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Damage Tolerance of Carbon Fiber Woven Composite Doped with MWCNTs under Low-velocity Impact
Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 173 (2017) 440 – 446
11th International Symposium on Plasticity and Impact Mechanics, Implast 2016
Damage Tolerance of Carbon Fiber Woven Composite Doped with MWCNTs under Low-Velocity Impact Prashant Rawata*& Kalyan Kumar Singhb a* b
Research Scholar, Department of Mechanical Engineering, Indian Institute of Technology (ISM), Dhanbad, 826004, India Assistant Professor, Department of Mechanical Engineering, Indian Institute of Technology (ISM), Dhanbad, 826004, India
Abstract Fiber reinforced polymer (FRP) composites have versatile application as advanced structural material in many industries. Light weight, high aspect ratio with unique mechanical, electrical, thermal properties make it future of advanced material applications. This study addresses the enhancement in damage tolerance of carbon fiber laminate using multiwall carbon nanotubes (MWCNTs) as well as optimum value for maximum augmentation has been proposed. MWCNTs reinforced (neat, 0.25%, 0.50%, 0.75% and 1% of resin weight) carbon fiber laminates were fabricated. The carbon fiber woven composite laminate with eight layers and symmetrical design were fabricated using hand lay-up technique assisted by vacuum bagging method at 0.9 mm of Hg pressure. Results confirmed that reinforcing MWCNT enhancement in damage tolerance is possible and 0.25 wt. % is optimum doping value to achieve maximum damage tolerance. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2016 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-reviewunder under responsibility oforganizing the organizing committee of Implast Peer-review responsibility of the committee of Implast 2016 2016. Keywords: FRP; MWCNT; Symmetrical Laminate; damage tolerance
1. Introduction In the last two decades, composite materials have been increasingly applied in many industries due to highperformance properties or mass ratio. For structural applications like aeronautics and aerospace industry, marine industry and spacecraft equipment where component mass plays a significant role, Fiber reinforced polymer (FRP)
* Corresponding author. Tel.: +91-9472745795.
E-mail address: [email protected]
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of Implast 2016
doi:10.1016/j.proeng.2016.12.061
Prashant Rawat and Kalyan Kumar Singh / Procedia Engineering 173 (2017) 440 – 446
441
Composites are widely used due to high strength and stiffness, low mass, design flexibility, better thermal, electrical properties, etc. The continuous increasing effort to improve mechanical properties has directed several modifications like sandwich structures [1, 2], hybrid composite laminates [3, 4, 5], nano-fillers and nanotubes reinforced FRP composites [6, 7] and design modification [8, 9]. These research investigations clearly reported about the high potential to enhance composite material properties beyond its natural limits. Carbon nanotubes were introduced in 1991 by S. Iijima [10]. They offer an aspect ratio of 1000, which is more than any other material on our planet. On the basis of synthesis methods single wall carbon nanotubes (SWCNT) and multiwall carbon nanotubes (MWCNT) are the two categories of CNTs. These carbon nanotubes are used as primary and/or secondary reinforcement. Using CNTs as a secondary doping element, i.e. mixing in resins provides augmentation in material properties. A. K. Gupta et al. [11] performed a tensile test on three-phased nano composite and reported about 50.8% enhancement in tensile strength by adding 2wt. % MWCNTs. P. Costa et al. [12] examined mechanical and electromechanical properties of CNT/SBS matrix composites for sensor applications their result justified CNT/SBS composites offered higher gauge factor for strains up to 5%. Z. Fan et al. [13] improved ILSS properties of GFRP composites using MWCNTs as secondary reinforcement and concluded 33.1% increment in interlaminar shear strength at 2 wt. % oxidized multiwall carbon nanotubes. Their research work also proposed Injection and double vacuum assisted resin transfer moulding (IDVARTM). D. C. Davis et al. [14] worked on T-T fatigue damage using SWCNT and concluded about the greater durability of SWCNT-based carbon/epoxy composites. Therefore, it is clear that composite