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Experimental evaluation of sisal fiber reinforced laminated composites in wood beams

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  • Save International Journal of Composite M aterials 2012, 2(5): 97-100 DOI: 10.5923/j.cmaterials.20120205.05 Experimental Evaluation of the Employment of a Laminated Composite Material with Sisal Fibres as Reinforcement in Timber Beams Samuel Sander Carvalho, Jezrael Rossetti Dutra, André Cerávolo de Carvalho, Luciano Machado Gomes Vieira, André Luis Christoforo* Department of M echanical Engineering, Federal University of São João del-Rei, 36.307-352, Brazil Abstract Timber is the oldest construction materials in the world, have been widely used in structures in addition to having a high longevity, if treated properly (maintenance). If this does not occur, the wood deteriorates due to the action of insects, fungi and other aggressive agents. There are several materials and techniques used to reinforce the damaged parts. This paper presents an experimental study ofEucalyptus grandis and Pinus elliiottiitimber beams rein forced with sisal fibres laminated composite materials. The co mposite material and the wood were prepared for testing. In order to simulate the defect, some parts were cracked. The study was to determine the maximu m load (rupture) applied on the timberin the conditions: without defect, with defect and without composite and with defect and with composite, aiming to verify the efficiency of the laminate as reinforcement in the wooden beams. The experimental results indicate the possible use of the laminated composite as reinforcement, presenting considerable increase in the maximu m strength supported by the timber when compared to unreinforced cracked condition, being more efficient for the Pinus elliiottii species. Keywords Laminate Co mposite, Sisal Fibre, Timber Beams, Structural Reinforcement 1. Introduction Bea ms are structural ele ments present in most of buildings. Among the usual materials engineering h ighlights the wood, to be from natural and renewable source, low density and good mechanical performance. Timber structures when not treated properly can present problems due to the attack of biological degrading agents that contribute to the loss of their physical and mechanical properties, comp ro mising the integrity of the structural components. The study of repair and reinforcement in the structure of wood has been the focus of technical and scientific papers, aimed at developing viable solutions to be used in the recovery of the same[1-7]. Of the possible materials used as reinforcement and repair wooden structures stand out from the composites, because it is a material designed, in order to obtain a resultant mechanical properties superior to those of constituent p h as es [8]. The use of vegetable fibres such as sisal [9-14], co ir, jute, bananaand bamboo as reinforcement in laminates composite are cons idered as a good so lut ion , sho w go od tens ile * Corresponding author: (André Luis Christoforo) Published online at Copyright © 2012 Scientific & Academic Publishing. All Rights Reserved strength[15-18], and are materials biodegradable and of low cost when compared to synthetic fibres[19]. With the purpose of developing alternatives as reinforcement in beams, this paper aims at the development and characterization of co mposite laminated polymer matrix reinforced with sisal fibres to be used as reinforcement in Eucalyptus grandis and Pinus elliottii timber beams. The wooden beams with and without the use of the composite laminate is tested in bending, by making use of the static three point bending tests, and comparing the maximu m strengths condition to the faultless timber, and defective unreinforced and re inforced, and faulty, ma king it possible to evaluate the efficiency of the manufacture composite. 2. Material and Methods The raw material used is a vegetable fiber and sisal as reinforcement and resin epoxy as matrix fase. The laminate composite was manufacture with a layer. The fiber used was obtained fro mthe Sisal co mpany (Brazil), with caution as the use of fibres fro m the same batch. The Pinus elliottii and Eucalyptus grandis timber used in the fabrication of the specimens was obtained in a local sawmill in São João del-Rei (M G-Brazil), having as a precaut ionary pre-screeni ng of samples free defects. Brackets have been manufactured of cast iron with 225 mm by 160 mm wide synthetic enamel coated. The sisal 98 Samuel Sander Carvalho et al.: Experimental Evaluation of the Employment of a Laminated Composite M aterial with Sisal Fibres as Reinforcement in Timber Beams fibers were woven in a direction perpendicular to the length of the square, so as to stay closer to each other (Figure 1), and with tension on the nodes from the seams positioned on the metal rods, not allowing the presence of nodes in the structure of the laminate. Figure 1. Woven of sisal fibres To elaborate the composite material, the volu me of the fibre should correspond to thirty precents of the total[8], and the remain ing seventy percents should correspond to the volume of resin. Fro m these data the total weight of resin to be applied in the co mposite was then calculated. adhesion was performed by use of the resin wh ile maintaining a bonding with 10cm2of area of each side groove (Figure 2c) and curing by seven days. For adhesion of the laminate to the timber (Figure 3d) was used in the same proportions resin used to manufacture the composite. The mechanical bending tests were performed in an EMIC testing machine with loading speed of 1 mm/ min. The modulus of elasticity (Em) and strength flexural modulus (fm) of the specimenswithout defect (no failure) was obtained according to the Brazilian standard NBR 7190[13], respectively expressed by Equations 1 and 2, F10% and F50% and 10% and 50% of maximu m load (Fmax), L is the length of the useful parts (distance between supports) and b and hthe width and height measures of the cross section respectively. Em = 4 (F50% ⋅ (δ50% − F10% ) ⋅ L3 − δ10% ) ⋅ b ⋅ h3 (1) fm = 3⋅ Fmax ⋅ L 2 ⋅ b ⋅ h2 (2) The dimensions of the specimens follo wing the L≥21·h relation, neglecting the effect o f shear forces in the calcu lus of the displacements[20-22]. 