UUnniivveerrssiittyy ooff SSoouutthh CCaarroolliinnaa SScchhoollaarr CCoommmmoonnss Theses and Dissertations 8-9-2014 DDiieelleeccttrriicc PPrrooppeerrttiieess ooff CCoommppoossiittee MMaatteerriiaallss dduurriinngg DDaammaaggee AAccccuummuullaattiioonn aanndd FFrraaccttuurree Md. Rassel Raihan University of South Carolina - Columbia Follow this and additional works at: https://scholarcommons.sc.edu/etd Part of the Mechanical Engineering Commons RReeccoommmmeennddeedd CCiittaattiioonn Raihan, M.(2014). Dielectric Properties of Composite Materials during Damage Accumulation and Fracture. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/2896 This Open Access Dissertation is brought to you by Scholar Commons. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. Dielectric Properties of Composite Materials during Damage Accumulation and Fracture by Md. Rassel Raihan Bachelor of Science Bangladesh University of Engineering & Technology, 2007 Master of Engineering University of South Carolina, 2012 Submitted in Partial Fulfillment of the Requirements For the Degree of Doctor of Philosophy in Mechanical Engineering College of Engineering and Computing University of South Carolina 2014 Accepted by: Kenneth L. Reifsnider, Major Professor Prasun K. Majumdar, Committee Member Fanglin Chen, Committee Member Harry J. Ploehn, Committee Member Lacy Ford, Vice Provost and Dean of Graduate Studies © Copyright by Md Rassel Raihan, 2014 All Rights Reserved. ii DEDICATION This dissertation is dedicated to my Parents, Brothers and my Wife for their endless love, support and encouragement. iii ACKNOWLEDGEMENTS I would like to thank Dr. Kenneth Reifsnider, my dissertation research advisor, for his invaluable advice, guidance, and support that made this work possible. His encouraging words and positive way of thinking motivated me throughout my doctoral research. I didn’t just learn how to excel in research from Dr. Reifsnider, but I also learned how to motivate others. It has been enjoyable, challenging and above all an educational experience working with him. I would also like to thank the other members of my advisory committee. I am grateful to Dr. Majumdar for his help and support from the very first day of my graduate life both in experimental and academic activities. His enthusiasm and dedication towards the scientific research has been an inspiration to my research. Dr. Chen has been a tremendous asset. It is rare to find an instructor that has such a genuine concern for students as Dr. Chen. Considerable knowledge was gained through participation in his course on Fuel Cells. Dr. Ploehn has been a pleasure to work with, and a privilege to be associated with a gentleman with such a distinguished career in scientific research. I really appreciate the help of my colleagues, Jon-Michael Adkins, Jeffrey Baker, Fazle Rabbi and Lee Woolley, during my doctoral research. I would like to thank my Parents and Brothers for their sacrifices and unselfish love and support. Lastly but not least, I would like to thank, the love of my life, my wife Piya for all her support throughout this process. I am forever thankful and truly blessed to have her in my life. iv ABSTRACT Fiber reinforced polymer matrix composite materials have many unique properties and their high performance makes them available to use in many advanced technologies i.e. aerospace, microelectronics, and energy storage. There is a correlation that exists between the long term behavior of those materials under combined mechanical, thermal, and electrical fields, and the functional properties and characteristics of the composite materials that requires a fundamental understanding of the material state changes caused by deformation and damage accumulation. This will ultimately lead, for example, to the design and synthesis of optimal multifunctional material systems. Composite materials are heterogeneous and the complex morphology of these material systems has been investigated for decades to achieve multi-functionality and reliable performance in extreme environments. These heterogeneous materials are inherently dielectric. Broadband Dielectric Spectroscopy (BbDS) is a robust tool for dielectric material characterization often used in polymer industries. In composite processing this method is employed to monitor the composite curing process. Dielectric spectra of heterogeneous materials are altered by many factors, e.g., electrical and structural interactions between particles, morphological heterogeneity, and shape and orientation of the constituent phases of the material system. During the service life of composites, damage occurs progressively and accumulates inside the materials. The process of microdefect interaction and accumulation to create a final fracture path is an active research area. v The present research is designed to investigate material state change using a new non-invasive interrogation method for establishing not only internal integrity but also the nature and distribution of internal material structure and defect morphology changes by using Broadband Dielectric Spectroscopy (BbDS) to detect and characterize permittivity changes during the history of loading. Interpretations of the results by analysis of discrete local details, and prognosis of performance will be discussed by the introduction of a new technique, called Generalized Compliance, which directly and quantitatively reflects material state changes. A two dimensional computational model was also developed using COMSOLTM. The effects of volume fraction and the distribution of the defects inside the material volume, and influence of the permittivities and ohmic conductivities of the host material and defects on the effective dielectric behavior of the resulting composite as a function of applied frequency spectra are discussed. Single frequency dielectric behavior with increasing defect development inside the composite is used to interpret the in-situ BbDS experimental results for the progressive damage of the material systems investigated. vi TABLE OF CONTENTS DEDICATION .................................................................................................... iii ACKNOWLEDGEMENTS .................................................................................... iv ABSTRACT........................................................................................................ v LIST OF FIGURES ........................................................................................... viii CHAPTER 1 INTRODUCTION .............................................................................. 