modification using carbon nanotubes provides better properties in every aspect, i.e. mechanical, thermal and/or electrical behavior. Aerospace, spacecraft, marine industries use carbon-fiber/epoxy composites in high proportion. These composite components, during their service life experience impact events (low, high or hyper velocity) commonly [7, 15]. Thus, for these industries damage resistance against impact loading becomes a subject of major concern. M. Tehrani et al. [16] studied impact damage of three phased carbon fiber woven reinforced with 2 wt. % of resins MWCNT in order to find out improvement in mechanical properties by adding MWCNTs. Their research highlighted about attaining good dispersion of MWCNTs in matrix improves 12% improvement in young’s modulus and 23.3% enhancement in energy absorption. W. Hufenbach et al. [17] performed Charpy impact tests on aerospace composite structures and validated results using finite element approach. They concluded residual stiffness and strengths could be modified using +45/-45 lay-up. V. Kostopouloset al. [18] enhanced the impact and after-impact properties of 0.5 wt. % reinforced MWCNT reinforced CFRP laminate. Impact energy for MWCNT doped sample absorbed higher energy as well as showed lower delamination in C-scan testing. M. Siegfried et al. [19] investigated impact and residual afterimpact properties by adding 0.25 wt% carbon nanotubes of three types (i) normal, (ii) aged CNT and (iii) functionalized CNT. The results of this study confirmed about the positive influence of CNT addition, CF/epoxy/CNTa (a = aged) showed maximum improvement of 22% in GIIC test. Modification of resin using carbon nanotubes act as a stiff barrier that hinders crack progression. Moreover, matrix carries the load after the crack has been initiated [16]. Previous work [7] reported about the lack of ranging analysis regarding CNT reinforcement. Several researchers reported about augmentation in impact property by adding carbon nanotubes, but only a few studies discussed the optimized value for maximum energy absorption. In this paper, drop weight impact behavior of three phased MWCNT/carbon-woven/epoxy composite is analyzed experimentally, using drop weight impact tower. 2. Fabrication of composite material The primary reinforcement material used in the proposed research was woven carbon fiber 12 K 800 TEX 600 GSM provided by CFW Enterprises (Delhi, India). The secondary reinforcing material in the matrix were multiwall carbon nanotubes supplied by United Nanotech Innovations Pvt. Ltd. (Bangalore, India) of 5-20 nm thickness and 110 micron length with a purity level of 98%. Carbon woven was cut in square layers of 28 mm X 28 mm in two orientations (00/900) and (+450/-450). Mixing of multiwall carbon nanotubes and resins were done by using probe ultrasonicator. Initially, MWCNTs were mixed with epoxy (bisphenol-A) and this solution was sonicated for 1 hour. To avoid excessive heat generation solution was kept in an ice bucket. Secondly, hardener was poured into the MWCNT/epoxy solution with 10:1 (epoxy: hardener) ratio and further sonicated for 15 minutes. Carbon woven layer (00/900) was kept on the flat surface, then two-phased resin solution applied using a soft brush and then second woven layer (+450/-450) was placed over first. To squeeze the extra resin, the heavy iron roller was rolled after placing four layers. Similarly, eight layered symmetrical carbon fiber laminate [(00/900) / (+450/-450) / (+450/-450) / (00/900) //
442
Prashant Rawat and Kalyan Kumar Singh / Procedia Engineering 173 (2017) 440 – 446
(00/900) / (+450/-450) / (+450/-450) / (00/900)] (figure 1.a) was prepared. Finally, wet laminate was kept in a vacuum bag (0.9 mm Hg pressure) to extract maximum resins (figure 1.b) to get good fiber volume fraction.
Figure 1: (a) Symmetrical layup design, (b) Vacuum bagging setup and resin extraction 3. Testing Methods Drop weight impact tests were conducted using Instron-CEAST 9350 (figure 2.a) with a hemispherical headed cylindrical impactor made of steel with 12.7 mm diameter. Carbon/epoxy laminates were cut as per ASTM D7136 (figure 2.b) and tested using 10 kg impactor mass at 6 m/sec. The corresponding energy value was 94.14 J. Testing specimens were rigidly clamped by an upper movable jaw of containing a circular frame with a hollow circular area (at center) of diameter 76 mm shown in figure 2.c.
