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epoxy multiscale composite pipes
Composites Part B 96 (2016) 1e6
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Composites Part B journal homepage: www.elsevier.com/locate/compositesb
Evaluating the effectiveness of nanofillers in filament wound carbon/epoxy multiscale composite pipes Tugay Üstün a, Hasan Ulus a, Salim Egemen Karabulut a, Volkan Eskizeybek b, *, € Omer Sinan S¸ahin a, Ahmet Avcı a, Okan Demir a a b
Department of Mechanical Engineering, Selçuk University, Konya, Turkey Department of Materials Science and Engineering, Çanakkale Onsekiz Mart University, Çanakkale, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history: Received 3 August 2015 Accepted 6 April 2016 Available online 13 April 2016
The performance of filament wound (FW) composite pipes is considered to be fundamentally governed by fiber properties and winding angles; however, matrix dominated properties such as axial and hoop strengths are also responsible in design of FW composite pipes. This paper presents the experimental results of a project aiming to assess the benefits of addition of carbon nanotubes (CNTs) and/or boron nitride nanoplates (BNNPs) as nanofillers within epoxy matrix of FW carbon fiber composite pipes. The nanofillers enhance the burst and hoop strengths up to 17.0% and 31.7%, respectively, over the control samples. Failure analysis revealed that the morphologies of nanofillers play an important role on the matrix toughening and strengthening the fiberematrix interface. Highest mechanical performance of the multiscale composite pipes was obtained with the addition of CNTs and BNNPs within the epoxy matrix concurrently related with the synergetic effect of the two different nanofillers. © 2016 Elsevier Ltd. All rights reserved.
Keywords: A. Nano-structures B. Residual/Internal stress D. Mechanical Testing D. Fractography E. Filament winding
1. Introduction Filament wound (FW) fiber reinforced pipes have many advantages such as high specific stiffness and strength. The efficiency of filament winding process and above mentioned advantages have made this type of pipes good candidates for the storage of compressed hydrogen or of compressed and liquefied natural gas lines [1,2] Carbon fiber is a good choice for FW pipes because of its low density and high strength. Generally, FW composite pipes are made of carbon fiber/epoxy since smooth internal surface FW pipes lead lower friction during fluid flow. However carbon fiber reinforced plastics have some shortcomings such as brittleness and low resistance to crack propagation. Mechanical and failure behaviors of FW pipes have extensively investigated in the literature [3e9]. It is reported that mechanical properties mainly governed by fiber properties and winding parameters such as an optimum winding angle of 55 was recommended for close ended pipes [10,11]. It is well known that the mechanical properties of matrix become important since the damage of FW pipes initiates as matrix damage followed by formation of leakage path, delamination and
* Corresponding author. E-mail address: [email protected] (V. Eskizeybek). http://dx.doi.org/10.1016/j.compositesb.2016.04.031 1359-8368/© 2016 Elsevier Ltd. All rights reserved.
finally fiber breakage occurs [3,5,6]. Interfacial properties for fiber reinforced composites are a matrix dominant property and usually limit the design [15]. The addition of nanofillers was considered as the most efficient way to enhance mechanical properties of fiber reinforced polymer composites, since the combination of conventional fiber and nanofillers in polymer matrices had led to a new generation of multiscale, multifunctional, three-phase materials with high performance [12e14]. Among various nanofillers, carbon nanotubes (CNTs) have served as an ideal filler for high performance composites due to their unique physical properties like high strength and aspect ratio [15,16]. It is reported that interlaminar shear strength [17], fracture toughness [18e20] and load transfer ability [21] can be enhanced by addition of CNTs such as pullout, rupture, and crack bridging [22,23] mechanisms. Many researchers have focused on development of CNTs containing fiber reinforced polymers [24,25]. The effects of morphology and type of nano particles upon interfacial strength between matrix and reinforcement have been investigated [26e29]. In addition, the effects of volume fraction of the nano reinforcements [30] and dispersion quality [31] upon mechanical properties of materials have been also studied. Boron nitride has been paid attention due to its high thermal and low electrical conductivities [32e34]. The crystal structure of hexagonal boron nitride is very similar to graphite except for the
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difference in the stacking sequence of layers [35]. In our previous study [36], it was showed that boron nitride addition into epoxy resin can result in notable increase of tensile strength. It is reported that the highest strength increase has obtained at 0.3% BN content while highest toughness increase has been obtained at 0.5% BN content. The literature survey revealed that, the effects of nanofiller modification upon mechanical behaviors of FW pipes have received little attention. In this study, MWCNTs and/or BNNPs filled epoxy resin matrix FW carbon fiber composite pipes were successfully fabricated with winding angle of 55 , and the variation of burst and hoop strengths were evaluated with the standard tests. The effectiveness of nanofillers with different morphologies on damage development of carbon fiber composite pipes and their microreinforcing behavior were proposed.
Fig. 1. Filament winding process of carbon fiber/epoxy composite pipes. The inset represents winding angle as ±55 .
2. Experimental 2.1. Materials The nanofillers, MWCNTs (purity >95%, diameter 30e50 nm, length 10e30 mm) and BNNPs (diameter ~250 nm and thickness ~50 nm) were provided from Times Nano Company and BORTEK, respectively. The reinforcement, carbon fibers (800 tex) were purchased from DowAksa, Turkey. The preferred resin system is Araldite MY 740/HY 918/DY062 (Vantico Ltd) bisphenol-A epoxy resin system with 100:85:0.5 weight ratios. 2.2. Fabrication of the FW composite pipes In collaboration with a manufacturer of composite pipes and tubes, carbon fiber reinforced epoxy composite pipes were manufactured by filament winding to allow experimental manipulation of the fabrication process. For getting a control group one group of pipes were produced without adding nanofillers. The amounts of nano particles were chosen based on our previous study [41]. Firstly, the epoxy resin system with agents was prepared, following, the required amount of nanofillers were added into the epoxy resin and mixed mechanically for 30 min and additional 30 min with ultrasonically. The temperature of epoxy resin was maintained as 35 C in order to reduce the viscosity of resin for obtaining complete wetting and better saturation. Table 1 shows the composition of nanofiller added epoxy resin used for filament winding operation. Secondly, FW carbon fiber composite pipes were fabricated using a filament winding machine at the winding angle ±55 on a preheated (60 C) mandrel as shown Fig. 1. The pipes were cured in an oven for 80 C/2 h þ 120 C/4 h, and then cooled down to room temperature, subsequently. The average internal diameter and wall thickness of filament wound pipes were measured as 72 mm and 3 mm, respectively.
standards. A lab made open ended apparatus was used to utilize the short time hydraulic burst pressure. The apparatus allows the pipe to shrink and expand in diameter freely which results regarding the axial stress as zero (Fig. 2). The internal pressure was generated by a PLC controlled hydraulic pump. During the tests, the pressure was continuously and uniformly increased until failure occurs. Test durations were measured until specimen fails to specify loading rates individually in order to develop burst damage within the range of 60 and 70 s of loading time for all specimens. The burst strengths are also determined according to Equation (2)
S ¼ Pðd þ tÞ=2t Where;
(1)
S hoop stress (MPa), P internal pressure (MPa), d average inside diameter (mm), t average wall thickness (mm). So, the burst pressures have been converted to burst strength values.