3. Results andDiscussions Os testes realizados com as madeiras íntegras geraram fraturas frágeis (Figura 4a) e também por propagação de trincas (Figuras 4b, 4c e 4d). Figure 2. Dimensions of the specimens: (a) Flawless; (b) defective (a) (a) (b) (c) (b) (d) Figure 3. (a) Laminate sisal; (b) Flawless timber; (c) Bonding area; (d) (c) Composite fixed on timber Eight specimens of timber, four of each species, were made by sawing them pris matic shape with square cross section with dimensions60×2.5×2.5cm (Figure 2). Four of these (two of each species) were damagein the centre of their bases, measuring 8×2.5×1cm (Figures 3b and 3c). Finally, two of the specimen defective (one for each species) have been reinforced with the laminate (Figure 3a) and its (d) Figure 4. Fractures in timber due to the imposition of load on the bending test. (a) Fragile Fracture – Pinus elliiottii; (b) Fracture by crack propagation – Pinus elliiottii; (c) and (d) Fracture by crack propagation – Eucalyptus grandis International Journal of Composite M aterials 2012, 2(5): 97-100 99 The tests performed with the wood cracked generated crack propagation precisely in points where there stress concentrators, as shown in Figure 5. Fro m Figure 8 it is noted that the intact samples shows the maximu m fo rce (FMAX) higher than the strengthened, which in turn was superior to those at the specimens with defects. It is also noted that Pinus support a load lower than the Eucalyptus in all conditions tested, but can also be seen in Table 1. (a) (b) Figure 5. Fractures in the woods cracked by the imposition of load on the bending test. Fracture by crack propagation in a region of stress concentration: (a) Eucalyptus grandis and (b) Pinus elliiottii Finally, tests carried out with the additional have differentfailure mechanis ms. While in the Pinus was disruption of the composite material (Figure 6), there was a break in Eucalyptusspecies, which has subsequently damage the composite material (Figure 7). Figure 6. Specimen of Pinus intact with rupture of the composite material in bending test (left top) Table 1. Maximum load achieved in bending tests. Expe rimental Conditions Intact Pinus Flawless Pinus Reinforced Pinus Intact Eucalyptus Flawless Eucalyptus Reinforced Eucalyptus FMAX (N) 1235.64 1873.07 264.78 441.30 1549.45 2530.12 529.56 627.63 The cracks in Pinus provided an average drop in maximu m load in relation to intact timber about 82.96%, while the reinforcement was able to increase the maximu m load supported by 66.66% co mpared to flawless Pinus.Eucalyptus already cracked gave an average drop in maximu m load in relation to intact timber about 74.04%, while the reinforcement was able to increase the maximu m load supported by 18.52% co mpared to flawless Eucalyptus.Given the above, it appears that when the timber is not enhanced fracture during the imposition o f charges, the strengthening of the composite material has become mo re efficient. Table 2 shows the individual values of the modulus of elasticity in bending (Em) and fle xura l strength modulus (fm) obtained for the intact Pinus elliiottiiand Eucalyptus grandis timber. In Table 2, the Eucalyptushad a higher modulus of elasticity and flexu ral strength modulus that Pinus timber. Figure 7. Specimen of Eucalyptus intact (top) and its disruption in the bending test (bottom) Figure 8 illustrates the behaviour of the relationships between displacements and forces applied in the specimens obtained during the bending tests for the eight experimental co n d itio n s . Table 2. Mechanical propert ies of the t imber obt ained by t he stat ic three points bending test FMAX (N) fm (MPa) Em (MPa) 1235.64 6.17 Pinus 1873.07 9.35 8250 13544 1549.45 7.73 Eucalyptus 2530.12 12.63 10428 17041 4. Conclusions Figure 8. Results obtained in the bending test Currently, researches are being directed to the production of la minates for structural reinforce ment and low cost. These factors are affected by material selection, environ mental conditions of rolling, the characteristics of the tooling and manufacturing methodology. After a few tests on the materials presented in this work, we can conclude that the flawless specimens had a considerable reduction of its resistance to bending in relation to the intact timber. The addition of natural fiber reinforcement allo wed reasonable increase in the flexural 100 Samuel Sander Carvalho et al.: Experimental Evaluation of the Employment of a Laminated Composite M aterial with Sisal Fibres as Reinforcement in Timber Beams strength modulus of the flawless timber. In future studies, we intend to evaluate other bonding areas, new timber species and the variation in the nu mber of layers used in the preparation of the composite. [10] X. Lu, M. Q. Zhang, M. Z. Rong, D. L. Yue, G. C. Yang, “The preparation of self-reinforced sisal fiber composites”. Poly mers & Poly mer Co mposites, Vol. 12, no. 4, p. 297-308, 2004. [11] S. Taj, M . A. Munawar, S. U. Khan, “Natural fiber-reinforced poly mer co mposites”. Proc. Pakistan Acad. Sci. vol. 44, no 2, p. 129-144, 2007. REFERENCES [1] H., Cruz; J., Custodio,; J., Nascimento; M ., Empis, “Execução e Controle de qualidade da reparação de estruturas de madeira com colas epoxídicas e FRPS”, 1º Congresso Ibérico Americano sobre a M adeira na construção. CIM AD, 2004. [2] J. Cunha; D. A. Jr., Souza, “Avaliação estrutural de peças de madeira reforçadas com fibras de carbono”. Revista Engenharia Civil, Nº 20. Universidade Federal de Uberlândia, Uberlândia – M G, 2004. [3] R. F., Carvalho, “Compósitos de fibras de sisal para uso em reforço de estruturas de madeira”. Tese de doutorado em Ciência e Engenharia de M ateriais. Escola de Engenharia de São Carlos, Universidade de São Paulo, São Carlos – SP, 2005. [4] A. Borri; M . Corradi; A. Grazini, “A method for flexural reinforcement of old Wood beams with CFRP materials”. Reinforced Plastics. Perugia, Italy. 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