yang lebih baik hingga kegagalan yang kira-kira 3.56% (daripada 42.07 hingga 40.56. MPa), 1.96% (daripada 99.88 hingga 97.92 MPa ) dan 14.55% (daripada ...
EFFECT OF BIAXIAL FABRIC PRESTRESSING ON THE MECHANICAL PROPERTIES OF PLAIN–WEAVE E–GLASS/POLYESTER COMPOSITES
By
NAWRAS HAIDAR MOSTAFA
Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, in Fulfillment of the Requirements for the Degree of Doctor of Philosophy
May 2017
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Copyright © Universiti Putra Malaysia
DEDICATION
This thesis is dedicated to my parents and my wife for their love and support. Without them, none of this would have been possible.
Nawras H. Mostafa May 2017
ii
Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment of the requirement for the degree of doctor of philosophy
EFFECT OF BIAXIAL FABRIC PRESTRESSING ON THE MECHANICAL PROPERTIES OF PLAIN–WEAVE E–GLASS/POLYESTER COMPOSITES By NAWRAS HAIDAR MOSTAFA May 2017
Chair: Associate Professor Nur Ismarrubie Zahari, PhD Faculty: Engineering
It is of interest whether induced residual stresses would affect the mechanical properties of fibre–reinforced composites. One of the methods that can be used for altering the induced residual stresses within the matrix is the method of fibre prestressing. Although this method was previously used for developing the mechanical properties of unidirectional composites, its application to the woven composites was very rare. There are many applications of composite materials where woven fabric has been used instead of unidirectional fibre such as for helmets, armours, boats, and the automotive components. The mechanical properties of woven composite may be improved without increasing its volume and/or weight. Therefore, this study emphasizes on improving the mechanical properties and fatigue behaviour of the plain–weave composite by applying biaxial fabric prestressing.
iii
Firstly, the induced residual stresses within the composite’s constituents due to fibre prestress was calculated theoretically by developing the macro-mechanics theory. Secondly, numerical modelling of the prestressed composites was implemented using ANSYS® software for validating the theoretical results and estimating the full distribution of the residual stresses within the composite’s constituents. The biaxial prestressing frame was used for providing biaxial fabric pretension load. Prestressed composites were manufactured with different levels of prestressing ranging from 25 to 100 MPa and prepared at different fibre orientation angles such as 0, 15, 30 and 45o. Lastly, experimental tests such as tensile, flexural and fatigue were conducted on the E–glass plain–weave/polyester resin composite in order to assess the advantages that might result from applying biaxial fabric prestressing. Theoretical results showed that the level of the induced residual stresses within the composite’s constituents depends on fibre prestress level, fibre volume fraction, and the elastic properties of the composite’s constituents. Residual stresses calculated by the developed macro–mechanics theory were in agreement with those obtained by the numerical modelling and previous studies of no less than 1.53%. Numerical simulation of the prestressed composite showed that the maximum induced residual stresses due to fibre prestressing were located at the fibre–matrix interface. Increasing the fibre prestress level increases both the induced compressive residual stresses within the matrix and the fibre–matrix interfacial shearing stress. Experimental results showed that prestressing level of 50 MPa offered the highest improvement in the quasi–static properties and fatigue life behaviour. Enhancements in the tensile and flexural properties were about 20% (from 3.74 to 4.4 GPa of tensile modulus and from 35 to 42 MPa of critical stress) and 15% (from 2.54 to 2.96 GPa of flexural modulus and from 87.11 to 99.88 MPa of flexural strength), respectively. Fatigue cycles to failure iv
were prolonged up to 43% (from 19949 to 28594 cycles) at 0.4 normalised peak stress in comparison with non–prestressed counterparts. The levels of improvement were reduced with increasing the fibre orientation to 45o. Empirical functions were estimated to include the prestress effect in the tensile, flexural and fatigue behaviours. Prestressed composite specimens with 50 MPa showed a decline in the improved tensile strength, flexural strength and fatigue cycles to failure which were about 3.56 % (from 42.07 to 40.56 MPa), 1.96% (from 99.88 to 97.92 MPa) and 14.55% (from 28594 to 24432 cycles) after six months since they were manufactured, respectively. These declines resulted from the stress relaxation effect within the matrix. Considering all findings, it was concluded that the proposed prestressing method enhanced the mechanical properties of the plain–weave composite. This improvement resulted from increasing the composite resistance against quasi–static and fatigue loadings by reducing both fibre waviness and the tensile residual stresses induced within the matrix. The fibre prestress method enhanced the mechanical properties of the plain–weave composite in both on–axis and off–axis directions. These improvements still existed after complete redistribution of the induced residual stresses within the matrix.