2.3. Characterizations 2.3.1. Burst pressure tests The short time hydraulic burst pressure tests were performed with at least five samples according to ASTM D1599-99 Table 1 Compositions of modified epoxy resin. Case
% MWCNT (by weight)
% BNNP (by weight)
Epoxy
1 2 3 4
0 0.3 0 0.3
0 0 0.5 0.5
All Of Remaining Remaining Remaining
Fig. 2. Open ended short time hydraulic burst pressure test apparatus with schematic presentation showing the fluid input during bust tests.
T. Üstün et al. / Composites Part B 96 (2016) 1e6
2.3.2. The tensile hoop tests The hoop tensile strength tests were performed with using special apparatus which is described to ASTM D-2290-12 standard. By definition, the hoop strength of tubes was measured by loading 1.27 cm wide rings cut from the tubes using a split-D fixture. In this loading method, two semi-circular metal inserts are pulled apart using a pin and clevis arrangement to apply load in the hoop direction. After the prepared samples were lubricated according to the standard in order to reduce friction during test, the samples were connected semicircular support bearings. The rings were loaded at 1 mm/min in tension while recording the strains at 10 Hz. The hoop strength is described by;
sa ¼ Pb =2Am
(2)
Where;
sa apparent yield or ultimate tensile stress of the specimen (MPa), P maximum or breaking load, or both (N), Am minimum cross-sectional area of the two measurements. 2.3.3. Fracture surface analysis A Zeiss Evo LS 10 scanning electron microscope (SEM) was used to examine surface morphology of the CNT modified PWGFs and the fracture surfaces of specimens. The samples were sputter coated with 4 nm thick gold layer and imaged at an acceleration voltage of 15e25 kV. 3. Results and discussions 3.1. The burst strength The burst pressure test results are given in Fig. 3. The burst strength of CF/epoxy pipes was obtained as 410 MPa. Moreover, the CNTs and BNNPs modified CF pipes showed higher burst strengths. The burst strengths were enhanced by 4.8%, 11.0% and 17.0%, with the addition of CNTs, BNNPs and CNTs-BNNPs into epoxy matrix respectively. The enhancement was consisted with the results of our previous works [41]. It is well known that modifying polymer matrix with nanofillers enhances primarily mechanical properties by generating multiscale and multifunctional materials with higher performance. Note, CNTs and BNNPs with different physical and chemical properties were used to modify CF/epoxy composite pipes to relate their characteristic properties particularly in the filament wounded CF pipe. It is clear that CNTs modification of the epoxy matrix results higher burst strength than BNNPs although the nanofiller amount of CNTs is comparatively less with respect to
Fig. 3. Short time internal pressure test results, burst pressures and hoop strengths.
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BNNPs. Based on these results, it is evident that the physical properties of nanofillers within the matrix play a key role on improving mechanical performance [37]. The higher mechanical performance of CNTs modified hybrid pipes with respect to BNNPs/ epoxy CF pipes can be attributed higher mechanical properties of CNTs rather than BNNPs [38e40]. In addition, the difference in morphologies of nanofillers governed toughening mechanisms such as crack bridging and pullout for CNTs added hybrid pipes while crack pinning and bifurcation for BNNPs modified hybrid pipes could also lead to the difference as obtained by the burst tests [36,41]. However, CNTs-BNNPs modified hybrid composite pipes showed highest burst stress. It implied that reinforcing mechanisms of both nanofillers as mentioned above on static burst performance should contribute concurrently as synergetic effect while increased amount of nanofillers could be effectively dispersed within the matrix. Generally, all the samples exhibit characteristic failure properties of fiber reinforced composite pipes in macro-scale. Fig. 4 represents images of the neat and hybrid carbon fiber pipes failed during burst pressure tests. The main failure mechanism for the all samples was stated as intensive fiber damage occurred with unsteady crack propagation around the leakage region of the pipe. Note, the black color nature of the carbon fiber composite pipes limits to observe early stages of failure; however, micro cracking and crack coalescence at radial direction originated oil leakage was clearly seen before pipe failure. Conversely, similar failure behaviors stated for the test samples, different crack propagation characteristics were observed to be related with the type of nanofiller within the epoxy matrix. Two types of crack propagation were identified from failed specimens. The crack propagation through fiber axis indicates fiberematrix interface debonding while fiber breakage in axial direction of pipe was related with hoop stress. Several observations can be made regarding failed samples after bust tests. The failure of control samples subjected to internal pressure progressed with unsteady crack propagation along both of fiber and pipe axes. This characteristic crack propagation behavior can be explained by morphological and dimensional changes of the pipes upon internal pressure loading. It is clearly observed that the diameter of the pipes increased; consequently, bending occurred with increasing internal pressure characteristic bottleneck effect around the ends of pipes. Due to the nature of bending, axial tensile and compression regions exist at the cross-section of pipe leading different stress conditions [9,42]. However, the bending dominated failure of the filament wound composite pipes is specifically controlled by winding angle. In the case of ±55 of winding angle, shear or transverse failure would occur at the tensile side of the pipe since compression side is subjected to buckling which inhibits the increased value of circumferential stress due to internal pressure [42]. The proposed loading scenario on the tube wall and fiber bundles was represented in Fig. 5. In our case, all the pipes failed from tensile side of the pipe with a leakage indicating matrix cracking started at the inner surface of pipe and propagated radially through outer surface. Previous investigations including authors' [43e47] indicated that nanofillers used for matrix modification of conventional composites enhance the energy absorption characteristics due to increased interfacial bonding, crack pinning [48]. Nanofillers constrain the matrix deformation less than micro particles [31] and result in better ductility and toughness. Nanofillers, nano-particles or nano-platelets can stop the crack propagation along the original direction [48] and also result in crack branching which results in toughening if agglomeration is minimized [49]. Applied high internal pressure results in change of the circular form of the pipe cross-section due to deformations related with increased diameter and bending deflections after loading. Moreover, the diametrical
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Fig. 4. Burst failure of the carbon fiber/epoxy composite pipe samples. The arrows show the direction of fiber and pipe axes; a) control sample without nanofiller additives, b) CNTs added multi scale composite pipe sample, c) BNNPs added multi scale composite pipe sample, d) CNTs and BNNPs added hybrid multi scale composite pipe sample.
Fig. 5. Schematic presentation of the proposed loading state of carbon fiber/epoxy composite pipes subjected to internal pressure.
