Date of Award

2018

Document Type

Open Access Dissertation

Department

Mechanical Engineering

Sub-Department

College of Engineering and Computing

First Advisor

Xinyu Huang

Abstract

The relation between the progress of damage and the acoustic emission (AE) activity of a nuclear grade Sif-SiCm composite tubing under internal pressure was studied. The nuclear grade Sif-SiCm composite tubing is manufactured by the company General Atomics (GA) and made of nuclear grade HI Nicalon type S fiber preforms following a chemical vapor infiltration (CVI) technique. Sif-SiCm composites are good candidates to replace current nuclear fuel cladding materials because of the good chemical stability and strength at high temperatures. In this work, a Sif-SiCm composite tubing was tested under internal pressure at room temperature (RT) to study the damage behavior under hoop loading conditions that occur during a Loss of Coolant Accident (LOCA). In an additional effort, a Pellet Cladding Mechanical Interaction (PCMI) resulting from Reactivity Initiated Accident (RIA) conditions and a thermal shock, meant to represent a reactor reflood, were simulated. The PCMI was simulated by loading the Sif-SiCm composite tubing, at temperature of 1373 oK (1100 oC), using a solid surrogate and a heating technique that induces temperature gradients through the wall of the Sif-SiCm composite tubing. The thermal shock was simulated by quenching a Sif-SiCm composite tubing in water. In all tests, the AE technique was used to monitor the progress of damage by recording the acoustic emission activity within the material using a miniature AE sensor. Digital image correlation (DIC) was used to calculate the full-field strain distribution on the outer surface of the sample. In the case of the high temperature test, a high temperature resistant speckle patter and a light filtering technique were used. Microscopic and XCT imaging were used to analyze the damage in the samples caused by the applied load. In the case of the internal pressure loading, a method that relates the acoustic emission activity within the material and the progress of damage is proposed. Damage is the representation of the deterioration of the elastic constants when a load is applied and is typically represented by a damage variable. By finding a correlation between the AE parameters and the damage variable it is possible to predict strains/stresses under specific uniaxial loading conditions. Finally, the Continuum Damage Mechanics method was used to model the mechanical strains of the Sif-SiCm composite tubing under internal pressure and will be compared to the method proposed.

Rights

© 2018, Luis H. Alva

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