Mechanical and microstructural characterization of nuclear grade PCEA graphite

This thesis presents a comprehensive experimental characterization of PCEA (Petroleum Coke Extruded and Annealed) nuclear-grade graphite with emphasis on its density uniformity, elastic and strength properties, and microstructural fracture mechanisms. Bulk density measurements showed that PCEA graphite exhibits excellent homogeneity, with no measurable anisotropy between with-grain and against-grain orientations. A slight radial density gradient was identified, with marginally higher densities at the billet periphery, a trend consistently reflected in the mechanical properties. Dynamic Young’s and shear moduli obtained from fundamental frequency resonance testing revealed minor elastic anisotropy and narrow data scatter, indicating high structural uniformity. Comparison of static and dynamic modulus values demonstrated that microcrack closure and frictional effects strongly influence stiffness during static loading, while dynamic measurements capture the intrinsic crystalline elastic response. Flexural, tensile, and compressive strength tests confirmed that the edge region of the billet exhibits slightly higher mechanical performance than the center, correlating with local density variations. Tensile and split-disk tests produced comparable strength values, with the split-disk method showing reduced variability and thus offering a reliable, space-efficient alternative for irradiation studies. Weibull statistical analysis across all mechanical tests verified predictable quasi-brittle behavior and provided representative reliability parameters. Digital Image Correlation (DIC) revealed fundamentally different deformation mechanisms under tension and compression. Tensile loading produced linear elastic behavior followed by abrupt fracture initiated at microstructural flaws, whereas compression induced non-linear stress–strain response governed by pore collapse, crack closure, shear banding, and progressive damage accumulation. Microstructural observations using SEM identified the heterogeneous filler–binder–pore network characteristic of PCEA graphite and linked fracture behavior to mechanisms such as crack deflection, branching, and ligament bridging. Collectively, these results establish a robust understanding structure and properties of PCEA graphite, confirming its mechanical reliability and providing essential baseline data for its potential application in high-temperature nuclear reactor components.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Nuclear, Plasma, Radiolgc Engr

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Hossain, Tamim

Contributors dc:contributor

• Stubbins, James F
• Heuser, Brent

• PCEA graphite, Nuclear-grade graphite, Mechanical properties, Weibull statistics, Digital Image Correlation (DIC), Microstructural characterization, Fracture mechanisms

Statement dc:rights

• Copyright 2025 Tamim Hossain

Language dc:language

en

Handle dc:identifier

https://hdl.handle.net/2142/132813

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/132813