v
Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk ijazah doktor falsafah
KESAN PRATEGASAN FABRIK DWIPAKSI KE ATAS SIFAT-SIFAT MEKANIKAL KOMPOSIT E-KACA/POLIESTER TENUNAN-BIASA
Oleh NAWRAS HAIDAR MOSTAFA Mei 2017
Pengerusi: Profesor Madya Nur Ismarrubie Zahari, PhD Fakulti: Kejuruteraan
Adalah sesuatu yang diminati sama ada tegasan baki akan memberi kesan kepada sifat mekanikal bahan komposit bertetulang-gentian. Salah satu kaedah yang boleh digunakan untuk mengubah tegasan baki yang diaruhi di dalam matriks ialah kaedah prategasan gentian. Walaupun kaedah tersebut sebelum ini digunakan untuk membangunkan
sifat-sifat mekanikal
komposit satu-arah, penggunaanya
bagi
komposit tenunan sangat jarang berlaku. Terdapat banyak penggunaan bahan komposit di mana fabrik tenun telah digunakan dan bukan gentian satu-arah seperti untuk topi keledar, perisai, bot, dan komponen automotif. Sifat mekanikal komposit tenunan boleh ditambah baik tanpa meningkatkan isipadu dan/atau beratnya. Oleh itu, kajian ini memberi penekanan kepada peningkatan sifat mekanikal dan tingkah laku lesu komposit tenunan biasa dengan menggunakan prategasan fabrik dwipaksa. vi
Pertama, tegasan baki teraruh di dalam juzuk komposit akibat prategasan gentian dikira secara teori dengan membangunkan teori makro-mekanik. Kedua, pemodelan berangka bagi komposit prategasan telah dilaksanakan menggunakan perisian ANSYS® untuk mengesahkan hasil teori dan menganggarkan agihan sepenuhnya tegasan baki di dalam juzuk komposit ini. Bingkai prategasan dwipaksi digunakan untuk menyediakan beban prategangan fabrik dwipaksa. Komposit prategasan telah dibuat dengan tahap prategasan yang berbeza berjulat antara 25 hingga 100 MPa dan disediakan dengan sudut orientasi gentian yang berbeza seperti 0, 15, 30 dan 45o. Keputusan ujikaji seperti tegangan, lenturan dan lesu telah dijalankan ke atas komposit tenunan-biasa sistem E-kaca/poliester untuk menilai kelebihan yang mungkin timbul daripada penggunaan prategasan dwipaksa fabrik. Keputusan teori menunjukkan bahawa tahap tegasan baki yang teraruh di dalam juzuk komposit bergantung pada tahap prategasan gentian, pecahan isipadu gentian, dan sifat elastik juzuk komposit. Tegasan baki yang dikira dengan teori makro-mekanik yang dibangunkan adalah sepadan dengan yang diperoleh oleh pemodelan berangka dan kajian terdahulu dengan nilai kurang daripada 1.53%. Simulasi berangka komposit prategasan menunjukkan bahawa tegasan baki teraruh maksimum disebabkan oleh prategasan gentian terletak pada antara muka gentian-matriks. Meningkatkan tahap prategasan gentian boleh meningkatkan keduadua tegasan sisa mampatan teraruh di dalam matriks dan tegasan ricih antara muka serat-matriks. Keputusan ujikaji menunjukkan bahawa paras prategasan 50 MPa boleh memberikan peningkatan tertinggi bagi sifat-sifat kuasi-statik dan tingkah laku jangka hidup lesu. Tambahan pada sifat tegangan dan lenturan adalah lebih kurang 20% (daripada 3.74 hingga 4.4 GPa modulus tegangan dan 35 hingga 42 MPa tegasan kritikal) dan 15% (daripada 2.54 hingga 2.96 GPa modulus lenturan dan dari 87.11 vii
hingga 99.88 MPa kekuatan lenturan) masing-masing. Kitaran sehingga kegagalan lesu telah dipanjangkan hingga 43% (daripada 19949 hingga 28594 kitaran) pada tekanan puncak normal 0.4 berbanding dengan yang tanpa-prategasan. Tahap peningkatan telah dikurangkan dengan meningkatkan orientasi gentian ke arah pincang. Fungsi empirikal dianggarkan termasuk kesan prategasan ke atas tingkah laku tegangan, kelenturan dan lesu. Spesimen komposit prategasan dengan 50 MPa menunjukkan penurunan dalam kekuatan tegangan, kekuatan lenturan dan kitaran lesu yang lebih baik hingga kegagalan yang kira-kira 3.56% (daripada 42.07 hingga 40.56 MPa), 1.96% (daripada 99.88 hingga 97.92 MPa ) dan 14.55% (daripada 28594 hingga 24432 kitaran )selepas enam bulan dibuat, masing-masing. Penurunan ini adalah hasil daripada kesan tekanan santaian di dalam matriks. Berdasarkan kepada penemuan, disimpulkan bahawa kaedah prategasan yang dicadangkan
dapat
meningkatkan
sifat
mekanikal
komposit
tenunan-
biasa. Peningkatan ini hasil daripada peningkatan rintangan komposit terhadap beban kuasi-statik dan lesu dengan mengurangkan kedua-dua sifat berombak gentian dan tegasan baki tegangan di dalam matriks. Kaedah prategasan serat dapat meningkatkan sifat-sifat mekanik komposit tenunan di kedua-dua arahpaksi dan arah nentang-paksi. Peningkatan ini masih wujud selepas pengedaran semula sepenuhnya tegasan baki yang diaruh dalam matriks.
