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Mechanical properties of polyester fiber glass composites

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  • Save International Journal of Composite M aterials 2012, 2(6): 147-151 DOI: 10.5923/j.cmaterials.20120206.06 Mechanical Properties of a Polyester Fibre Glass Composite Aramide F. O.1,*, Atanda P. O.2, Olorunniwo O. E.2 1M etallurgical and M aterials Engineering Department, Federal University of Technology, Akure, Ondo State, Nigeria 2M aterials Science and Engineering Department, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria Abstract In the present work, mechanical p roperties of laminates fabricated by Hand lay-up technique using fibre glass (woven-mat) of density 3.6 N/ m2 and general purpose polyester resin was investigated. Fibre glass polyester composite samples were fabricated with d ifferent fibre glass volume fractions (A-0.05, B-0.10, C-0.15, C-0.20, D-0.25 and E-0.30). The materials properties; ultimate tensile strength, Young’s modulus of elasticity, elastic strain, and impact strength of the materials were determined through standard tests on standard test samples. It was observed that the various mechanical properties (exclud ing the impact strength) were improved with increase in fibre g lass volume and that the fibre glasspolyester co mposite is characterized by h igh toughness. It was concluded that the optimu m fibre g lass volume fraction for the composite is 0.25. Keywords Laminates, Fibre Glass (Woven-Mat) Polyester Co mposite, Toughness 1. Introduction Co mposite materials are materials that co mbine t wo or more materials (a selected filler or reinforcing elements and compatible matrix b inder) that have quite different properties that when combined offer properties wh ich are mo re desirable than the properties of the individual materials . The different materials work together to give the composite unique properties, but with in the co mposite you can easily see the different materia ls, they do not dissolve or blend into each other. The key characteristics of co mposites is the • Specific strength (the strength to weight ratio σ/ρ) • Specific stiffness or specific modulus (the stiffnessto-weight ratio E/ ρ) • Tailored material (since co mposites are co mposed of 2 or more “phases”, they can be formulated to meet the needs of a specific applicat ion with considerable ease) Fiber-reinforced co mposites are being increasingly used as alternatives for conventional materials primarily because of their high specific strength, specific stiffness and tailorable properties. In addition the viscoelastic character of composites render them suitable for high performance structural applications like aerospace, marine, automob ile, satellites, sports goods, robots, and thermal insulation structures like cryostats for low temperature technology, hydrogen technology tanks, in superconductivity and also in biomed icine for body compatib le implants[1, 2, 3 and 4]. * Corresponding author: (Aramide F.O.) Published online at e Copyright © 2012 Scientific & Academic Publishing. All Rights Reserved The above properties are strongly dependent on the factors such as the matrix and fibre material and their volu me fractions, the fibre orientation, the applied stress levels and strain rates, as well as the loading conditions and the nature of fibre poly mer interface [5, 6, 7]. Interface is said to be the heart of the composite. The local response of fibre matrix interface within the composite plays an important role in determining the gross mechanical performance [8]. It provides a means of stress transfer fro m fibre to fibre through the matrix. In recent times, there has been a remarkable growth in the large-scale production of fibre and/or filler reinforced epo xy matrix co mposites. Because of their high strength-to-weight and stiffness-to-weight ratios, they are extensively used for a wide variety of structural applications as in aerospace, automotive and chemical industries [9]. On account of their good combination of properties, fiber reinforced poly mer composites (FRPCs) are used for producing a number of mechanical co mponents such as gears, cams, wheels, brakes, clutches, bearings and seals. Most of these are subjected to tribological loading conditions. The FRPCs exhib it relat ively low densities and they can also be tailored for our design requirements by altering the stacking sequences to provide high strength and stiffness in the direction of high loading [10]. The aim of this research is to exp lore the possibility of reinforcing a polyester resin mat rix co mposite with woven mat fibre glass and to establish the optimu m vo lu me fraction. 