ROLE OF FIBER-MATRIX INTERFACE ON MECHANICAL AND TRIBOLOGICAL PROPERTIES OF CARBON FABRICPOLYETHERIMIDE COMPOSITES by SUDHIR TI WAR! Industrial Tribology Machine Dynamics and Maintenance Engineering Centre (ITMMEC) Submitted in fulfillment of the requirements of the degree of Doctor of Philosophy to the INDIAN INSTITUTE OF TECHNOLOGY DELHI FEBURARY 2011 CERTIFICATE This is to certify that the thesis entitled "Role of Fiber-Matrix Interface on Mechanical and Tribological Properties of Carbon Fabric-Polyetlrerimide Composites" being submitted by Mr. Sudhir Tiwari to Industrial Tribology Machine Dynamics and Maintenance Engineering Centre (ITMMEC), Indian Institute of Technology Delhi is worth of consideration for the award of degree of Doctor of Philosophy and is a record of the original bonafide research work carried out by him under our guidance and supervision and has fulfilled the requirement for the submission of this thesis, which to our knowledge has reached the requisite standard. The results contained in this thesis are original and have not been submitted, in part or full, to any other University or Institute for the award of any degree or diploma. Dr. Stephane Panier Associate Professor Polymers and Composites Technology & Mechanical Engineering Department Ecole des Mines de Douai, Douai Cedex France Dr. Jayashree Bijwe Professor Industrial Tribology Machine Dynamics and Maintenance Engineering Centre (ITMMEC) Indian Institute of Technology Delhi Acknowledgement First of all I would like to offer utmost thanks to Lord Shiva for his benevolent shower of grace that led me throughout this arduous work, which would have been otherwise impossible. I find words falling short in expressing the multitude of ever flowing gratitude to my supervisors Prof. Jayashree Bijwe and Dr. Stephane Panier, because of their impetus, sustained efforts, able and persistent guidance, the research work could be undertaken and fostered me with the strength and spirit to see to its culmination. I would like to extend my sincere thanks to Prof. N. Tandon, Head ITMMEC and the members of my Ph. D committee Dr. Mangla Joshi and Dr. R. K. Pandey. I take immense pleasure in expressing my sincere gratitude to Prof. P. R. Bijwe, whose affection and blessings kept me going throughout this period. My sincere thanks to Prof. Brigitte Mute!, University of Lille, France for extending the facility of plasma treatment to the carbon fabric. I extend whole hearted thanks to Dr. P. S. Datta, Principal Scientist, Division of Agriculture Physics, IARI, New Delhi, India for extending y-irradiation facility for this work. My special thanks to colleagues, Dr. Nidh Dureja, Dr. Bimlesh Lochab, Dr. Mukesh Kumar, Mr. Mohit Sharma, Ms. Sini N.K., Mr. N. Aranganathan, Mr. Ajay Kadiyala, Mr. Sanjeev Sharma and Mr. Kuldeep Singh for their all time cooperation and help during the entire period. I would like to thank to all the technical staff of ITMMEC for their cordial association and help rendered during the tenure of this work especially Mr. Avtar Singh (JTS), Mr. Pratap Chand (JLA), Mr. Samaivir Singh (SLA), Mr. Mohan Singh (JTS), Mr. S. K. Kapoor (JTS) and Mr. J. Tuteja (Lab Suptd.). It is my pleasure to express my indebtedness to my Parents for their love and moral support which has kept me intact and spirited throughout this work. I express my deep heartfelt gratitude to my beloved wife Bhawana for her patience, understanding, incessant love and co-operation throughout this period. (Sudhir Tiwari) ii ABSTRACT Studies on the tribology of fiber reinforced polymer matrix composites have assumed a paramount significance in the current scenario which demands high performance and thermally stable tribo-materials which can perform reliably under high PV conditions without applying any conventional lubricants. Contemporary research being dominated by development of newer materials with multiple applications, it was aimed to develop composites based on carbon fabric (CF) and thermoplastic specialty polymer, Polyetherimide (PEI). These in the form of composites materials have immense