Figure 2: (a) Drop weight impact tower, (b) CFRP laminate and (c) Boundary conditions for LVI impact
Prashant Rawat and Kalyan Kumar Singh / Procedia Engineering 173 (2017) 440 – 446
443
4. Results and discussion 4.1 Energy absorption The impact energy transmitted by the impactor to the composite laminate is known as total impact energy (TEA). Energy absorption capacity of composite material without failure is called maximum energy absorption (EA). The highest value of energy shown on the Y-axis in Figure 3 which represents the EA capacity for proposed neat and MWCNT modified composite laminates. Maximum energy absorption was observed for 0.25 wt. % MWCNT reinforced composite laminate. While, doping more than 0.5 wt.% reduces energy absorption. Minimum energy absorption was observed for 0.75 wt. % doping. While at 1 wt. % doping energy absorption further increases near neat carbon/epoxy laminate.
80 70
Energy [J]
60 50 40 30
0% 0.25 % 0.5 % 0.75 % 1.0 %
20 10 0
0
2
4
6
8
10
12
14
Time [ms]
Figure 3: Energy vs. Time respond of three phased composite 4.2 Force response Figure 4 represents the force-displacement respond for proposed carbon/epoxy laminates, neat carbon fiber/epoxy, and MWCNT doped carbon fiber/epoxy laminates. These curves do not show much difference in pattern while sudden force drop indicates rapid delamination and for doping 0.5 wt. % MWCNTs. Instant drop in force value indicates sudden failure of the interface and failure of the MWCNTs-Epoxy link at this doping level. Moreover, peak load value of 0.25 and 0.5 wt. % reinforcement is nearly same, but 0.25 wt. % doping has better interface bonding as no sudden failure was observed at this doping level. Force response of proposed laminate clearly justifies the importance of interfacial bonding between MWCNTs and resins at 0.25 wt. % ratio.
444
Prashant Rawat and Kalyan Kumar Singh / Procedia Engineering 173 (2017) 440 – 446 12000
0.00% 0.25% 0.50% 0.75% 1.00%
10000
Force [N]
8000 6000 4000 2000 0 0
5
10
15
20
Deformation [mm]
Figure 4: Force-deformation curves 4.3 Damage Evaluation Damage caused by drop weight impact on CFRP laminate is a mixture of three principle failure matrix cracking, delamination of plies and fiber fracture. Hemisphere-ended impactor causes maximum damage to the back face of the composite laminate [20]. Thus a pyramidal damage area at back face was compared to justify the importance of MWCNTs modification in carbon/epoxy laminates. The minimum pyramidal damage area was detected for 0.25 wt. % MWCNT doping i.e. 17.12 mm X 17.42 mm in weft and warp direction respectively, while the height of the pyramid measured 9 mm. Table 1 shows the pyramidal damage area for proposed neat and modified CFRP composite laminates.
S. No.
Doping % of MWCNT
1 2 3 4 5
Neat CFRP 0.25 wt. % 0.50 wt. % 0.75 wt. % 1.00 wt. %
Damage in weft direction (w) in mm 18.79 17.12 20.23 20.87 20.59
Damage in warp direction (L) in mm 20.79 17.12 19.31 19.28 19.30
Pyramidal height (h) in mm 11.9 9 10 12 12.3
Prashant Rawat and Kalyan Kumar Singh / Procedia Engineering 173 (2017) 440 – 446
445
Figure 5: Pyramidal damage of carbon/epoxy laminate 5. Conclusions Drop weight impact testing of three phased carbon/epoxy composite laminate was done successfully and the findings of the proposed work as follows: x x
Multiwall carbon nanotube-reinforced carbon fiber laminates have better energy absorption capacity as compared to neat CFRP laminate. The optimum value of MWCNT doping is 0.25 wt. %, at this doping percentage the energy absorption, has been increased by 18.03 % as well as 23.65 % reduction in the rectangular damage area as compared to unmodified CFRP composite laminate.
