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Self-repairing fiber polymer composites: mechanisms and properties
Self-repairing fiber polymer composites: mechanisms and properties
5
R. Kumar1, N. Rajesh Jesudoss Hynes2, P. Senthamaraikannan3, Anish Khan4,5, Sanjay Mavinkere Rangappa6, Suchart Siengchin6, S.R. Sundara Bharathi7, Abdullah Mohamed Asiri4,5 and Imran Khan8 1 Department of Mechanical Engineering, Vels Institute of Science, Technology & Advanced Studies, Chennai, India, 2Department of Mechanical Engineering, Mepco Schlenk Engineering College, Sivakasi, India, 3Department of Mechanical Engineering, Kamaraj College of Engineering and Technology, Virudhunagar, India, 4Chemistry Departments, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia, 5 Centre of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah, Saudi Arabia, 6Department of Mechanical and Process Engineering, The Sirindhorn International Thai-German Graduate School of Engineering (TGGS), King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand, 7Department of Mechanical Engineering, National Engineering College, Kovilpatti, India, 8Applied Sciences and Humanities Section, University Polytechnic, Faculty of Engineering and Technology, Aligarh Muslim University, Aligarh, India
5.1
Introduction
The structures of fiber with polymer matrix composite are supposed to be delamination crack produced by the impact loading, stresses, and ecological degradation [1 3]. The delamination crack in-between the layers has rigorously reduced the mechanical properties such as compression strength and fatigue life of the developed polymeric composites [4 6]. Also, when the bonded composite materials have delamination damage effect, the tensile strength and fatigue life of those materials are reduced. There are several techniques available to destroy the initiation and development of delamination cracks in the polymer composite including hardened resin, thermoplastic interleaving, and reinforcement by 3D weaving and pinning. Although these techniques are used to resist the initiation of delamination cracks, the growth of the cracks remains unrepaired till the component becomes a failure. Autonomic repair technique in the self-healing is a solution to the problem of delamination damage, which is accomplished by a way of dispersion of small containers into the polymer matrix including a healing liquid agent with low viscosity and catalyst [7 9]. Gradually, the self-healing process begins at the growth of delamination crack, which leads to breaking of the containers and then discharging Self-Healing Composite Materials. DOI: https://doi.org/10.1016/B978-0-12-817354-1.00005-3 © 2020 Elsevier Inc. All rights reserved.
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Self-Healing Composite Materials
Figure 5.1 Self-healing process [10].
of healing liquid from the containers into the crack. This stored fluid of healing agent acts as a polymer capsule to resolve the damage. Fig. 5.1 shows the principle of self-healing process. The polymerization process is done inside the crack by the reaction of the catalyst with healing agent and then it is used to recover the strength of the composite material. Based on the proper selection and distribution of the healing agent and catalyst, the repairing and recovery of material properties are achieved [10]. It is noted that the performances of self-healing process are mainly dependent upon the activation of the healing agent at the high ambient temperature conditions from 240 C to 280 C, which is practically impossible till now to achieve a high self-healing efficiency [11]. For example, mainly the polymeric composite is appropriate in the aircraft applications, which may endure a low temperature of 260 C; at that temperature all the types of healing agent fluid have attained the frozen stage and they cannot be activated. For this reason, researchers are motivated to develop the self-healing systems in order to withstand the environmental conditions. Only a few investigators have tried to develop the novel healing agents for activation at a low temperature of 10 C [12,13] and influence of ultralow temperature [14]. In general, the self-healing process utilized the small size capsules in order to store the fluid of the healing agent. The size of this type of capsule is typically 10 500 µm and it is dispersed into the polymer matrix of about 2% 20% [15]. Fig. 5.2 shows different types of capsules in the polymeric composite material. In general, this type of capsule is robust enough to handle the force created during manufacturing of self-healing composite and also it should be broken to release the core healing agent to repair the fracture once it is produced in the composite [16 18]. Good adhesion properties to the surrounding polymer material is required in all such applications [19 23]. However, there are some disadvantages in the applications of capsule method in the self-healing process such as low quantity of self-healing liquid is stored to restore the strength and repair the cracks and that they are single-use only [24 29]. Therefore there is a demand and high research needs were required to resolve this problem [30 36]. From this demand, implementation of hollow fibers came into
Self-repairing fiber polymer composites: mechanisms and properties
73
Figure 5.2 (A) Ethylidene norbornene filled Melamine-urea-formaldehyde capsules (B) Dicyclopentadiene Filed urea-formaldehyde capsules (C) Dicyclopentadiene with urea-formaldehyde capsules embedded in the crack (D) dicyclopentadiene filled nanosized capsule [15].
