SELCUK UNIVERSITY
INTERNATIONAL CONFERENCE ON ADVANCED TECHNOLOGY & SCIENCES
PROCEEDINGS BOOK
Mechanical Engineering
September 01-03, 2016 Konya / TURKEY
International Conference on Advanced Technology & Sciences
3th International Conference, ICAT’16 Konya, Turkey, September 01-03, 2016 Proceedings
Editors Ismail SARITAS Omer Faruk BAY Kemal TUTUNCU
International Conference on Advanced Technology & Sciences, ICAT’16 Proceedings of the 3th International Conference on Advanced Technology & Sciences Konya, Turkey, September 01-03, 2016 * This conference is supported by TUBITAK (The Scientific & Technological Research Council of Turkey) 2223- B Support Program for Scientific Activities.
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Tensile and flexural behavior of nano-silica modified carbon/Kevlar hybrid composites Ahmet Erkliğ*, Arkan Jabbar*, Mohamad Alsaadi*+ *
Gaziantep University, Faculty of Engineering, Mechanical Engineering Department, Gaziantep 27310, Turkey.
+
University of Technology, Materials Engineering Department, Baghdad 10066, Iraq
[email protected] ,
[email protected] [email protected] incorporation of a well-disperse nano-silica improved the tensile modulus and strength of about 38% and 24%, respectively. Singh et al. [6] presented a review of the kevlar fiber characterizations. They indicated that the anisotropic nature of the Kevlar fiber was due to its unique properties such as higher strength to mass ratio and modulus. Manjunatha [7] examined the tensile and fatigue behavior of nano-silica particles modified glass fiber reinforced epoxy (GFRP) composite, the tensile strength increased by about 19% and 5%, whereas the modulus increased by about 17% and 7% in the bulk epoxy and GFRP composite. Ferreira et al. [8] reported that the addition of nano clays within woven bidirectional Kevlar fabric/epoxy composites reduced the strength and increased the stiffness of the composite in both tension and bend loading, respectively. Dong et al. [9] studied the flexural behavior of hybrid composites reinforced by S-2 glass and T700S carbon fibers in an intra-ply configuration. The specimens were manufactured using the hand lay-up process and tested in a three-point bend configuration. It was shown that, utilization of intra-ply hybridization could improve the flexural strength and flexural modulus. Pincheira et al. [10] investigated the effects of aramid fibers contribution on mechanical properties of a twill weave hybrid carbon– aramid fiber reinforce epoxy composite. They concluded that the presence of aramid fiber presents a more ductile response with respect to the carbon reinforcement. Woo and Kim [11] studied the high strain-rate failure characteristics of the carbon/Kevlar hybrid composite that subjected to compressive loading. They found the failure process of the carbon/Kevlar hybrid woven composite showed initial matrix fracture and then brittle carbon fiber breakage Subsequently, multiple failure mechanisms appeared, such as fiber-matrix debonding, fiber pull-out, excessive deformation and breakage in the Kevlar fiber tips including splitting and fibrillation. wan et al. [12] used the two-step surface treated carbon/Kevlar hybrid fibers-reinforced composite with varying fiber–matrix interfacial bonding to show a positive hybrid effect on flexural strength, indicating the existence of hybrid effect is related to the nature of fiber-matrix interface. Based on the above researches, researchers have been investigated tensile and flexural properties of the nano-particle modified composite laminates. To the best of found knowledge, researchers in literature did not inspect the effect
Abstract—The purpose of this article is to investigate the effect of different particle contents of nano-silica on the tensile and flexural properties of intralaminar carbon/Kevlar hybrid composites. Twill 2/2 woven carbon/Kevlar fiber was used as reinforced fiber with epoxy resin. Five weight fractions (0.5%, 1%, 1.5%, 2.5% and 3%) were used for production of laminated composites. Then, test samples were produced according to ASTM standards. Results showed that addition of nano-silica to carbon/Kevlar composite increased the tensile and flexural strength. Nano-silica contents of 3 wt% gave the highest tensile strength and 1.5 wt% gave the highest flexural strength among the other ratios. Keywords— Carbon/Kevlar fiber, nano-silica, hybrid composite.
