It was performed in tap water at 95 ☌ (and normal pressure) and in an autoclave at a temperature of 125 ☌.
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The ageing in water was carried out according to ISO 1817 (1985). SWELLINGĭuring ageing in water and oil, swelling (change in volume) of the testpieces was measured.
Stress relaxation, in tension, was determined according to ISO 6914 (1985), method A (constant elongation). Relaxation in compression was determined according to ISO 3384 (1991), method A (all force measurements carried out at the testing temperature). The tension set was determined according ISO 2285 (1995), method 2 (constant elongation). The compression set was determined according to ISO 815 (1991) with a small testpiece (type B, diameter 13 mm, thickness 6.3 mm). The hardness of the rubber materials (IRHD) was determined according to ISO 48 (1994) on all testpieces. For air-aged testpieces, the tensile stress at an elongation of 100% was also measured. Tensile strength and elongation at break were measured according to ISO 37 (1994) for all materials. Albihn, in Elastomers and Components, 2006 4.2 METHODS TENSILE STRENGTH AND ELONGATION AT BREAK A similar observation is also made by Mortazavi and Moghaddam 2010 which found that leafiran fibers (with 26% lignin) had a greater elongation than kenaf (17% lignin), jute (9% lignin), and pineapple (8.3% lignin) fibers. Also, this result is supported by the observation made by Agu et al., which concluded that a high content of lignin increases the extension ability of natural fibers ( Agu et al., 2012). These authors have concluded that the regression graph of failure strain lignin content shows that an increase in lignin content increases the failure strain.
When hemicelluloses fail, the stresses are transferred to microfibrils ( Komuraiah et al., 2014). Cellulose corresponds to high stresses and hemicelluloses to low ones. The stress–strain curve of natural fibers is nonlinear. The addition of bagasse fiber reduced the bending strength and hardness of the composite. On the other hand, percentage elongation and impact strength increased with the increase of bagasse content in the composite, due to the more elastic nature of natural fibers in comparison to resin. As bagasse content increased, the modulus of elasticity and ultimate compressive strength decreased. (2012), have shown that the decrease in ultimate tensile strength with an increase in bagasse fiber content is due to voids present in the material. In contrast to this finding, Tewari et al. Increasing concentrations of natural plant fiber resulted in increased tensile strength and water vapor permeability but decreased elongation at break.
(2010), concluded that the NaOH treatment was shown to be more effective than the silane treatment. Surface chemical treatment, such as NaOH treatment, improved the elongation of the fiber almost twofold, but no improvement in tensile strength was observed ( Du et al., 2015). Generally the inclusion of natural plant fibers into thermoplastics, such as polyethylene or other thermoplastic polymers, results in a decrease in elongation at break but an increase in Young's modulus. This statement can clearly be seen from Table 3.3, where fibers with high elongation values show lower strength and Young's modulus values. Bast and leaf fibers have lower elongation at break compared to industrially man-made fiber as well as seed or stalk fibers. In general, synthetic fibers show better mechanical and physical properties compared to the natural fiber, whereas the specific modulus and elongation at break are better in natural fibers than the synthetic fibers, which is considered as an important factor in polymer engineering composites. The elongation at break can be determined by tensile testing in accordance with EN ISO 527.
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It expresses the capability of natural plant fiber to resist changes of shape without crack formation. Djafari Petroudy, in Advanced High Strength Natural Fibre Composites in Construction, 2017 3.4.2 Elongation at break (%)Įlongation at break, also known as fracture strain, is the ratio between changed length and initial length after breakage of the test specimen.
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