Table 5.1 Comparison of properties of conventional fiber with hollow fiber [45]. Type
Fiber diameter (µm)
Ultimate tensile strength (GPa)
Young’s modulus (GPa)
T300
7
3.53
235
Hollow fiber
38.4
0.52
249.4
existence for storing and transporting more amount of healing agent fluid to repair the damage in the polymeric composites [37 42]. Hollow fibers are long vessels used to store more amount of healing agent and dispersed into the polymer matrix [43,44]. Table 5.1 shows the mechanical properties of conventional and hollow fibers. This form of fibers comprises a one-part resin system, a two-part resin and hardener system, or a resin system with a catalyst or hardener enclosed in the polymer matrix composite [46]. Different approaches for making the hollow fiber self-healing system are given in Table 5.2. This information shows the current research level activity and helps to improve the investigation of this research area.
74
Self-Healing Composite Materials
Table 5.2 Different mechanisms and strategies followed by the investigators. Selfhealing systems
Mechanism
Strategy
References
Hollow fibers
Bleeding
Bleeding of stored healing agent from the vessels to repair the crack
[46 49]
Blood flow vascular network
Two or three dimensional vascular network has allowed the healing agent to be refilled and transformed to failure zone
[50,51]
5.2
Bleeding mechanism
Fig. 5.3 shows a typical hollow fiber’s approach and microstructure of hollow fibers. Hucker et al. [43] produced the hollow glass fiber in the range of diameter from 30 to 100 mm. The developed hollow fibers are embedded into the glass fiber reinforced polymer matrix composite and filled with an uncured resin material to impart the functionality of self-healing to the composite. During a failure, hollow fibers get fractured leads to imitating the recovery of composite properties by way of the healing process in which the healing agent passes through from fracture opening to infiltrate the failure area. It acts as a barrier to the dangerous effects from the failure of the composite matrix and delamination and also avoids additional matrix crack propagation. This type of repairing procedure is also related to the bleeding mechanism in the biological systems.
5.3
Blood flow vascular network mechanism
The approach of hollow fiber self-healing system described above is related to the several healing agents and it is exhibited to resolve the propagation and growth of the crack in the present fracture site only. However, the amount of healing agent in each hollow fiber is still limited. This difficulty is completely overcome by the vascular network self-healing approach. In this case, healing fluids are transferred with a logical evolution to the required fracture sites by the way of serially interconnected networks [15]. These networks were potentially connected to an external pump system, therefore refilling of healing agent for distribution could be done continuously at a constant rate. Self-healing with this interconnected healing agent networks is systematically related to the above approach. But this approach of vascular healing network is theoretically and visually related to the approach of healing system in the animals and plants.
Self-repairing fiber polymer composites: mechanisms and properties
75
Figure 5.3 (A) Schematic diagram of hollow fibers composites (B) SEM image of hollow fiber [43].
Figure 5.4 (A) Capillary network system (B) Microvascular network system [15].
5.4
Mechanical testing
The mechanical properties of hollow fiber embedded polymeric composite are determined by various testing methods such as flexural, impact, tensile, and compression in order to quantify the effect of hollow fiber’s performance (Fig. 5.4).
76
Self-Healing Composite Materials
Figure 5.5 Schematic arrangement and dimensions for flexural testing [48].
5.5
Flexural testing
Pang et al. [48] studied the flexural strength of fabricated hollow glass fiber/epoxy preimpregnated tape composites. The standard dimensions of samples for four-point bend flexural testing used are 80 mm (length), 25 mm (width), and 2 mm (depth), which is displayed in Fig. 5.5. The observed results from the flexural testing have demonstrated that a significant amount of strength lost after testing has repaired by the action of self-healing agent within the hollow fibers. Fig. 5.6 and Table 5.3 show the flexural testing results for all the samples. With the intention to offer a reasonable comparison of the testing data, flexural strengths of the samples from B to E have been normalized to a nominal 1%/weight recovery healing agent fluid inside the hollow fibers. During compression testing, all the specimen were subjected to compression load when testing was commenced with the damaged face of the specimen. This was because healing agent repair would have negligible effect. Also, the samples from B to E were employed to measure the degradation rate of the repair healing agent effectiveness over a time duration. Each sample was retained for various periods from 0 to 9 weeks before proceeding to damage, allowed to self-heal for a 24-h duration in the atmospheric conditions and then permitted for flexural testing.
