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Title: Micro and Nano structured Hierarchical Carbon Fibre Composites
Other Titles: Micro- en nanogestructureerde hiërarchische koolstofvezelcomposieten
Authors: Aravand, Mohammadali
Issue Date: 25-Feb-2015
Abstract: Hierarchically structured fibre reinforced poly mer (FRP) composites are a new generation of struc tural materials with high potential for tailored d esign. The increased degree of freedom in material selection and design is the main advantage o f these materials over conventional composites. Ho wever, the available literature still lacks a comp rehensive study on the structure-property relation ship and the interactions between the constit uents in these composite materials.
This wor k aims at exploring various aspects of new hi erarchically structured carbon fibre polymer compo sites (CFRP) with the goal of understanding the in terplay between the different components in r elation to their mechanical properties and fractur e. Multiwall carbon nanotubes (CNTs) and a ph ase separating thermoplastic modifier (polyoxymeth ylene (POM)) are the main structural elements ¨used to form the microstructure of the studied ma terials.
The principal approach adopted in t his work is to establish an initial understanding¨ of the structure-property relationship in binary ( POM/epoxy or CNT/epoxy) and ternary (POM/CNT/epoxy ) bulk resin blends. This involves a study of the¨ phase morphology, dynamic mechanical properties, a nd fracture toughness of various types of bulk res in blends with different compositions. At the next ¨step, fiber reinforced composites based on the pr eviously studied matrix blends are produced a nd characterized. Considering the challenges invol ved in the processing of the POM modified matrix b lends into the corresponding composites at high te mperature, a new manufacturing technique based on¨ resin transfer molding is developed and furth er optimized. The knowledge acquired during the st udy of the matrix blends is employed to expla in morphological observations as well as fracture¨ properties and damage behaviour monitored during q uasi-static tensile loading of the produced lamina tes. A correlation between the microstructure and phase morphology of the matrix and the proper ties of the laminates is established.
It is shown that phase separated POM particles are able to enhance fracture toughness of bulk e poxy resins, as long as the particulate morph ology is dominant. Fracture toughness and ultimate ¨mechanical properties of the bulk resin materials ¨are shown to be highly sensitive to the phas e morphology of the phase-separated blend. Th erefore, any external factors affecting phase sepa ration of the thermoplastic modified blends can dr astically influence resulting properties. For ¨instance, it is illustrated that the presence of¨ fiber reinforcement changes the phase morphology o f the matrix and, hence, affects the transfer ¨of the toughness improvements of the bulk re sin to the laminates.
Inclusion of CNTs is a lso shown to influence the phase morphology of the¨bulk resin as well as the microstructure of the r esulting hierarchical laminates. It is shown¨ that CNTs limit mass diffusion during phase separa tion of the thermoplastic phase, causing redu ction in the particle size of the resulting thermo plastic particles. This in turn affects the fractu re toughness of the bulk resin blends and damage d evelopment in the resulting CFRP laminate. In this part of the work, a new approach for incorpo ration of CNTs in the POM modified matrices is int roduced, in which the phase separating thermoplast ic particles are surrounded by clusters of CNT agg lomerates.
Table of Contents: Abstract v Contents xiii List of Figures xix List of Tables xxix
1 General introduction 1 1.1 Motivationandaim ........................ 1
1.2 Micro/nano structure - Materials selection . . . . . . . 1.2.1 Nanoscale..................... 1.2.2 Microscale.....................
