INVESTIGATION ON MECHANICAL BEHAVIOUR OF GLASS FIBER REINFORCED WITH POLYURETHANE FOAM AND HONEYCOMB

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1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 4, April 2018, pp , Article ID: IJMET_09_04_031 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed INVESTIGATION ON MECHANICAL BEHAVIOUR OF GLASS FIBER REINFORCED WITH POLYURETHANE FOAM AND HONEYCOMB D. V. Manidhar, Sai Krishna. V, Vishnu Prakash and Deepa. A School of Mechanical Engineering, VIT, Vellore, Tamil Nadu, India ABSTRACT The composite materials are used widely in our daily life in various forms. The employability of these sandwich composites in the aerospace, shipbuilding, construction of the bridges and different kind of architectures is increasing these days. To make the better sandwich composite with the combination of the glass fiber as skins and polyurethane foam (PUF), hexagonal structured honeycomb as a core is used and then tested. The fabrication of the sandwich composite is made using the vacuum bag molding technique. The fabricated samples are then tested using flexural test. The testing results which were obtained compared with the analysis done in the ANSYS. The main aim is to determine the better composite of the different foams. Keywords: Vacuum bag molding, glass fiber, flexural test, polyurethane foam, honeycomb. Cite this Article: D. V. Manidhar, Sai Krishna. V, Vishnu Prakash and Deepa. A, Investigation on Mechanical Behaviour of Glass Fiber Reinforced with Polyurethane Foam and Honeycomb, International Journal of Mechanical Engineering and Technology, 9(4), 2018, pp INTRODUCTION The composites are used for the various purposes to improve the mechanical properties and increase the usability in various fields. Sandwich composites are fabricated using the two thin layers as the skins and the core at the centre which is thicker. The skins can be made of the carbon fibre or the glass fibre and the core can be made of almost any material of structure. There are numerous studies that have been done on the fabrication of the sandwich composites using the various cores and the skins. The fabrication of the sandwich composite is using the polyurethane foam as the core and glass fibre as the skins is done. But there are mainly four kinds of core those are solid or foam, web, honeycomb and truss or corrugated editor@iaeme.com

2 Investigation on Mechanical Behaviour of Glass Fiber Reinforced with Polyurethane Foam and Honeycomb The fabrication is done using the vacuum bag moulding technique and they have done the compression testing and flexural test for different core materials [1]. The testing of the sandwich composite made of the polyurethene foam and the glass fibre was done [2]. The new composite is made and tested using the compression test. Then the results were analysed using the ABAQUS software [3]. Some researchers made the engineering structures like the wind turbines and many more which states that, in construction of the any structure we have to consider the many components like the in plane and out plane stresses [4]. The work has been done on the problems faced during the development of the honeycomb sandwich panel. This study is on the stresses that are acted on the honeycomb sandwich composite. To fabricate the honeycomb sandwich composite with the different thickness they have made the design process [5]. The work has been done with the polyurethane foam which reinforced with the coir fibre core. The characterisation was done on the composite where glass fibre is used as the core. Then the density test and the flexural test through which the mechanical properties were calculated [6]. The research was concentrated on the determination of the mechanical properties and the structures for the glass fibre reinforced plastic laminate composite which mainly employed in aero designs. The specimens are made using hand layup process and then be cured in the autoclave [7]. A comparative study on the mechanical properties of multilayer composite of anodized and non-anodized Al-foils alternatively sandwiched by hot rolling and performed hardness test, tensile strength, 3 point flexural test, optical microscope, x-ray diffraction technique, SEM analysis, energy dispersive spectrometry and concluded that these properties values were more than of pure material used as core [8]. The flexure behaviour of the sandwich composites in different positions has been researched [9]. The Flexure behaviour of the core formed at the different temparatures in wet and dry condition [10]. The fabrication of the sandwich composites with different thicknesses of the face sheets and varied span length has been done and tested the samples with three point and four point bend test [11]. The design of the sandwich composites for the heavier loads has been tested [12]. Presently we are manufacturing the sandwich composites using glass fibre as skins, polyurethane foam and honeycomb as the core material. These glass fibres are taken in the form of GFRP which is a reinforced polymer and used as the skins on top and bottom of the foam. This foam serves as the core material. This sandwich composite can be reinforced using different moulding processes like hot compression, hot rolling, hot vacuum bag moulding, vacuum bag moulding. The Vacuum bag moulding process is used for the reinforcement of the different layers of the composites. The sandwich composites usage has been increased drastically due to the advancement in the technology and due to the need of materials with better properties and wide range of applications. These sandwich composites were studied by the numerous scientists and technologists to employ them in their fields. These are mainly used in the construction of the aircrafts, ships, trains car doors etc., The main theme of the sandwich composites is that the outer layers or the face sheets are designed to withstand the bending load and the core is made to withstand the shear load. 2. EXPERIMENTAL SETUP In vacuum bag moulding we make the sandwich composite using the polyurethane foam, honeycomb as core and GFRP as the skins. This process is done using in a vacuum bag connected to the vacuum pump. The vacuum pump helps to achieve the vacuum required for the process which is one atmospheric pressure. The vacuum pump operates at voltage of 250V with a motor power of 750W. The maximum continuous time of the pump is 45 mins. Glass fibres are chosen due to the very good material properties. They are also resistant to the corrosive environment and high temperatures. The polyurethane foam and honeycomb editor@iaeme.com