Self-repairing fiber polymer composites: mechanisms and properties
77
900
Flexural strength (MPa)
800 700 600 500 400 300 200 100 F dam.
E 9 weeks
D 6 weeks
C 3 weeks
B 0 weeks
A undamaged
0
Figure 5.6 Flexural testing results [48].
Table 5.3 Flexural strength from the four-point bend flexural testing [48]. Sample type and conditions
Flexural strength (MPa)
Percentage of undamaged state
A/Undamaged
733
100
B/0 weeks stored, damaged, and repaired
682
93
C/3 weeks stored, damaged, and repaired
546
75
D/6 weeks stored, damaged, and repaired
574
78
E/9 weeks stored, damaged, and repaired
404
55
F/damaged
547
75
Williams et al. [52] investigated the flexural strength of T300/914 carbon fiber reinforced with epoxy resin and dispersed the filled hollow glass fibers into the polymer matrix composite. This research work studied the influence of the hollow fiber on the carbon fiber reinforced polymeric composite properties and also determined the self-healing efficiency under the quasi-static impact loading condition. Commercially available healing agent of Cytec Cycom 823 was employed for this investigation.
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Self-Healing Composite Materials
Fig. 5.7 shows the intra-ply shear cracks in the composite material. They determined that the shear cracks’ thickness was 10 lm which was lesser than the delamination (30 lm) due to that a capillary action was produced to transport the healing agent into the fracture zone by the application of capillary force. Therefore through this crevice, healing agent is easily transported into the crack to repair this damage. Fig. 5.8 shows the load displacement plots that were drawn from the data of flexural testing. The curves represent the influence of fracture and healing agents on the flexural testing for the developed composites embedded with hollow fiber. The damaged sample under the flexural load appeared as an intermittent reduction in load and then failure was attained. It perhaps attributed to the growth of crack and delamination, which leads to reducing the load-bearing capacity of a composite.
Figure 5.7 Stopping of shear cracks by hollow fibre in the polymeric composite [52].
Undamaged
Damaged
Healed
900 800 700
Load (N)
600 500 400 300 200 100 0 0
2
4
6
8
Displacement (mm)
Figure 5.8 Load displacement curves for 70 lm spaced hollow fibre composite [52].
10
Self-repairing fiber polymer composites: mechanisms and properties
79
Table 5.4 Results of flexural testing [52]. Type of sample/loading condition
Flexural strength (MPa) Plain composite
Composite with healing system
Undamaged sample
583.3
534.9
Damaged sample at 1700 N
538.6
527.3
Damaged sample at 2000 N
405
443.7
Healed sample at 1700 N
529
Healed sample at 2000 N
519.6
Figure 5.9 Optical micrograph of impact damaged composite [48].
On the other hand, the healed sample performs to repair the fracture sites, stopping the propagation of crack and thereby postponing the composite failure to a greater load level. It also shows a higher degree of closeness in-between the performance of healed and undamaged composite. Table 5.4 shows the flexural test data analysis for the 70-lm spaced fibers. It displays the largest reduction in the flexural strength of undamaged sample by 8%.
5.6
Impact testing
Fig. 5.9 shows a cross-sectional impact damaged composite including delamination, cracking of matrix, and fracture of hollow fiber. The induced damage is presented within or adjacent to the layers of hollow fiber layers and thereby generating the
80
Self-Healing Composite Materials
Table 5.5 Results of impact testing [48]. Indentation force (N)
800
1000
1200
1400
1600
Impact energy (J)
0.25
0.43
0.62
0.80
1.13
96.14 83.31 Tensile strength (N/mm2)
100
75
50
25
0 Solid fiber
Hollow fiber
Figure 5.10 Tensile testing results [53].
circumstances for self-healing through healing agent within the hollow fibers. Table 5.5 shows that the results were observed from the impact testing machine. The fracture occured in the hollow fibers (0 and 90 layers) is permitted to mixing of hardener and healing agent and thus permits the beginning of healing process while at the same time stimulating penetration of cracks and delamination by capillary action. The main aspect is that the impact energy must be of a sufficient threshold value in order to break hollow fiber layers. This threshold value can be used for different applications by the overall self-healing layers within the stack of laminate.