viii
ACKNOWLEDGEMENTS
All praises be to almighty Allah, the lord of whole creations, for inspiring and guiding me towards the utmost goodness I also would like to express my sincere gratitude and appreciation to my supervisor Assoc. Prof. Dr. Nur Ismarrubie Zahari for her priceless guidance, continued supervision, advice, comment, encouragement and support throughout the research journey. Many thanks and gratitude also goes to the supervisory committee for their guidance and advice. Also, I would like to express my utmost appreciation and gratitude to Universiti Putra Malaysia (GP–IPS/2015/9463000) for the financial support. The research was partially
supported
by
Fundamental
Research
Grant
Scheme
(FRGS/1/2012/TKO1/UPM/02/1) by the Ministry of Higher Education Malaysia. Special thanks to Mr. Ahmad Shaifudin, Mr. Muhammad Wildan and Mr. Mohd Saiful for their technical supports Finally, I would like to thank the University of Babylon, Ministry of Higher Education and Scientific Research, Iraq for the financial supporting of the scholarship.
Nawras Haidar Mostafa May 2017
ix
APPROVAL I certify that a Thesis Examination Committee has met on (date of viva voce) to conduct the final examination of Nawras Haidar Mostafa on his thesis entitled “Effect of biaxial fabric prestressing on the mechanical properties of plain–weave Eglass/polyester composites” in accordance with the Universities and University Colleges Act 1971 and the Constitution of the Universiti Putra Malaysia [P.U.(A) 106] 15 March 1998. The Committee recommends that the student be awarded the degree of doctor of philosophy. Members of the Thesis Examination Committee were as follows: Nuraini Abdul Aziz, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Chairman) Barkawi Sahari, PhD Professor Ir Faculty of Engineering Universiti Putra Malaysia (Internal Examiner) Edi Syams Zainudin, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Internal Examiner) Raj Das, PhD Associate Professor Department of Mechanical Engineering/Faculty of Engineering The University of Auckland New Zeland (External Examiner)
________________________ Mohd Fadlee, PhD Assoc. Prof. and Deputy Dean School of Graduate Studies Universiti Putra Malaysia Date:
x
This thesis was submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfilment of the requirement for the degree of Doctor of Philosophy. The members of the Supervisory Committee were as follows: Nur Ismarrubie Bt Zahari, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Chairman) Mohd Sapuan B. Salit, PhD Professor Ir Faculty of Engineering Universiti Putra Malaysia (Member) Mohamed Thariq B. Hameed Sultan, PhD Associate Professor Ir Faculty of Engineering Aerospace Manufacturing Research Centre (AMRC) Universiti Putra Malaysia (Member)
________________________ Robiah Yunus, PhD Professor and Dean School of Graduate Studies Universiti Putra Malaysia Date:
xi
Declaration by Graduate Student I hereby confirm that:
this thesis is my original work; quotations, illustrations and citations have been duly referenced; this thesis has not been submitted previously or concurrently for any other degree at any other institutions; intellectual property from the thesis and copyright of thesis are fully-owned by Universiti Putra Malaysia, as according to the Universiti Putra Malaysia (Research) Rules 2012; written permission must be obtained from supervisor and the office of Deputy Vice-Chancellor (Research and Innovation) before thesis is published (in the form of written, printed or in electronic form) including books, journals, modules, proceedings, popular writings, seminar papers, manuscripts, posters, reports, lecture notes, learning modules or any other materials as stated in the Universiti Putra Malaysia (Research) Rules 2012; there is no plagiarism or data falsification/fabrication in the thesis, and scholarly integrity is upheld as according to the Universiti Putra Malaysia (Graduate Studies) Rules 2003 (Revision 2012-2013) and the Universiti Putra Malaysia (Research) Rules 2012. The thesis has undergone plagiarism detection software.
Signature: ________________________
Date: __________________
Name and Matric No.: _________________________________________
xii
Declaration by Members of Supervisory Committee This is to confirm that:
the research conducted and the writing of this thesis was under our supervision; supervision responsibilities as stated in the Universiti Putra Malaysia (Graduate Studies) Rules 2003 (Revision 2012-2013) are adhered to.
