ENERGY ABSORBING ABILITY OF WOOD/POLYESTER COMPOSITE LAMINATES by ...

210 Pages·2015·4.34 MB·English

by  Shayesteh Haghdan

ENERGY ABSORBING ABILITY OF WOOD/POLYESTER COMPOSITE
LAMINATES
by

SHAYESTEH HAGHDAN

B.Sc., Natural Resources Engineering, University of Tehran, 2006
M.Sc., Natural Resources Engineering, University of Tehran, 2008

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY
in
THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES
(Forestry)

THE UNIVERSITY OF BRITISH COLUMBIA
(Vancouver)

August 2015

© Shayesteh Haghdan, 2015
Abstract

Currently used energy absorbers in transportation industries are made of synthetic fiber/polymer
composites as an alternative to their metal counterparts. These composites are stiff and strong but
are somewhat brittle when subjected to impact load which limits their application when high
energy absorbing ability is required. Wood, in contrast, has a high stiffness and strength to
weight ratio and exhibits a higher deflection before failure. Despite the extensive research on the
mechanical properties of synthetic fiber/polymer composites few researches are available on the
effects of wood composite configuration and densification and its lamination set-up on its impact
and compressive properties.

This research focused on the use of wood in the form of thin veneer to reinforce polyester
and composites of them were fabricated using hand lay-up and compression molding, in different
thicknesses. Various wood configurations were used to create unidirectional, cross-ply, and
woven mats. The effects of each mat configuration on the impact properties of wood/polyester
composites and the lamination and curing processes were investigated and discussed. The gap of
knowledge on the wettability of wood to the polyester resin was informed in this dissertation
using contact angle measurements and roughness tests. Energy absorbing behavior and dominant
fracture mechanisms of wood/polyester laminates subjected to quasi-static compression and
shear loading were examined and the results were compared with the lab-made glass
fiber/polyester composites.

ii
Findings of this study demonstrated that the effect of wood configuration on the impact
properties of the polyester composites was significant. Wood densification improved the impact
performance of composites but this improvement was not statistically significant. It was found
that wood composites had an impact energy equivalent to that of glass fiber laminates.

iii
Preface
Shayesteh Haghdan, dissertation author, was the lead investigator, responsible for the concept
development and experiment design, the research and data analysis, and manuscript composition.
Dr. Gregory Smith was the research supervisor who provided guidance throughout the project,
commented, and edited all four manuscripts. Dr. Thomas Tannert was the co-author in two of the
manuscripts and contributed to concept refinement and manuscript edits.

 A version of Chapter 2 has been published: Haghdan, S., Smith, G, D., 2015, “Natural
fiber reinforced polyester composites: a literature review”, Journal of Reinforced Plastics
and Composites, Vol. 34, No. 14, pp. 1179-1190.

 A version of Chapter 3 has been published: Haghdan, S., Tannert, T., Smith, G, D., 2015,
“Effects of reinforcement configuration and densification on impact strength of wood
veneer/polyester composites”, Journal of Composite Materials, Vol 49, No 10, pp. 1161-
1170.

 A version of Chapter 4 has been published: Haghdan, S., Tannert, T., Smith, G, D., 2015,
“Wettability and impact performance of wood veneer/polyester composites”,
Bioresources, Vol. 10, No. 3, pp. 5633-5654.

 A version of Chapter 5 has been published: Haghdan, S., Smith, G, D., 2015, “Fracture
mechanisms of wood/polyester laminates under quasi-static compression and shear
loading”, Composites Part A, Vol 74, pp. 114-122.
iv
Table of Contents