2. Materials and Methods 148 Aramide F. O. et al.: M echanical Properties of a Polyester Fibre Glass Composite The materials and equipment used for this project work are: Po lyester resin, Methyl Ethyl Ketone Pero xide (catalyst), Cobalt 2% in solution as accelerator, Fibre Glass, Poly Vinyl Acetone as mould release agent, and Ethanol: This is used to clean off the left over of polyester material fro m the beaker and other apparatus. Weighing balance: This is used to measure the polyester resin, fibre g lass, accelerator and cataly s t. The silicone rubber mould is cleaned and its surface is coated with hard wax to serve as a mould release agent. A weighed gel coat of unsaturated polyester resin containing curing additives (catalyst and accelerator) is then brushed evenly over the mould surface. Th is is to ensure the formation o f a pure resin outer surface to the mould ing. After the gel coat has become stiff, successive alternate layers of weighed fibre g lass reinforcement (chopped strand mat in this case) and resin are applied. The fibre glass are fully wetted and impregnated with resin by rolle rs. A fina l sealing layer of resin is then applied. When the laminate was fully hardened, it was stripped fro m the mould and trimmed to size using hand file. Several samp les of vary ing fibre content, ranging fro m A (5% fibre content) to F (30% fibre content) were prepared using the above described method. 2.1. Tensile Testing The tensile tests were performed on INSTRON 1195 at a fixed crosshead speed of 10mm min-1. Samples were prepared according to ASTM D412 and tensile strength of standard and conditioned samples was calculated. 2.2. Impact Test Two samples for each set A, B, C, D, E and F cast using the same method described above. A mould of uniform rectangular cross section was used to prepare Izod samples of uniform thickness. The impact tests were performed on various sample determine the impact strengths by the “V-notch method using the Honsfield Balance Impact Testing Machine. Prior to mounting on the machine, the test sample is notched to a depth of 2 mm with v-shaped hand file. The notched test sample was then mounted on the impact-testing mach ine, which is the operated to apply a (constant) impact force on the test sample. The impact strength (the amount of impact energy the specimen absorbed before y ield ing) was then read off the calibrated scale on the impact testing machine. 3. Results and Discussion The results obtained from the tests conducted on various samples was recorded in Table 1., while Figure 1. relates the effect of fibre glass volu me fraction on the modulus of elasticity of the system; Figure 2. shows the effect of fib re glass volume fraction on the ultimate tensile strength of the system; Figure 3. depicts effect of fibre glass volume fraction on elastic strain of the system; Figure 4 elucidates effect of fibre g lass volume fract ion on the average absorbed energy of the system; Figure 5 shows ultimate tensile strength – strain curve of the system. Modulus of Elasticity E (Nmm-2) 105 95 85 75 65 55 0.05 0.1 0.15 0.2 0.25 0.3 Fibre Volume Fraction Figure 1. Effect of Fibre Glass Volume Fraction on the Modulus of Elasticity of the System International Journal of Composite M aterials 2012, 2(6): 147-151 149 Ultimate Tensile Strength (Nmm -2) 2.1 1.9 1.7 1.5 1.3 1.1 0.9 0.7 0.5 0.05 0.1 0.15 0.2 0.25 0.3 Fibre Volume Fraction Figure 2. Effect of Fibre Glass Volume Fraction on the Ultimate Tensile Strength of the System 19 17 Strain (10-3) 15 13 11 9 0.05 0.1 0.15 0.2 0.25 0.3 Fibre Volume Fraction Sample Identity A B C D E F Figure 3. Effect of Fibre Glass Volume Fraction on Strain of the System Table 1. Mechanical Properties of the Test Samples Fibre Volume Fract io n 0.05 0.10 0.15 0.20 0.25 0.30 Strain (10-3) 9.5 12.9 15.3 18.7 20.0 18.4 Ultimate Tensile Strength (Nmm-2) 0.545 0.866 1.139 1.451 1.601 2.030 Modulus of Elasticity E (Nmm-2) 57.36 67.13 74.44 77.63 80.05 110.32 Average Absorbed Energy (J) 43.875 43.538 42.863 42.525 41.850 41.175 150 Aramide F. O. et al.: M echanical Properties of a Polyester Fibre Glass Composite Fro m Figures 1., 2. and 3. it can be seen clearly that the modulus of elasticity, ult imate tensile strength, and elastic strain of the system respectively increases with increase in the increase in fibre glass volume fraction. The greater the modulus, the stiffer the material, or the smaller the elastic strain that results from the applicat ion of a given stress [7, 11]. As seen in Figure 1., it reveals that with the increase in fibre g lass volume in the composite samples, it becomes stiffer; considering Figure 3. it will be observed that the elastic strain increase with increase in fib re glass volu me fraction, it attains the maximu m value at around 0.25 fib re glass volume fraction, it there after reduces with further increase in fibre glass volume fraction. Figures 1 and 2 only show only little change (reduction) in modulus of elasticity and UTS respectively at 0.25 fibre glass volume fraction this could be attributed to the fact that glass fibres are characterized by their high strength, good temperature and corrosion resistance, and low price [12]. 