5.7
Tensile testing
Balaji et al. [53] studied the influence of reinforcement on the mechanical properties of the developed polymer composites. The composite specimen were made by the hand layup technique individually with the E glass and hollow fibers. Low density of hollow fiber in comparison with E glass fiber decreases the whole weight of the composites. Fig. 5.10 shows the result of tensile strength from the ultimate tensile testing machine. It denoted that the hollow fiber embedded polymer composite reveals the tensile strength of 96.14 N/mm2 and was considerably higher than that of E glass fiber composite. Thus it was revealed that the hollow nature of hollow fiber offers higher contribution for improving the mechanical properties of the polymeric composites. Therefore from this result, it was concluded
Self-repairing fiber polymer composites: mechanisms and properties
81
Figure 5.11 Compression samples after testing showing broom type failure mode [54].
that the composite with the reinforcement of hollow fiber shows potentially greater advantage than the conventional polymer composite in different engineering fields.
5.8
Compression testing
Hucker et al. [54] reported the mechanical performance of developed hollow fiber reinforced polymeric composites using compression testing. The compression strength of composites was measured using bespoke technique. A significant degree of scatter was noticed for the strength of compression of the different combinations of composites examined. But the suggested results identified that the significant enhancements for the compression strength of hollow fiber embedded composites were around 20% 25%. Fig. 5.11 shows the specimens after compression testing, which shows the broom-type failure mode. In the testing specimens, a small gauge section was allowed for a single measurement of compression strength. It was noticed that the dimensions of testing specimen [10.07 mm (width) 3 2.37 mm (thick)] should be made identical and thereby reduce the variations in the measuring load. The measured compression strength for each specimen is displayed in Table 5.6. Fig. 5.12 shows the specific compression strength of composites which notice the positive effect on the load-bearing capability. The specific compression strength seemed to enhance to a value 10% above the values for developed hollow fiber embedded composites (K2 5 22%) were examined. This value was perhaps further increased by the more reinforcement of fibers by 65%.
5.9
Summary
The research area of autonomic self-repairing healing materials has offered different processes to initiate the function of healing process to repair the damage in the
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Self-Healing Composite Materials
Table 5.6 Results of compression testing [54]. Type of specimen
Gross fiber volume
Density (kg/m3)
Compression strength (MPa)
Specific compression strength (m2/s2)
30/0
0.43
1641
757
0.46
30/25
0.48
1417
760
0.54
45/0
0.43
1573
855
0.54
45/25
0.45
1341
779
0.58
45/40
0.45
1249
665
0.53
60/0
0.45
1682
947
0.56
60/25
0.46
1441
860
0.6
60/50
0.46
1294
640
0.5
Figure 5.12 Specific compression strength result [54].
polymeric composites. In this chapter, a detailed and summarized report of this current research work related to the hollow fiber dispersion into the polymeric composite is provided.