References [1]
H. Wang, K. R. Ramakrishnan, K. Shankar, Experimental study of the medium velocity impact response of sandwich panels with different cores, Mat. & Des. 99 (2016) 68–82. [2] G.-C. Yu, L.-J. Feng, L.-Z. Wu, Thermal and mechanical properties of a multifunctional composite square honeycomb sandwich structure, Mat. & Des. 102 (2016) 238–246. [3] F. Sarasini, J. Tirillò, L. Ferrante, M. Valente, T. Valente, L. Lampani, P. Gaudenzi, S. Cioffi, S. Iannace, L. Sorrentino, Drop-weight impact behaviour of woven hybrid basalt–carbon/epoxy composites, Comp. Part B: Eng. 59 (2014) 204-220. [4] C. C Angrizani, M. O H Cioffi, A. J Zattera, S. C Amico, Analysis of curaua/glass hybrid interlayer laminates, Jour. of Reinforced Plast. and Comp. (Sage) 33 (5) (2014) 472-478. [5] R. Petrucci, C. Santulli, D. Puglia, E. Nisini, F. Sarasini, J. Tirillò, L. Torre, G. Minak, J.M. Kenny, Impact and post-impact damage characterisation of hybrid composite laminates based on basalt fibres in combination with flax, hemp and glass fibres manufactured by vacuum infusion, Comp. Part B: Engg. 69 (2015) 507–515. [6] E. G. Koricho, A. Khomenko, M. Haqa, L. T. Drzal, G. Belingardi, B. Martorana, Effect of hybrid (micro- and nano-) fillers on impact response of GFRP composite, Comp. Str. 134 (2015.) 789–798. [7] P. Rawat, K. K. Singh, An impact behavior analysis of CNT-based fiber reinforced composites validated by LS-DYNA: A Review, Poly. Comp. (Wiley online library). doi: 10.1002/pc. 23573 (2015). [8] K. K. Singh, N. K. Singh, R. Jha, Analysis of Symmetric and asymmetric glass fiber reinforced plastic laminates subjected to low velocity impact, Jour. of comp. mat (Sage) doi:10.1177/0021998315596594 (2015). [9] K. K. Singh, R. K. Singh, P. S. Chandel, P. Kumar, An Asymmetric FRP laminate with a circular precrack to determine impact induced damage, Poly. Comp. (Wiley InterScience) 29 (12) (2008)1378–1383. [10] S. Iijima, Helical microtubules of graphitic carbon, Lett. to Nat. 354 (1991) 56 – 58. [11] A. K. Gupta, S. P. Harsha, Studies of Mechanical Properties of Multiwall Nanotube Based Polymer Composites, Jour. of Nanotechn. in Engg. and Medi. 5 (2014) (3).
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[12] P. Costa, J. Silva, A. A.-Casaos, M.T. Martinez, M.J. Abad, J. Viana, S. Lanceros-Mendez, Effect of carbon nanotube type and functionalization on the electrical, thermal, mechanical and electromechanical properties of carbon nanotube/styrene–butadiene–styrene composites for large strain sensor applications, Comp. Part B: Engg. 61 (2014) 136–146. [13] Z. Fan, M. H. Santare, S. G. Advani, Interlaminar shear strength of glass fiber reinforced epoxy composites enhanced with multi-walled carbon nanotubes, Comp. Part A: Appl. Sci. and Manuf. 39 (3) (2008) 540–554. [14] D. C. Davis, J. W. Wilkerson, J. Zhu, V. G. Hadjiev, A strategy for improving mechanical properties of a fiber reinforced epoxy composite using functionalized carbon nanotubes, Comp. Sci. and Tech. 71 (2011) 1089-1097. [15] S. Agarwal, K. K. Singh and P. K. Sarkar, Impact damage of Fiber Reinforced Polymer matrix composite- A review, Jour. of comp. mat. 48 (2014) 317-332. [16] M. Tehrani, A.Y. Boroujeni, T.B. Hartman, T.P. Haugh, S.W. Case, M.S. Al-Haik, Mechanical characterization and impact damage assessment of a woven carbon fiber reinforced carbon nanotube–epoxy composite, Comp. Sci. and Techn. 75 (11) (2013) 42–48. [17] W. Hufenbach, F. M. Ibraim, A. Langkamp, R. Böhm, A. Hornig, Charpy impact tests on composite structures – An experimental and numerical investigation, Comp. Sci. and Techn. 68 (23) (2008) 2391–2400. [18] V. Kostopoulos, A. Baltopoulos, P. Karapappas, A. Vavouliotis, A. Paipetis, Impact and after-impact properties of carbon fibre reinforced composites enhanced with multi-wall carbon nanotubes, Comp. Sci. and Tech. 70 (2009) 553–563. [19] M. Siegfried, C. Tola, M. Claes, S. V. Lomov, I. Verpoest, L. Gorbatikh, Impact and residual after impact properties of carbon fiber/epoxy composites modified with carbon nanotubes, Comp. Str. 111 (2014) 488-496. [20] T. Mitrevski, I.H. Marshall, R. Thomson, R. Jones, B. Whittingham, The effect of impactor shape on the impact response of composite laminates composite laminates, Comp. Str. 67 (2) (2005)139–148.