expansion of the pipe lead fiber debonding due to increased shear stress between the fiber bundles. The CNTs and BNNPs modification of epoxy matrix also contributed to enhance resistance over shear deformations of pipes. So, enhanced burst strength values were obtained with nanofiller addition into polymer matrix. Specifically, branched crack propagation along axial direction of pipe was observed for the CNTs and BNNTs added hybrid pipes after failure indicating improved fiberematrix interface properties. We observed tendency to hoop stress dominated catastrophic failure for the CNTs and BNNPs modified pipes rather than shear stress dominated failure along fiber direction as identified for the unmodified composite pipes. SEM is utilized to discover damage formation and progression of carbon fiber pipes in micro scale. We mainly focused on fiberematrix interface since the nanofillers addition into matrix enhances the adhesion between fiber and matrix and the morphology around the fibers should be different with respect to unmodified composite pipes. Typical SEM images of fracture surfaces' after bust test were represented in Fig. 6. Fig. 6a represents pulled-out fibers from epoxy matrix for control sample. The clear evidence of catastrophic brittle failure beyond unsteady crack growth can be seen with individually standing fractured carbon fibers. Moreover,
smooth surfaces of pulled-out fibers indicate that shear stress at the interface overcome interfacial strength and resulted interface debonding during crack propagation. However, the fracture surfaces of CNTs and BNNPs modified pipes exhibit relatively rougher surfaces due to presence of more resin rich zones in between the fibers attributed to improved adhesion at the fiberematrix interface (Fig. 6b). The partial epoxy ruptures at the pulled out fiber slots are an evidence of better interfacial interactions for the hybrid composite pipes. Higher magnification SEM images of fracture surfaces confirm the improved interfacial adhesion with CNT and BNNPs addition of epoxy matrix. Fig. 6c shows the pulled-out fiber surfaces from control samples after failure at higher magnifications. The surfaces of fibers are clean as shown by arrows indicating adhesion failure at the interface due to weak interfacial strength. On the other hand, matrix coated carbon fibers as indicated by arrows were observed for the nanofiller added composite pipes as seen in Fig. 6d. According to this observation, the addition of nanofillers enhances the resistance of shear failure at the interface by revealing improved interfacial strength and force the crack to advance through surrounding matrix instead of interface region. These results clearly express that the addition of CNTs and BNNPs into epoxy matrix improves especially matrix dominated properties of carbon fiber pipes, and therefore, mechanical properties such as bust strength enhances. 3.2. The tensile hoop strength The results of hoop tensile strength are given in Fig. 7. The average hoop tensile strength values for unmodified pipes are calculated as 377 MPa. The calculated hoop strengths were enhanced as 11.0%, 26.2% and 31.7% with BNNPs, CNTs and CNTsBNNPs modification of epoxy matrix, respectively. In general, the obtained data consisted with the burst pressure tests indicating the tests conducted correctly. The samples were exhibit similar failure behavior characteristics compared to burst tests, and again, the effect of nanofillers on crack propagation behavior revealed itself during failure of samples (Fig. 8). The crack propagation of control samples started from the
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Fig. 6. SEM images of the bust test fracture surfaces of fabricated multi-scale hybrid composite pipes a) control sample without nanofiller additives, b) CNTs and BNNPs added hybrid multi scale composite pipe sample, c) high magnification SEM image of pulled fibers captured from control sample, d) high magnification SEM image of pulled fibers captured from CNTs and BNNPs added hybrid multi scale composite pipe sample (The arrows in the figures show the pulled out fibers).
fiberematrix interface for unmodified composite pipes. On the other hand, the CNT, BNNP and CNT-BNNP modified samples failed with intensive fiber breakage since the crack propagation developed through parallel to hoop axis. The macroscopic failure behaviors of the hoop samples indicate that the addition nanofillers within the epoxy matrix improved mechanical properties of matrix and adhesion at the fiberematrix interface. In detail, it can be said that crack bifurcation and branching mechanisms were frequently observed for CNT modified samples rather than BNNPs modified samples. We believe the CNT modification also enhances the ductility of epoxy matrix or bridging cracks in micro scale, and thereby, unsteady state crack propagation tendency of samples decreases. 4. Conclusion
Fig. 7. The tensile hoop test results of samples.
edges and progressed through axial direction of hoop. However, the crack propagated in fiber direction with increasing load and the failure of hoops occurred as fiber breakage, subsequently. This observation supports our statements about relatively weak
The contribution of adding nanofillers within the polymer matrix for the FW carbon/epoxy composite pipes were systematically evaluated in details. The addition of MWCNTs and BNNPs enhanced mechanical properties including burst and hoop strengths of FW carbon/epoxy composite pipes. Specifically, burst strength of the multiscale composite pipes was improved barely with addition nanofillers (0.5 BNNPsþ0.3 MWCNTs %wt) up to 17.0% since the burst strength of fiber reinforced composite pipes is mainly fiber dominated mechanical property. However, hoop strength of the
Fig. 8. Appearance of test specimens before and after the hoop tensile test representing crack propagation behaviors as depicted with solid lines.
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hybrid pipes was raised to 494 MPa, that is, a 31% increase over that of composite pipes without nanofillers. The performance of CNTs added pipes was higher than BNNPs reinforced multiscale composite pipes for both of burst and tensile hoop tests which is attributed to higher mechanical properties and 1D morphology leading better interfacial adhesion due to their high surface area of CNTs compared with BNNPs. Interestingly, the different morphologies of the nanofillers generated a synergetic effect when those of nanofillers was added into epoxy matrix concurrently; and consequently, the micro crack initiation and the corresponding propagation stages were delayed with different micro mechanisms such as crack bridging and bifurcation. Fracture surface analysis supported the positive effects of nanofillers on interfacial adhesion of carbon fiber and epoxy matrix. For future consideration, both additives should be implemented to the FW carbon fiber/epoxy composite pipes to test for fatigue performance and to reveal the contribution of nanofillers on energy absorption capacity. Acknowledgments
[20]
[21] [22]
[23] [24]
[25]
[26] [27]
[28]
This study has been financially funded by The Scientific and Technological Research Council of Turkey (TUBITAK) under grant number: MAG-112M145.
[30]
References
[31]