1.3 Thesisoutline.......................
2 State of the art
2.1 High performance CFRP epoxy composites . . . . . .
2.2 Damage initiation and growth in epoxy based CFRPs
2.3 Fracturemodesandfracturetoughness. . . . . . . . .
..... 4 ..... 4 ..... 4 ..... 6
9
..... 9 ..... 10 . . . . . 13
2.3.1 Fractureenergy(G)approach............... 14 2.3.2 Locallizedstressfield(K)approach. . . . . . . . . . . . 15
xiii
xiv
CONTENTS
3
2.3.3 Plasticdeformationzone.................. 16
2.3.4 Thicknessconsiderations.................. 16
2.4 Toughening of epoxy resins and their composites . . . . . . . . 18
2.4.1 Thermoplasticmodifiedepoxyresins . . . . . . . . . . . 20
2.4.2 Reaction induced phase separation (RIPS) . . . . . . . . 21
2.4.3 Fracturetoughnessmechanisms. . . . . . . . . . . . . . 24
2.4.4 Polyoxymethylene (POM) as a toughening component . 28
2.5 Carbonnanotubemodifiedepoxyresins . . . . . . . . . . . . . 30
2.5.1 CNTsandtoughnessofepoxyresins . . . . . . . . . . . 31
2.5.2 CNTs in fiber reinforced epoxy composites . . . . . . . . 32
2.5.2.1 FRP composites based on CNT modified epoxy matrices...................... 33
2.5.2.2 FRP composites based on CNT modified fibers 35
2.6 Hybridepoxyresins ........................ 37 2.6.1 Hybridepoxymatrices................... 37
2.6.2 FRP composites based on hybrid epoxy matrices . . . . 39 2.7 Conclusions............................. 39
Binary matrix systems 41 3.1 TP/epoxyblends.......................... 41
3.1.1 Experimental........................ 42
3.1.1.1 Materials ..................... 42
3.1.1.2 Preparationoftheblends............ 43
3.1.1.3 Characterization techniques . . . . . . . . . . . 43
3.1.2 Resultsanddiscussion................... 46
3.1.2.1 Phasemorphology................ 51
3.1.2.2 Dynamic mechanical properties . . . . . . . . . 53
3.1.2.3 Tensileproperties ................ 53
CONTENTS xv
3.1.2.4 Mode I fracture toughness analysis . . . . . . . 55 3.1.3 Conclusions......................... 61 3.2 CNT/epoxyblends......................... 62
3.2.1 Introduction ........................ 62
3.2.2 Experimental........................ 63 3.2.2.1 Materials ..................... 63
3.2.2.2 Characterizationmethods. . . . . . . . . . . . 65
3.2.3 Resultsanddiscussion................... 67
3.2.3.1 Masterbatch(stage1).............. 67
3.2.3.2 Diluted masterbatch (stage 2) . . . . . . . . . 69
3.2.3.3 Transition from liquid to solid (stage 3) . . . . 71
3.2.3.4 Solid(cured) nanocomposite (stage4) . . . . . . 74
3.2.4 Conclusions......................... 76
4 Ternary matrix systems 79 4.1 Experimental ............................ 80
4.1.1 Materials .......................... 80
4.1.2 Samplepreparation .................... 80
4.1.2.1 TernaryECNT/POMblends . . . . . . . . . . 80 4.1.2.2 TernaryE/POMCNT .............. 81 4.1.3 Characterizationtechniques................ 82
4.1.3.1 DMAmeasurements............... 82
4.1.3.2 ModeIfracturetoughness . . . . . . . . . . . 82
4.1.3.3 Microscopic characterization . . . . . . . . . . 83
4.2 Resultsanddiscussion ....................... 83 4.2.1 Morphologyandphasebehaviour . . . . . . . . . . . . . 83 4.2.1.1 ECNT/POMternaryblends . . . . . . . . . . 83
xvi
CONTENTS
5
Fiber reinforced polymer composites based on multiphase matrices 93
5.1 CFRP laminates based on binary POM/epoxy matrices . . . . 93
5.1.1 Experimental........................ 93
5.1.1.1 Materials ..................... 93
5.1.1.2 Preparationoftheblends............ 94
5.1.1.3 Manufacturing of CFRP laminates . . . . . . . 94
5.1.2 TestingandCharacterization ............... 100 5.1.2.1 Tensiletesting .................. 100 5.1.2.2 Mode I interlaminar fracture toughness . . . . 106 5.1.2.3 Microscopic characterization . . . . . . . . . . 106
5.1.3 Resultsanddiscussion................... 107
5.1.3.1 Morphological observations . . . . . . . . . . . 107
5.1.3.2 Tensile properties in fiber direction . . . . . . 110
5.1.3.3 Tensile properties in bias ± 45° direction . . . 121
5.1.3.4 Mode I interlaminar fracture toughness results 123
5.2 CFRPlaminatesbasedonternarymatrices . . . . . . . . . . . 127 5.2.1 Morphologicalobservations ................ 127 5.2.2 Tensilepropertiesinfiberdirection . . . . . . . . . . . . 128 5.2.3 Conclusions......................... 135
Conclusions and recommendations for future work 137 6.1 Phase behaviour and fracture toughness of the bulk resin blends 138 6.1.1 POMmodifiedbinarymatrices .............. 138
6
4.2.2
4.2.1.2 E/POMCNTternaryblends . . . . . . . . . . 85 Dynamicmechanicalproperties.............. 87 ModeIfracturetoughnessanalysis . . . . . . . . . . . . 88
4.2.3
4.3 Conclusions............................. 91
CONTENTS xvii
6.1.2 CNTmodifiedbinarymatrices .............. 139
6.1.3 CNT/POM modified ternary matrices . . . . . . . . . . 139
6.2 CFRP composite laminates based on modified matrices . . . . 140
6.2.1 CFRP laminates based on POM modified binary matrices 140
6.2.2 CFRP laminates based on CNT/POM modified ternary matrices........................... 140
6.3 Recommendationsforfuturework ................ 142
A Preparation and characterization of unidirectional carbon fibre
composites 145
B Micro-scale strain mapping of FRP composites 150
C POM-modified CFRP laminates based on CNT grafted (fuzzy) carbon fabrics 152
D POM particles deformed during fracture (particle crack tearing) 157
E Design sketches 159
Bibliography 169 Curriculum Vitae 189
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Structural Composites and Alloys, Integrity and Nondestructive Testing

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