3 D. V. Manidhar, Sai Krishna. V, Vishnu Prakash and Deepa. A have the very good material properties like thermal properties and strength to weight properties. The sandwich panels are made using the vacuum bag moulding and then tested using the three point bending test to determine the maximum stress that can be applied on the specimen. 3. EXPERIMENTAL WORK 3.1. VACUUM BAGGING The glass fiber and the core are kept on the mould along with the peel ply and breather on top. The stacked layers of composite from the wet layup process are placed in a vacuum bag and then closed on three sides. A vacuum connector valve is inserted through the bag with a dam at its base. Finally, the fourth side is sealed and vacuum hose connected to the connector valve. The number of layers that need to be used in the fabrication of the sandwich composite are calculated using the skin to core weight ratio and the volume of the epoxy need to be used. Sandwich composite with skin to core ratio of 1:3 is taken. The volume of fabric in skins is taken as 30%. The epoxy and hardener are taken as the ratio of the 10: FABRICATION The sandwich composite is designed using the Polyurethane foam and honeycomb structure using the above design considerations. The number of layers of glass fiber is taken as the 8 with the gsm of 220. The volume of the epoxy and hardener are cc and cc. But when we are fabricating the samples we take the more amount of the resin and hardener so that even if the epoxy gets wasted during the fabrication it will not affect the final sandwich panel. The figure 1 shown below is the picture that are taken during the vacuum bag molding of the sandwich panel and the figure 2 is picture taken after taking sandwich panel out from the vacuum bag. The vacuum through the valve opened, and the vacuum pump switches on. The pump may run for 40 min. It must ensure that the vacuum through the valve closed before the vacuum pump is turned off. The layup is left to cure at room temperature for hours. Figure 1 Vacuum bag molding Figure 2 Sandwich panel taken out from vacuum bag editor@iaeme.com