ScienceDirect Procedia Engineering 173 (2017) 440 – 446
11th International Symposium on Plasticity and Impact Mechanics, Implast 2016
Damage Tolerance of Carbon Fiber Woven Composite Doped with MWCNTs under Low-Velocity Impact Prashant Rawata*& Kalyan Kumar Singhb a* b
Research Scholar, Department of Mechanical Engineering, Indian Institute of Technology (ISM), Dhanbad, 826004, India Assistant Professor, Department of Mechanical Engineering, Indian Institute of Technology (ISM), Dhanbad, 826004, India
Abstract Fiber reinforced polymer (FRP) composites have versatile application as advanced structural material in many industries. Light weight, high aspect ratio with unique mechanical, electrical, thermal properties make it future of advanced material applications. This study addresses the enhancement in damage tolerance of carbon fiber laminate using multiwall carbon nanotubes (MWCNTs) as well as optimum value for maximum augmentation has been proposed. MWCNTs reinforced (neat, 0.25%, 0.50%, 0.75% and 1% of resin weight) carbon fiber laminates were fabricated. The carbon fiber woven composite laminate with eight layers and symmetrical design were fabricated using hand lay-up technique assisted by vacuum bagging method at 0.9 mm of Hg pressure. Results confirmed that reinforcing MWCNT enhancement in damage tolerance is possible and 0.25 wt. % is optimum doping value to achieve maximum damage tolerance. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2016 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-reviewunder under responsibility oforganizing the organizing committee of Implast Peer-review responsibility of the committee of Implast 2016 2016. Keywords: FRP; MWCNT; Symmetrical Laminate; damage tolerance
1. Introduction In the last two decades, composite materials have been increasingly applied in many industries due to highperformance properties or mass ratio. For structural applications like aeronautics and aerospace industry, marine industry and spacecraft equipment where component mass plays a significant role, Fiber reinforced polymer (FRP)
* Corresponding author. Tel.: +91-9472745795.
E-mail address: [email protected]
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of Implast 2016
doi:10.1016/j.proeng.2016.12.061
Prashant Rawat and Kalyan Kumar Singh / Procedia Engineering 173 (2017) 440 – 446
441
Composites are widely used due to high strength and stiffness, low mass, design flexibility, better thermal, electrical properties, etc. The continuous increasing effort to improve mechanical properties has directed several modifications like sandwich structures [1, 2], hybrid composite laminates [3, 4, 5], nano-fillers and nanotubes reinforced FRP composites [6, 7] and design modification [8, 9]. These research investigations clearly reported about the high potential to enhance composite material properties beyond its natural limits. Carbon nanotubes were introduced in 1991 by S. Iijima [10]. They offer an aspect ratio of 1000, which is more than any other material on our planet. On the basis of synthesis methods single wall carbon nanotubes (SWCNT) and multiwall carbon nanotubes (MWCNT) are the two categories of CNTs. These carbon nanotubes are used as primary and/or secondary reinforcement. Using CNTs as a secondary doping element, i.e. mixing in resins provides augmentation in material properties. A. K. Gupta et al. [11] performed a tensile test on three-phased nano composite and reported about 50.8% enhancement in tensile strength by adding 2wt. % MWCNTs. P. Costa et al. [12] examined mechanical and electromechanical properties of CNT/SBS matrix composites for sensor applications their result justified CNT/SBS composites offered higher gauge factor for strains up to 5%. Z. Fan et al. [13] improved ILSS properties of GFRP composites using MWCNTs as secondary reinforcement and concluded 33.1% increment in interlaminar shear strength at 2 wt. % oxidized multiwall carbon nanotubes. Their research work also proposed Injection and double vacuum assisted resin transfer moulding (IDVARTM). D. C. Davis et al. [14] worked on T-T fatigue damage using SWCNT and concluded about the greater durability of SWCNT-based carbon/epoxy composites. Therefore, it is clear that composite modification using carbon nanotubes provides better properties in every