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Mechanical Aging of Thermoset Polymer

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Mechanical Aging of Thermoset Polymer Mechanical Aging of Thermoset Polymer by Teng Cui A thesis submitted in conformity with the requirements for the degree of Master of Applied Science Department of Mechanical and Industrial Engineering University of Toronto © Copyright by Teng Cui 2016 Mechanical Aging of Thermoset Polymer Teng Cui Master of Applied Science Department of Mechanical and Industrial Engineering University of Toronto 2016 Abstract Polymer aging is a time-dependent process of various changes to the material under the influence of one or more environmental factors. Thermoset polymers experience mechanical properties degradation when subjected to different aging conditions. It is the objective of this research to conduct accelerated tests, supported by limited MD simulations, to determine the degradation behaviors of an epoxy polymer under water immersion, UV radiation, and elevated temperature. To investigate the effect upon mechanical properties, tensile tests were conducted for more than 270 days. In addition, molecular dynamics (MD) simulations were conducted to investigate the water absorption effect on the elastic properties of the epoxy. The results revealed that water absorption has both plasticization and anti-plasticization effects; UV radiation could lead to post- curing reactions and epoxy embrittlement; thermal aging can also further cure the epoxy initially, but longer thermal aging leads to softening effect. ii Acknowledgments Firstly, I would like to express my sincere appreciation and gratitude to my supervisor Professor Shaker A. Meguid for his continued guidance and cultivation during my master. I would not have been able to achieve these accomplishments without his dedication, encouragement, and instruction. I am deeply impressed by his enthusiasm, dedication, teaching ability, and research expertise. All of these qualities will be my model and will always lead me in my future life. In addition, I also extend many thanks to the Anonymous Sponsor, who provides the financial support for the completion of this research. Next, I want to thank my lab colleague Mr. Pieter Verberne for his extensive help with the test design and experiments. He also offered me many assistance and suggestions on many problems that I encountered during the completion of my thesis. From him, I have also learned many important qualities that a good researcher should have. I would like to extend thanks to all the members in Mechanics and Aerospace Design laboratory (MADL). It has been a great pleasure to work in such an excellent group. Finally, I would like to extend my sincere gratitude to my family, my father Guoqing Cui, my mother Lijun Zhang, my sister Miao Cui, and my brother Xiang Cui, for their wholehearted love and unlimited support. I also want to express my gratitude for my girlfriend Xinyi Zhang for her understanding and encouragements. iii Table of Contents Abstract .......................................................................................................................................... ii Acknowledgments ......................................................................................................................... ii Abbreviations ............................................................................................................................... vi Notations ...................................................................................................................................... vii Table of Contents ......................................................................................................................... iv List of Tables .............................................................................................................................. viii List of Figures ............................................................................................................................... ix Introduction and Justification ..............................................................................1 1.1 Aging of Polymers ...............................................................................................................1 1.2 Problem Statement ...............................................................................................................2 1.3 Research Objectives .............................................................................................................3 1.4 Method of Approach ............................................................................................................3 1.5 Thesis Layout .......................................................................................................................4 Literature Review ..................................................................................................5 2.1 Water Aging .........................................................................................................................5 2.2 UV Aging .............................................................................................................................8 2.3 Thermal Aging ...................................................................................................................11 Experimental and Molecular Dynamics Investigations....................................13 3.1 Material Details and Sample Preparation ..........................................................................13 3.2 Aging Methodology ...........................................................................................................15 3.2.1 Water Immersion ...................................................................................................15 3.2.2 UV Radiation .........................................................................................................16 3.2.3 Thermal Aging .......................................................................................................17 iv 3.3 Characterization of Mechanical Properties ........................................................................18 3.3.1 Tensile Testing .......................................................................................................18 3.3.2 Fracture Surface Examination................................................................................18 3.4 Molecular Dynamics Modelling of Water Absorption ......................................................18 3.4.1 Pure Epoxy Model .................................................................................................19 3.4.2 Epoxy-Water Model...............................................................................................21 3.4.3 Water Diffusion Coefficient and Elastic Properties ...............................................22 Results and Discussions .......................................................................................25 4.1 Water Aging Results ..........................................................................................................25 4.1.1 Tensile Properties due to Water Aging ..................................................................25 4.1.2 Fracture Surface Morphology due to Water Aging ...............................................30 4.1.3 Fracture Surface Topology due to Water Aging ....................................................32 4.1.4 MD Results ............................................................................................................34 4.2 UV Aging Results ..............................................................................................................36 4.2.1 Tensile Properties due to UV Aging ......................................................................36 4.2.2 Fracture Surface Morphology due to UV Aging ...................................................40 4.3 Thermal Aging Results ......................................................................................................43 4.3.1 Tensile Properties due to Thermal Aging ..............................................................43 4.3.2 Fracture Surface Morphology due to Thermal Aging............................................46 Conclusions and Future Work ............................................................................49 5.1 Statement of the Problem ...................................................................................................49 5.2 Conclusions ........................................................................................................................49 5.3 Thesis Contributions ..........................................................................................................50 5.4 Future Work .......................................................................................................................51 References .....................................................................................................................................52 v Abbreviations AFM Atomic Force Microscopy CVFF Consistent Valence Forcefield FTIR Fourier Transform Infrared RH Relative Humidity MD Molecular Dynamics MSD Mean Square Displacement NMR Nuclear Magnetic Resonance NPT Isothermal-isobaric NVT Canonical PALS Positron Annihilation Lifetime Spectroscopy SEM Scanning Electron Microscopy TMPC Tetramethyl Bisphenol-A Polycarbonate UV Ultraviolet XPS X-ray Photoelectron Spectroscopy vi Notations 퐶푖푗푘푙 General form of elastic coefficient matrix 퐶훼훽 Elastic coefficient matrix for isotropic materials 퐷 Water diffusion coefficient 퐸 Young’s modulus 퐺 Shear modulus 퐾 Bulk modulus 푅 Location
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