potential for structural components as well as triboapplications such as bearings, gears, bearing cages, bushes, slides wherein the components encounter severe damages due to combination of wear modes operative simultaneously such as adhesive, abrasive, fretting, fretting-fatigue etc. The fabric reinforcement is unique in the sense that it provides bidirectional strength and possesses a drape quality that facilitates ease in production of complex shaped parts without wrinkles. Carbon fibers are widely used as reinforced materials in composite due to their interesting properties such as high specific strength, high thermal resistance, low expansion coefficient etc. Carbon fibers, though very expensive, are most favored for tailoring high performance composites and tribo-composites. Their surface, however, is chemically inactive/inert leading to the most potential problem of inadequate adhesion and hence weaker composite. It is desired to treat them with a proper treatment prior to its use in composites. Several types of reported surface treatments of carbon fibers are classified in two categories. First, improves adhesion by enhancing physical bonds such as by roughening it leading to more surface area and a large number of contact points, micro-pores or surface pits on already porous carbon fiber surface. The second on other hand, iii involves chemical reactions leading to inclusion of reactive functional groups that promote good chemical bonding with the polymer matrix. Interestingly any surface treatment method especially, which etches fiber's surface also leads to affect the strength of fiber adversely. First effect called as positive effect leads to enhancement in fiber-matrix adhesion and hence improvement in strength of composite since matrix supports the fibers more firmly. Simultaneously, other effect which is in negative direction reduces the strength of fibers due to etching contributing to deteriorate the strength of composite. The final strength composite depends on net contribution of these two opposing effects. It is hence imperative to optimize the extent of treatment to get the maximum possible enhancement in performance properties of composite. Since adequate literature is not available, it was decided to treat the CF by HNO3, cold remote nitrogen-oxygen plasma (CRNOP), gamma (y) ray irradiation and rare earth compound (YbF3) with varying doses and to develop 4 series of composites with Polyetherimide (PEI) keeping all other parameters such as type and amount of CF (PAN based, twill weave, z 55-56%vol), processing technique (impregnation followed by compression molding) constant so that the performance of all the composites could be compared. The selection of treatment methods was done in such a way that either no papers on treatment are available (e.g for Nano-particles) or no papers are available on their exploration for tribological applications (e.g. y- radiation and CRNOP) or a method though very popular but not investigated systematically (e.g. HNO3). Based on this in all, 4 series of composites (total 17 composites) were developed, characterized and tribo-evaluated in adhesive and abrasive wear modes. Chapter 1 elaborates on the introduction to the subject followed by gaps in literature and motivation to work with objective and research plan. iv Chapter 2 presents detailed literature survey on various treatment methods for CF and their influence on various properties of fibers and the composites developed based on these treated fibers including tribo-performance. Chapter 3 elaborates on the details of materials procured and methods selected for surface treatment of CF followed by formulation, development of 4 series containing 17 composites based on treated fabric along with their designations. Chapter 4 presents characterization techniques {Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy-Attenuated Total Reflectance (FTIR-ATR), Raman spectroscopy and mechanical testing) used for fibers (untreated and treated) along with the results. It also presents the details of characterization techniques for