4 Investigation on Mechanical Behaviour of Glass Fiber Reinforced with Polyurethane Foam and Honeycomb 3.3. CUTTING OF SAMPLES The samples are cut down to the required dimensions using the length to width ratio. The obtained sandwich panel was measured and made the markings to the required dimensions. The markings are made giving some deviations so that the sample length doesn t become smaller after cutting down. The width of the sample is decided using the thickness of the panel after taking out from the vacuum bag. The width should be approximately double the thickness of the sample. The length should be decided considering the span length TESTING The flexural test method is used to determine the flexural strength of the composites. The samples are cut down to the dimensions that are suitable for the flexural test. Samples were tested using three point bending apparatus considering span length. Figures shown below represent the flexural test specimen under loading. The three samples of polyurethane and three samples of honeycomb composite were tested on the instron testing machine. During the test, Flexure Load vs. Flexure deflection of the beam was recorded. The figure 3 shows the flexure test of the PUF sample and figure 4 is the flexure test of the honeycomb sample. Figure 3 Flexure test of PUF sample Figure 4 Flexure test of Honeycomb sample 4. RESULTS AND DISCUSSIONS The 3 point bending test is used to calculate the flexural stress acting on the sample. In this test the sample is placed on the two cylinders and the load is applied on the top of the sample. As the forces applied on the sample at 3 different positions this test is called the 3 point bending test. The span length should be considered while performing the testing FLEXURE TEST FOR POLYUREATHANE FOAM AND HONEYCOMB The Flexure test is the three point bending test which was done on the universal testing machine. Though this test we get the graphs of the Flexure load versus flexure extension. The peak load that can be applied on the sample can be recorded along with the deflection of the sample from the neutral position. From those peak loads and the deflection, we can calculate the various values like the flexural rigidity, shear deflection, bending stress, normal stress and much more. The graph can be recorded during the testing against load and the deflection. Where the peak on the graph shows the maximum load that can be applied at the maximum deflection. The Table 1 shows all the graphs of the polyurethane foam and the honeycomb sandwich specimens editor@iaeme.com

5 D. V. Manidhar, Sai Krishna. V, Vishnu Prakash and Deepa. A Table 1 Flexure test values of the polyurethane foam and the Honeycomb Sample no. Flexure load vs Flexure extension Peak Load N Deflection Mm Polyurethane foam sample Honeycomb samples editor@iaeme.com

6 Investigation on Mechanical Behaviour of Glass Fiber Reinforced with Polyurethane Foam and Honeycomb 4.2. Calculations of the Polyurethane foam and Honeycomb The values of the Flexural Rigidity, Flexural Rigidity per unit width, Shear Deflection, Stress, Strength, Strength per unit width, Normal Stress are all shown in the Tables below. The Table 2 has the Polyurethane foam values, Table 3 has the Honeycomb values. Peak Load N Deflection Mm Flexural Rigidity Nmm Table 2 Calculation for Polyurethane foam Flexural Rigidity/ width Nmm 2 /m m 10 3 Shear Deflection Mm Stress N/mm 2 Strength Nmm Strength /width Nmm/ mm Normal Stress N/mm Peak Load N Deflection Mm Flexural Rigidity Nmm Table 3 Calculation for Honeycomb Flexural Rigidity/ width Nmm 2 / mm 10 3 Shear Deflection Mm Stress N/mm 2 Strength Nmm Strength /width Nmm/ mm Normal Stress N/mm Analysis of the PUF sandwich composite The analysis was done on the Polyurethane foam sample. The Three point bending test was done in the analysis. The picture shown below represents the analysis done in the ANSYS. The dimensions details were considered from the physical sample which was made and tested in the UTM machine. The test setup details were taken from experimental setup. The Figure 5 below shows the analysis of the polyurethane foam specimen. The mechanical properties of the sandwich composite structures fabricated with glass fiber reinforced with polyurethane (PUF) and honeycomb are determined. The individual behavior of the composites where polyurethane foam and honeycomb were used as core GFRP was used as face sheets was determined. The properties were determined by performing three point bending test on these materials in universal testing machine. The universal testing machine (UTM) provided values of load and the deflection for each sample. Graphs of Flexure load versus Flexure extension were plotted for each sample from the UTM. From the graph we determined the peak load corresponding to ultimate stress of each specimen editor@iaeme.com

