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Towards understanding deformation mechanisms in 3D layered solids under compression
Zhao, Xingyuan
Zhao, Xingyuan
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2024
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2025-11-26
Abstract
This thesis explores the unique rate-dependent behavior and applications of 3D layered materials known for their anisotropic properties. Specifically, MAX phases are distinguished by their kink band formation, a distinct deformation mechanism in layered materials. These materials effectively bridge the properties of metals and ceramics, offering a balance of strength and toughness. This combination of attributes positions MAX phases as promising candidates for advanced applications, such as in high-efficiency engine components and nuclear cladding systems, which demand resilience against both static and dynamic loading environments.
The research focuses on the compressive behavior of MAX phases, particularly highly oriented Ti$_3$SiC$_2$ polycrystalline samples prepared through hot forging.~The influence of global grain orientation along the c-axis, strain rate, composition, and stress state on the compressive response is explored experimentally.~A~Kolsky (or split-Hopkinson) bar is utilized to assess the dynamic compressive response under uniaxial, biaxial (planar confinement), and triaxial (radial confinement) conditions.~Additionally, a modified nonlinear buckling theory is developed to analytically examine kinking deformation behavior at the continuum scale.
Observations from macroscopic ultra-high-speed visualization during loading and microscopic post-mortem fractography indicate that confinement states significantly affect both macroscopic failure patterns and microscopic fracture mechanisms.~Notably, biaxial loading with dynamic load edge-on to the grains and 80~MPa planar confinement parallel to the c-axis resulted in the highest dynamic compressive strength observed (1636$\pm$136~MPa), a 66\% increase compared to the unconfined uniaxial condition.~This planar confinement appears to delay crack propagation and enhance inelastic deformation. Radial confinement at 70~MPa showed potential for inelastic deformation and ductile fracture surfaces, a first for MAX phases, though it was less conducive to kink band formation.~These findings underscore the critical competition between brittle and pseudo-ductile deformation mechanisms enhancing compressive strength and broaden our understanding of how to tailor the use of next-generation layered materials for specific applications.
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