Failure of in-plane heterostructures: insights from molecular and continuum perspectives
Date
2021
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
Understanding the mechanical failure of in-plane (planer) heterogeneous systems at both nano- and continuum-scales can shape the future nano-electronics and composite material industries. Besides, interchanging the concepts of mechanics between multiple length scales (nano-to-continuum or continuum-to-nano) can dramatically accelerate the material engineering process. The contemporary scientific community still lacks the understanding of several mechanical aspects of the failure of in-plane heterostructures at both nano- and continuum-scales. This dissertation comprehensively studies the failure of in-plane heterostructures under mechanical loading from molecular modeling, continuum modeling, and continuum-scale experiments. With a focus on the nanoscale fracture of two-dimensional in-plane heterostructures, simple finite element modeling (FEM) simulations are utilized to evaluate the capability of capturing the qualitative behavior of the atomic systems. In the continuum-scale experiments, the mode-I fracture of an in-plane homogeneous bi-layer polymer system is investigated with various interface conditions. ☐ The molecular modeling framework is used to study the mechanical response of graphene and hexagonal boron nitride (hBN) under uniaxial tension. The anisotropic strength and toughness in pristine graphene and hBN lattices are discussed. Additionally, it is shown that line- and point-defects are pronounced influencers of the strength and toughness in the low-dimensional hexagonal lattices. ☐ A generic in-plane heterostructure with a defect-free interface is simulated in an atomistic framework. The defect-free interface facilitates understanding the exclusive influence of the interface inclination and material contrast on the effective failure properties (i.e. strength and toughness) of the system. A set of in-house developed Stillinger-Weber (SW) interatomic potentials are used to form defect-free interfaces at the nanoscale. The non-linear constitutive behaviors of the atomic systems are introduced into a set sequential multiscale FEM simulations. It is found that one can predict the actual effective properties of the heterostructures by employing single molecular simulation and a set of FEM simulations. This work is extended to graphene/hBN in-plane heterostructures and bi-crystalline graphene, and the influence of the grain boundary structures on effective strength and toughness is investigated. As implemented in the FEM simulations, the simple continuum theories are found to be incapable of capturing the qualitative misorientation angle-dependent failure properties of bi-crystalline graphene. ☐ The effective inter-granular and trans-granular fracture properties (i.e. fracture strength and toughness) of graphene/hBN in-plane heterostructures and bi-crystalline graphene are discussed from a molecular viewpoint. To understand the transition from the crack penetration to the crack deflection in generic in-plane heterostructures, a cohesive energy-based crack deflection criterion is introduced. The cohesive energy parameter in the SW interatomic potentials is altered to modulate the interface and the bulk layer properties. A phase field-based finite element modeling is utilized to comprehend the post-deflection fracture of in-plane heterogeneous systems. Applying the concept of altering interfacial properties by varying the cohesive energy parameter, an experimental scheme is devised to study the `crack penetration to deflection transition' in an in-plane bi-layer polymer system. The duration of the interface curing is altered to attain different interfacial properties using a single polymer-solvent combination. Additional insights into the curing time-dependent interfacial strength are also discussed.
Description
Keywords
In-plane heterostructures, Failure