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[3] Heslehurst RB. Challenges in the repair of composite structures-Part II. SAMPE J 1997;33:16 21. [4] Ashby MF, Gibson LJ, Wegst U, Olive R. The mechanical properties of natural materials. I. Material property charts. Proc R Soc Lond Ser A 1995;450A:123 40. [5] Williams KA, Dreyer DR, Bielawski CW. The underlying chemistry of self-healing materials. MRS Bull 2008;33:759 65. [6] Trask RS, Williams HR, Bond IP. Self-healing polymer composite: mimicking nature to enhance performance. Bioinsp Biomim 2007;2:1 9. [7] White SR, Sottos NR, Geubelle PH, Moore JS, Kessler MR, Sriram SR, et al. Autonomic healing of polymer composites. Nature 2001;409:794 7. [8] Keller MW, Blaiszik BJ, White SR, Sottos NR. Recent advances in self-healing materials systems. Adaptive structures: engineering applications. John Wiley & Sons; 2007. p. 247 60. [9] Wu DY, Meure S, Solomon D. Self-healing polymeric materials: a review of recent developments. Prog Polym Sci 2008;33:479 522. [10] Kessler MR. Self-healing: a new paradigm in materials design. Proc Inst Mech Eng G, J Aerosp Eng 2007;221G:479 95. [11] Wang Y, Pham DT, Zhang Z, Li J, Ji C, Liu Y, et al. Sustainable self-healing at ultralow temperatures in structural composites incorporating hollow vessels and heating elements. R Soc Open Sci 2016;3:160488. [12] Schunack M, Gragert M, Do¨hler D, Michael P, Binder WH. Low-temperature Cu(I)catalyzed reactions for self-healing polymers. Macromol Chem Phys 2012;213:205 14. [13] Hillewaere XKD, Prez FED. Fifteen chemistries for autonomous external self-healing polymers and composites. Prog Polym Sci 2015;49 50:121 53. [14] Raimondo M, Longo P, Mariconda A, Guadagno L. Healing agent for the activation of self-healing function at low temperature. Adv Compos Mater 2015;24:519 29. [15] Mauldin TC, Kessler MR. Self-healing polymers and composites. Int Mater Rev 2010;55(6):317 46. [16] Murphy EB, Wudl F. The world of smart healable materials. Prog Polym Sci 2010;35:223 51. [17] Yuan YC, Yin T, Rong MZ, Zhang MQ. Self healing in polymers and polymer composites. Concepts, realization and outlook: a review. Express Polym Lett 2008;2:238 50. [18] White SR, Caruso MM, Moore JS. Autonomic healing of polymers. MRS Bull 2008;33:766 9. [19] Jung D, Hegeman A, Sottos NR, Geubelle PH, White SR. Self-healing composites using embedded microspheres. Am Soc Mech Eng, Mater Div 1997;80:265 75. [20] Bielawski CW, Grubbs RH. Living ring-opening metathesis polymerization. Prog Polym Sci 2007;32:1 29. [21] Nguyen ST, Johnson LK, Grubbs RH. Ring-opening metathesis polymerization (ROMP) of norbornene by a group VIII carbene complex in protic media. J Am Chem Soc 1992;114:3974 5. [22] Kessler MR, White SR. Cure kinetics of the ring-opening metathesis polymerization of dicyclopentadiene. J Polym Sci A 2002;40A:2373 83. [23] White SR, Sottos NR, Geubelle PH, Moore JS, Kessler MR, Sriram SR, et al. Autonomic healing of polymer composites. Nature 2001;409:794 7. [24] Brown EN, Sottos NR, White SR. Fracture testing of self-healing polymer composite. Exp Mech 2002;42:372 9.
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Self-Healing Composite Materials
[25] Brown EN, White SR, Sottos NR. Retardation and repair of fatigue cracks in a microcapsule toughened epoxy composite Part I: Manual infiltration. Compos Sci Technol 2005;65:2466 73. [26] Brown EN, White SR, Sottos NR. Retardation and repair of fatigue cracks in a microcapsule toughened epoxy composite Part II: In situ self-healing. Compos Sci Technol 2005;65:2474 80. [27] Jones AS, Rule JD, Moore JS, Sottos NR, White SR. Life extension of self-healing polymers with rapidly growing fatigue cracks. J R Soc Interface 2007;4:395 403. [28] Chipara MD, Chipara M, Shansky E, Zaleski JM. Self-healing of high elasticity block copolymers. Polym Adv Technol 2009;20:427 31. [29] Rong MZ, Zhang MQ, Zhang W. A novel self-healing epoxy system with microencapsulated epoxy and imidazole curing agent. Adv Compos Lett 2007;16:167 72. [30] Yin T, Rong MZ, Zhang MQ, Yang GC. Self-healing epoxy composites preparation and effect of the healant consisting of microencapsulated epoxy and