UNIVERSITY OF PATRAS SCHOOL OF ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING & AERONAYTICS APPLIED MECHANICS LABORATORY «Development of improved, multi-functional, nano-structured polymer based adhesives with applications in the bonding of composite components and the repair of engineering structures with composite patches» by Fiamegkou Ch. Eleni Mechanical Engineer, MSc PhD Thesis PATRA 2015 UNIVERSITY OF PATRAS SCHOOL OF ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING & AERONAYTICS APPLIED MECHANICS LABORATORY «Development of improved, multi-functional, nano-structured polymer based adhesives with applications in the bonding of composite components and the repair of engineering structures with composite patches» by Fiamegkou Ch. Eleni Mechanical Engineer, MSc PhD Thesis The research has been co-financed by the European Union (European Social Fund ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) Research Funding Program: Heracleitus II. Investing in knowledge society through the European Social Fund. ΠΑΝΕΠΙΣΤΗΜΙΟ ΠΑΤΡΑΣ ΠΟΛΥΤΕΧΝΙΚΗ ΣΧΟΛΗ ΤΜΗΜΑ ΜΗΧΑΝΟΛΟΓΩΝ ΚΑΙ ΑΕΡΟΝΑΥΠΗΓΩΝ ΜΗΧΑΝΙΚΩΝ «Ανάπτυξη βελτιωμένων, πολύ-λειτουργικών, νάνο-δομημένων πολυμερών συγκολλητικών υλικών με εφαρμογές στη σύνδεση δομών από σύνθετα υλικά και τις επισκευές κατασκευών με σύνθετα υλικά» Φιαμέγκου Χρ. Ελένη Μηχανολόγος Μηχανικός, MSc Διδακτορική Διατριβή ΠΑΤΡΑ 2015 Fiamegkou Eleni PhD THESIS Acknowledgements First, I would like to express my sincere gratitude to my supervisor, Prof. Vassilio Kostopoulo for his continued guidance and support throughout my study and research. Additionally, I would like to thank him for the opportunities that he gave me to enrich my knowledge and my experiences through scientific projects, papers, collaborations and participation at conferences. Also, I would like to thank Prof. Klaus Friedrich (of University of Kaiserslautern in Germany) and Prof. Theodoro Matika (of Department of Materials Science and Engineering, University of Ioannina), both members of my PhD’s advisory committee, for their comments and assistance with my research. I am particularly grateful to Prof. Klaus Friedrich who visited the University of Patras two times in past so as to be updated on the progress of my work and to support me. Continuing I cannot leave out Dr. Stavros Tsantzalis and sincerely thank him for his essential contribution and psychological support with the challenges of my PhD. I should admit that he was the “deus ex machina” that saved the day when things were near a dead-end. Moreover, I would like to thank Dr. Elia Eliopoulo and Mrs. Panagiota Kervetzoglou as their advices and guidelines were catalytic for the development of my work. Additionally, I really thank Dr. Petro Karapappa for his direct and indirect (exceptionally significant) support to my work. Besides I give my thanks to Mrs. Christina Kostagiannakopoulou who except from an excellent colleague has been a real friend that contributed so that my stay in AML to be pleasant all these years. Moreover I thank Dr. Antoni Vavoulioti for our very good collaboration beyond my PhD thesis as well as for his time to discuss on it. Nevertheless, I also owe my graditude to a number of people of the Applied Mechanics Laboratory (AML) that namely are not in a particular order: Dr. Thanassis Koatzakolios, Dr. Dimitris Mazarakos, Dr. Nikolao Athanasopoulo, Mr. Alexi Solomou and Mr. Thodori Machaira. Finally it is an honour for me to express my gratitude to my parents Christo and Martha as well as to my sisters Nikolitsa and Philippia-Maria for their great encouragement and their boundless support during all years of my PhD studies and in particular during the period that I was faced with a lot of difficulties. I Fiamegkou Eleni PhD THESIS Ευχαριστίες Ολοκληρώνοντας τη διδακτορική μου διατριβή οφείλω, και νιώθω συνάμα την εσωτερική ανάγκη, να αναγνωρίσω την άμεση και έμμεση συνεισφορά πολλών προσώπων σε αυτή, καθώς, επίσης, να τους εκφράσω τις ευχαριστίες μου. Πρωτίστως, θα ήθελα, λοιπόν, να ευχαριστήσω τον επιβλέποντα Καθηγητή μου Βασίλειο Κωστόπουλο, για την ευκαιρία που μου έδωσε να εκπονήσω την παρούσα διδακτορική διατριβή, για τη συνεχή του καθοδήγηση, και την εν γένει αμέριστη στήριξη που μου παρείχε, καθ’ όλη τη