1 CHAPTER 2 LITERATURE REVIEW .................................................................... 5 CHAPTER 3 EXPERIMENTAL FACILITIES ......................................................... 25 CHAPTER 4 DIELECTRIC STUDY OF SOFC COMPOSITE MATERIALS ............... 35 CHAPTER 5 IN-SITU DIELECTRIC STUDY OF COMPOSITE MATERIALS ............ 46 CHAPTER 6 EX-SITU DIELECTRIC STUDY AND PROGNOSIS BASED ON INITIAL DIELECTRIC PROPERTIES ................................................................................ 63 CHAPTER 7 NUMERICAL ANALYSIS ................................................................ 91 CHAPTER 8 CONCLUSION ............................................................................. 118 REFERENCES ................................................................................................ 122 vii LIST OF FIGURES Figure 1.1 Volvo car body panel serve as battery ................................................................2 Figure 2.1 matrix crack initiation from fiber/matrix debonding ..........................................6 Figure 2.2 Examples of matrix crack in (a) continuous fiber and (b) woven fiber polymeric composites ..........................................................................................................6 Figure 2.3 Interlaminar delamination crack formed due to joining of two adjacent matrix cracks in a fiber reinforced composite laminate ..................................................................7 Figure 2.4 Adjacent fiber fractures in interior of carbon-epoxy composite ........................8 Figure 2.5 Off-axis Response of Woven Composite (45 Degree Tension) .........................9 Figure 2.6: A plot of the typical growth of damage and reduction in stiffness and remaining strength throughout the life of the composite ...................................................10 Figure 2.7 Schematic of SAM technique ...........................................................................11 Figure 2.8: Tensile test of a cross-ply laminate, showing the stress/strain curve and dependent capacitance and dielectric dissipation (at 1 MHz and 100 mV) of a CFRP specimen ............................................................................................................................13 Figure 2.9: Change in resistance for 90◦ samples ..............................................................13 Figure 2.10 Dielectric responses of material constituents at broad band frequency ranges .................................................................................................................................14 Figure 2.11 Basic Polarization mechanisms in the material ..............................................17 Figure 2.12 Figure 2.12 Time dependence of polarization, P, when a constant electric field is applied at t=ξ .........................................................................................................18 Figure 2.13: Real permittivity ɛ’(ω) (solid line) and imaginary permittivity ɛ”(ω) of the complex dielectric function for relaxation process of an ohmic conductor .......................20 Figure: 2.14 Real permittivity ɛ’(ω) (solid line) and imaginary permittivity ɛ”(ω) of the complex dielectric function for relaxation process of an ionic conductive material .........21 viii Figure 2.15: Changes in stress and in Z’ as a function of strain during a quasi-static loading................................................................................................................................23 Figure 2.16: Changes in stress and in Z” as a function of strain during a quasi-static loading................................................................................................................................23 Figure 2.17: As damage increases, the Bode plot will become more level at lower frequencies. The Nyquist plot shows a decrease in slope as damage grows .....................24 Figure 3.1 Novocontrol system ..........................................................................................26 Figure 3.2 Principle of a dielectric or impedance measurement ........................................27 Figure 3.3 Amplitude and phase relations between voltage and current of a sample capacitor for electric measurements ...................................................................................28 Figure 3.4 Probostat spring loads and regular 2-electrode 4-wire setup with dual gas supplies and thermocouple .................................................................................................30 Figure 3.5 Probostat base unit with feedthroughs ..............................................................31 Figure 3.6 MTS LandmarkTM and dielectric measurement set-up .....................................32 Figure 3.7 Xradia MicroXCT-400 Machine ......................................................................33 Figure 3.8 Basic Principle of MicroXCT ...........................................................................33 Figure 4.1 Broadband dielectric spectroscopy response of active and away from active regions of an SOFC button cell after 8 hr of operation (measured at room temperature). 36 Figure 4.2: BbDS response of two different morphology at 800C ....................................37 Figure 4.3: Difference in impedance in different electrode geometries (cellular vs. lamellar) .............................................................................................................................38 Figure 4.4 : Asymmetric variation of morphology from electrolyte side to the other .......39 Figure 4.5: Change in specimen conductivity with increasing temperature and temperature cycling ............................................................................................................40 Figure 4.6: Room temperature BbDS response of SOFC button cell with different electrolyte thickness ...........................................................................................................41 Figure 4.7: Electric modulus variation (real vs. imaginary part) for an undamaged (bottom) and damaged (top) SOFC ....................................................................................42 ix