[1] Takeichi N, Senoh H, Yokota T, Tsuruta H, Hamada K, Takeshita HT, et al. “Hybrid hydrogen storage vessel”, a novel high-pressure hydrogen storage vessel combined with hydrogen storage material. Int J Hydrogen Energy 2003;28(10):1121e9. [2] Vasiliev VV, Krikanov AA, Razin AF. New generation of filament-wound composite pressure vessels for commercial applications. Compos Struct 2003;62(3e4):449e59. [3] Gemi L, Tarakcioglu N, Akdemir A, Sahin OS. Progressive fatigue failure behavior of glass/epoxy (þ/- 75)(2) filament-wound pipes under pure internal pressure. Mater Des 2009;30(10):4293e8. [4] Rousseau J, Perreux D, Verdiere N. The influence of winding patterns on the damage behaviour of filament-wound pipes. Compos Sci Technol 1999;59(9): 1439e49. [5] Sahin OS, Akdemir A, Avci A, Gemi L. Fatigue crack growth behavior of filament wound composite pipes in corrosive environment. J Reinf Plast Comp 2009;28(24):2957e70. [6] Samanci A, Avci A, Tarakcioglu N, Sahin OS. Fatigue crack growth of filament wound GRP pipes with a surface crack under cyclic internal pressure. J Mater Sci 2008;43(16):5569e73. [7] Tarakcioglu N, Akdemir A, Avci A. Strength of filament wound GRP pipes with surface crack. Compos Part B-Eng 2001;32(2):131e8. [8] Xia M, Takayanagi H, Kemmochi K. Analysis of multi-layered filament-wound composite pipes under internal pressure. Compos Struct 2001;53(4):483e91. [9] Xia M, Takayanagi H, Kemmochi K. Bending behavior of filament-wound fiberreinforced sandwich pipes. Compos Struct 2002;56(2):201e10. [10] Morozov EV. The effect of filament-winding mosaic patterns on the strength of thin-walled composite shells. Compos Struct 2006;76(1e2):123e9. [11] Spencer B, Hull D. Effect of winding angle on the failure of filament wound pipe. Composites 1978;9(4):263e71. [12] Chou TW, Gao LM, Thostenson ET, Zhang ZG, Byun JH. An assessment of the science and technology of carbon nanotube-based fibers and composites. Compos Sci Technol 2010;70(1):1e19. [13] De Greef N, Gorbatikh L, Lomov SV, Verpoest I. Damage development in woven carbon fiber/epoxy composites modified with carbon nanotubes under tension in the bias direction. Compos Part A-Appl S 2011;42(11):1635e44. [14] Jia XL, Zhu JM, Li WB, Chen XP, Yang XP. Compressive and tensile response of CFRP cylinders induced by multi-walled carbon nanotubes. Compos Sci Technol 2015;110:35e44. [15] de la Vega A, Kinloch IA, Young RJ, Bauhofer W, Schulte K. Simultaneous global and local strain sensing in SWCNT-epoxy composites by Raman and impedance spectroscopy. Compos Sci Technol 2011;71(2):160e6. [16] Schadler LS, Giannaris SC, Ajayan PM. Load transfer in carbon nanotube epoxy composites. Appl Phys Lett 1998;73(26):3842e4. [17] Garcia EJ, Wardle BL, Hart AJ. Joining prepreg composite interfaces with aligned carbon nanotubes. Compos Part A-Appl S 2008;39(6):1065e70. [18] Bekyarova E, Thostenson ET, Yu A, Itkis ME, Fakhrutdinov D, Chou TW, et al. Functionalized single-walled carbon nanotubes for carbon fiber-epoxy composites. J Phys Chem C 2007;111(48):17865e71. [19] Godara A, Mezzo L, Luizi F, Warrier A, Lomov SV, van Vuure AW, et al. Influence of carbon nanotube reinforcement on the processing and the
[32]
[29]
[33]
[34] [35]
[36]
[37]
[38] [39]
[40] [41]
[42]
[43]
[44] [45]
[46]
[47]
[48] [49]
mechanical behaviour of carbon fiber/epoxy composites. Carbon 2009;47(12): 2914e23. Yokozeki T, Iwahori Y, Ishiwata S. Matrix cracking behaviors in carbon fiber/ epoxy laminates filled with cup-stacked carbon nanotubes (CSCNTs). Compos Part A-Appl S 2007;38(3):917e24. Thostenson ET, Li WZ, Wang DZ, Ren ZF, Chou TW. Carbon nanotube/carbon fiber hybrid multiscale composites. J Appl Phys 2002;91(9):6034e7. Thostenson ET, Chou TW. Aligned multi-walled carbon nanotube-reinforced composites: processing and mechanical characterization. J Phys D Appl Phys 2002;35(16):L77e80. Thostenson ET, Li CY, Chou TW. Nanocomposites in context. Compos Sci Technol 2005;65(3e4):491e516. Gojny FH, Wichmann MHG, Fiedler B, Bauhofer W, Schulte K. Influence of nano-modification on the mechanical and electrical properties of conventional fibre-reinforced composites. Compos Part A-Appl S 2005;36(11): 1525e35. Iwahori Y, Ishiwata S, Sumizawa T, Ishikawa T. Mechanical properties improvements in two-phase and three-phase composites using carbon nanofiber dispersed resin. Compos Part A-Appl S 2005;36(10):1430e9. Crosby AJ, Lee JY. Polymer nanocomposites: the “nano” effect on mechanical properties. Polym Rev 2007;47(2):217e29. Deshmanea C, Yuan Q, Perkins RS, Misra RDK. On striking variation in impact toughness of polyethylene-clay and polypropylene-clay nanocomposite systems: the effect of clay-polymer interaction. Mat Sci Eng A-Struct 2007;458(1e2):150e7. Fu SY, Feng XQ, Lauke B, Mai YW. Effects of particle size, particle/matrix interface adhesion and particle loading on mechanical properties of particulate-polymer composites. Compos Part B-Eng 2008;39(6):933e61. Lin JC. Investigation of impact behavior of various silica-reinforced polymeric matrix nanocomposites. Compos Struct 2008;84(2):125e31. Zhang H, Zhang Z, Friedrich K, Eger C. Property improvements of in situ epoxy nanocomposites with reduced interparticle distance at high nanosilica content. Acta Mater 2006;54(7):1833e42. Wetzel B, Rosso P, Haupert F, Friedrich K. Epoxy nanocomposites e fracture and toughening mechanisms. Eng Fract Mech 2006;73(16):2375e98. Ishida H, Rimdusit S. Very high thermal conductivity obtained by boron nitride-filled polybenzoxazine. Thermochim Acta 1998;320(1e2):177e86. Nag A, Raidongia K, Hembram KPSS, Datta R, Waghmare UV, Rao CNR. Graphene analogues of BN: novel synthesis and properties. Acs Nano 2010;4(3): 1539e44. Zhou WY, Qi SH, Li HD, Shao SY. Study on insulating thermal conductive BN/ HDPE composites. Thermochim Acta 2007;452(1):36e42. Chiang TH, Hsieh TE. A study of encapsulation resin containing hexagonal boron nitride (hBN) as inorganic filler. J Inorg Organomet P 2006;16(2): 175e83. Eskizeybek V, Avci A, Gulce A. The Mode I interlaminar fracture toughness of chemically carbon nanotube grafted glass fabric/epoxy multi-scale composite structures. Compos Part A-Appl S 2014;63:94e102. Li WK, Dichiara A, Bai JB. Carbon nanotube-graphene nanoplatelet hybrids as high-performance multifunctional reinforcements in epoxy composites. Compos Sci Technol 2013;74:221e7. Li LH, Chen Y, Stachurski ZH. Boron nitride nanotube reinforced polyurethane composites. Prog Nat Sci-Mater 2013;23(2):170e3. Salehi-Khojin A, Jalili N. Buckling of boron nitride nanotube reinforced piezoelectric polymeric composites subject to combined electro-thermomechanical loadings. Compos Sci Technol 2008;68(6):1489e501. Verma V, Jindal VK, Dharamvir K. Elastic moduli of a boron nitride nanotube. Nanotechnology 2007;18(43). Bashar M, Mertiny P, Sundararaj U. Effect of nanocomposite structures on fracture behavior of epoxy-clay nanocomposites prepared by different dispersion methods. J Nanomater 2014;2014:1e12. Natsuki T, Takayanagi H, Tsuda H, Kemmochi K. Prediction of bending strength for filament-wound composite pipes. J Reinf Plast Comp 2003;22(8): 695e710. Han JT, Cho K. Nanoparticle-induced enhancement in fracture toughness of highly loaded epoxy composites over a wide temperature range. J Mater Sci 2006;41(13):4239e45. Liu LQ, Wagner HD. Rubbery and glassy epoxy resins reinforced with carbon nanotubes. Compos Sci Technol 2005;65(11e12):1861e8. Ulus H, Ustun T, Eskizeybek V, Sahin OS, Avci A, Ekrem M. Boron nitrideMWCNT/epoxy hybrid nanocomposites: preparation and mechanical properties. Appl Surf Sci 2014;318:37e42. € Karabulut SE, Eskizeybek V, Avcı A. Low-velocity Ulus H, Üstün T, S¸ahin OS, impact behavior of carbon fiber/epoxy multiscale hybrid nanocomposites reinforced with multiwalled carbon nanotubes and boron nitride nanoplates. J Compos Mater 2015. http://dx.doi.org/10.1177/0021998315580835. Vlasveld DPN, Parlevliet PP, Bersee HEN, Picken SJ. Fibre-matrix adhesion in glass-fibre reinforced polyamide-6 silicate nanocomposites. Compos Part AAppl S 2005;36(1):1e11. Sun LY, Gibson RF, Gordaninejad F, Suhr J. Energy absorption capability of nanocomposites: a review. Compos Sci Technol 2009;69(14):2392e409. Gojny FH, Wichmann MHG, Fiedler B, Schulte K. Influence of different carbon nanotubes on the mechanical properties of epoxy matrix composites e a comparative study. Compos Sci Technol 2005;65(15e16): 2300e13.