διάρκεια της μελέτης και έρευνάς μου, όχι μόνο ως επιστήμονας, μεταλαμπαδεύοντάς μου τις γνώσεις του, αλλά και ως άνθρωπος. Επίσης, του είμαι ειλικρινά ευγνώμων για τις ευκαιρίες που μου έδωσε να εμπλουτίσω τις γνώσεις μου, πέραν του πλαισίου της διδακτορικής μου διατριβής, μέσω της συμμετοχής μου σε επιστημονικά προγράμματα, συνέδρια και δημοσιεύσεις. Επίσης, θα ήθελα να εκφράσω τις ευχαριστίες μου στον Καθηγητή Klaus Friedrich του Πανεπιστημίου Kaiserslautern της Γερμανίας, μέλος της τριμελούς συμβουλευτικής επιτροπής μου, ο οποίος παρευρέθηκε στο Πανεπιστήμιο Πατρών κατ’ επανάληψη για την παρακολούθηση της πορείας της διατριβής μου, παρέχοντάς μου πολύτιμες συμβουλές επ’ αυτής. Παράλληλα, ευχαριστώ τον Καθηγητή Θεόδωρο Ματίκα του Πανεπιστημίου Ιωαννίνων επίσης μέλος της τριμελούς συμβουλευτικής επιτροπής μου για τον ουσιαστικό σχολιασμό και βοήθειά του επί του «έργου» μου. Στη συνέχεια, θα ήταν ασυγχώρητη παράλειψή μου να μην ευχαριστήσω τον Δρ. Σταύρο Τσαντζαλή, όχι μόνο για την ουσιαστική συνεισφορά του, αλλά και για την ενθάρρυνση και τη ψυχολογική υποστήριξη που αφειδώς μου παρείχε στη δύσκολη πολλές φορές πορεία προς την εκπόνηση της διδακτορικής μου διατριβής. Θα πρέπει να παραδεχτώ πως ήταν ένα από τα πιο καθοριστικά άτομα για να παραμείνω συγκεντρωμένη στο στόχο μου. Ουσιαστικά θα μπορούσα να πω πως έδρασε ως «Από Μηχανής Θεός» στο πιο κρίσιμο σημείο. Επιπλέον, θα ήθελα να ευχαριστήσω το ν Δρ. Ηλία Ηλιόπο υλο και την κα. Παναγιώτα Κερβέτζογλου, η συμβολή των οποίων υπήρξε καταλυτική για την εξέλιξη της διατριβής μου. Δεν θα μπορούσα να ξεχάσω την κα. Χριστίνα Κωσταγιαννακοπούλου φίλη και συνεργάτιδα, η οποία ήταν πάντα εκεί για να με ακούσει και να συνεργαστεί κάνοντας την πορεία μου όλα αυτά τα χρόνια στο εργαστήριο Τεχνικής Μηχανικής και Ταλαντώσεων πραγματικά πιο ευχάριστη. Ευχαριστώ, επίσης, τον Δρ. Πέτρο Καραπαππά για την άμεση και έμμεση, εξαιρετικά σημαντική σε αμφότερες τις εκδοχές της, συνεισφορά του στο «έργο» μου. Πέραν των προαναφερθέντων προσώπων οφείλω να ευχαριστήσω τον Δρ. Αντώνη Βαβουλιώτη για την πολύ καλή συνεργασία μας εκτός πλαισίου II Fiamegkou Eleni PhD THESIS διδακτορικής διατριβής, αλλά και στο πλαίσιο αυτής, για το χρόνο που αφιέρωσε αρκετές φορές, παραβλέποντας το φόρτο της προσωπικής του εργασίας και κούρασης, προκειμένου να «συζητήσουμε» επ’ αυτής. Συνεχίζοντας θα ήθελα να ευχαριστήσω τους Δρ. Θανάση Κοτζακόλιο, Δρ. Δημήτρη Μαζαράκο και Δρ. Νίκο Αθανασόπουλο, τους οποίους χρειάστηκε να συμβουλευτώ κατά καιρούς. Ευχαριστώ, ιδιαιτέρως, επίσης τους κ. Θεόδωρο Μαχαίρα και κ. Αλέξη Σωλο μο ύ για όλη την πο λύ σημαντική “IT” εθελούσια υποστήριξή τους. Κλείνοντας ευχαριστώ όλη την οικογένειά μου για την αμέριστη συμπαράστασή της σε αυτή μου την προσπάθεια καθ’ όλη τη διάρκεια της πορείας μου. Ιδιαίτερα ευχαριστώ και αφιερώνω την παρούσα διατριβή στους γονείς μου Χρήστο και Μάρθα, οι οποίοι έχουν συμβάλει ολοκληρωτικά (πνευματικά, ψυχολογικά αλλά και υλικά) για αυτό που φτάνω να είμαι σήμερα. Μεγάλο ευχαριστώ στις αδελφές μου, Νικολίτσα και Φιλιππία-Μαρία, που με στηρίζουν με τον τρόπο τους καθημερινά στην επίτευξη των στόχων μου. III Fiamegkou Eleni PhD THESIS Acknowledgements ..................................................................................................................... I Contents Ευχαριστίες ................................................................................................................................ II Contents ....................................................................................................................................... I CHAPTER 1 – INTRODUCTION .......................................................................................... 1 1.1 Nano-Reinforced Polymers ................................................................................................... 1 1.2 Carbon Nanotubes (CNTs) .................................................................................................... 2 1.3 State of the Art of CNTs Reinforced Polymers Development .............................................. 6 1.4 Outline of the Dissertation .................................................................................................. 