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Title: Development of meso-scale geometry for enhanced mechanical properties of flax fibre reinforced composites
Author: Rayyaan, Rishad
ISNI:       0000 0004 7657 5513
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2017
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Biodegradability and environmental sustainability are key features that give natural fibre reinforced composites the potential to be used in different sectors of structural application. To replace synthetic fibres such as carbon or glass fibre in reinforced composites with natural fibres, the mechanical performance of the natural fibres needs to exhibit equivalence to some extent to that of the synthetic fibres. As far as the mechanical properties of the fibres are concerned, flax fibres exhibit excellent competency when compared with E-glass fibres in terms of the Young's modulus and tensile strength. However, efficient conversion of the fibre properties into their corresponding composite properties has been a challenge, due to the conventional textile processing methods that are utilised for the processing of flax fibres. These techniques impart disadvantageous features into the flax fibre preforms at both micro-scale and meso-scale level, which severely degrade mechanical performances of flax fibre reinforced composites (FFRC). Undulation of the fibres in a fabric, which is also known as 'crimp', is one of the detrimental features that derives from the conventional fabric manufacturing route. This performance degradation due to fibre waviness is amplified when flax fibres are concerned. The waviness instigates micro-compressive defects, known as kink bands in elementary flax fibres, which significantly undermine the performance of flax fibre reinforced composites. In this research, nonwoven flax tapes of highly aligned flax fibres have been manufactured, and composites reinforced from those nonwoven tapes have been compared with composites reinforced with woven Matt fabric and with warp knitted Unidirectional (UD) fabrics. To attain a hybridisation effect, another type of composite has been manufactured with surface veils of glass fibres attached on both the faces of the nonwoven tapes. A thermoset epoxy matrix has been used to produce all the composites at a curing temperature of 80 °C for 2 hours followed by post-curing at 120 °C for 6 hours. The fibre volume fraction has been analysed using three techniques including a mathematical method, a mechanical method, and by image analysis using ImageJ software. To understand the fabric behaviour during composite forming, dry fabric compaction has been conducted which suggests that a higher compressive pressure can yield a higher fibre volume fraction. Higher nesting has been observed for the Matt and UD fabric in comparison with the nonwoven tapes. This can be attributed to the smaller gaps between the adjacent fibres in the nonwoven tapes. Tensile properties, compressive properties and flexural properties have been evaluated for all the four types of composites. Nonwoven tape reinforced composites in comparison with Matt fabric reinforced composites regarding tensile strength and compressive strength have been observed to be 49% and 33% higher respectively. Flexural strength of both the types of composites have been observed to be the same. The undulation of the reinforcing fibres has been identified as the dominant criterion that governs the tensile, compression and flexural performances of those composites. A higher degree of the presence of undulation in the reinforcing fibres or yarns have been found to be liable for a greater number of resin rich area, an increased number of kink bands, and a lesser degree of homogeneity of the fibre distribution. All these parameters have been observed to directly influence the mechanical performances of the flax fibre reinforced composites.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: fabric compaction properties ; flexural properties ; Fractography ; resin rich area ; impregnation of lumens ; longitudinal compressive properties ; individualisation of elementary fibres ; longitudinal tensile properties ; composites ; elementary fibres ; micro-defects ; meso-scale geometry ; nonwoven ; Flax fibre ; technical fibres