composites for physical (density and % of fibers and voids) and mechanical properties {tensile strength (TS) and tensile modulus (TM), flexural strength (FS) and flexural modulus (FM), and interlaminar shear strength (ILSS)} were evaluated following the ASTM standards. All treatment methods showed significant improvement in mechanical properties of the composites. In each series the best performers were;, 1% 02+N2 plasma; 90 minutes of HNO3 oxidation; 300 kGy of y- rays dose and 0.3 wt% of YbF3. The improvement in ILSS of composites due to plasma, HNO3, y and YbF3 treatment was 53%, 71%, 58% and 61% respectively. Overall it was observed that • Treatment increased roughness of the fiber surface, which increased the surface area and provided more cites for better mechanical interlocking between the fiber and matrix. • FTIR-ATR analysis confirmed presence on oxygenated functional groups on CF after treatment, which increased chemical reactivity of the fiber. • Significant reduction in TS of fibers was observed for HNO3, while for plasma, y and YbF3 treatment reduction was marginal. v a Optimum value of dose of treatment was observed for HNO3 and YbF3 cases while for others properties increased continuously. Chapters 5 presents on the studies on adhesive wear of composites including methodology and selected operating variables followed by results, discussions, worn surface analysis and conclusions. Treated fabric composites showed superior properties and trends followed the pattern in the mechanical properties in general. Chapter 6 focuses on the abrasive wear of composites including methodology, results, and discussion and SEM studies on the worn surfaces. Treated fabric composites showed superior properties and wear trends followed the pattern in the mechanical properties especially ILSS. Chapter 7 presents salient conclusions on the studies carried out on the 17 composites, followed by the scope for future work. The treatment of fiber proved beneficial in improvement of mechanical performance of composites. Adhesive wear properties of composites were significantly improved after treatment of fabric. The nano-sized YbF3 treatment proved most effective while plasma treatment was least effective. In case of abrasive wear the HNO3 treatment proved most effective while plasma treatment provided the least improvement in the performance. vi CONTENTS Acknowledgement i Abstract iii List of Figures xiv List of Tables xix List of Abbreviations xx Page No. 1. INTRODUCTION 1.1 Polymer Materials and Composites as Tribo-materials 1.1.1 Types of fiber reinforced composites 1-22 1 3 1.1.1.1 Short fiber reinforced composites 3 1.1.1.2 Unidirectional (UD) fiber reinforced composites 3 1.1.1.3 Bi-directional fiber reinforced composites 4 1.2 Factors Influencing the Performance of BD Composites 4 1.2.1 Type of matrix 4 1.2.2 Type of reinforcement 5 1.2.3 Amount of fabric 5 1.2.4 Orientation of fabric with respect to the loading direction 5 1.2.5 Types of weave 6 1.2.6 Processing techniques 6 1.2.7 Quality of fiber-matrix interface 7 1.3 Carbon Fiber as a Reinforcement- Limitations and Remedies 7 1.4 Surface Treatment of the Carbon Fibers 7 1.5 Surface treatment of Fibers-Positive and Negative Effects 8 1.6 Treatment of Carbon Fibers-State of Art 9 1.6.1 Oxidation treatment 9 1.6.2 Plasma treatment 10 1.6.3 Gamma radiation treatment 10 vii 1.6.4Rare-earth salt suspension treatment 10 1.6.5Combination of methods 10 1.7 Research Gaps and Motivation of the Proposed Work 11 1.8 Objectives 13 1.9 Research Plan 13 2. Literature Survey 2.ATreatment of Carbon Fibers and its Effect on Fiber Properties 23-52 23 2.A.1Oxidation treatment 24 2.A.2 Plasma treatment 26 2.A.3Gamma ray radiation treatment 28 2.A.4 Rare earth compound treatment 29 2.A.5 Combined treatment methods 32 2.BEffect of Fiber Treatment on Performance Properties of Composites 2.B.1Oxidation treated fiber composites 33 33 2.B.1.1 Mechanical properties 33 2.B.1.2 Tribological properties 34 2.B.2Plasma treated fiber composites 36 2.B.2.1 Mechanical properties 36 2.B.2.2 Tribological properties 37 