12 1.5 References ........................................................................................................................... 16 PART Ι: PREDICTION OF EQUIVALENT PROPERTIES OF NANO-REINFORCED POLYMERS WITH CARBON NANOTUBES (CNTsRP) ................................................. 22 CHAPTER 2 – INTRODUCTION TO THE MODELING TECHNIQUES OF NANO- REINFORCED POLYMERS ................................................................................................ 22 2.1 Modeling Techniques of Nanoreinforced Polymers (NRPs) .............................................. 22 2.2 State of the Art of the CNTs-reinforced Polymers (CNTsRPs) Modeling .......................... 24 2.3 Basic Principles of Homogenization Theory and Techniques ............................................ 29 2.4 Outline and Objectives of Part I .......................................................................................... 41 2.5 References ........................................................................................................................... 42 CHAPTER 3 - EFFECTIVE ELASTIC PROPERTIES OF CNTs-REINFORCED POLYMERS (CNTRPs) ......................................................................................................... 47 3.1 Introduction ......................................................................................................................... 47 3.2 Effective Elastic Properties of 3D-dispersed CNTRPs ....................................................... 49 3.2.1 Prediction of CNTRPs Ideal Elastic Behaviour by Using Finite Elements Homogenization (FEH) Method. .............................................................................................. 49 3.2.2 Prediction of CNTRPs Ideal Elastic Behaviour by Using Mean Field Homogenization (MFH) Method .......................................................................................................................... 61 3.3 Short Reference to Available Experimental Data ............................................................... 64 3.4 Effective Elastic Properties of 3D-dispersed CNTRPs with InterPhase ............................. 70 3.4.1 Prediction of Elastic Behaviour of CNTRPs with InterPhase by Using Finite Elements Homogenization (FEH) Method ............................................................................................... 70 3.4.2 Prediction of Elastic Behaviour of CNTRPs with InterPhase by Using Mean Field Homogenization (MFH) Method. ............................................................................................. 80 3.5 Effective Elastic Properties of 3D-dispersed CNTRPs with Clustering ............................. 84 3.5.1 Prediction of Elastic Behaviour of CNTRPs with clusters by Using Finite Elements Homogenization (FEH) Method ............................................................................................... 84 I Fiamegkou Eleni PhD THESIS 3.5.2 Prediction of Elastic Behaviour of CNTRPs with Clusters by Using Mean Field Homogenization (MFH) Method. ............................................................................................. 93 3.6 Effective Elastic Properties of 3D-dispersed CNTRPs with Clustering and InterPhase ..... 97 3.6.1 Investigating the Synergistic effect of Clustering and InterPhase by Using Finite Elements Homogenization (FEH) Method. ............................................................................... 97 3.7 Brief Synopsys and Main Conclusions ............................................................................. 106 3.8 References ......................................................................................................................... 110 CHAPTER 4 - EFFECTIVE MECHANICAL PROPERTIES OF FAILURE OF CARBON NANOTUBES REINFORCED POLYMERS (CNTsRP). .............................. 115 4.1 Introduction ....................................................................................................................... 115 4.2 Effective Tensile and Shear Strength of 3D Perfectly Dispersed CNTsRP ...................... 115 4.2.1 Model Development ....................................................................................................... 115 4.2.2 Results and Discussion ................................................................................................... 