Mechanical Engineering ETDs

Publication Date

Spring 4-12-2022

Abstract

In this dissertation, a novel finite-element methodology called “embedded imperfections” is proposed and employed for computationally simulating various types of deformation instabilities observed in film-substrate structures subjected to mechanical loading. The approach involves the incorporation of elements having distinctive material properties within the film-substrate interface. One can interpret this practice as a deliberate distribution of material defects within the numerical model. It has been shown that embedded imperfections not only can trigger the onset of instability, but also can lead to “direct” simulation of deformation instability problems in that primary and subsequent instability modes can all be captured in a single analysis run, therefore an utterly seamless and continuous simulation of deformation instabilities will be achieved. The approach is robust and overcomes the existing computational obstacles regarding the simulation of large-scale deformation instability problems and paves the way for tackling many complex and unsolved deformation instability problems. The generality of the proposed technique in solving deformation instability problems is demonstrated. The study is performed in both 2D and 3D. We show that under various material, geometry, and loading considerations, different deformation instability patterns, from local surface wrinkling to global buckling of the entire structure and also coexisting wrinkle and buckle (hierarchical patterns), can be predicted. Effects of loading biaxiality, deformation history, imperfection distribution/size, bilayer/multi-layer film, substrate thickness, etc. on the formation and evolution of deformation instabilities are comprehensively studied. The obtained numerical solutions for benchmark problems converge to available analytical solutions. Imperfection-independent numerical solutions are achieved by proposing and exploiting the “periodic-cell approach” which simplifies the models by embedding only one imperfection, as discussed in this dissertation.

Keywords

Deformation instability, Wrinkle, Buckle, Thin film, Finite element analysis, Computational mechanics

Degree Name

Mechanical Engineering

Level of Degree

Doctoral

Department Name

Mechanical Engineering

First Committee Member (Chair)

Dr. Yu-Lin Shen

Second Committee Member

Dr. Tariq Khraishi

Third Committee Member

Dr. Nathan Jackson

Fourth Committee Member

Dr. Donghyeon Ryu

Sponsors

This study was supported by NASA EPSCoR CAN (grant #80NSSC17M0050), New Mexico Space Grant Consortium, and NASA’s Space Grant College, and Fellowship Program. Gratitude is also extended to the endowment support from the PNM Resources Foundation, through Professor Shen as the PNM Chair for Renewable Energy Research (in particular for supporting the research presented in the very last chapter). The author also acknowledges the Center for Advanced Research Computing (CARC) at University of New Mexico, supported in part by National Science Foundation, for providing the high-performance computing resources used in this work.

Document Type

Dissertation

Language

English

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