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Author ORCID Identifier

https://orcid.org/0000-0002-9763-4362

Date Available

8-26-2026

Year of Publication

2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Engineering

Department/School/Program

Mechanical Engineering

Faculty

Hailong Chen

Faculty

Jonathan F. Wenk

Abstract

Polycrystalline materials, composed of individual grains with varying grain size, shape, and crystallographic orientation are widely used in various engineering and industrial applications. Conventional applications of polycrystalline materials rely on the macroscopic performance, and the microstructural features are usually homogenized out. With the advancement of modern technologies and improvement of characterization methods, polycrystalline materials find their applications in meso- and micro-scale systems. At these length scales, the microscopic features including grain boundary characteristics significantly affect the material physical responses. As a result, the conventional continuum mechanics models become problematic, especially for material failure problems where the microstructural features play dominant roles.

Computational modeling the material behavior of polycrystalline materials based on their microscopic features and their constituent crystals has been an active field of research for several decades. At the microscale, the molecular dynamics (MD) simulation has been extensively applied to study the thermal and mechanical behavior of polycrystalline materials. The limitations of MD study are the short physical simulation time and small size of polycrystals. At the mesoscale, the discrete element method (DEM) and the phase field method (PFM) have been applied to study the failure of polycrystalline materials. The issues of these methods are the missing of grain boundary characteristics in the simulation. To address these limitations in existing computational methods for polycrystalline materials, a nonlocal discrete framework based on the lattice particle method (LPM) for modeling hexagonal close packed (HCP) polycrystalline materials at the mesoscale while incorporating grain boundary characteristics is developed.

Like MD, the LPM models each individual grain as an assembly of regularly packed material particles arranged according to the underlying atomic lattice. The crystallographic orientation of each individual grain is represented using lattice rotation. As a result, the grain boundary structure is explicitly modeled in LPM as the interface of two intersecting grains with different crystallographic orientations. To model the physical behavior of polycrystalline materials, nonlocal interaction among material particles is introduced through bonds, where each material particle interacts with neighboring material particles within a finite distance. The interaction between two particles depends on the collective states of all their neighbors. Different from MD, a top-down approach is adopted to determine the interaction in LPM based on the equivalency between the classical continuum models and the discrete description using LPM.

In this work, the details of the discrete framework are presented, including the formulation and verification of LPM for thermoelastic behavior of single HCP crystal, the extension of the modeling technique to HCP polycrystals, and applications of the discrete framework to model failure of various polycrystalline materials. Details on the generation of various polycrystal system using external package NEPER are also discussed. Future work are also highlighted.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2026.428

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