Options
Durability of flax fibre/bio-epoxy sustainable composites for structural application
Citation Link: https://doi.org/10.15480/882.2670
Publikationstyp
Doctoral Thesis
Publikationsdatum
2020
Sprache
English
Author
Advisor
Referee
Title Granting Institution
Technische Universität Hamburg
Place of Title Granting Institution
Hamburg
Examination Date
2020-02-03
TORE-URI
First published in
Number in series
37
Citation
Technisch-wissenschaftliche Schriftenreihe / TUHH Polymer Composites 37 (2020)
Environmental sustainability and eco-efficiency are important requirements for new generation of materials. Polymer composites reinforced with synthetic glass/carbon fibres are extensively applied in high performance structural components but they are not eco-friendly. Natural fibres (especially flax fibres) reinforced bio-based polymers therefore gain growing attention owing to their inherent environmental benefits and good specific mechanical properties. Recently, the application of sustainable natural fibre composites (NFCs) in structural components is of great interest to industry, however their durability is not well understood to date. The work investigates the moisture/water ageing effects and the mechanical durability of a flax fibre reinforced composites (FFCs) in long term.
Composite laminates are made of flax fibres and a bio-based epoxy via resin transfer moulding process. It is found that FFCs do exhibit good static mechanical properties. However, the mechanical properties show a sensitivity to water absorption. Composites modulus and fibres-matrix interfacial bonding decrease with water absorption, while composite strength shows distinct trends upon water absorption depending on the layout of fibres. In some cases water absorption has a positive effect on the composite strength. Tensile strength of [0°] FFCs in fibre direction demonstrates a decrease in the beginning of the water absorption and a followed increase of up to 15% higher than the strength at dry state. The water absorption sensitivity of FFCs is successfully improved by a furfuryl alcohol (FA) treatment approach proposed in this work. Both moisture absorption rate and retention properties are improved as a consequence of improved fibre-matrix and inter-fibre bonding.
Attention on the creep deformation of FFCs is highlighted. [0°] FFCs display appreciable creep deformation at low stress mainly caused by the time- dependent shear deformation of the matrices (hemicellulose/pectin matrix in flax fibres and the epoxy matrix). The creep deformation can be significant reduced by FA treatment approach proposed in this study. Water absorption can extend the creep rupture life of FFCs at high stress. The fatigue strength for a high number of cycles (1 million) is approximatively 120 MPa (40% of the ultimate tensile strength) for [0°] FFCs, and is approximately 40 MPa (55% of the ultimate tensile strength) for [±45°] FFCs. Interestingly, the fatigue dynamic modulus of [0°] FFCs increases over the fatigue life, evidenced by the increased slope of the hysteresis loop with the number of load cycles. The stiffening effect is attributed to the realignment of flax fibres over fatigue life.
Composite laminates are made of flax fibres and a bio-based epoxy via resin transfer moulding process. It is found that FFCs do exhibit good static mechanical properties. However, the mechanical properties show a sensitivity to water absorption. Composites modulus and fibres-matrix interfacial bonding decrease with water absorption, while composite strength shows distinct trends upon water absorption depending on the layout of fibres. In some cases water absorption has a positive effect on the composite strength. Tensile strength of [0°] FFCs in fibre direction demonstrates a decrease in the beginning of the water absorption and a followed increase of up to 15% higher than the strength at dry state. The water absorption sensitivity of FFCs is successfully improved by a furfuryl alcohol (FA) treatment approach proposed in this work. Both moisture absorption rate and retention properties are improved as a consequence of improved fibre-matrix and inter-fibre bonding.
Attention on the creep deformation of FFCs is highlighted. [0°] FFCs display appreciable creep deformation at low stress mainly caused by the time- dependent shear deformation of the matrices (hemicellulose/pectin matrix in flax fibres and the epoxy matrix). The creep deformation can be significant reduced by FA treatment approach proposed in this study. Water absorption can extend the creep rupture life of FFCs at high stress. The fatigue strength for a high number of cycles (1 million) is approximatively 120 MPa (40% of the ultimate tensile strength) for [0°] FFCs, and is approximately 40 MPa (55% of the ultimate tensile strength) for [±45°] FFCs. Interestingly, the fatigue dynamic modulus of [0°] FFCs increases over the fatigue life, evidenced by the increased slope of the hysteresis loop with the number of load cycles. The stiffening effect is attributed to the realignment of flax fibres over fatigue life.
DDC Class
600: Technik
620: Ingenieurwissenschaften
Loading...
Name
Yunlong Jia - dissertation for library.pdf
Size
10.95 MB
Format
Adobe PDF