2.B.3Gamma radiation treated fiber composites 37 2.B.3.1 Mechanical properties 37 2.B.3.2 Tribological properties 39 2.B.4Rare earth compound treated fiber composites 2.B.4.1 Mechanical properties 39 40 VIII 2.B.4.2 Tribological properties 41 2.B.5 Miscellaneous methods for CF treatment 43 2.B.6 Combined treatment studies 44 2.B.6.1 Mechanical properties 44 2.B.6.2 Tribological properties 46 3.Material and Methodology 3.1 Selection of Materials 53-63 53 3.1.1Selection of reinforcement for the composites 53 3.1.2Selection of the Polymer Matrix 54 3.1.3Selection of the nano-powder for the treatment 56 3.2 Selection of Treatment to Carbon Fabric 56 3.2.1Oxidation treatment 56 3.2.2 Plasma treatment 56 3.2.3Gamma irradiation treatment 59 3.2.4 YbF3 treatment 59 3.3 Development of Composites and Designations Appendix A 4.Characterization of Carbon Fibers and Composites 4.1 Characterization of Materials 4.1.1 Studies on surface of a carbon fabric 61 63 64-109 64 64 4.1.1.1 Scanning electron microscopy (SEM) and Field emission64 scanning electron microscopy (FESEM) 4.1.1.2 Fourier transforms infrared spectroscopy-Attenuated total65 reflectance (FTIR-ATR) 4.1.1.3 Raman spectroscopy 65 4.1.1.4 Fiber tow tension test 65 ix 4.1.1.5 Fiber-matrix adhesion test 4.1.2 Studies on composites 4.1.2.1 Physical characterization • • • ;ON :. :. Density of composites Fiber weight and volume fraction Void content (vol. %) 4.1.2.2 Mechanical characterization • • • Tensile strength and modulus Flexural strength and modulus Interlaminar shear strength (ILSS) 4.2 Results and Discussion 4.2.1 Studies on fibers 4.2.1.1 HNO3 treated CF • • • • • • SEM analysis FESEM analysis FTIR-ATR analysis Raman Spectroscopy analysis Fiber tension test Fiber matrix adhesion analysis 4.2.1.2 Plasma treated CF • • • • • • 76 SEM analysis FESEM analysis FTIR-ATR analysis Raman Spectroscopic analysis Fiber tension test Fiber matrix adhesion analysis 4.2.1.3 Gamma ray treated CF • • • 69 81 SEM analysis FESEM analysis FTIR-ATR analysis x • • • Raman Spectroscopic analysis Fiber tension test Fiber matrix adhesion analysis 4.2.1.4 YbF3 treated CF • SEM analysis • FESEM analysis • FTIR-ATR analysis • Raman Spectroscopic analysis • Fiber tension test • Fiber matrix analysis 4.2.2 Studies on composites 86 92 4.2.2.1 HNO3 treated CF composites • • Physical properties Mechanical properties 4.2.2.2 Plasma treated CF composites • • Physical properties Mechanical properties 4.2.2.3 Gamma ray treated CF composites • • Physical properties Mechanical properties 4.2.2.4 YbF3 treated CF composites • • 7l7 Physical properties Mechanical properties 4.3 Comparative performance evaluation 4.4 Conclusions • • • • 101 HNO3 treated samples Plasma treated samples Gamma ray treated samples YbF3 treated samples xi 5.Adhesive Wear Studies of Composites 5.1 Methodology of Evaluation of Adhesive Wear Performance 110-147 110 5.1.1Experimental set-up 110 5.1.2Operating parameters 112 5.2 Results and Discussion 112 5.2.1HNO3 treated CF composites 112 5.2.2 Plasma treated CF composites 120 5.2.3 Gamma ray treated CF composites 130 5.2.4 Ytterbium fluoride (YbF3) treated CF composites 138 5.2.5 Comparative Performance Evaluation 145 5.3 Conclusions 6. Abrasive Wear Studies of Composites 6.1 Methodology of Evaluation of Abrasive Wear Performance 146 148-185 148 6.1.1Experimental set-up 148 6.1.2Operating parameters 151 6.2 Results and Discussion 151 6.2.1HNO3 treated CF composites 151 6.2.2 Plasma treated CF composites 161 6.2.3 Gamma ray treated CF composites 170 6.2.4 Ytterbium fluoride (YbF3) treated CF composites 175 6.3 Comparative performance evaluation 7. Conclusions and Scope for Future Work 181 186-198 7.1 Overview of the work 186 7.2 Major Conclusions 187 xii 7.2.1 Effect of treatment on CF properties and mechanical performance of 187 composites (a) Tensile property (b) Flexural property (c) ILSS 7.2.2 Effect of treatment on tribological performance of Composites190 (a) Adhesive wear mode (b) Abrasive wear mode 7.3 Scope for Future Work Appendix-A 198
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