in the sample.

The analysis of the various strengths of the material in different conditions were accomplished by various measurement methods. These methods were comprised of stress and strain observation and calculations, through use of strain gauges and general stress measurement techniques and equations, DIC digital image correlation to verify loading angles and strains created by testing, AE acoustic emission to analyze sample failure by use of sound analysis and matrix/fiber failure events, and x-ray computed tomography(XCT) to analyze post-failure samples.

Samples were tested accordingly to map a failure profile for samples with the specific triaxial fiber architecture. This failure map was created to show the ability of a sample to resist failure when the principal stress is pointed to a given direction on the samples. The triaxially braided samples provided by General Atomics showed an abnormal weakness in torsional loading, which has a 45° principal stress angle. The samples proved strongest in the 2 uniaxial testing methods, and the samples in combined loading had the notable strength drop-off the closer the principal stress load angle reached 45° from either starting at 0° (hoop) or 90° (tensile). The samples had the highest tensile strength in the axial direction, due to the triaxial braid giving the most support to tensile loading due to fiber orientation. It was hypothesized after post processing that torsional strength drop-off could be due to the braid angle and orientation.

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