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Evaluating the effectiveness of nanofillers in filament wound carbon/epoxy multiscale composite pipes Tugay Üstün a, Hasan Ulus a, Salim Egemen Karabulut a, Volkan Eskizeybek b, *, € Omer Sinan S¸ahin a, Ahmet Avcı a, Okan Demir a a b
Department of Mechanical Engineering, Selçuk University, Konya, Turkey Department of Materials Science and Engineering, Çanakkale Onsekiz Mart University, Çanakkale, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history: Received 3 August 2015 Accepted 6 April 2016 Available online 13 April 2016
The performance of filament wound (FW) composite pipes is considered to be fundamentally governed by fiber properties and winding angles; however, matrix dominated properties such as axial and hoop strengths are also responsible in design of FW composite pipes. This paper presents the experimental results of a project aiming to assess the benefits of addition of carbon nanotubes (CNTs) and/or boron nitride nanoplates (BNNPs) as nanofillers within epoxy matrix of FW carbon fiber composite pipes. The nanofillers enhance the burst and hoop strengths up to 17.0% and 31.7%, respectively, over the control samples. Failure analysis revealed that the morphologies of nanofillers play an important role on the matrix toughening and strengthening the fiberematrix interface. Highest mechanical performance of the multiscale composite pipes was obtained with the addition of CNTs and BNNPs within the epoxy matrix concurrently related with the synergetic effect of the two different nanofillers. © 2016 Elsevier Ltd. All rights reserved.
Keywords: A. Nano-structures B. Residual/Internal stress D. Mechanical Testing D. Fractography E. Filament winding
1. Introduction Filament wound (FW) fiber reinforced pipes have many advantages such as high specific stiffness and strength. The efficiency of filament winding process and above mentioned advantages have made this type of pipes good candidates for the storage of compressed hydrogen or of compressed and liquefied natural gas lines [1,2] Carbon fiber is a good choice for FW pipes because of its low density and high strength. Generally, FW composite pipes are made of carbon fiber/epoxy since smooth internal surface FW pipes lead lower friction during fluid flow. However carbon fiber reinforced plastics have some shortcomings such as brittleness and low resistance to crack propagation. Mechanical and failure behaviors of FW pipes have extensively investigated in the literature [3e9]. It is reported that mechanical properties mainly governed by fiber properties and winding parameters such as an optimum winding angle of 55 was recommended for close ended pipes [10,11]. It is well known that the mechanical properties of matrix become important since the damage of FW pipes initiates as matrix damage followed by formation of leakage path, delamination and
* Corresponding author. E-mail address: [email protected] (V. Eskizeybek). http://dx.doi.org/10.1016/j.compositesb.2016.04.031 1359-8368/© 2016 Elsevier Ltd. All rights reserved.
finally fiber breakage occurs [3,5,6]. Interfacial properties for fiber reinforced composites are a matrix dominant property and usually limit the design [15]. The addition of nanofillers was considered as the most efficient way to enhance mechanical properties of fiber reinforced polymer composites, since the combination of conventional fiber and nanofillers in polymer matrices had led to a new generation of multiscale, multifunctional, three-phase materials with high performance [12e14]. Among various nanofillers, carbon nanotubes (CNTs) have served as an ideal filler for high performance composites due to their unique physical properties like high strength and aspect ratio [15,16]. It is reported that interlaminar shear strength [17], fracture toughness [18e20] and load transfer ability [21] can be enhanced by addition of CNTs such as pullout, rupture, and crack bridging [22,23] mechanisms. Many researchers have focused on development of CNTs containing fiber reinforced polymers [24,25]. The effects of morphology and type of nano particles upon interfacial strength between matrix and reinforcement have been investigated [26e29]. In addition, the effects of volume fraction of the nano reinforcements [30] and dispersion quality [31] upon mechanical properties of materials have been also studied. Boron nitride has been paid attention due to its high thermal and low electrical conductivities [32e34]. The crystal structure of hexagonal boron nitride is very similar to graphite except for the
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difference in the stacking sequence of layers [35]. In our previous study [36], it was showed that boron nitride addition into epoxy resin can result in notable increase of tensile strength. It is reported that the highest strength increase has obtained at 0.3% BN content while highest toughness increase has been obtained at 0.5% BN content. The literature survey revealed that, the effects of nanofiller modification upon mechanical behaviors of FW pipes have received little attention. In this study, MWCNTs and/or BNNPs filled epoxy resin matrix FW carbon fiber composite pipes were successfully fabricated with winding angle of 55 , and the variation of burst and hoop strengths were evaluated with the standard tests. The effectiveness of nanofillers with different morphologies on damage development of carbon fiber composite pipes and their microreinforcing behavior were proposed.
Fig. 1. Filament winding process of carbon fiber/epoxy composite pipes. The inset represents winding angle as ±55 .
2. Experimental 2.1. Materials The nanofillers, MWCNTs (purity >95%, diameter 30e50 nm, length 10e30 mm) and BNNPs (diameter ~250 nm and thickness ~50 nm) were provided from Times Nano Company and BORTEK, respectively. The reinforcement, carbon fibers (800 tex) were purchased from DowAksa, Turkey. The preferred resin system is Araldite MY 740/HY 918/DY062 (Vantico Ltd) bisphenol-A epoxy resin system with 100:85:0.5 weight ratios. 2.2. Fabrication of the FW composite pipes In collaboration with a manufacturer of composite pipes and tubes, carbon fiber reinforced epoxy composite pipes were manufactured by filament winding to allow experimental manipulation of the fabrication process. For getting a control group one group of pipes were produced without adding nanofillers. The amounts of nano particles were chosen based on our previous study [41]. Firstly, the epoxy resin system with agents was prepared, following, the required amount of nanofillers were added into the epoxy resin and mixed mechanically for 30 min and additional 30 min with ultrasonically. The temperature of epoxy resin was maintained as 35 C in order to reduce the viscosity of resin for obtaining complete wetting and better saturation. Table 1 shows the composition of nanofiller added epoxy resin used for filament winding operation. Secondly, FW carbon fiber composite pipes were fabricated using a filament winding machine at the winding angle ±55 on a preheated (60 C) mandrel as shown Fig. 1. The pipes were cured in an oven for 80 C/2 h þ 120 C/4 h, and then cooled down to room temperature, subsequently. The average internal diameter and wall thickness of filament wound pipes were measured as 72 mm and 3 mm, respectively.
standards. A lab made open ended apparatus was used to utilize the short time hydraulic burst pressure. The apparatus allows the pipe to shrink and expand in diameter freely which results regarding the axial stress as zero (Fig. 2). The internal pressure was generated by a PLC controlled hydraulic pump. During the tests, the pressure was continuously and uniformly increased until failure occurs. Test durations were measured until specimen fails to specify loading rates individually in order to develop burst damage within the range of 60 and 70 s of loading time for all specimens. The burst strengths are also determined according to Equation (2)
S ¼ Pðd þ tÞ=2t Where;
(1)
S hoop stress (MPa), P internal pressure (MPa), d average inside diameter (mm), t average wall thickness (mm). So, the burst pressures have been converted to burst strength values.