Signature: Name of Chairman of Supervisory Associate Professor Dr. Nur Ismarrubie Zahari Committee:
Signature: Name of Member of Supervisory Committee:
Professor Ir. Dr. Mohd Sapuan Salit
Signature: Name of Member of Supervisory Committee:
Associate Professor Ir. Dr. Mohamed Thariq Hameed Sultan
xiii
TABLE OF CONTENTS
Page ii iii vi ix x xii xiv xvii xix xxx
DEDICATION ABSTRACT ABSTRAK ACKNOWLEDGEMENTS APPROVAL DECLARATION TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF ABBREVIATIONS
CHAPTER 1
2
INTRODUCTION 1.1 General 1.2 Composite materials and their applications 1.3 Motivation 1.4 Problem statement 1.5 Scope and limitation of the study 1.6 Research hypotheses 1.7 Research objectives 1.8 Contributions of the study 1.9 Thesis layout LITERATURE REVIEW 2.1 Introduction 2.2 Manufacturing of composites 2.3 Matrix micro–cracking damage in composite materials 2.4 Residual stresses in composite materials 2.4.1 Effects of residual stresses on composite failure 2.4.2 Measurement of residual stresses 2.4.3 Determination of residual stresses 2.5 Failure of composite materials 2.5.1 Matrix cracking 2.5.2 Interfacial debonding/intra–ply debonding 2.5.3 Fibre breakage 2.5.4 Failure criteria of a lamina xiv
1 2 4 4 8 9 10 10 11
14 15 16 18 19 23 25 29 32 33 34 35
2.6 2.7 2.8 2.9 2.10
2.11
2.12 2.13 2.14 2.15 3
Stress analysis of laminated composite Types of fibre pretension (prestressing) methods The proposed governing mechanisms associated with prestressing Fibre pretension concepts Application mechanisms of fibre prestressing methods 2.10.1 Elastically fibre prestressed PMCs (EFPPMCs) 2.10.2 Viscoelastically fibre prestressed PMCs (VEFPPMCs) Mechanical behaviour of PMCs 2.11.1 Tensile behaviour 2.11.2 Flexural behaviour 2.11.3 Fatigue behaviour 2.11.4 Longevity of fibre prestressed PMCs Overview of fibre prestressing studies Potential applications and future trends of fibre prestressed composites Evaluation of fibre prestressing methodologies Summary
METHODOLOGY 3.1 Introduction 3.2 Research methodology 3.3 Performing the fibre prestressing method 3.4 Stresses analysis of PMCs 3.4.1 Modelling based on the macro–mechanical level 3.4.2 Modelling based on finite element method (FEM) 3.5 Experimental tests 3.5.1 Raw materials 3.5.2 Prestressing frame 3.5.3 Composite sample fabrication 3.5.4 Tensile test 3.5.5 Flexural test 3.5.6 Fatigue test 3.5.7 Evaluation of EFPPMCs with time (longevity aspects) 3.5.8 Failure morphology observation 3.6 Summary
xv
36 44 45 56 58 58 68 69 69 77 84 96 105 106 108 112
114 115 118 126 126 136 144 144 147 152 159 162 165 171 172 173
4
5
RESULTS AND DISCUSSION 4.1 Introduction 4.2 Theoretical analysis results 4.3 Numerical results 4.4 Experimental results 4.4.1 Properties of composite’s constituent materials 4.4.2 Tensile test 4.4.3 Flexural test 4.4.4 Fatigue test 4.4.5 Effect of stress relaxation on the longevity aspect 4.5 Summary CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE STUDIES 5.1 Theoretical analysis of prestressed composites 5.2 Numerical modelling of prestressed composites 5.3 Quasi–static mechanical properties, fatigue behaviour and longevity 5.4 Recommendations for future studies
REFERENCES APPENDICIES BIODATA OF A STUDENT LIST OF PUBLICATIONS
174 175 188 198 198 203 224 235 253 256
258 259 260 262 264 289 328 329
xvi
LIST OF TABLES
Table
Page
2.1
Techniques of residual stresses reduction in the polymeric composites
23
2.2
The average strain released using EFPI and FBG sensors with 108 MPa prestressed composite (Krishnamurthy et al., 2016)
25
2.3
Unstressed and prestressed unidirectional tensile properties (Brown, 1976)
47
2.4
Effect of fibre prestressing on the mean strength of a unidirectional carbon fibre/epoxy composite (Chi and Chou, 1983)
49
2.5
Mechanical properties (with standard deviations) of the prestressed and non-pre-stressed laminate (Schulte and Marissen, 1992)
70
2.6
Flexural modulus of nylon 6,6-epoxy composites (Pang and Fancey, 2009)
79
2.7
Prestressing methodologies and their limitations
110
2.8
The positive and negative aspects of the elastic and viscoelastic prestressing methods
111
2.9
The accomplished and pending tests related to prestressed PMCs
112
3.1
The standard properties of the E–glass woven fabric (EWR600)
145
3.2
Standard properties of the unsaturated polyester resin (Reversol P9509)
145
3.3
Approximated geometrical parameters of the plain–weave fabric lamina (E–glass/polyester) under different biaxial fabric prestressing levels
147
3.4
Number of tested samples for different tests
147
4.1
Residual stress in the matrix for a composite fabricated from a range of fibre volume fractions (unidirectional fibre) and prestressed at different levels using two theoretical models
176
4.2
Residual stress in the fibre for a composite fabricated from a range of fibre volume fractions (unidirectional fibre) and prestressed at different levels using two theoretical models
176
xvii
4.3
Thermomechanical properties of a composite system used by Krishnamurthy (2006)
178
4.4
Residual strain measurements versus current work results
178
4.5
Residual stresses within the matrix induced by fibre prestress only using Naik’s (Naik and Ganesh, 1995) and Gay’s (Gay, 2015) approaches
181
4.6
Tensile residual stresses in the fibre after matrix cure due to applying different biaxial fabric prestressing levels
183
4.7
Average tensile properties of the E-glass fibre and polyester resin