aspect, i.e. mechanical, thermal and/or electrical behavior. Aerospace, spacecraft, marine industries use carbon-fiber/epoxy composites in high proportion. These composite components, during their service life experience impact events (low, high or hyper velocity) commonly [7, 15]. Thus, for these industries damage resistance against impact loading becomes a subject of major concern. M. Tehrani et al. [16] studied impact damage of three phased carbon fiber woven reinforced with 2 wt. % of resins MWCNT in order to find out improvement in mechanical properties by adding MWCNTs. Their research highlighted about attaining good dispersion of MWCNTs in matrix improves 12% improvement in young’s modulus and 23.3% enhancement in energy absorption. W. Hufenbach et al. [17] performed Charpy impact tests on aerospace composite structures and validated results using finite element approach. They concluded residual stiffness and strengths could be modified using +45/-45 lay-up. V. Kostopouloset al. [18] enhanced the impact and after-impact properties of 0.5 wt. % reinforced MWCNT reinforced CFRP laminate. Impact energy for MWCNT doped sample absorbed higher energy as well as showed lower delamination in C-scan testing. M. Siegfried et al. [19] investigated impact and residual afterimpact properties by adding 0.25 wt% carbon nanotubes of three types (i) normal, (ii) aged CNT and (iii) functionalized CNT. The results of this study confirmed about the positive influence of CNT addition, CF/epoxy/CNTa (a = aged) showed maximum improvement of 22% in GIIC test. Modification of resin using carbon nanotubes act as a stiff barrier that hinders crack progression. Moreover, matrix carries the load after the crack has been initiated [16]. Previous work [7] reported about the lack of ranging analysis regarding CNT reinforcement. Several researchers reported about augmentation in impact property by adding carbon nanotubes, but only a few studies discussed the optimized value for maximum energy absorption. In this paper, drop weight impact behavior of three phased MWCNT/carbon-woven/epoxy composite is analyzed experimentally, using drop weight impact tower. 2. Fabrication of composite material The primary reinforcement material used in the proposed research was woven carbon fiber 12 K 800 TEX 600 GSM provided by CFW Enterprises (Delhi, India). The secondary reinforcing material in the matrix were multiwall carbon nanotubes supplied by United Nanotech Innovations Pvt. Ltd. (Bangalore, India) of 5-20 nm thickness and 110 micron length with a purity level of 98%. Carbon woven was cut in square layers of 28 mm X 28 mm in two orientations (00/900) and (+450/-450). Mixing of multiwall carbon nanotubes and resins were done by using probe ultrasonicator. Initially, MWCNTs were mixed with epoxy (bisphenol-A) and this solution was sonicated for 1 hour. To avoid excessive heat generation solution was kept in an ice bucket. Secondly, hardener was poured into the MWCNT/epoxy solution with 10:1 (epoxy: hardener) ratio and further sonicated for 15 minutes. Carbon woven layer (00/900) was kept on the flat surface, then two-phased resin solution applied using a soft brush and then second woven layer (+450/-450) was placed over first. To squeeze the extra resin, the heavy iron roller was rolled after placing four layers. Similarly, eight layered symmetrical carbon fiber laminate [(00/900) / (+450/-450) / (+450/-450) / (00/900) //
442
Prashant Rawat and Kalyan Kumar Singh / Procedia Engineering 173 (2017) 440 – 446
(00/900) / (+450/-450) / (+450/-450) / (00/900)] (figure 1.a) was prepared. Finally, wet laminate was kept in a vacuum bag (0.9 mm Hg pressure) to extract maximum resins (figure 1.b) to get good fiber volume fraction.
Figure 1: (a) Symmetrical layup design, (b) Vacuum bagging setup and resin extraction 3. Testing Methods Drop weight impact tests were conducted using Instron-CEAST 9350 (figure 2.a) with a hemispherical headed cylindrical impactor made of steel with 12.7 mm diameter. Carbon/epoxy laminates were cut as per ASTM D7136 (figure 2.b) and tested using 10 kg impactor mass at 6 m/sec. The corresponding energy value was 94.14 J. Testing specimens were rigidly clamped by an upper movable jaw of containing a circular frame with a hollow circular area (at center) of diameter 76 mm shown in figure 2.c.