latent curing agent. Compos Sci Technol 2007;67:201 12. [31] Yin T, Rong MZ, Zhang MQ, Zhao JQ. Durability of self-healing woven glass fabric/ epoxy composites. Smart Mater Struct 2009;18:1 7. [32] Yin T, Rong MZ, Zhang MQ. Self-healing of cracks in epoxy composites. Adv Mater Res 2008;47 50:282 5. [33] Yin T, Zhou L, Rong MZ, Zhang MQ. Self-healing woven glass fabric/epoxy composites with the healant consisting of micro-encapsulated epoxy and latent curing agent. Smart Mater Struct 2008;17:1 8. [34] Yin T, Rong MZ, Wu J, Chen H, Zhang MQ. Healing of impact damage in woven glass fabric reinforced epoxy composites. Composites, Part A 2008;39A:1479 87. [35] Yuan YC, Rong MZ, Zhang MQ, Chen J, Yang GC, Li XM. Self-healing polymeric materials using epoxy/mercaptan as the healant. Macromolecules 2008;41:5197 202. [36] Xiao DZ, Yuan YC, Rong MZ, Zhang MQ. Self-healing epoxy based on cationic chain polymerization. Polymer 2009;50:2967 75. [37] Xiao DZ, Yuan YC, Rong MZ, Zhang MQ. A facile strategy for preparing self-healing polymer composites by incorporation of cationic catalyst-loaded vegetable fibers. Adv Funct Mater 2009;19:2289 96. [38] Keller MW, White SR, Sottos NR. A self-healing poly(dimethyl siloxane) elastomer. Adv Funct Mater 2007;17:2399 404. [39] Beiermann BA, Keller MW, Sottos NR. Self-healing flexible laminates for resealing of puncture damage. Smart Mater Struct 2009;18:1 7. Shchukin DG, Mohwald H. Self-repairing coatings containing active nanoreservoirs. Small 2007;3:926 43. [40] Andreeva DV, Shchukin DG. Smart self-repairing protective coatings. Mater Today 2008;11:24 30. [41] Kumar A, Stephenson LD, Murray JN. Self-healing coatings for steel. Prog Org Coat 2006;55:244 53. [42] Sauvant-Moynot V, Gonzales S, Kittel J. Self-healing coating: an alternative route for anticorrosion protection. Prog Org Coat 2008;63:307 15. [43] Hucker M, Bond IP, Foreman A, Hudd J. Optimisation of hollow glass fibers and their composites. Adv Compos Lett 1999;8:181 9. [44] Hucker MJ, Bond IP, Haq S, Bleay S, Foreman A. Influence of manufacturing parameters on the tensile strengths of hollow and solid glass fibers. J Mater Sci 2002;37:309 15.
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[45] Curtis PT, Travis SWG. Hollow carbon fibers for high performance polymer composites. Plast Rubber Compos. 1999;28(5):201 9. [46] Bleay SM, Loader CB, Hawyes VJ, Humberstone L, Curtis PT. A smart repair system for polymer matrix composites. Composites, Part A, 32. 2001. p. 1767 76. [47] Pang JWC, Bond IP. Bleeding composites-damage detection and self-repair using a biomimetic approach. Composites, Part A 2005;36:183 8. [48] Pang JWC, Bond IP. A hollow fiber reinforced polymer composite encompassing selfhealing and enhanced damage visibility. Compos Sci Technol 2005;65:1791 9. [49] Trask RS, Bond IP. Biomimetic self-healing of advanced composite structures using hollow glass fibers. Smart Mater Struct 2006;15:704 10. [50] Toohey KS, White SR, Sottos NR. Microvascular networks for self-healing polymer coatings. In: Fifteenth United States national congress of theoretical and applied mechanics, Boulder, CO; 2006. [51] Williams HR, Trask RS, Bond IP. Vascular self-healing composite sandwich structures. In: Fifteenth United States national congress of theoretical and applied mechanics, Boulder, CO; June 2006. [52] Williams G, Trask R, Bond I. A self-healing carbon fiber reinforced polymer for aerospace applications. Composites, Part A 2007;38:1525 32. [53] Balaji R, Sasikumar M, Jeyanthi S. Characterisation of hollow glass fiber reinforced vinyl-ester composites. Ind J Sci Technol 2016;9(48):1 5. [54] Hucker M, Bond I, Bleay S, Haq S. Experimental evaluation of unidirectional hollow glass fiber/epoxy composites under compressive loading. Composites, Part A 2003;34:927 32.
Further reading Aıssa B, Therriault D, Haddad E, Jamroz W. Self-healing materials systems: overview of major approaches and recent developed technologies. Adv Mater Sci Eng 2012;1 17. Sanada K, Itaya N, Shindo Y. Self-healing of interfacial debonding in fiber-reinforced polymers and effect of microstructure on strength recovery. Open Mech Eng J 2008;2:97 103.