199
4.8
Tensile test results of composite sample batches at different initial fibre preloadings
205
4.9
Typical tensile test results for non–prestressed samples tested at different orientations with respect to the warp yarn
207
4.10
Comparison between theoretical and experimental results of the tensile elastic modulus of the plain-weave composite with different fibre orientation angles
213
4.11
Polynomial’s coefficients of the tensile elastic modulus at different orientation angles and prestressing levels
216
4.12
Polynomial’s coefficients of the tensile strength at different orientation angles and prestressing levels
217
4.13
Mean values of flexural properties for prestressed samples aligned at warp
225
4.14
Polynomial’s coefficients of the flexural modulus at different orientation angles and prestressing levels
230
4.15
Polynomial’s coefficients of the flexural strength at different orientation angles and prestressing levels
230
4.16
Tensile strength decay per decade for composite samples with different fibre orientations and prestressing levels
239
4.17
Polynomial’s coefficients of the 𝑆-𝑁𝑓 at different orientation angles
247
4.18
Summary of the Weibull’s modulus of non–prestressed and prestressed composites samples
252
xviii
LIST OF FIGURES
Figure
Page
2.1
Weight gain curves for [0/±45/0]s composites conditioned in 50 oC distilled water (Li, 2000)
17
2.2
Tensile strength for ±45 laminates at different testing temperatures, dry and wet (Li, 2000)
18
2.3
Defects caused by residual stresses (Stamatopoulos, 2011; Parlevliet et al., 2007b). (a) Fibre waviness, (b) matrix cracking, (c) interlaminar delamination, and (d) warpage
20
2.4
Cracked composites (Talreja, 2016). (a) Crack initiation along fibre–matrix interfaces, (b) crack spread between the interlaced yarns of woven composites
21
2.5
Induced residual strain in [02/±45]s graphite/polyimide composite specimens (Daniel and Liber, 1977)
25
2.6
Failure mechanisms of unidirectional fibre–reinforced composites (Montesano, 2012). (a) Matrix cracking, (b) fibre fracture, and (c) fibre–matrix interface debonding
29
2.7
Schematic representation of damage development in plain– woven fabric composites during loading. (a) Quasi–static tensile damage (Naik, 2003) and (b) fatigue damage (on–axis) (Montesano, 2012)
31
2.8
Examples of matrix cracks observed in: (a) Continuous fibre cross–ply laminates (Katerelos et al., 2008) and (b) woven fabric polymer composite laminates (Rios-Soberanis et al., 2012; Talreja and Singh, 2012)
32
2.9
Intra–ply debonding occurring in woven fabric–reinforced composites (Naik et al., 2001)
34
2.10
Fibre breakage in fibre–reinforced composite (Lingang, 2013)
34
2.11
Principal directions of the unidirectional laminated composite material (Jones, 1999)
35
2.12
Geometrical parameters of a typical plain–weave fabric lamina unit cell and its idealisation according to Naik and Ganesh (1995). (a) Cross–section in fill direction, (b) cross–section in warp direction, and (c) idealised unit cell
42
xix
2.13
Schematic representation of a fibre which undergoes bending Mills and Dauksys (1973)
46
2.14
Prestressing equipment used by Brown (1976)
47
2.15
A schematic view of fibre prestressing by bending as used by Chi and Chou (1983)
48
2.16
In–plane and out–of–plane fibre waviness examples (Potter et al., 2008)
50
2.17
Effect of residual stresses in composites failure by crack propagation: (a) Non–prestressed composite without external load, (b) non–prestressed composite with external load, and (c) fibre–prestressed composite with external load
52
2.18
Number of initial transverse cracks versus strain (Schulte and Marissen, 1992)
52
2.19
A scheme of fracture by impact in non–prestressed and prestressed samples: (a) Crack propagated through shearing the fibre, (b) Crack propagated along fibre/matrix interfacial region
54
2.20
Schematic diagram of the crack developing in the silica modified glass fibre–reinforced epoxy composite (Cao and Cameron, 2006b)
55
2.21
Schematic representation of mechanism–V (Pang and Fancey, 2009): (a) Effect of remaining tension force on the vertical force, and (b) neutral axis shifting due to the presence of the compressive residual stress within the matrix
56
2.22
The apparatus used by Zhigun (1968)
57
2.23
The rig used by Jorge et al. (1990) for fabricating the prestressed composite plates
59
2.24
The dead–weight prestressing rig used by: (a) Sadiq (2007), and (b) Schlichting et al. (2010)
60
2.25
The prestressing device with V–shaped slots used by Schulte and Marissen (1992)
61
2.26
The schematic representation of pressure forming moulds used by Bekampienė et al. (2011)
62
2.27
Schematic drawing of the pretensioning device used by Hadi and Ashton (1998)
63
xx
2.28
Schematic drawing of the hydraulic cylinder–prestressing device used by Tuttle et al. (1996)
64
2.29
Schematic drawing of a horizontal tensiometer machine device used by Motahhari and Cameron (1999, 1998, 1997)
64
2.30
The fibre–stretching frame used by Zhao and Cameron (1998)
65
2.31
The fibre–stretching frame used by Krishnamurthy (2006) and Daynes et al. (2010, 2008)
66
2.32
Fibre misalignment near end–tab region (Krishnamurthy, 2006)
67
2.33
Biaxial fibre prestressing frame used by Jevons (2004)
68
2.34
Effect of fibre prestress on the tensile properties of E– glass/polyester composite (Jorge et al., 1990): (a) Tensile strength, and (b) tensile elastic modulus