Abstract .......................................................................................................................................... ii
Preface ........................................................................................................................................... iv
Table of Contents ...........................................................................................................................v
List of Tables ................................................................................................................................ ix
List of Figures .................................................................................................................................x
List of Abbreviations ................................................................................................................. xiv
Acknowledgements ......................................................................................................................xv
Dedication ................................................................................................................................... xvi
Chapter 1: Introduction ................................................................................................................1
1.1 Background ..................................................................................................................... 1
1.1.1 Impact behavior of wood/polymer composites ........................................................... 5
1.1.2 Energy absorbing ability of composites ...................................................................... 6
1.1.3 Wood densification ..................................................................................................... 8
1.2 Research problem statement ......................................................................................... 10
1.3 Research objectives ....................................................................................................... 11
1.4 Organization of the dissertation .................................................................................... 12
Chapter 2: Natural fiber reinforced polyester composites: a literature review .....................14
2.1 Synopsis ........................................................................................................................ 14
2.2 Plant fiber/polyester composites ................................................................................... 14
2.2.1 Hemp fiber ................................................................................................................ 14
2.2.1.1 Fiber loading and fiber length effects ............................................................... 15
2.2.1.2 Chemical treatments effects .............................................................................. 16
2.2.2 Jute fiber.................................................................................................................... 17
2.2.2.1 Fiber loading effects ......................................................................................... 17
2.2.2.2 Chemical treatments effects .............................................................................. 19
2.2.2.3 Long-term water absorption effects .................................................................. 20
2.2.3 Banana fiber .............................................................................................................. 21
2.2.4 Sisal fiber .................................................................................................................. 23
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2.2.4.1 Chemical treatments effects .............................................................................. 24
2.2.4.2 Manufacturing methods effects ......................................................................... 25
2.2.5 Coir fibers ................................................................................................................. 26
2.2.6 Kenaf fibers ............................................................................................................... 27
2.2.7 Other plant fibers ...................................................................................................... 29
2.2.7.1 Chemical treatments effects .............................................................................. 29
2.2.7.2 Fiber loading and filler size effects ................................................................... 31
2.3 Hybrid fiber/polyester composites ................................................................................ 31
2.3.1 Glass fiber-plant fiber/polyester ............................................................................... 31
2.3.1.1 Glass fiber-jute/polyester .................................................................................. 32
2.3.1.2 Glass Fiber-sisal/polyester ................................................................................ 33
2.3.1.3 Glass fiber-pineapple leaf and sisal/polyester................................................... 34
2.3.1.4 Glass fiber-oil palm/polyester ........................................................................... 35
2.3.2 Plant fiber-plant fiber/polyester ................................................................................ 36
2.3.3 Glass fiber-wood/polyester ....................................................................................... 37
2.4 Wood/polyester composites .......................................................................................... 38
2.4.1 Chemical treatments effects ...................................................................................... 39
2.4.2 Densification and configuration effects .................................................................... 40
2.5 Summary ....................................................................................................................... 41
Chapter 3: Effects of reinforcement configuration and densification on impact strength of
wood veneer/polyester composites ..............................................................................................43
3.1 Synopsis ........................................................................................................................ 43
3.2 Introduction ................................................................................................................... 44
3.3 Experimental investigation ........................................................................................... 45
3.3.1 Materials ................................................................................................................... 45
3.3.2 Composite manufacturing ......................................................................................... 47
3.3.3 Test methods ............................................................................................................. 49
3.4 Results ........................................................................................................................... 51
3.5 Discussion ..................................................................................................................... 54
3.6 Conclusions ................................................................................................................... 56
vi
Chapter 4: Wettability and impact performance of wood veneer/polyester composites ......67
4.1 Synopsis ........................................................................................................................ 67
4.2 Introduction ................................................................................................................... 68
4.3 Experimental investigation ........................................................................................... 71
4.3.1 Materials ................................................................................................................... 71
4.3.2 Specimen description ................................................................................................ 72
4.3.3 Composite manufacturing ......................................................................................... 73
4.3.4 Test methods ............................................................................................................. 75
4.3.4.1 Impact test ......................................................................................................... 75
4.3.4.2 Contact angle measurement .............................................................................. 76
4.3.4.3 Surface roughness measurement ....................................................................... 77
4.4 Results and Discussion ................................................................................................. 77
4.4.1 Laminating process ................................................................................................... 77
4.4.2 Microscopic observation ........................................................................................... 79
4.4.3 Fracture mechanisms ................................................................................................ 81
4.4.4 Impact energy............................................................................................................ 82
4.4.5 Wettability of wood veneers ..................................................................................... 83
4.4.6 Surface roughness of wood veneers .......................................................................... 86
4.5 Conclusions ................................................................................................................... 88
Chapter 5: Fracture mechanisms of wood/polyester laminates under quasi-static
compression and shear loading .................................................................................................104
5.1 Synopsis ...................................................................................................................... 104
5.2 Introduction ................................................................................................................. 105
5.3 Experimental investigation ......................................................................................... 108
5.3.1 Materials ................................................................................................................. 108
5.3.2 Specimen description .............................................................................................. 108
5.3.3 Composite manufacturing ....................................................................................... 112
5.3.4 Test methods ........................................................................................................... 113
5.4 Results ......................................................................................................................... 114
5.4.1 Compressive properties of laminates ...................................................................... 114
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5.4.1.1 Effect of symmetry ......................................................................................... 115
5.4.1.2 Effect of balance ............................................................................................. 115
5.4.1.3 Effect of number of lamina ............................................................................. 116
5.4.1.4 Wood/polyester vs. glass fiber/polyester and the commercial treatments ...... 116
5.4.2 Comparison of load-displacement curves ............................................................... 117
5.4.2.1 Glass fiber/polyester (GP)............................................................................... 117
5.4.2.2 Eight-layers symmetric with face layers of 90 (8SB) ..................................... 117
5.4.2.3 Twelve-layers symmetric with face layers of 90 (12SB)................................ 118
5.4.3 Fracture mechanisms of other treatments ............................................................... 118
5.5 Discussion ................................................................................................................... 120
5.5.1 Effect of symmetry, balance, and number of lamina .............................................. 120
5.5.2 Wood/polyester vs. glass fiber/polyester and the commercial treatments .............. 121
5.5.3 Fracture mechanisms .............................................................................................. 122
5.6 Conclusions ................................................................................................................. 123
Chapter 6: Conclusion ...............................................................................................................137
6.1 Project summary ......................................................................................................... 137
6.2 Conclusions ................................................................................................................. 142
6.3 Outlook ....................................................................................................................... 143
Bibliography ...............................................................................................................................144
Appendices ..................................................................................................................................160
Appendix A Plot of failure and non-failure using staircase method ....................................... 160
Appendix B ANOVA results for the effects of reinforcement configuration and densification
on impact strength of wood veneer/polyester composites ...................................................... 161
Appendix C ANOVA results for the wettability and impact performance of wood
veneer/polyester composites ................................................................................................... 169
Appendix D Stress-strain curve in 8SB and 12NS samples ................................................... 190
Appendix E ANOVA results for the fracture mechanisms of wood/polyester laminates under
quasi-static compression and shear loading ............................................................................ 191
Appendix F SEM micrographs of fracture mechanisms of 12SB laminates: delamination and
transverse crack ....................................................................................................................... 194
viii
List of Tables
Table 3.1 List of treatments, including mass and volume fractions of components; n= 20
replicates for each impact energy mean and St.Dev. Note: W denotes wood, P polyester, and GF
glass fiber. ..................................................................................................................................... 58
Table 4.1 Comparison of the three wood species......................................................................... 89
Table4.2 List of treatments and mass fractions of components. .................................................. 90
Table4.3 Average contact angle (initial and after 5 seconds) and surface roughness values of
different wood veneers (n= 5 replicates for each angle measurement; n=15 for each roughness
measurement). ............................................................................................................................... 91
Table 5.1 List of treatments........................................................................................................ 125
Table 5.2 Mean compressive properties of laminates and the associated St. Dev. (n= 8
replicates). ................................................................................................................................... 126

