Effect of Thickness and Fiber Orientation on Flexural Strength of GFRP Composites Mahesh Chandrashekhar Swamy 1, Parmeshwar Patil 2, Shivaji D. Chame 3, 1 Associate Prof., Dept. of Mechanical Engg., M.S.Bidve Engg. College, Latur (SRTMU, Nanded) 2 Asst. Prof., Dept. of Mechanical Engg., G.N.D. Engg. College, Bidar (VTU, Belgavi) 3 PG Student, M.E. Machine Design, M.S.Bidve Engg. College, Latur (SRTMU, Nanded) Abstract This paper examines flexural strength of E- glass/epoxy composite laminates. The specimens were made from three different fiber orientations (i) Bi woven glass fibers (ii) Unidirectional glass fiber or 1D and (iii) Bi directional glass fiber or 2D with thicknesses of 2, 4 and 6 each.these specimens were tested for flexural strength in three point bending test fixture according to ASTM D790 to evaluate the flexural properties. The result shows that, for same thickness unidirectional glass/epoxy composite laminates have more flexural strength over other types of laminates. Keywords: Unidirectional, Bidirectional, Bi woven Glass Epoxy laminates, Flexural Strength, Three point Bending Machine. Introduction Composite materials have growing demand for applications in different areas like aerospace, automotive, marine, transportation and bridges in civil engineering. Structural composite is a mixture of two or more constituents (or phases) fiber and matrix with different physical/chemical properties at the macroscopic or microscopic scale. Fibers are the principal load-carrying constituents while the surrounding matrix helps to keep them in desired location and orientation and also act as a load transfer medium between them. The designers are in search of materials which withstand the effect of all variety of loading conditions and at the same time at a very competitive price. The composites are complex material and their properties vary as the constituents change in any of its parameters like fiber orientation, stacking sequence, fiber NCADOMS-2016 Special Issue 1 Page 83
volume fraction or the matrix and the method of fabrication. Hence, in the present paper an effort is made to characterize the composites by designing the testing equipments, test procedures and more importantly careful conduction of tests. An experimental investigation was conducted by K.G Satish et al. [1] to study the effect of hybrid composite specimen subject to in-plane tensile and compressive loading. From the investigations it is revealed that, the specimens with higher percentage of steel sustain greater loads & also the strengths are superior in case of 0/90 oriented specimen. By this they come to know the laminated specimens with higher percentage of steel sustain greater loads irrespective of fiber orientations. Further the specimens sustain greater loads in 0/90 specimens than in other orientations thus can be stated that fiber orientation is a significant factor. Also the change in compressive strength is quite marginal from 30-45% of steel content due to poor interfacial bonding resulting into large de lamination and failure of the laminated specimens. Keshavamurthy Y C et al. [2] have investigated the tensile properties of fiber reinforced angle ply laminated composites. The tensile properties of Glass/Epoxy with 0 0 fiber orientation yielded in high strength when compared with 30 0 & 45 0 for the same load, size & shape. P. Feraboli et al. [3] investigated inter laminar shear strength of carbon/ epoxy laminates. The finite element analyses were developed using ANSYS software, allowing for better insight on the mechanics of de lamination in four-point bending, and showed extremely good agreement with the experimental values. O.Velecela et al.[4] studied steady state quasi-static compression of GFRP monolithic laminates & sandwich panels made of randomly oriented continuous filament mat. The effect of facing / laminate thickness trigger collapse system and aspect ratio on their failure mechanism & their energy absorption capabilities examined. The experimental data showed, high value of energy absorbed per unit mass were predominant failure of the thickest monolithic laminates. Momchil Dimchev et al. [5] studied the effect of carbon nano-fibers on the tensile and compression properties of hollow particles filled composites. The result of this study showed that the addition of 0.25wt. % carbon nano-fibers result in improvement in tensile modulus and strength compared to similar syntactic foam compositions that did not contain nano-fibers. R Velmurugan et al,[6] have studied the mechanical properties of glass/palm fiber NCADOMS-2016 Special Issue 1 Page 84