2.3. Characterizations 2.3.1. Burst pressure tests The short time hydraulic burst pressure tests were performed with at least five samples according to ASTM D1599-99 Table 1 Compositions of modified epoxy resin. Case
% MWCNT (by weight)
% BNNP (by weight)
Epoxy
1 2 3 4
0 0.3 0 0.3
0 0 0.5 0.5
All Of Remaining Remaining Remaining
Fig. 2. Open ended short time hydraulic burst pressure test apparatus with schematic presentation showing the fluid input during bust tests.
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2.3.2. The tensile hoop tests The hoop tensile strength tests were performed with using special apparatus which is described to ASTM D-2290-12 standard. By definition, the hoop strength of tubes was measured by loading 1.27 cm wide rings cut from the tubes using a split-D fixture. In this loading method, two semi-circular metal inserts are pulled apart using a pin and clevis arrangement to apply load in the hoop direction. After the prepared samples were lubricated according to the standard in order to reduce friction during test, the samples were connected semicircular support bearings. The rings were loaded at 1 mm/min in tension while recording the strains at 10 Hz. The hoop strength is described by;
sa ¼ Pb =2Am
(2)
Where;
sa apparent yield or ultimate tensile stress of the specimen (MPa), P maximum or breaking load, or both (N), Am minimum cross-sectional area of the two measurements. 2.3.3. Fracture surface analysis A Zeiss Evo LS 10 scanning electron microscope (SEM) was used to examine surface morphology of the CNT modified PWGFs and the fracture surfaces of specimens. The samples were sputter coated with 4 nm thick gold layer and imaged at an acceleration voltage of 15e25 kV. 3. Results and discussions 3.1. The burst strength The burst pressure test results are given in Fig. 3. The burst strength of CF/epoxy pipes was obtained as 410 MPa. Moreover, the CNTs and BNNPs modified CF pipes showed higher burst strengths. The burst strengths were enhanced by 4.8%, 11.0% and 17.0%, with the addition of CNTs, BNNPs and CNTs-BNNPs into epoxy matrix respectively. The enhancement was consisted with the results of our previous works [41]. It is well known that modifying polymer matrix with nanofillers enhances primarily mechanical properties by generating multiscale and multifunctional materials with higher performance. Note, CNTs and BNNPs with different physical and chemical properties were used to modify CF/epoxy composite pipes to relate their characteristic properties particularly in the filament wounded CF pipe. It is clear that CNTs modification of the epoxy matrix results higher burst strength than BNNPs although the nanofiller amount of CNTs is comparatively less with respect to
Fig. 3. Short time internal pressure test results, burst pressures and hoop strengths.
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BNNPs. Based on these results, it is evident that the physical properties of nanofillers within the matrix play a key role on improving mechanical performance [37]. The higher mechanical performance of CNTs modified hybrid pipes with respect to BNNPs/ epoxy CF pipes can be attributed higher mechanical properties of CNTs rather than BNNPs [38e40]. In addition, the difference in morphologies of nanofillers governed toughening mechanisms such as crack bridging and pullout for CNTs added hybrid pipes while crack pinning and bifurcation for BNNPs modified hybrid pipes could also lead to the difference as obtained by the burst tests [36,41]. However, CNTs-BNNPs modified hybrid composite pipes showed highest burst stress. It implied that reinforcing mechanisms of both nanofillers as mentioned above on static burst performance should contribute concurrently as synergetic effect while increased amount of nanofillers could be effectively dispersed within the matrix. Generally, all the samples exhibit characteristic failure properties of fiber reinforced composite pipes in macro-scale. Fig. 4 represents images of the neat and hybrid carbon fiber pipes failed during burst pressure tests. The main failure mechanism for the all samples was stated as intensive fiber damage occurred with unsteady crack propagation around the leakage region of the pipe. Note, the black color nature of the carbon fiber composite pipes limits to observe early stages of failure; however, micro cracking and crack coalescence at radial direction originated oil leakage was clearly seen before pipe failure. Conversely, similar failure behaviors stated for the test samples, different crack propagation characteristics were observed to be related with the type of nanofiller within the epoxy matrix. Two types of crack propagation were identified from failed specimens. The crack propagation through fiber axis indicates fiberematrix interface debonding while fiber breakage in axial direction of pipe was related with hoop stress. Several observations can be made regarding failed samples after bust tests. The failure of control samples subjected to internal pressure progressed with unsteady crack propagation along both of fiber and pipe axes. This characteristic crack propagation behavior can be explained by morphological and dimensional changes of the pipes upon internal pressure loading. It is clearly observed that the diameter of the pipes increased; consequently, bending occurred with increasing internal pressure characteristic bottleneck effect around the ends of pipes. Due to the nature of bending, axial tensile and compression regions exist at the cross-section of pipe leading different stress conditions [9,42]. However, the bending dominated failure of the filament wound composite pipes is specifically controlled by winding angle. In the case of ±55 of winding angle, shear or transverse failure would occur at the tensile side of the pipe since compression side is subjected to buckling which inhibits the increased value of circumferential stress due to internal pressure [42]. The proposed loading scenario on the tube wall and fiber bundles was represented in Fig. 5. In our case, all the pipes failed from tensile side of the pipe with a leakage indicating matrix cracking started at the inner surface of pipe and propagated radially through outer surface. Previous investigations including authors' [43e47] indicated that nanofillers used for matrix modification of conventional composites enhance the energy absorption characteristics due to increased interfacial bonding, crack pinning [48]. Nanofillers constrain the matrix deformation less than micro particles [31] and result in better ductility and toughness. Nanofillers, nano-particles or nano-platelets can stop the crack propagation along the original direction [48] and also result in crack branching which results in toughening if agglomeration is minimized [49]. Applied high internal pressure results in change of the circular form of the pipe cross-section due to deformations related with increased diameter and bending deflections after loading. Moreover, the diametrical
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Fig. 4. Burst failure of the carbon fiber/epoxy composite pipe samples. The arrows show the direction of fiber and pipe axes; a) control sample without nanofiller additives, b) CNTs added multi scale composite pipe sample, c) BNNPs added multi scale composite pipe sample, d) CNTs and BNNPs added hybrid multi scale composite pipe sample.
Fig. 5. Schematic presentation of the proposed loading state of carbon fiber/epoxy composite pipes subjected to internal pressure.