5
R. Kumar1, N. Rajesh Jesudoss Hynes2, P. Senthamaraikannan3, Anish Khan4,5, Sanjay Mavinkere Rangappa6, Suchart Siengchin6, S.R. Sundara Bharathi7, Abdullah Mohamed Asiri4,5 and Imran Khan8 1 Department of Mechanical Engineering, Vels Institute of Science, Technology & Advanced Studies, Chennai, India, 2Department of Mechanical Engineering, Mepco Schlenk Engineering College, Sivakasi, India, 3Department of Mechanical Engineering, Kamaraj College of Engineering and Technology, Virudhunagar, India, 4Chemistry Departments, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia, 5 Centre of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah, Saudi Arabia, 6Department of Mechanical and Process Engineering, The Sirindhorn International Thai-German Graduate School of Engineering (TGGS), King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand, 7Department of Mechanical Engineering, National Engineering College, Kovilpatti, India, 8Applied Sciences and Humanities Section, University Polytechnic, Faculty of Engineering and Technology, Aligarh Muslim University, Aligarh, India
5.1
Introduction
The structures of fiber with polymer matrix composite are supposed to be delamination crack produced by the impact loading, stresses, and ecological degradation [1 3]. The delamination crack in-between the layers has rigorously reduced the mechanical properties such as compression strength and fatigue life of the developed polymeric composites [4 6]. Also, when the bonded composite materials have delamination damage effect, the tensile strength and fatigue life of those materials are reduced. There are several techniques available to destroy the initiation and development of delamination cracks in the polymer composite including hardened resin, thermoplastic interleaving, and reinforcement by 3D weaving and pinning. Although these techniques are used to resist the initiation of delamination cracks, the growth of the cracks remains unrepaired till the component becomes a failure. Autonomic repair technique in the self-healing is a solution to the problem of delamination damage, which is accomplished by a way of dispersion of small containers into the polymer matrix including a healing liquid agent with low viscosity and catalyst [7 9]. Gradually, the self-healing process begins at the growth of delamination crack, which leads to breaking of the containers and then discharging Self-Healing Composite Materials. DOI: https://doi.org/10.1016/B978-0-12-817354-1.00005-3 © 2020 Elsevier Inc. All rights reserved.
72
Self-Healing Composite Materials
Figure 5.1 Self-healing process [10].
of healing liquid from the containers into the crack. This stored fluid of healing agent acts as a polymer capsule to resolve the damage. Fig. 5.1 shows the principle of self-healing process. The polymerization process is done inside the crack by the reaction of the catalyst with healing agent and then it is used to recover the strength of the composite material. Based on the proper selection and distribution of the healing agent and catalyst, the repairing and recovery of material properties are achieved [10]. It is noted that the performances of self-healing process are mainly dependent upon the activation of the healing agent at the high ambient temperature conditions from 240 C to 280 C, which is practically impossible till now to achieve a high self-healing efficiency [11]. For example, mainly the polymeric composite is appropriate in the aircraft applications, which may endure a low temperature of 260 C; at that temperature all the types of healing agent fluid have attained the frozen stage and they cannot be activated. For this reason, researchers are motivated to develop the self-healing systems in order to withstand the environmental conditions. Only a few investigators have tried to develop the novel healing agents for activation at a low temperature of 10 C [12,13] and influence of ultralow temperature [14]. In general, the self-healing process utilized the small size capsules in order to store the fluid of the healing agent. The size of this type of capsule is typically 10 500 µm and it is dispersed into the polymer matrix of about 2% 20% [15]. Fig. 5.2 shows different types of capsules in the polymeric composite material. In general, this type of capsule is robust enough to handle the force created during manufacturing of self-healing composite and also it should be broken to release the core healing agent to repair the fracture once it is produced in the composite [16 18]. Good adhesion properties to the surrounding polymer material is required in all such applications [19 23]. However, there are some disadvantages in the applications of capsule method in the self-healing process such as low quantity of self-healing liquid is stored to restore the strength and repair the cracks and that they are single-use only [24 29]. Therefore there is a demand and high research needs were required to resolve this problem [30 36]. From this demand, implementation of hollow fibers came into
Self-repairing fiber polymer composites: mechanisms and properties
73
Figure 5.2 (A) Ethylidene norbornene filled Melamine-urea-formaldehyde capsules (B) Dicyclopentadiene Filed urea-formaldehyde capsules (C) Dicyclopentadiene with urea-formaldehyde capsules embedded in the crack (D) dicyclopentadiene filled nanosized capsule [15].