69
2.35
Stress-strain curves of aluminium alloy and VIRALL laminates with different levels of fibre prestress (Sui et al., 1995)
71
2.36
Tensile strength and modulus as a function of prestress (Zhao and Cameron, 1998)
71
2.37
Variation of composite elastic modulus with fibre volume fraction at different fibre prestress levels (Hadi and Ashton, 1998)
72
2.38
Effect of fibre prestress on shape and position of initial damage envelopes for S-glass/epoxy laminate (Dvorak and Suvorov, 2000)
72
2.39
Failure strain as a function of prestress (Krishnamurthy, 2006)
73
2.40
The tensile curves of composite material reinforced with (Bekampienė et al., 2011): (a) Cotton, and (b) glass fabric
74
2.41
Tensile stress–strain plots for a batch of test (prestressed) and control samples showing typical curve shape. Strain-limited toughness is determined from the shaded area under each curve (Pang and Fancey, 2008)
75
2.42
Effect of fibre prestrain on the tensile properties of final composites (Zaidi et al., 2015). (a) Tensile strength, and (b) tensile elastic modulus
76
xxi
2.43
Tensile properties of a carbon fibre/epoxy composite versus the prestressing level (Abdullah and Hassan, 2016): (a) Ultimate strength, and (b) tensile elastic modulus
76
2.44
Flexural strength and modulus as a function of prestress (Zhao and Cameron, 1998)
77
2.45
Flexural properties versus prestressing level foe E-glass/epoxy composites (Motahhari and Cameron, 1999): (a) Flexural modulus, and (b) flexural strength
78
2.46
Flexural properties comparison of the unidirectional E–glass fibre/epoxy composite samples (Cao and Cameron, 2006a): (a) Flexural strength, and (b) flexural modulus
80
2.47
Flexural strength versus fibre pretension level (Širvaitienė et al., 2013b)
81
2.48
Flexural modulus values determined from the three-point bend tests. Each value represents the mean of three samples with corresponding standard error (Fazal and Fancey, 2013a)
82
2.49
Effect of prestressing on the flexural properties of final composites (Zaidi et al., 2015). (a) Flexural strength, and (b) flexural modulus
83
2.50
Flexural properties of a carbon fibre/epoxy composite versus the prestressing level (Abdullah and Hassan, 2016): (a) Flexural strength, and (b) flexural modulus
83
2.51
Comparison of the tension/tension fatigue results for composites consist of the glass fibre/different types of epoxy resins (Fernando and Al-khodairi, 2003): (a) Straight line fitting, and (b) quadratic fitting
85
2.52
Modulus decay and damage accumulation in woven fabric composites during fatigue life (Naik, 2003)
86
2.53
Fatigue life of woven fabric composites (Pandita et al., 2001)
87
2.54
The stress-cycles curves of composite sample at different orientations (Tamuzs et al., 2004)
88
2.55
Changes in the elastic modulus during a cyclic loading at 0o (Tamuzs et al., 2004)
89
2.56
Normalized S–Nf relationships at different temperatures (Kawai and Taniguchi, 2006). (a) Room temperature, and (b) 100 oC
90
xxii
2.57
Maximum stress-fatigue cycles relationships (Kawai and Matsuda, 2012)
91
2.58
S–N curves at symmetrical sinusoidal loading (R = -1) for three directions of specimens (Tamuzs et al., 2008)
91
2.59
Typical curve of reduction of modulus during the cyclic loading (Tamuzs et al., 2008)
92
2.60
Fatigue stress-life curves for a VIRALL laminate with various levels of prestraining (Sui et al., 1996)
93
2.61
Comparison of normalised fatigue of non-prestressed and prestressed composites (Krishnamurthy, 2006): (a) Tensiontension, and (b) tension-compression
95
2.62
Creep behaviour of polymers (Papanicolaou and Zaoutsos, 2011): (a) Application of constant stress, (b) strain response
96
2.63
Stress relaxation in polymers (Papanicolaou and Zaoutsos, 2011): (a) Application of constant strain, and (b) stress relaxation
97
2.64
Analysis of stress relaxation data of nylon 6,6 (Fancey, 2005)
100
2.65
Total compliance plotted as a function of creep time for carbon fibre/epoxy composite at a creep stress of 169.2 MPa measured at different temperatures (Raghavan and Meshii, 1997)
101
2.66
Experimental creep compliance of [0,90]6 plain weave carbon/epoxy composite at various temperatures and 450 MPa (Gupta and Raghavan, 2010)
101
2.67
Effect of fibre reinforcement on Epoxy adhesive (Miravalles, 2007)
102
2.68
Creep curves of the polyester and polymer matrix composites (holding peak stresses: for matrix, 35 MPa; composites 40% and 50%, 140 MPa) by Kang et al., (2009)
103
2.69
Comparison of experimental creep of plain weave carbon/epoxy composites under on-axis (0) loading and offaxis (45o) loading at a stress of 20% ultimate tensile strength and a temperature of 80 oC (Gupta and Raghavan, 2010)
104
2.70
Filament winding (Gay, 2015)
107
3.1
Flow chart of research methodology
117
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3.2
Schematic representation of fibre prestressing during the manufacturing process and its effects on load–deflection behaviour
119
3.3
Axially loaded composite bar
121
3.4
Plain–weave fabric undergoes the prestressing process
125
3.5
Deformation in an orthotropic material
127
3.6
Rotation of principal fibre material axes from x-y axes
132
3.7
Representation of an elementary structure and typical mesh model of a UFRC
139
3.8
Effect of element number on the matrix residual stress at fibre– matrix interface with fibre prestress of 25 MPa.