expansion of the pipe lead fiber debonding due to increased shear stress between the fiber bundles. The CNTs and BNNPs modification of epoxy matrix also contributed to enhance resistance over shear deformations of pipes. So, enhanced burst strength values were obtained with nanofiller addition into polymer matrix. Specifically, branched crack propagation along axial direction of pipe was observed for the CNTs and BNNTs added hybrid pipes after failure indicating improved fiberematrix interface properties. We observed tendency to hoop stress dominated catastrophic failure for the CNTs and BNNPs modified pipes rather than shear stress dominated failure along fiber direction as identified for the unmodified composite pipes. SEM is utilized to discover damage formation and progression of carbon fiber pipes in micro scale. We mainly focused on fiberematrix interface since the nanofillers addition into matrix enhances the adhesion between fiber and matrix and the morphology around the fibers should be different with respect to unmodified composite pipes. Typical SEM images of fracture surfaces' after bust test were represented in Fig. 6. Fig. 6a represents pulled-out fibers from epoxy matrix for control sample. The clear evidence of catastrophic brittle failure beyond unsteady crack growth can be seen with individually standing fractured carbon fibers. Moreover,
smooth surfaces of pulled-out fibers indicate that shear stress at the interface overcome interfacial strength and resulted interface debonding during crack propagation. However, the fracture surfaces of CNTs and BNNPs modified pipes exhibit relatively rougher surfaces due to presence of more resin rich zones in between the fibers attributed to improved adhesion at the fiberematrix interface (Fig. 6b). The partial epoxy ruptures at the pulled out fiber slots are an evidence of better interfacial interactions for the hybrid composite pipes. Higher magnification SEM images of fracture surfaces confirm the improved interfacial adhesion with CNT and BNNPs addition of epoxy matrix. Fig. 6c shows the pulled-out fiber surfaces from control samples after failure at higher magnifications. The surfaces of fibers are clean as shown by arrows indicating adhesion failure at the interface due to weak interfacial strength. On the other hand, matrix coated carbon fibers as indicated by arrows were observed for the nanofiller added composite pipes as seen in Fig. 6d. According to this observation, the addition of nanofillers enhances the resistance of shear failure at the interface by revealing improved interfacial strength and force the crack to advance through surrounding matrix instead of interface region. These results clearly express that the addition of CNTs and BNNPs into epoxy matrix improves especially matrix dominated properties of carbon fiber pipes, and therefore, mechanical properties such as bust strength enhances. 3.2. The tensile hoop strength The results of hoop tensile strength are given in Fig. 7. The average hoop tensile strength values for unmodified pipes are calculated as 377 MPa. The calculated hoop strengths were enhanced as 11.0%, 26.2% and 31.7% with BNNPs, CNTs and CNTsBNNPs modification of epoxy matrix, respectively. In general, the obtained data consisted with the burst pressure tests indicating the tests conducted correctly. The samples were exhibit similar failure behavior characteristics compared to burst tests, and again, the effect of nanofillers on crack propagation behavior revealed itself during failure of samples (Fig. 8). The crack propagation of control samples started from the
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Fig. 6. SEM images of the bust test fracture surfaces of fabricated multi-scale hybrid composite pipes a) control sample without nanofiller additives, b) CNTs and BNNPs added hybrid multi scale composite pipe sample, c) high magnification SEM image of pulled fibers captured from control sample, d) high magnification SEM image of pulled fibers captured from CNTs and BNNPs added hybrid multi scale composite pipe sample (The arrows in the figures show the pulled out fibers).
fiberematrix interface for unmodified composite pipes. On the other hand, the CNT, BNNP and CNT-BNNP modified samples failed with intensive fiber breakage since the crack propagation developed through parallel to hoop axis. The macroscopic failure behaviors of the hoop samples indicate that the addition nanofillers within the epoxy matrix improved mechanical properties of matrix and adhesion at the fiberematrix interface. In detail, it can be said that crack bifurcation and branching mechanisms were frequently observed for CNT modified samples rather than BNNPs modified samples. We believe the CNT modification also enhances the ductility of epoxy matrix or bridging cracks in micro scale, and thereby, unsteady state crack propagation tendency of samples decreases. 4. Conclusion
Fig. 7. The tensile hoop test results of samples.
edges and progressed through axial direction of hoop. However, the crack propagated in fiber direction with increasing load and the failure of hoops occurred as fiber breakage, subsequently. This observation supports our statements about relatively weak
The contribution of adding nanofillers within the polymer matrix for the FW carbon/epoxy composite pipes were systematically evaluated in details. The addition of MWCNTs and BNNPs enhanced mechanical properties including burst and hoop strengths of FW carbon/epoxy composite pipes. Specifically, burst strength of the multiscale composite pipes was improved barely with addition nanofillers (0.5 BNNPsþ0.3 MWCNTs %wt) up to 17.0% since the burst strength of fiber reinforced composite pipes is mainly fiber dominated mechanical property. However, hoop strength of the
Fig. 8. Appearance of test specimens before and after the hoop tensile test representing crack propagation behaviors as depicted with solid lines.
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hybrid pipes was raised to 494 MPa, that is, a 31% increase over that of composite pipes without nanofillers. The performance of CNTs added pipes was higher than BNNPs reinforced multiscale composite pipes for both of burst and tensile hoop tests which is attributed to higher mechanical properties and 1D morphology leading better interfacial adhesion due to their high surface area of CNTs compared with BNNPs. Interestingly, the different morphologies of the nanofillers generated a synergetic effect when those of nanofillers was added into epoxy matrix concurrently; and consequently, the micro crack initiation and the corresponding propagation stages were delayed with different micro mechanisms such as crack bridging and bifurcation. Fracture surface analysis supported the positive effects of nanofillers on interfacial adhesion of carbon fiber and epoxy matrix. For future consideration, both additives should be implemented to the FW carbon fiber/epoxy composite pipes to test for fatigue performance and to reveal the contribution of nanofillers on energy absorption capacity. Acknowledgments
[20]
[21] [22]
[23] [24]
[25]
[26] [27]
[28]
This study has been financially funded by The Scientific and Technological Research Council of Turkey (TUBITAK) under grant number: MAG-112M145.
[30]
References
[31]
