Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Mechanical and Materials Engineering

Supervisor

Dr. Liying Y. Jiang

Abstract

Instability of thin film structures as buckling and wrinkling are important issues in various fields such as skin aging, mechanics of scars, metrology of the material properties of thin layers, coating of the surfaces and etc. Similar to the buckling, highly ordered patterns of wrinkles may be developed on the film‒substrate due to compressive stresses. They may cause a failure of the system as structural damage or inappropriate operation, however once they are well understood, it is possible to control and even use them properly in various systems such as the gossamer structures in the space, stretchable electronics, eyelike digital cameras and wound healing in surgery.

In this thesis, the mechanical instability of the thin film is considered analytically and numerically by solving the eigenvalue problem for the governing equation of the system, and the effects of the different factors on the instability parameters such as load, amplitude, wavenumber and length of the wrinkles are studied. Different problems such as wrinkling within an area on the film, and buckling and wrinkling of the non‒uniform systems with variable geometry and material properties for both of the film and substrate are investigated. It is shown that the effects of the non‒uniformity of the system are very significant in localization of the wrinkles on the film; however, such a factor has been ignored by many researchers to simplify the problems. In fact, for the non‒uniform systems, the wrinkles accumulate around the weakest locations of the system with lower stiffness and the wrinkling parameters are highly affected by the non‒uniformity effects. Such effects are important especially in thin film technology where the thickness of the film is in the order of Micro/Nano scale and the uniformity of the system is unreliable.

The results of this dissertation are useful in the design and applications of thin films in science, technology and industry. They consider the relation of the loading and structural stiffness with the wrinkling parameters and provide more insight into the physics of the localization of the wrinkling on the thin structures, how and why wrinkles are accumulated at some positions. Therefore, deliberate application of these results provides appropriate tools to control and use the buckling and wrinkling of thin films effectively in different fields.


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