139
3.9
Representation of an elementary structure and typical mesh model of a PWRC
141
3.10
Geometry of element type SOLID185
141
3.11
The plan–view of the biaxial fabric prestressing rig
149
3.12
The hydraulic system used in applying and measuring the fabric pretension
152
3.13
Accuracy of the pressure gauge–hydraulic system
152
3.14
Samples with different fibre orientation angles (on-axis and offaxis)
154
3.15
Interlacing angle in the plain-weave fabric
158
3.16
Specimen dimensions of tensile test according to ASTM D3039 (2014)
159
3.17
Specimen dimensions according to ASTM D638 (2004)
159
3.18
Setting the E–glass yarn
160
3.19
Tensile test machine, INSTRON 3382
160
3.20
Flexural test machine, INSTRON 3365
162
3.21
Specimen dimension of flexural test and its setting
164
3.22
Fatigue parameters of the load-time curve
166
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3.23
Fatigue test machine, INSTRON 8874
169
3.24
KAPA Multistation testing machine
172
4.1
Longitudinal residual stresses within the matrix of a unidirectional composite cured at 50 oC and cooled down to 25 o C with different levels of fibre prestress
179
4.2
Transverse residual stresses within the matrix of a unidirectional composite cured at 50 oC and cooled down to 25 o C with different levels of fibre prestress
181
4.3
Longitudinal residual stresses (warp direction) within the matrix of a plain–weave composite cured at 50 oC and cooled down to 25 oC with different levels of equi–biaxial fabric prestress
182
4.4
Transverse residual stresses (weft direction) within the matrix of a plain–weave composite cured at 50 oC and cooled down to 25 oC with different levels of equi–biaxial fabric prestress
182
4.5
Total axial stress versus applied external axial stress in the composite lamina (E-glass/Polyester) cured at 50 oC and cooled down to 25 oC and prestressed with different levels
183
4.6
Total flexural stress versus applied flexural stress in the composite lamina (E-glass/Polyester) cured at 50 oC and cooled-down to 25 oC and prestressed with different levels
184
4.7
Applied maximum fatigue stress versus fatigue cycles to failure in the composite lamina (E-glass/Polyester) cured at 50 oC and cooled down to 25 oC and prestressed with different levels
185
4.8
Effect of the fibre elastic modulus on the induced residual stresses in the composite’s constituents in the fibre with prestressing level equals to 25 MPa
187
4.9
Effect of the matrix elastic modulus on the induced residual stresses in the composite’s constituents in the matrix with prestressing level equals to 25 MPa
187
4.10
Axial stress distribution within the matrix due to applying different fibre prestressing levels. (a) 25 MPa, (b) 50 MPa, (c) 75 MPa, and (d) 100 MPa
190
4.11
Axial stress distribution in the matrix along its radial direction due to applying different fibre prestressing levels
190
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4.12
Shear stress distribution in the unidirectional composite due to applying different fibre prestressing levels. (a) 25 MPa, (b) 50 MPa, (c) 75 MPa, and (d) 100 MPa
191
4.13
Shear stress distribution in the matrix along its radial direction due to applying different fibre prestressing levels
191
4.14
Axial stress distribution within the matrix due to applying different equi–biaxial fabric prestressing levels at 25 oC. (a) 25 MPa, (b) 50 MPa, (c) 75 MPa, and (d) 100 MPa
193
4.15
Compressive residual distribution within the matrix due to applying different equi–biaxial fabric prestressing levels at 25 o C
194
4.16
Comparison between analytical and numerical (FEM) results of induced residual stresses within the matrix of equi–biaxial prestressed plain–weave composites at 25 oC
195
4.17
Axial stress at the outer surface of the matrix due to applying axial or transverse loads with different fibre prestress levels
196
4.18
Maximum bending stress distribution of the tensioned part of the matrix under transverse loading of 30 N
196
4.19
Maximum bending stress distribution of the non-prestressed and prestressed samples; the applied transverse load is equal to 30 N
197
4.20
Tensile stress-strain curves of the composite’s constituents used in this work. (a) E–glass fibre, and (b) polyester resin
199
4.21
Normalised stress vs logarithmic fatigue cycles (S–Nf) of the composite’s constituent materials. The arrowheads indicated that these samples survived for one million cycles.