ix
List of Figures
Figure 1.1 Relationship between Chapters 3 to 5 ........................................................................ 13
Figure 3.1 Douglas fir: (a) original sheet 0.6 mm thick; (b) woven sheet before trimming edges;
(c) veneer edges deformation after densification; and (d) woven sheet of 2 mm veneer strips,
circles show strips cracks and splits.............................................................................................. 59
Figure 3.2 Woven veneer sheet after edge trimming: (a) undensified 5 mm strips; (b) densified
5 mm strips; (c) undensified 12 mm strips; and (d) densified 12 mm strips. ............................... 60
Figure 3.3 Control samples: (a) ball resting on sample after impact, and (b) after removing ball.
....................................................................................................................................................... 61
Figure 3.4 Comparison of failure patterns: (a) densified veneer; (b) UOP; (c) WOP, top surface;
(d) WOP, bottom surface; (e) circular crack in G-UDP; (f) starlike crack in GP; (g) CrossOP; and
(h) G-CrossOP. ............................................................................................................................. 62
Figure 3.5 Comparison of mean impact energy of treatments (error bars represent 95%
confidence intervals). .................................................................................................................... 63
Figure 3.6 Light micrographs of veneer cross section before and after densification;
densification happened in tangential direction of the growth rings (vertically in the micrograph).
....................................................................................................................................................... 64
Figure 3.7 SEM micrographs of resin distribution; (a) control veneer sheet – no resin applied;
(b) wood-polyester composite; (c) tracheids pit in wood-polyester composite, (d) the individual
glass fibers surrounded by polyester matrix in GP composites. ................................................... 65
Figure 3.8 Relationship between Chapters 3 and 4 ...................................................................... 66
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