121 4.2.2.1 Effective Tensile Strength ........................................................................................... 121 4.2.2.2 Effective Shear Strength ............................................................................................. 124 4.3 Brief Synopsis and Conclusions ........................................................................................ 128 4.4 References ......................................................................................................................... 129 CHAPTER 5 - EFFECTIVE THERMAL PROPERTIES OF CNTs-REINFORCED POLYMERS (CNTRPs) ....................................................................................................... 130 5.1 Introduction ....................................................................................................................... 130 5.2 Influence of the Interfacial Thermal Resistance on the Effective Thermal Conductivity of 3D-dispersed CNTRPs. ........................................................................................................... 131 5.3 Synopsis and Main Conclusions ....................................................................................... 158 5.4 References ......................................................................................................................... 159 PART II: CARBON NANOTUBES-REINFORCED POLYMERIC ADHESIVELY BONDED JOINTS ................................................................................................................ 164 CHAPTER 6 – INTRODUCTION IN THE MODELING TECHNIQUES OF POLYMERIC ADHESIVELY BONDED JOINTS ........................................................... 164 6.1 Introduction to Adhesive Joints and Repairs..................................................................... 164 6.2 Types of Adhesives ........................................................................................................... 167 6.3 Adhesive Joints and Repairs: Loading and Configurations .............................................. 168 6.5 Adhesive Joints Numerical Analysis ................................................................................ 176 6.6 Short Reference to Basics of Cohesive Zone Model ......................................................... 181 6.7 Outline and Objectives of Part II ...................................................................................... 185 6.8 References ......................................................................................................................... 186 II Fiamegkou Eleni PhD THESIS CHAPTER 7 - NUMERICAL ANALYSIS OF POLYMERIC-ADHESIVELY BONDED JOINTS .................................................................................................................................. 194 7.1 Introduction ....................................................................................................................... 194 7.2 Using Cohesive Zone Model CZM for the Prediction of Single Lap Joint SLJ Failure Behaviour ................................................................................................................................ 194 7.2.1 Geometry of SLJ ............................................................................................................ 194 7.2.2 Modeling Approach ....................................................................................................... 196 7.2.3 Determination of “Penalty” Stiffness ............................................................................. 197 7.2.4 Model Development ....................................................................................................... 201 7.2.5 Results and Discussion ................................................................................................... 209 7.2.5.1 The effect of “Intefacial” (Penalty) Stiffness .............................................................. 209 7.2.5.2 Linear Elastic Response of SLJ - Cohesive Elements versus Continuum Elements ... 210 7.2.5.3 Failure Analysis of SLJ ............................................................................................... 215 7.2.5.4 2D Model versus 3D Model ........................................................................................ 