44 43.5 Average Absorbed Energy (J) 43 42.5 42 41.5 41 0.05 0.1 0.15 0.2 0.25 0.3 Fibre Volume Fraction Figure 4. Effect of Fibre Glass Volume Fraction on the Average Absorbed Energy of the System Ultimate Tensile Strength (Nmm -2) 2 1.7 1.4 1.1 0.8 0.5 9 12 15 18 Strain (10-3) Figure 5. Ultimate Tensile Strength – Strain Curve of the System International Journal of Composite M aterials 2012, 2(6): 147-151 151 Figure 4. shows that the impact strength of the samples decreases with increase in fibre glass volume fraction; this is expected because glass is know with its poor resistance to impact force. Observing the Table 1 of data above, it will be seen clea rly that there is little change in the absorbed energy, this shows that the fibre glass contributes little to the impact strength of the composite. Glass and other brittle materials have a very low resistance to crack propagation, as there is no mechanis m to cope with the stress concentrations which arise fro m cracks and flaws. According to fracture mechanics, cracks greater than a critical length will propagate catastrophically under load. In bulk, glass is relatively weak, due to the many cracks wh ich fo rm when it cools. Figures 1., 2., 3. and 5., point to the fact that the composite resulting fro m the fibre glass- polyester is characterize by high toughness (resistance to crack propagation). In this case, a mechanism for crack stopping exists because of the presence of many fibre / matrix in terfaces . Science and Engineering, O.A.U., Ile-Ife) during the bench work of this research. REFERENCES [1] M angalgiri P.D. (1999) Composite materials for aerospace applications. Bulletin of M aterials Science;22(3): 657–664 [2] Lynn J.C. (1990) Polymer composite characterization for automotive structural applications. Journal of Composites Technology and Research;12(4):229–231. [3] Fabian P.E., Rice J.A., M unshi N.A., Humer K. and Weber H.W. (2002) Novel Radiation-Resistant Insulation Systems for Fusion M agnets. Fusion and Engineering Design; 61(1):795-799 [4] Wróbel, G. and Wierzbicki, Ł. (2007) Ultrasonic methods in diagnostics of glass-polyester composites, Journal of Achievements in M aterials and M anufacturing Engineering, Vol 20 (1-2) 4. Conclusions [5] Habak, E., (1991); M echanical behaviour of woven glass fibre reinforced composites under impact compression load. Composites 22(2):129–134. Fro m the discussion thus far, it can be concluded that: • ult imate tensile strength of the fibre glass polyester composite increases with increase in the fibre glass volume fraction • the Young’s modulus of elasticity of the co mposite increases with the fibre g lass volume fraction • the elastic strain of the co mposite increases with the fibre g lass volume fraction up to 0.25, and then subsequently decreases with further increase in fibre g lass volume fraction. • absorbed energy (impact strength) of the composite samples on the other hand reduces with increase in fibre glass volume fract ion. • generally, fibre g lass- polyester is characterize by high toughness (resistance to crack propagation). [6] Hsiao, H. M ., Daniel, I. M ., & Cordes, R.D. (1999). Strain rate effects on the transverse compressive and Shear behavior of unidirectional composites. Journal of Composite M aterials, 33, 1620-1642. 39903301703. [7] Aramide, F.O., Oladele, I.O. and Folorunso, D.O. (2009); Evaluation of the Effect of Fiber Volume Fraction on the M echanical Properties of a Polymer M atrix Composite Issue 14, 134-141 [8] Zhou, L.M . (1993); M icromechanical characterization of fibre/matrix interfaces Composites Science and Technology 48(1-4):227-236. [9] ASM Hand book, 1992, M aterials Park, Ohio, USA, ASM International, Volume 18. [10] Pascoe, M .W., (1973) “Plain and filled plastics materials in bearing: a review.” Tribology, Vol. 6 No. 5, pp. 184-190. ACKNOWLEDGEMENTS The authors would like to acknowledge the assistance rendered by Mr Alo F.I., Mr A minu, Mr Omo layo, Mr Olaoye and Mr So lanke, (all of the Depart ment o f Materials [11] Callister, W.D. (2000).M aterials science and Engineering: An Introduction. John Wiley and sons, Inc., New York [12] Dag Lukkassen and Annette M eidell, (2008); Advanced M aterials and Structures and their Fabrication Processes Book manuscript, Narvik University College, HiN, p68.

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