Figure 2: (a) Drop weight impact tower, (b) CFRP laminate and (c) Boundary conditions for LVI impact
Prashant Rawat and Kalyan Kumar Singh / Procedia Engineering 173 (2017) 440 – 446
443
4. Results and discussion 4.1 Energy absorption The impact energy transmitted by the impactor to the composite laminate is known as total impact energy (TEA). Energy absorption capacity of composite material without failure is called maximum energy absorption (EA). The highest value of energy shown on the Y-axis in Figure 3 which represents the EA capacity for proposed neat and MWCNT modified composite laminates. Maximum energy absorption was observed for 0.25 wt. % MWCNT reinforced composite laminate. While, doping more than 0.5 wt.% reduces energy absorption. Minimum energy absorption was observed for 0.75 wt. % doping. While at 1 wt. % doping energy absorption further increases near neat carbon/epoxy laminate.
80 70
Energy [J]
60 50 40 30
0% 0.25 % 0.5 % 0.75 % 1.0 %
20 10 0
0
2
4
6
8
10
12
14
Time [ms]
Figure 3: Energy vs. Time respond of three phased composite 4.2 Force response Figure 4 represents the force-displacement respond for proposed carbon/epoxy laminates, neat carbon fiber/epoxy, and MWCNT doped carbon fiber/epoxy laminates. These curves do not show much difference in pattern while sudden force drop indicates rapid delamination and for doping 0.5 wt. % MWCNTs. Instant drop in force value indicates sudden failure of the interface and failure of the MWCNTs-Epoxy link at this doping level. Moreover, peak load value of 0.25 and 0.5 wt. % reinforcement is nearly same, but 0.25 wt. % doping has better interface bonding as no sudden failure was observed at this doping level. Force response of proposed laminate clearly justifies the importance of interfacial bonding between MWCNTs and resins at 0.25 wt. % ratio.
444
Prashant Rawat and Kalyan Kumar Singh / Procedia Engineering 173 (2017) 440 – 446 12000
0.00% 0.25% 0.50% 0.75% 1.00%
10000
Force [N]
8000 6000 4000 2000 0 0
5
10
15
20
Deformation [mm]
Figure 4: Force-deformation curves 4.3 Damage Evaluation Damage caused by drop weight impact on CFRP laminate is a mixture of three principle failure matrix cracking, delamination of plies and fiber fracture. Hemisphere-ended impactor causes maximum damage to the back face of the composite laminate [20]. Thus a pyramidal damage area at back face was compared to justify the importance of MWCNTs modification in carbon/epoxy laminates. The minimum pyramidal damage area was detected for 0.25 wt. % MWCNT doping i.e. 17.12 mm X 17.42 mm in weft and warp direction respectively, while the height of the pyramid measured 9 mm. Table 1 shows the pyramidal damage area for proposed neat and modified CFRP composite laminates.
S. No.
Doping % of MWCNT
1 2 3 4 5
Neat CFRP 0.25 wt. % 0.50 wt. % 0.75 wt. % 1.00 wt. %
Damage in weft direction (w) in mm 18.79 17.12 20.23 20.87 20.59
Damage in warp direction (L) in mm 20.79 17.12 19.31 19.28 19.30
Pyramidal height (h) in mm 11.9 9 10 12 12.3
Prashant Rawat and Kalyan Kumar Singh / Procedia Engineering 173 (2017) 440 – 446
445
Figure 5: Pyramidal damage of carbon/epoxy laminate 5. Conclusions Drop weight impact testing of three phased carbon/epoxy composite laminate was done successfully and the findings of the proposed work as follows: x x
Multiwall carbon nanotube-reinforced carbon fiber laminates have better energy absorption capacity as compared to neat CFRP laminate. The optimum value of MWCNT doping is 0.25 wt. %, at this doping percentage the energy absorption, has been increased by 18.03 % as well as 23.65 % reduction in the rectangular damage area as compared to unmodified CFRP composite laminate.
References [1]
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