I. INTRODUCTION In recently years, the applications of polymer composites have been increased and that attributed to mechanical properties improvement by adding high strength fibers to brittle matrix. Furthermore, this improvement may be increased with using rigid inorganic particulate filler within polymer matrix, which leads to increase the applications of polymer base composites. These applications can be very useful such as medical industries, renewable energy application, automobile, aviation and aerospace. Some researchers [1, 2] toughened epoxy matrix by incorporating thermoplastics and rubber particles. Both of them cause mixture viscosity elevation after mixing with epoxy resin, which lead to difficulties in lamination process and thus decreasing in modulus and strength values. Therefore, using rigid particle can improve the mechanical properties of composite. Marjetka and conradi [3] concluded that the filled of a polymer matrix with nano-silica particles gives significant increase in the modulus and strength of the matrix to the overall composite properties. Alsaadi and Erkliğ [4] also reported similar findings, such that the maximum improvement of tensile strength, tensile modulus, flexural modulus and flexural strength were improved by17.8% for the 17.8%, 11.3%, 32.0% and 36.4% at nano-silica particle content of 1.0 wt% compared to unfilled polymer composite. Jumahata et al. [5] studied the effect of nano-silica with 5–25 wt% particle content on the tensile stress-strain results of epoxy A 40 wt% nano-silica/epoxy. They found that the
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of nano-silica content on tensile and flexural properties of intralaminar carbon/Kevlar fiber reinforced epoxy (CKRE) composite. In this work, the tensile and flexural of CKRE composite were calculated with the use of nano-silica particles. In addition, the nano-silica variation of 0.5, 1.0, 1.5, 2.5 and 3 wt% contents were incorporated with CKRE composites.
Temperature
Temperature (°C)
II. MATERIALS AND METHODS Epoxy risen (Momentive-MGS L285) mixed with the hardener (Momentive-MGS H285) by a stoichiometric ratio of 100:40. Carbon/Kevlar twill 2/2 woven with areal density of 190 g/m2 and thickness 0.23 mm are used as reinforcement in the lamina and it has high impact resistance and tensile strength. All above materials were supplied by DOST Chemical Industrial Raw Materials Industry, Turkey. Nanosilica was obtained from Grafen Chemical Industries, Turkey with a high purity 99.5%, average particle size of (15 nm), specific surface area (300 g/m2) and bulk density (0.05 g/cm3). Eight Layers of carbon/Kevlar were prepared to show hybridization effects. The composites prepared for this study by adding silica nanoparticles filler in epoxy resin with five different weight percentage fractions as 0.5, 1.0, 1.5, 2.5 and 3.0 wt%. Epoxy resin was mixed with nano-silica particles for 20 minutes after that the hardener was added and mixed to obtain homogeneity, afterword the mixture was poured upon the layers layer after layer to the last one (8 layers) (Fig. 1), then laminated fabrics was laid on the flat mold (Fig. 2) and subjected to 120 kPa pressure for 1 h curing time with 80°C temperature (Fig. 3), Then, the composite laminates were cooled to room temperature under pressure for three hours at least. Finally the composite laminate removed from the mold to get a fine finished composite plate.
Fig. 1 Hand lay-up process
90 80 70 60 50
Fig. 3 The curing process. 40
The produced composite laminate in size of 220 mm × 200 mm was cut to the required size specimens according to the standards ASTM D 638 [13] for tensile test and ASTM D 790 [14] for flexural test, by using CNC machine. The produced tensile and flexural test specimens were given in Fig. 4.
(a)
(b)
Fig. 4 (a) Tensile specimens, (b) flexural specimens.
