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Open Jeffkim MS Thesis.Pdf The Pennsylvania State University The Graduate School Department of Engineering Science and Mechanics FABRICATION AND CHARACTERIZATION OF HIGH DAMPING CARBON FIBER COMPOSITES WITH CARBON NANOTUBE INTERLAYERS A Thesis in Engineering Science and Mechanics by Jeffrey J. Kim © 2019 Jeffrey J. Kim Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science May 2019 The thesis of Jeffrey J. Kim was reviewed and approved* by the following: Charles E. Bakis Distinguished Professor of Engineering Science and Mechanics Thesis Co-Advisor Edward C. Smith Professor of Aerospace Engineering Thesis Co-Advisor Namiko Yamamoto Assistant Professor of Aerospace Engineering Judith A. Todd P.B. Breneman Chair and Professor of Engineering Science and Mechanics Head of the Department of Engineering Science and Mechanics *Signatures are on file in the Graduate School iii ABSTRACT Carbon/epoxy (c/ep) composite rotorcraft blades, consisting of carbon fibers in a matrix of epoxy, are commonly used to manufacture rotorcraft blades because of their good balance of mass, stiffness, and strength properties. Recent interest in rigid (hingeless) rotorcraft blades has brought attention to the need for higher amounts of damping in c/ep rotorcraft blades. Previous investigations have demonstrated that adding small amounts of carbon nanotubes (CNTs) to epoxy increases damping without degrading stiffness by a combined effect of reinforcement and stick-slip behavior at the CNT/epoxy interface. Limited evidence in the literature suggests that CNTs increase the damping of c/ep composites, as well, although a more thorough investigation aimed maximizing the improvement in c/ep damping with CNTs and assessing damping behavior over a range of simulated operating conditions for rotorcraft blades is required to advance the state-of-the-art. The objectives of this investigation are to explore in detail the potential of CNTs for increasing the damping of c/ep laminates across a range of loading and environmental conditions. Because of the strain sensitivity of the stick-slip damping mechanism of CNTs and the high force required to develop meaningful strains in c/ep laminates, tensile tests in a servo-hydraulic load frame were used to acquire cyclic force and strain data as functions of time. Software was written to extract the phase shift between force and load along with the storage modulus (E’), loss modulus (E”), and loss factor (tan ) under particular loading regimens and environmental conditions. Three types of CNTs, long CNT buckypaper, short CNT buckypaper, and aligned CNT yarn, and two types of surfactants, Triton X-100 and sodium dodecyl sulfate, were the primary material variations investigated. The combination of CNT yarn and Triton X-100 was selected over the other material variations due to its superior damping performance. The addition iv of 10 vol.% of aligned CNT yarn in [0/±45]s c/ep laminates increased tan δ and (E”) as much as 310% and 340%, respectively with negligible change in E’ and tensile strength. Following 106 cycles of strain excursions between 300 µε and 4000 µε in the [0/±45]s laminate with YN10%- TX4, tan δ increased by 42% versus the initial tan δ. Similear YN10%-TX4 laminates showed moderate increases in tan δ and E” as temperature was increased to 65°C. v TABLE OF CONTENTS LIST OF FIGURES ............................................................................................................ vii LIST OF TABLES .............................................................................................................. xi ACKNOWLEDGEMENTS ................................................................................................ xiii Chapter 1 Introduction ....................................................................................................... 1 1.1 Background ............................................................................................................ 1 1.1.1 Vibration of Structures ................................................................................ 1 1.1.2 Definition of dynamic properties ................................................................. 2 1.1.3 CNT Damping – Stick Slip Mechanism ....................................................... 5 1.1.4 Fabrication of CNT Buckypaper and Yarn ................................................... 7 1. 2 Objectives............................................................................................................. 8 Chapter 2 Specimen Preparation......................................................................................... 9 2.1 Materials ............................................................................................................... 9 2.2 Short Buckypaper Fabrication ................................................................................ 12 2.3 C/ep Prepregs ........................................................................................................ 13 2.4 C/ep Composite Laminate ...................................................................................... 18 2.5 Resin Infiltration .................................................................................................... 25 2.5.1 CNT Yarn ................................................................................................... 25 2.5.2 Buckypaper ................................................................................................. 27 2.5.3 Specimens for Volume Fraction Analysis .................................................... 27 2.6 Tensile Strength Specimen ..................................................................................... 29 2.7 Pullout Specimen ................................................................................................... 29 Chapter 3 Test Methods ..................................................................................................... 31 3.1 Specimen Quality Check ........................................................................................ 31 3.1.1 Field Emission Scanning Electron Microscopy ............................................ 31 3.1.2 Optical Microscopy ..................................................................................... 32 3.2 Damping test ......................................................................................................... 34 3.2.1 Overview of Test Setup ............................................................................... 35 3.2.2 Method of Collecting Strain Signal .............................................................. 36 3.2.3 Collection and Preliminary Process of Raw Data ......................................... 41 3.2.4 Damping Data Analysis ............................................................................... 45 3.2.5 Limitation and Error .................................................................................... 48 3.2.6 Damping Conditions.................................................................................... 48 3.3 Tensile Strength ..................................................................................................... 51 3.4 Yarn Pullout Test ................................................................................................... 52 Chapter 4 Results and Discussion ....................................................................................... 55 vi 4.1 Specimen Quality Check ........................................................................................ 55 4.1.1 Resin Infiltration and Aspect Ratio .............................................................. 55 4.1.2 Volume Fraction Analysis ........................................................................... 56 4.2 Damping Test ........................................................................................................ 56 4.2.1 Repeatability and Limitation........................................................................ 56 4.2.2 Material Selection ....................................................................................... 59 4.2.3 Material Design - CNT and Surfactant Concentration .................................. 63 4.2.4 Damping Conditions.................................................................................... 66 4.3 Tensile Strength ..................................................................................................... 76 4.4 Yarn Pullout Test ................................................................................................... 76 Chapter 5 Conclusions and Recommendations ................................................................... 78 5.1 Conclusions ........................................................................................................... 78 5.2 Recommendations ................................................................................................. 79 References .......................................................................................................................... 81 Appendix A Auxiliary Data................................................................................................ 89 Appendix B Damping Matlab Code.................................................................................... 100 Appendix C Non-Technical Abstract .................................................................................. 102 vii LIST OF FIGURES Figure 1-1: Representation of dynamic properties. ..............................................................
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