Molecular simulations of deformation, failure and fracture of nanostructured materials

Ashfaq Adnan, Purdue University

Abstract

The performance of materials depends on their properties, which in turn depend on the atomic structure, composition, microstructure, defects and interfaces. With our continuing thrust to build light-weight structures without compromising any or their material properties, recent paradigm of synthesizing and processing advanced materials emphasizes the so called bottom-up approach, an approach that involves tailored assembly of atoms and molecules, from the atomic or molecular scale to the macroscopic scale. Nanostructured materials, often characterized by their length scale being close to the atomic scale, have attracted a great interest by their potential to demonstrate phenomenal properties compared to conventional materials. Experimental results on nano materials, however, showed a diverse pool of results. Processing difficulties, unavailability of characterization tools and techniques, and mostly our immature knowledge in this field are often considered as the reasons why there is such a disparity between prediction and reality. The main focus of this thesis is to provide quantitative evidence on the stability, deformation and fracture mechanism of materials at the nanoscale. Using a computational method called Molecular Dynamics (MD), various nanoscale phenomena related to the stability of freestanding thin films, the fracture mechanism of crystalline nanostructures, deformation of polymer nanocomposites, and the strength of thin adhesive joints have been addressed in this work. A new approach has been developed to illustrate the underlying mechanism for the morphology-induced stability of freestanding films. The study on fracture of nanocrystalline materials focuses on the thermodynamic origins of defect formation in materials, their evolution and response to mechanical forces. Atomistic evidences have been provided to exemplify that polymer based multi-phased nanostructures are highly affected by the local structural change in polymers at their interfaces which eventually bring size dependent material behavior at the nanoscale. For instance, the atomistic simulations on nanocomposites and thin adhesives demonstrate why materials become size dependent at the nano scale.

Degree

Ph.D.

Advisors

Sun, Purdue University.

Subject Area

Aerospace engineering

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