7 D. V. Manidhar, Sai Krishna. V, Vishnu Prakash and Deepa. A Figure 5 Analysis of the PUF sandwich composite 5. CONCLUSION Form the graphs and the table we can conclude that, honeycomb has better properties compared to the PUF. Here for the peak load we noted the corresponding extension. We also noticed that honeycomb specimen was deformed to a quite larger extent than PUF specimen and it could still regain its original shape unlike PUF specimen which broke after ultimate point. From the Ansys analysis, it can be noted that for the given load the maximum normal stress is approximately equal to the normal stress that we got from the experimental calculations. At maximum load corresponding value of deflection, flexural rigidity, bending stress and normal stress are noted for PUF and honeycomb sample. For PUF Composite, there is not any specific trend is present.the highest value of flexural rigidity x10 6 N-mm2 is found at maximum load of N. Deflection at peak load and shear deflection is found to be match. Similarly the value bending stress and normal stress is also found to be similar. For Honeycomb, there is a specific trend is found. As the peak load increased, value of flexural rigidity is also increased and so as the values of bending stress, normal stress and shear deflection is also increased. The maximum value of flexural rigidity 54.4x10 6 N-mm 2 is found at N. The value bending stress and normal stress is also found to be similar. The future work, as the 3 point bending test done on these samples, different testings like impact test, compression test, and tensile tests can be done on all the composites. By changing the thickness of the core, the tests can be conducted and then compared between the different composites. REFERENCES [1] Sunith Babu, L. and Shivanand, H.K. Mechanical Characterization of PU based sandwich Composites with variation in core density. International Journal of Materials Science and Applications, 4(4), 2015, pp [2] Fam, A. and Sharaf, T. Flexural performance of sandwich panels comprising polyurethane core and GFRP skins and ribs of various configurations. Composite Structures, 92(12), 2010, pp [3] Mohamed, M., Anandan, S., Huo, Z., Birman, V., Volz, J. and Chandrashekhara, K. Manufacturing and characterization of polyurethane based sandwich composite structures. Composite Structures, 123, 2015, pp [4] Norlin, P. and Reuterlov, S. The role of sandwich composites in turbine blades. Reinforced Plastics (UK), 46(3), 2002, pp editor@iaeme.com

8 Investigation on Mechanical Behaviour of Glass Fiber Reinforced with Polyurethane Foam and Honeycomb [5] Liang, S. and Chen, H.L. Investigation on the square cell honeycomb structures under axial loading. Composite structures, 72(4), 2006, pp [6] Azmi, M.A., Abdullah, H.Z. and Idris, M.I. Properties of polyurethane foam/coconut coir fiber as a core material and as a sandwich composites component. In IOP Conference Series: Materials Science and Engineering 50(1), 2013, p.p , IOP Publishing. [7] Khairul fahmi bin rosli A study of glass fiber- reinforced plastics in aircraft industry thesis submitted to university Technical Malaysia Melaka, [8] Jovanović, M.T., Nenad, I.L.I.Ć., Cvijović-Alagić, I., Maksimović, V. and Slavica, Z.E.C. Multilayer aluminum composites prepared by rolling of pure and anodized aluminum foils. Transactions of Nonferrous Metals Society of China, 27(9), 2017, pp [9] Manalo, A.C., Aravinthan, T., Karunasena, W. and Islam, M.M. Flexural behaviour of structural fibre composite sandwich beams in flatwise and edgewise positions. Composite Structures, 92(4), 2010, pp [10] Mirzapour, A., Beheshty, M.H. and Vafayan, M. The response of sandwich panels with rigid polyurethane foam cores under flexural loading. Iranian polymer journal, 14(12), 2005, pp [11] Kumar, M.V. and Soragaon, B. Fabrication and evaluation of multilayered polyurethane foam core sandwich panels for static flexural stiffness. Procedia Engineering, 97, 2014, pp [12] Kim, J. and Swanson, S.R. Design of sandwich structures for concentrated loading. Composite Structures, 52(3-4), 2001, pp [13] Mathivanan Periasamy, Behavior of Tensile, Flexural and Interlaminar Shear Strength of Microfilled Aluminium-Glass Fiber Reinforced Plastic Sandwich Panels, International Journal of Mechanical Engineering and Technology, 7(6), 2016, pp editor@iaeme.com