waste sandwich composites. The tensile, flexural, shear and impact properties were studied and found 58-65-wt% fibers showed good flexural strength. S. Channabasavaraju et al, [7] evaluated tensile and flexural properties of glass, graphite and Kevlar fiber reinforced polymer matrix composites. The results have showed the variation in the fiber types has significant effect on the tensile and flexural properties of composite materials. Vinod B. et al, [8] have studied the effect of fiber orientation on the flexural properties of PALF reinforced bisphenol composites. The results revealed that, fiber orientation have great effect on the flexural properties of fiber reinforced polymer matrix composites. The objective of the present study is to characterize E- glass/epoxy laminates for flexural strength and to determine the effect of laminate thickness and fiber orientations on flexural strength. Materials and Processing The material and their properties selected for the study are listed in table.1 given below: Properties Reinforcing material Matrix material Hardener E-glass fiber of 360GSM Bidirectional woven roving, 1D and 2D Epoxy Resin (LY556 [Araldite] Density 2.55 g/cm 3 Young s modulus 72 Gpa, Tensile strength 2.2 Gpa, Tensile Elongation 2.4 % Aspect (visual) clear, pale yellow liquid Viscosity at 25 C (ISO 9371B) 10000-12000 [MPa s] Density at 25 C (ISO 1675) 1.15-1.20 [g/cm 3 ] HY 951 [Aradur] At 20 0 C 1:1 in water Boiling point > 200 o C, Thermal decomposition > 200 o C, Flash point : 110 0 C Density : 1 g/cm 3 Table.1 Materials and their properties The GFRP laminates are carefully fabricated by using hand lay-up technique of size 25cm X 25cm. The prepared laminates of E-glass/epoxy laminates are shown in Fig.1 NCADOMS-2016 Special Issue 1 Page 85
Bidirectional woven roving laminate 1D laminate 2D laminate (0-90 0 ) Fig. 1: Fabricated laminates Preparation of samples for flexural test as per ASTM: D 790 According to ASTM D 790 the specimen dimensions for the flexural strength are: the support span should be 16 times the depth of the beam. Specimen width shall not exceed one fourth of the support span for the specimen greater than 3.2 depth. The specimen shall be long enough to allow for over hanging on each end of at least 10 % of the support span. The specimens of GFRP laminates are prepared according to the following dimensions. Sample specimens according to ASTM D790 are shown in fig. 2. For thickness, D =2, length L = 16D = 16 X 2= 32, width B= L/4= 32/4 = 8 For thickness, D =4, length L = 16D = 16 X 4= 64, width B= L/4= 64/4 =16 For thickness, D =6, length L = 16D = 16 X 6= 96, width B= L/4= 96/4 =24 Bidirectional woven roving fiber with 0-90 0 orientation Specimens of unidirectional (1D&2D) fiber NCADOMS-2016 Special Issue 1 Page 86
Fig. 2 Specimens for flexural test Flexural Strength Flexural strength is a material s ability to resist deformation under load. In this project the flexural testing was performed on the bidirectional woven roving glass/epoxy specimens and 1D, 2D glass/epoxy composite specimens of size 75x12.7x2, 75x12.7x4 and 75x12.7x6. The specimens were subjected to 3 point bending test on computer controlled UTM of 10 kn at Raghavendra laboratory, Bangalore as per ASTM: D 790-10,7.2.1. The distance between the two supports was maintained at 40. The loading arrangement is shown in figure 3. The data is recorded during the 3-point bend test to evaluate the flexural strength. Fig.3 Flexural loading arrangement NCADOMS-2016 Special Issue 1 Page 87
RESULTS AND DISCUSSION Flexural strength is a mechanical parameter for the material property, which measures the bending strength or fracture strength of the materials. It is the ability of the material to resist deformation under loading, this is also called as 3-point bending test The flexural strength is calculated based on the peak load obtained in the flexural test (3 point bending test) using the equation (a). σ = 3FL/2bd 2 ------------------------------------------------------------------ (a) Where, σ = Flexural strength, F= Load at fracture point in N, b= width of rectangular section, d= thickness of rectangular section Flexural strain of polymer matrix composites is evaluated by equation (b). e = 6Dd/L 2 ------------------------------------------------------------------------(b) Where, e = Flexural strain at the outer surface of the laminate D = Maximum deflection of the center of the beam in d = Depth or thickness in L = Support span in Flexural results of bidirectional woven roving glass/epoxy composite laminates. The calculated values of flexural strength and strain are tabulated in table 2. SL No. Specimen Maximum Flexural Flexural Thickness, Peak Load, N deflection D, Strength, Mpa strain, 1 2 266.03 2.6 195.7 0.02437 2 4 1100.00 3.0 226.4 0.04500 NCADOMS-2016 Special Issue 1 Page 88
