Browsing by Author "Towo, Arnold"
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Item Fatigue of sisal fibre reinforced composites: Constant-life diagrams and hysteresis loop capture(Elsevier, 2007-09-06) Towo, Arnold; Ansell, Martin P.Composite materials have been manufactured using untreated or 0.06 M NaOH treated sisal fibre bundles in a polyester or epoxy matrix. Mechanical tests have been conducted to establish the static properties of the composites which have been used to calculate the maximum loads used during fatigue testing. Composites containing alkali treated fibre bundles have better mechanical properties than those with untreated fibre bundles. Alkali treatment has the greatest effect for polyester resin matrices. S–N diagrams constructed from fatigue data at stress ratios of R = 0.1 (tension–tension) and R = -1 (reversed loading) show improvement in the fatigue lives of composites following alkali treatment of sisal fibre bundles. Constant-life diagrams for epoxy matrix composites with untreated or alkali treated fibre bundles show the superiority of the alkali treated fibre composites for low cycle fatigue. Composites loaded in tension–tension fatigue (R = 0.1) exhibit hysteresis loops with diminishing loop area with increasing number of cycles. The composites loaded in reversed loading fatigue (R = -1) generate loops with increasing loop area with increasing number of cycles. Failure modes in tension–tension and reversed loading are very different with a distinctive buckling failure mode at R = -1.Item Weibull analysis of microbond shear strength at sisal fibre-polyester resin interfaces(VSP, 2005) Towo, Arnold; Ansell, Martin P.; Pastor, M-L; Packham, DAn analysis has been made of the tensile strength of sisal fibres and the interfacial adhesion between fibres and polyester resin droplets. Density and microscopy methods were used to determine the cross-sectional area of the sisal fibres. The average tensile strength of treated sisal fibres decreased by a modest amount following treatment with 0.06 M NaOH. However, this treatment resulted in a substantial increase in the interfacial shear strength at the sisal fibre to polyester resin interface. Weibull analysis has been used successfully to analyse variability in tensile strengths and interfacial shear strength using probability of failure plots. Scanning electron microscopy has revealed the shape of resin droplets on the surface of treated and untreated sisal fibres and contact angles are much lower for droplets on treated fibres. Damage to the surface of fibres has been examined following shear testing. Weibull analysis is an effective tool for characterising highly variable fibre properties and evaluating the level of adhesion between polymer resin and the fibre surface.