218 7.4 Brief Synopsys and Conclusions ....................................................................................... 224 7.5 References ......................................................................................................................... 225 CHAPTER 8 - DEVELOPING A TWO-STEP MULT-SCALE MODELING PROCEDURE FOR THE PREDICTION OF CNTs-REINFORCED ADHESIVELY BONDED ALUMIMIUM-ALMUNIUM SINGLE LAP JOINT MACROSCOPIC RESPONSE............................................................................................................................ 228 8.1 Introduction ....................................................................................................................... 228 8. 2 Two-Step Multi-scale Modeling Procedure ..................................................................... 229 8. 3 Brief Synopsys and Conclusions ...................................................................................... 238 8.4 References ......................................................................................................................... 239 CHAPTER 9 – MAIN CONCLUSIONS AND PROPOSALS FOR FURTHER INVESTIGATION ................................................................................................................ 241 9.1 Brief Synopsis and Main Conclusions of Dissertation...................................................... 241 9.2 Proposal of Future Work ................................................................................................... 253 APPENDICES: ...................................................................................................................... 254 APPENDIX 1- Lap Shear Response of Considered Adhesive ........................................... 254 APPENDIX 2 - Prediction of Effective Shear Modulus of CNTs-Reinforced Adhesives by Applying Finite Element Homogenization Procedure of the Chapter 3. ......................... 255 APPENDIX 3 - Investigating the Isotropy of the CNTs-reinforced Polymer Structures 257 III Fiamegkou Eleni PhD THESIS CHAPTER 1 – INTRODUCTION 1.1 Nano-Reinforced Polymers Polymer nanocomposites/ Nano-reinforced Polymer (NRPs) have been attracting main interest of the research community in the field of composite development the last 25 years. This specific category of polymer composites contains at least one of the reinforced phases on the order of nanometer (e.g. nanotubes, nanofibers, nanoclays etc.). Their predominance against the microcomposites (e.g fiber reinforced polymers etc.) derives from the unique properties inherent to the nanoinclusions employed. The transition from microscaled to nanoscaled particles yields dramatic changes in the nanocomposites’ physical properties. Nanoscale materials have a large surface area for a given volume [1]. Since many important chemical and physical interactions are governed by surfaces and surface properties, a nanostructured material can have substantially different properties from a larger-dimensional material of the same composition. Generally, it has been shown that for particles and fibre geometries the surface area per unit volume is inversely proportional to the material’s diameter, thus, the smaller the diameter, the greater the surface area per unit volume [1]. Typically a change in particle diameter, or fibre diameter from the micrometer to nanometer range, will affect the surface area-to-volume ratio by three orders of magnitude [2]. Therefore the NRPs have been proposed as a powerful tool for generating new multifunctional materials with improved mechanical, physical and chemical properties without the alteration of the polymer matrix chemical formulation. Moreover the NRPs tend to replace the commonly used polymer matrices at mutilscale composites structures such as the fiber reinforced polymer composites (FRPs) and the adhesively bonded joints when the improvement of the matrix dominant properties is demanded. Thanks to their great properties and their multifunctional character, the NRPs are special candidate materials for industries like aerospace, automotive and others industries (e.g. sporting goods ect.) where the conventional composites are applied. 1