[1] Takeichi N, Senoh H, Yokota T, Tsuruta H, Hamada K, Takeshita HT, et al. “Hybrid hydrogen storage vessel”, a novel high-pressure hydrogen storage vessel combined with hydrogen storage material. Int J Hydrogen Energy 2003;28(10):1121e9. [2] Vasiliev VV, Krikanov AA, Razin AF. New generation of filament-wound composite pressure vessels for commercial applications. Compos Struct 2003;62(3e4):449e59. [3] Gemi L, Tarakcioglu N, Akdemir A, Sahin OS. Progressive fatigue failure behavior of glass/epoxy (þ/- 75)(2) filament-wound pipes under pure internal pressure. Mater Des 2009;30(10):4293e8. [4] Rousseau J, Perreux D, Verdiere N. The influence of winding patterns on the damage behaviour of filament-wound pipes. Compos Sci Technol 1999;59(9): 1439e49. [5] Sahin OS, Akdemir A, Avci A, Gemi L. Fatigue crack growth behavior of filament wound composite pipes in corrosive environment. J Reinf Plast Comp 2009;28(24):2957e70. [6] Samanci A, Avci A, Tarakcioglu N, Sahin OS. Fatigue crack growth of filament wound GRP pipes with a surface crack under cyclic internal pressure. J Mater Sci 2008;43(16):5569e73. [7] Tarakcioglu N, Akdemir A, Avci A. Strength of filament wound GRP pipes with surface crack. Compos Part B-Eng 2001;32(2):131e8. [8] Xia M, Takayanagi H, Kemmochi K. Analysis of multi-layered filament-wound composite pipes under internal pressure. Compos Struct 2001;53(4):483e91. [9] Xia M, Takayanagi H, Kemmochi K. Bending behavior of filament-wound fiberreinforced sandwich pipes. Compos Struct 2002;56(2):201e10. [10] Morozov EV. The effect of filament-winding mosaic patterns on the strength of thin-walled composite shells. Compos Struct 2006;76(1e2):123e9. [11] Spencer B, Hull D. Effect of winding angle on the failure of filament wound pipe. Composites 1978;9(4):263e71. [12] Chou TW, Gao LM, Thostenson ET, Zhang ZG, Byun JH. An assessment of the science and technology of carbon nanotube-based fibers and composites. Compos Sci Technol 2010;70(1):1e19. [13] De Greef N, Gorbatikh L, Lomov SV, Verpoest I. Damage development in woven carbon fiber/epoxy composites modified with carbon nanotubes under tension in the bias direction. Compos Part A-Appl S 2011;42(11):1635e44. [14] Jia XL, Zhu JM, Li WB, Chen XP, Yang XP. Compressive and tensile response of CFRP cylinders induced by multi-walled carbon nanotubes. Compos Sci Technol 2015;110:35e44. [15] de la Vega A, Kinloch IA, Young RJ, Bauhofer W, Schulte K. Simultaneous global and local strain sensing in SWCNT-epoxy composites by Raman and impedance spectroscopy. Compos Sci Technol 2011;71(2):160e6. [16] Schadler LS, Giannaris SC, Ajayan PM. Load transfer in carbon nanotube epoxy composites. Appl Phys Lett 1998;73(26):3842e4. [17] Garcia EJ, Wardle BL, Hart AJ. Joining prepreg composite interfaces with aligned carbon nanotubes. Compos Part A-Appl S 2008;39(6):1065e70. [18] Bekyarova E, Thostenson ET, Yu A, Itkis ME, Fakhrutdinov D, Chou TW, et al. Functionalized single-walled carbon nanotubes for carbon fiber-epoxy composites. J Phys Chem C 2007;111(48):17865e71. [19] Godara A, Mezzo L, Luizi F, Warrier A, Lomov SV, van Vuure AW, et al. Influence of carbon nanotube reinforcement on the processing and the
[32]
[29]
[33]
[34] [35]
[36]
[37]
[38] [39]
[40] [41]
[42]
[43]
[44] [45]
[46]
[47]
[48] [49]
mechanical behaviour of carbon fiber/epoxy composites. Carbon 2009;47(12): 2914e23. Yokozeki T, Iwahori Y, Ishiwata S. Matrix cracking behaviors in carbon fiber/ epoxy laminates filled with cup-stacked carbon nanotubes (CSCNTs). Compos Part A-Appl S 2007;38(3):917e24. Thostenson ET, Li WZ, Wang DZ, Ren ZF, Chou TW. Carbon nanotube/carbon fiber hybrid multiscale composites. J Appl Phys 2002;91(9):6034e7. Thostenson ET, Chou TW. Aligned multi-walled carbon nanotube-reinforced composites: processing and mechanical characterization. J Phys D Appl Phys 2002;35(16):L77e80. Thostenson ET, Li CY, Chou TW. Nanocomposites in context. Compos Sci Technol 2005;65(3e4):491e516. Gojny FH, Wichmann MHG, Fiedler B, Bauhofer W, Schulte K. Influence of nano-modification on the mechanical and electrical properties of conventional fibre-reinforced composites. Compos Part A-Appl S 2005;36(11): 1525e35. Iwahori Y, Ishiwata S, Sumizawa T, Ishikawa T. Mechanical properties improvements in two-phase and three-phase composites using carbon nanofiber dispersed resin. Compos Part A-Appl S 2005;36(10):1430e9. Crosby AJ, Lee JY. Polymer nanocomposites: the “nano” effect on mechanical properties. Polym Rev 2007;47(2):217e29. Deshmanea C, Yuan Q, Perkins RS, Misra RDK. On striking variation in impact toughness of polyethylene-clay and polypropylene-clay nanocomposite systems: the effect of clay-polymer interaction. Mat Sci Eng A-Struct 2007;458(1e2):150e7. Fu SY, Feng XQ, Lauke B, Mai YW. Effects of particle size, particle/matrix interface adhesion and particle loading on mechanical properties of particulate-polymer composites. Compos Part B-Eng 2008;39(6):933e61. Lin JC. Investigation of impact behavior of various silica-reinforced polymeric matrix nanocomposites. Compos Struct 2008;84(2):125e31. Zhang H, Zhang Z, Friedrich K, Eger C. Property improvements of in situ epoxy nanocomposites with reduced interparticle distance at high nanosilica content. Acta Mater 2006;54(7):1833e42. Wetzel B, Rosso P, Haupert F, Friedrich K. Epoxy nanocomposites e fracture and toughening mechanisms. Eng Fract Mech 2006;73(16):2375e98. Ishida H, Rimdusit S. Very high thermal conductivity obtained by boron nitride-filled polybenzoxazine. Thermochim Acta 1998;320(1e2):177e86. Nag A, Raidongia K, Hembram KPSS, Datta R, Waghmare UV, Rao CNR. Graphene analogues of BN: novel synthesis and properties. Acs Nano 2010;4(3): 1539e44. Zhou WY, Qi SH, Li HD, Shao SY. Study on insulating thermal conductive BN/ HDPE composites. Thermochim Acta 2007;452(1):36e42. Chiang TH, Hsieh TE. A study of encapsulation resin containing hexagonal boron nitride (hBN) as inorganic filler. J Inorg Organomet P 2006;16(2): 175e83. Eskizeybek V, Avci A, Gulce A. The Mode I interlaminar fracture toughness of chemically carbon nanotube grafted glass fabric/epoxy multi-scale composite structures. Compos Part A-Appl S 2014;63:94e102. Li WK, Dichiara A, Bai JB. Carbon nanotube-graphene nanoplatelet hybrids as high-performance multifunctional reinforcements in epoxy composites. Compos Sci Technol 2013;74:221e7. Li LH, Chen Y, Stachurski ZH. Boron nitride nanotube reinforced polyurethane composites. Prog Nat Sci-Mater 2013;23(2):170e3. Salehi-Khojin A, Jalili N. Buckling of boron nitride nanotube reinforced piezoelectric polymeric composites subject to combined electro-thermomechanical loadings. Compos Sci Technol 2008;68(6):1489e501. Verma V, Jindal VK, Dharamvir K. Elastic moduli of a boron nitride nanotube. Nanotechnology 2007;18(43). Bashar M, Mertiny P, Sundararaj U. Effect of nanocomposite structures on fracture behavior of epoxy-clay nanocomposites prepared by different dispersion methods. J Nanomater 2014;2014:1e12. Natsuki T, Takayanagi H, Tsuda H, Kemmochi K. Prediction of bending strength for filament-wound composite pipes. J Reinf Plast Comp 2003;22(8): 695e710. Han JT, Cho K. Nanoparticle-induced enhancement in fracture toughness of highly loaded epoxy composites over a wide temperature range. J Mater Sci 2006;41(13):4239e45. Liu LQ, Wagner HD. Rubbery and glassy epoxy resins reinforced with carbon nanotubes. Compos Sci Technol 2005;65(11e12):1861e8. Ulus H, Ustun T, Eskizeybek V, Sahin OS, Avci A, Ekrem M. Boron nitrideMWCNT/epoxy hybrid nanocomposites: preparation and mechanical properties. Appl Surf Sci 2014;318:37e42. € Karabulut SE, Eskizeybek V, Avcı A. Low-velocity Ulus H, Üstün T, S¸ahin OS, impact behavior of carbon fiber/epoxy multiscale hybrid nanocomposites reinforced with multiwalled carbon nanotubes and boron nitride nanoplates. J Compos Mater 2015. http://dx.doi.org/10.1177/0021998315580835. Vlasveld DPN, Parlevliet PP, Bersee HEN, Picken SJ. Fibre-matrix adhesion in glass-fibre reinforced polyamide-6 silicate nanocomposites. Compos Part AAppl S 2005;36(1):1e11. Sun LY, Gibson RF, Gordaninejad F, Suhr J. Energy absorption capability of nanocomposites: a review. Compos Sci Technol 2009;69(14):2392e409. Gojny FH, Wichmann MHG, Fiedler B, Schulte K. Influence of different carbon nanotubes on the mechanical properties of epoxy matrix composites e a comparative study. Compos Sci Technol 2005;65(15e16): 2300e13.