3 6 3700.00 3.5 312.5 0.07875 Table 2. Flexural results of bidirectional woven roving glass/epoxy composite laminates Flexural results of unidirectional (1D) glass/epoxy composite laminates. The calculated values of flexural strength and strain are tabulated in table 3. SL No. Specimen Maximum Flexural Flexural Thickness, Peak Load, N deflection D, Strength, Mpa strain, 1 2 992.10 7.086 729.82 0.0664 2 4 2983.42 9.112 857.30 0.1367 3 6 7756.89 10.83 990.66 0.2436 Table 3. Flexural results of unidirectional (1D) glass/epoxy composite laminates Flexural results of 2D (0-90 0 ) glass/epoxy composite laminates. The calculated values of flexural strength and strain are tabulated in table 4. SL No. Specimen Maximum Flexural Flexural Thickness, Peak Load, N deflection D, Strength, Mpa strain, 1 2 542.82 8.1375 399.32 0.0762 2 4 1522.89 8.6530 437.61 0.1290 3 6 4008.24 9.0170 511.90 0.2028 Table 4. Flexural results of 2D (0-90 0 ) glass/epoxy composite laminates NCADOMS-2016 Special Issue 1 Page 89
Fig. 4: Effect of thickness on the flexural strength of bidirectional woven roving laminates Fig. 5: Effect of thickness on the flexural strength of unidirectional (1D) laminates NCADOMS-2016 Special Issue 1 Page 90
Fig. 6: Effect of thickness on the flexural strength of 2D (0-90 0 ) laminates The effect of thickness on flexural strength of bidirectional woven roving glass/epoxy composite is shown in fig. 4 which reveals that, the flexural strength increased with increase in the thickness of laminate. The maximum value of flexural strength was 312.5 MPa for 6 thick laminate. The effect of thickness on flexural strength of unidirectional (1D) glass/epoxy composite is shown in fig. 5 which shows that, the flexural strength increased with increase in the thickness of laminate. The maximum value of flexural strength was 7756.89 MPa for 6 thick laminate. The effect of thickness on flexural strength of 2D (0-90 0 ) glass/epoxy composite laminates is shown in fig. 6 which shows that, the flexural strength increased with increase in the thickness of laminate. The maximum value of flexural strength was 511.90 MPa for 6 thick laminate. CONCLUSIONS Based on the experimental results of flexural strength and ILSS of glass/epoxy composite laminates of different fiber orientation, the following conclusions are drawn. NCADOMS-2016 Special Issue 1 Page 91
The thickness of specimens has significant effect on the flexural strength and it increases with thickness of laminates Among the three types of fiber orientations, the unidirectional (1D) glass epoxy laminates are found to have more flexural strength than others. The bidirectional woven roving s glass epoxy laminates have least strengths among the three types. REFERENCES [1] K. G. Satis, B. Siddeswarappa2, K. Mohamed Kaleemulla Characterization of In-Plane Mechanical Properties of Laminated Hybrid Composites Journal of Minerals & Materials Characterization & Engineering, Vol. 9, No.2, pp.105-114, 2010 [2] Keshavamurthy Y C, Dr. Nanjundaradhya N V, Dr. Ramesh S Sharma,Dr. R S Kulkarni, Investigation of Tensile Properties of Fiber Reinforced Angle Ply laminated composites International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459,Volume 2, Issue4, April 2012) [3] PAOLO FERABOLI, ELOF PEITSO, FRANCESCO D, ELEO ANDTYLER C, EVELAND Characterization of Prepreg-Based Discontinuous Carbon Fiber/Epoxy Systems, Aeronautics and Astronautics, University of Washington Box 352400, Seattle, WA 98195-2400, USA [4] O. Velecela, M. S. Found, C. Soutis Crushing energy absorption of GFRP sandwich panels and corresponding monolithic laminates Composites Part A-applied Science and Manufacturing - COMPOS PART A-APPL SCI MANUF 01/2007; 38(4):1149-1158. DOI:10.1016/j.compositesa.2006.06.002 [5] Momchil Dimchev, Ryan Caeti, Nikhil Gupta, Effect of carbon nanofibers on tensile and compressive characteristics of hollow particle filled composites Composite Materials and Mechanics Laboratory, Department of Mechanical and Aerospace Engineering, Polytechnic Institute of New York University, Brooklyn, NY 11201, USA Materials & Design - MATER DESIGN 01/2010; 31(3):1332-1337. DOI:10.1016/j.matdes.2009.09.007 [6] R Velmurgan, V Manikandan, Mechanical properties of glass/palmyra fiber waste sandwich composite materials, Indian Journal of Engineering & Material sciences, Vol. 12, December 2005, pp.563-570 NCADOMS-2016 Special Issue 1 Page 92
[7] S Channabasavaraju, Dr. H.K Shivanad, Santhosh Kumar S, Evaluation of tensile and flexural properties of polymer matrix composites, International journal of Modern Engineering research(ijmer) vol. 3 Issue5, Spe-Oct.2013 pp-3317-3180, ISSN:2249-6645 [8] Vonod B, Sudev L J, Effect of fiber orientation on the flexural properties of PALF reinforced bisphenol composites, International Journal of science and engineering applications, Volume 2, Issue 8,2013 ISSN-2319-7560 NCADOMS-2016 Special Issue 1 Page 93