200
4.22
Creep compliance versus time history of the E–glass fibre at a constant applied stress of 100 MPa
201
4.23
Stress versus time history of the polyester resin at a constant applied strain of 0.078%
202
4.24
Prediction of the stress redistribution of polyester resin using Fancey’s model (Fancey, 2005)
203
4.25
Samples with different fibre prestressing conditions. (a) Unloaded fabric (uncontrolled), (b) uniaxially loaded (weft), and (c) equi–biaxially loaded
205
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4.26
Typical tensile stress–strain curves for composite samples tested at different fibre orientations. (a) Non–prestressed samples, and (b) prestressed samples with 50 MPa
208
4.27
Specimens fractured in quasi–static tension. (a) Warp direction (0o), (b) 15o with respect to warp, (c) 30o with respect to warp, and (d) bias direction (45o)
209
4.28
Micrographs of the failure types for prestressed specimens subjected to tensile load. (a) Matrix cracking, (b) fibre–matrix debonding
211
4.29
Quasi–static tensile properties of composite samples with different levels of equi–biaxial fabric prestressing tested at different fibre orientations. (a) Tensile elastic modulus, and (b) ultimate tensile strength
212
4.30
Tensile properties changing with fabric prestressing level at different orientation angles. (a) Tensile elastic modulus, and (b) critical stress
214
4.31
Comparison between the predicted empirical equations and the experimental data. (a) Tensile modulus, and (b) tensile strength.
218
4.32
Frictional parameter versus fibre prestressing level
219
4.33
Effect of biaxial fabric prestress on the percentage crimp along the warp and weft yarns
220
4.34
Micrographs of fabric within the composite. (a) Without fabric prestressing, and (b) with fabric prestressing (50 MPa)
222
4.35
Limited toughness changing with fabric prestressing level at different orientation angles
221
4.36
In-plane shearing of the composite caused by inclined yarn (off-axis)
223
4.37
Typical load–deflection curves of composite samples with different levels of fabric prestressing
224
4.38
The details of the mechanisms that attribute to the enhancement in flexural properties of equi–biaxial fabric prestressing composites. (a) Improving the straightness of yarns, and (b) increasing the contact pressure and reducing crimping
226
4.39
Flexural properties changing with fabric prestressing level at different orientation angles. (a) Flexural modulus, and (b) flexural strength
228
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4.40
Comparison between the predicted empirical equations and the experimental data. (a) Flexural modulus, and (b) Flexural strength.
231
4.41
The directions of bending and compressive residual stresses
232
4.42
Failure pattern images of specimens subjected to three–point bending test
234
4.43
Normalised stress vs logarithmic fatigue cycles (S–Nf) of composite samples with different levels of equi–biaxial fabric prestressing tested at different fibre orientations. (a) At 0o, (b) at 15o, (c) at 30o, and (d) at 45o
238
4.44
Non–prestressed and prestressed specimens failed at different normalised peak stresses
244
4.45
Normalised stiffness evolution at 0.55 of normalised peak stress
241
4.46
The map of adopting the fabric–prestressing method to improve fatigue life or vice versa
246
4.47
Comparison between the predicted empirical equations and the experimental data of normalised stress vs fatigue cycles to failure (S–Nf) at different fibre orientations. (a) 0o, (b) 15o, (c) 30o, and (d) 45o.
250
4.48
Weibull’s distribution for fatigue life of the 50 MPa prestressed samples at different normalised peak stress tested at on-axis
252
4.49
Effect of longevity on the quasi–static properties of prestressed samples. (a) Critical stress, (b) flexural strength
254
4.50
Effect of longevity on the fatigue life of prestressed samples at 50 MPa (S=0.55)
255
A-1
Biaxial prestressing frame and its dimensions
289
A-2
Details of the mould used in this work (symmetrical part)
290
B-1
Composite bar’s dimensions (axisymmetric)
291
B-2
Axial stress distribution in the matrix with different fibre prestressing levels. (a) Non–prestressed, (b) prestressed with 25 MPa, (c) prestressed with 50 MPa, (d) prestressed with 75 MPa, and (e) prestressed with 100 MPa
294
C-1
A composite beam’s geometry and loading details
295
xxviii
C-2
Flexural stress distribution for selected elements around the mid–span of the composite beam with different fibre prestressing levels. (a) Non–prestressed, (b) prestressed with 25 MPa, (c) prestressed with 50 MPa, (d) prestressed with 75 MPa, and (e) prestressed with 100 MPa
xxix
300
LIST OF ABBRIVATIONS
PMCs
Polymeric Matrix Composites
EFPPMCs
Elastically Fibre Prestressed PMCs
VEFPPMCs
Viscoelastically Fibre Prestressed PMCs
FEM
Finite Element Method
ANSYS
Analysis System
MEKP
Methyl Ethyl Ketone Peroxide
UNC
Unified Coarse
E–glass
Electrical–grade glass
EWR600
E–glass woven roving with area density of 600 g/m2
UFRC
Unidirectional Fibre–Reinforced Composite
PWRC
Plain–Weave Fabric Reinforced Composite
ASTM
American Society for Testing and Materials
EFPI
Extrinsic Fabry–Pérot Interferometric
FBG
Fibre Bragg Grating
ERSG
Electrical Resistance Strain Gauge
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