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Permanent link (DOI): https://doi.org/10.7939/R3NS0M479

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Characterization and Modeling of Natural-Fibres-Reinforced composites (Moisture Absorption Kinetics, Monotonic Behaviour and Cyclic Behaviour) Open Access

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Other title
Subject/Keyword
Monotonic Behaviour
Natural-Fiber-Reinforced Polymer
LDPE
HDPE
Moisture Absorption
Tensile
Fatigue
Modeling
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Fotouh, Ahmed
Supervisor and department
Lipsett, Michael (Mechanical Engineering, University of Alberta)
Wolodko, John (Advanced Materials, Alberta Innovates - Technology Futures: AITF)
Examining committee member and department
Nychka, John A. (Chemical and Materials Engineering, University of Alberta)
Ulven, Chad A. (Mechanical Engineering, North Dakota State University: NDSU)
Xia, Zihui (Mechanical Engineering, University of Alberta)
Ayranci, Cagri (Mechanical Engineering, University of Alberta)
Department
Department of Mechanical Engineering
Specialization

Date accepted
2014-09-26T14:48:08Z
Graduation date
2014-11
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
Natural fibres have been shown to offer a good potential in replacing or supplementing synthetic fibres in composite material applications. To fully utilize these new materials in design, however, engineering models of the mechanical behaviour need to be developed and validated. In this research, the moisture absorption and mechanical behaviour of hemp-fibre-reinforced polyethylene composites at various fibre volume fractions were investigated and modelled. In terms of environmental exposure, the effects of fibre volume fraction (vf) and matrix crystallinity along with matrix stiffness and contraction on the mechanisms of moisture sorption were investigated. The maximum amount of absorbed moisture (Mtmax) was determined for each fibre volume fraction. The composite diffusion coefficient (D) was measured to distinguish the ability of water molecules to diffuse into the biocomposite. The increase in the matrix crystallinity level in addition vf of the tested composites increased the moisture absorption rate. Fickian diffusion was found to be the dominant moisture diffusion behaviour. The stress-strain behaviour of the hemp fibre composites were analyzed and modelled for both monotonic (rate dependent) and cyclic loading conditions. An exponential model was developed to simulate the monotonic stress-strain uniaxial behaviour. A strain rate hardening detected and a model was developed by applying the non-linear form of Norton-Hoff rheology model for viscoplastic material to simulate the relationship between the strain rate ( ε ) and each mechanical property of the tested composites. The strain rate hardening model was later incorporated with an exponential model to develop a new general stress-strain model to simulate the monotonic tensile behaviour of the tested natural-fiber-reinforced composites. The developed new model took into account the effect of ε and vf of the composite as well as the effect of moisture absorption. Fatigue tests were also performed at two fibre volume fractions as well as the reinforced polymer under both wet and dry conditions. The fatigue strength of the polymer was slightly improved by addition of hemp fibers; though, the sensitivity of the developed fatigue life curves did not change. A generalized model was developed using the normalized fatigue life diagrams. These diagrams were normalized by a new developed modified stress level (Sm). The previously developed strain rate hardening model was then incorporated into the fatigue model to capture the effect of the changes in the loading rate. The new fatigue model was capable of predicting the fatigue life at different frequencies (f), fatigue stress ratios (R), fatigue stress amplitudes (Δσ) and vf. Additionally, the fatigue model succeeded to simulate the degradation effect of moisture absorption on the fatigue strength. The new developed models provide essential tools for designers to incorporate this new material into a new generation of reliable products.
Language
English
DOI
doi:10.7939/R3NS0M479
Rights
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Chapter 2 is a modified version of a paper that was published as Ahmed Fotouh, J. D. Wolodko, M. Lipsett, “A Review of Aspects Affecting Performance and Modeling of Short-Natural-Fiber-Reinforced Polymers under Monotonic and Cyclic Loading Conditions”, Journal of Polymer Composites, Mar. 06th, 2014, DOI: 10.1002/pc.22955.Chapter 3 is a modified version of a paper that was published as Ahmed Fotouh, J. D. Wolodko, M. Lipsett, “Isotherm Moisture Absorption Kinetics in Natural-Fiber-Reinforced Polymer under Immersion Conditions”, Journal of Material Composites, May 15th, 2014, DOI: 10.1177/0021998314533366.Chapter 4 is a modified version of a paper that was published as Ahmed Fotouh, J. D. Wolodko, M. Lipsett, “Characterization and Modeling of Strain Rate Hardening in Natural-Fiber-Reinforced Viscoplastic Polymer”, Journal of Polymer Composites, Feb. 06th, 2014, DOI: 10.1002/pc.22894.Chapter 5 is a modified version of a paper that was published as Ahmed Fotouh, J. D. Wolodko, M. Lipsett, “Uniaxial Tensile Behaviour Modeling of Natural-Fiber-Reinforced Viscoplastic Polymer Using Normalize Stress-Strain Curves”, Journal of Material Composites , Aug. 21st, 2014, DOI: 10.1177/0021998314547427.Chapter 6 is a modified version of a paper that was published as Ahmed Fotouh, J. D. Wolodko, M. Lipsett, “Fatigue of Natural Fiber Thermoplastic Composites”, Journal of Composites Part B: Engineering, Vol. 62, pp. 175-192, Jun. 20th, 2014.

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