III. MECHANICAL TESTS The tensile and flexural properties of the composite specimens were determined at room temperature using the Shimadzu testing machine AG-X series (Kyoto, Japan) (Fig. 5a and b). Suitable specimens were prepared with size of 165 × 13 mm for a gauge length of 50 mm for tensile test and 200 ×12.7 with span to thickness ratio of 32:1 for flexural test. The thickness of tensile and flexural specimens was in range of 2.5±0.1 mm due to variation of nano-silica content. The crosshead speed was 2 mm/min for tensile test and 3 mm/min for flexural test. At least four specimens were tested for each composite and the average value was depended. The flexural properties were determined from the test machine data’s by using the following equations.
Fig. 2 Production unit 2 3Pmax L D h D F 1 6 4 2bh 2 L L L
F
6 Dh L2
(1)
(2)
Where L, b and h are the span, width and depth of the specimen, respectively, D is the maximum deflection before failure and P is the load at a given point on the load-deflection curve.
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Therefore, the highest improvement of flexural strength was obtained at 1.5 wt% content of nano-silica with maximum increment of 54.2%. The flexural tests showed a linear response of the stress-strain curves (Fig. 7) of the studied composites, then the fracture was occurred and the flexural strength decreased gradually. This figure also indicates that the failure strain is significantly increased with addition of nano-silica particles. As shown in Fig. 8, the specimens failed at the specimen center by bending load that failure was started with matrix cracking then fibers breakage and carbon/Kevlar layers delamination between compression and tension sides.
a
TABLE I TENSILE AND FLEXURAL PROPERTIES OF CARBON/KEVLAR REINFORCED EPOXY COMPOSITE MODIFIED BY NANO- SILICA PARTICLES.
b
Composite type
NS content (wt%)
Tensile strength (MPa)
Elongation at break (%)
Flexural strength (MPa)
CKRE CKRE-NS0.5 CKRE-NS1 CKRE-NS1.5 CKRE-NS2.5 CKRE-NS3
0 0.5 1 1.5 2.5 3
372 (±07) 406 (±04) 429 (±10) 448 (±06) 491 (±12) 546 (±09)
2.77 (±0.09) 3.12 (±0.18) 2.98 (±0.10) 3.45 (±0.15) 3.27 (±0.12) 3.67 (±0.17)
428 (±10) 548 (±15) 581 (±17) 659 (±12) 526 (±09) 474 (±19)
Fig. 5 (a) Tensile specimen under tensile test using Shimadzu AG-X series testing machine. (b) Flexural test.
IV. RESULTS AND DISCUSSION Table I displays the tensile and flexural properties of CKRE and CKRE-NS composites for various nano-silica contents. As shown in Fig. 6 and corresponding data in Table I, the addition of nano-silica always improved composite tensile strength at the studied percentages. The maximum improvement in tensile strength is 46.8% at particle content 3 wt%. Moreover, the elongation at break also increased with the addition of nano-silica particles. Hence, the elongation at break increased by 32.5% with addition of nano-silica having 3wt%. All the specimens were broken without any nicking and the fracture surfaces were flat (Fig. 8), that means the specimens fail in a brittle fashion during tensile test. Besides, there was no effective reducing in the cross sectional area of the specimens. In addition, whether it was filled or unfilled with nano-silica particles, the tensile samples were failed at higher stress. This suggests that the nanofiller-matrix interaction is very strong therefore the nanocomposites exhibited higher strength compared to the pristine intralaminar hybrid composites. As shown in Table I and Fig. 7, flexural strength has been improved by addition of nano-silica particles to the CKRE. Hence, the composite flexural strength was increased from 428 MPa for unfilled CKRE to reach 659 MPa with nanosilica content of 1.5 wt%, afterword flexural strength follows the trend of decreasing to reach 474 MPa at content of 3 wt%.
Fig. 6 Tensile stress-strain curves of the composites.
This improvement of tensile and flexural properties attributed to the chemical compatibility of the nano-silica particles with epoxy resin and S-glass fibers in the composite laminate system. Furthermore, the flexural properties were degraded when nano-silica content exceeded 1.5 wt% and that may be ascribed to the particle aggregation phenomena which forming weaknesses in composite laminate and decreasing flexural strength.
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[2]
M.R. Dadfar, F. Ghadami, “Effect of rubber modification on fracture toughness properties of glass reinforced hot cured epoxy composites,” Mater. Des., vol. 47(0), pp. 16–20, May 2013. [3] M. Cnradi,” Nano silica reinforced polymer composites,” Materials and technology, vol. 47, pp. 285–293, Mar. 2013. [4] M. Alsaadi, A. Erkliğ, “Mechanical properties and mixed-mode fracture toughness (i + iii) of silica nanoparticles reinforced polymer composites,” METECH conference, Istanbul, Turkey, pp. 6–15, Nov. 2015. [5] A. Jumahata,,C. Soutis, S. Abdullah , S. Kasolang, “Tensile Properties of Nanosilica/Epoxy Nanocomposites” Procedia Engineering, Vol. 41, pp. 1634-1640, 2012. [6] T. Singh, S. Samanta, “characterization of kevlar fiber and its composites” 4th International Conference on Materials Processing and Characterization, Materials Today: Proceedings, Vol. 2, pp. 1381– 1387, 2015. [7] C.M. Manjunatha, A.C. Taylor, A.J. Kinloch, S. Sprenger, “the tensile fatigue behavior of a silica nanoparticle-modified glass fibre reinforced epoxy composite,” Composites Science and Technology, Vol. 70, pp. 193-199, 2010. [8] J. Ferreira, P. Reis, J. Costa, M. Richardson, “Fatigue behaviour of Kevlar composites with nano clay-filled epoxy resin,” Frank Bauer a,∗, Roman -22-Flyunt a, Konstanze Czihal a, Helmut Length b2007. [9] C. Dong, I.J. Davies, “Optimal design for the flexural behaviour of glass and carbon fiber reinforced polymer hybrid composites,” Materials and Design, Vol. 37, pp. 450-457, 2012. [10] G. Pincheira, C. Canales, C. Medina,E. Fernandez, P. Flores, “Influence of aramid fibers on the mechanical behavior of a hybrid carbon–aramid–reinforced epoxy composite,” J Materials: Design and Applications, vol. 0, pp. 1–9, Nov. 2015. [11] SC. Woo, TW. Kim, “High strain-rate failure in carbon/Kevlar hybrid woven composites via a novel SHPB-AE coupled test,” Composites Part B, vol. 97, pp. 317–328, Dec. 2016.
Fig. 7 Flexural stress-strain curves of the composites.
(a)
[12] Y. Z. Wan, , J. J. Lian, Y. Huang, Y. L. Wang, G. C. Chen, “Two-step surface treatment of 3D braided carbon/Kevlar hybrid fabric and influence on mechanical performance of its composites,” Materials Science and Engineering: A, vol. 429(1), pp. 304-311, 2006. [13] ASTM D 638-10 2010 Standard Test Method for Tensile Properties of Plastics. [14] ASTM D 790-10 2010 Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials.
(b)
Fig. 8 Failed specimens (a) Tensile (b) Flexural.
V. CONCLUSIONS The effects of nano-silica particles with variation in content on tensile and flexural properties of the carbon/Kevlar fabric/epoxy composites were inspected. The highest improvement of the tensile and flexural strength for CKRENS composites was obtained at nano-silica content of 3 and 1.5 wt%, with maximum increment of 46.8% and 54.2%, respectively. Generally, the tensile and flexural failure strains of the CKRE-NS composites were increased. Indeed the above mechanical properties were improved with nano-silica addition. Hence, this performance indicates the good adhesion strength and chemical compatibility of the nano-silica particles with carbon/Kevlar fabric/epoxy composite system. REFERENCES [1]
V. D.Heijden, L. Daelemans, D. B. Schoenmaker, D. L. Baere, H. Rachier, V. W. Paepegem, “ interlaminar toughening of resin transfer moulded glass fibre epoxy laminates by polycaprolactone electrospun nanofibres,” Compos. Sci. Technol., vol. 104 (19), pp. 66–73, Nov. 2014.
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