Table 5.1 Comparison of properties of conventional fiber with hollow fiber [45]. Type
Fiber diameter (µm)
Ultimate tensile strength (GPa)
Young’s modulus (GPa)
T300
7
3.53
235
Hollow fiber
38.4
0.52
249.4
existence for storing and transporting more amount of healing agent fluid to repair the damage in the polymeric composites [37 42]. Hollow fibers are long vessels used to store more amount of healing agent and dispersed into the polymer matrix [43,44]. Table 5.1 shows the mechanical properties of conventional and hollow fibers. This form of fibers comprises a one-part resin system, a two-part resin and hardener system, or a resin system with a catalyst or hardener enclosed in the polymer matrix composite [46]. Different approaches for making the hollow fiber self-healing system are given in Table 5.2. This information shows the current research level activity and helps to improve the investigation of this research area.
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Table 5.2 Different mechanisms and strategies followed by the investigators. Selfhealing systems
Mechanism
Strategy
References
Hollow fibers
Bleeding
Bleeding of stored healing agent from the vessels to repair the crack
[46 49]
Blood flow vascular network
Two or three dimensional vascular network has allowed the healing agent to be refilled and transformed to failure zone
[50,51]
5.2
Bleeding mechanism
Fig. 5.3 shows a typical hollow fiber’s approach and microstructure of hollow fibers. Hucker et al. [43] produced the hollow glass fiber in the range of diameter from 30 to 100 mm. The developed hollow fibers are embedded into the glass fiber reinforced polymer matrix composite and filled with an uncured resin material to impart the functionality of self-healing to the composite. During a failure, hollow fibers get fractured leads to imitating the recovery of composite properties by way of the healing process in which the healing agent passes through from fracture opening to infiltrate the failure area. It acts as a barrier to the dangerous effects from the failure of the composite matrix and delamination and also avoids additional matrix crack propagation. This type of repairing procedure is also related to the bleeding mechanism in the biological systems.
5.3
Blood flow vascular network mechanism
The approach of hollow fiber self-healing system described above is related to the several healing agents and it is exhibited to resolve the propagation and growth of the crack in the present fracture site only. However, the amount of healing agent in each hollow fiber is still limited. This difficulty is completely overcome by the vascular network self-healing approach. In this case, healing fluids are transferred with a logical evolution to the required fracture sites by the way of serially interconnected networks [15]. These networks were potentially connected to an external pump system, therefore refilling of healing agent for distribution could be done continuously at a constant rate. Self-healing with this interconnected healing agent networks is systematically related to the above approach. But this approach of vascular healing network is theoretically and visually related to the approach of healing system in the animals and plants.
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Figure 5.3 (A) Schematic diagram of hollow fibers composites (B) SEM image of hollow fiber [43].
Figure 5.4 (A) Capillary network system (B) Microvascular network system [15].
5.4
Mechanical testing
The mechanical properties of hollow fiber embedded polymeric composite are determined by various testing methods such as flexural, impact, tensile, and compression in order to quantify the effect of hollow fiber’s performance (Fig. 5.4).
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Self-Healing Composite Materials
Figure 5.5 Schematic arrangement and dimensions for flexural testing [48].
5.5
Flexural testing
Pang et al. [48] studied the flexural strength of fabricated hollow glass fiber/epoxy preimpregnated tape composites. The standard dimensions of samples for four-point bend flexural testing used are 80 mm (length), 25 mm (width), and 2 mm (depth), which is displayed in Fig. 5.5. The observed results from the flexural testing have demonstrated that a significant amount of strength lost after testing has repaired by the action of self-healing agent within the hollow fibers. Fig. 5.6 and Table 5.3 show the flexural testing results for all the samples. With the intention to offer a reasonable comparison of the testing data, flexural strengths of the samples from B to E have been normalized to a nominal 1%/weight recovery healing agent fluid inside the hollow fibers. During compression testing, all the specimen were subjected to compression load when testing was commenced with the damaged face of the specimen. This was because healing agent repair would have negligible effect. Also, the samples from B to E were employed to measure the degradation rate of the repair healing agent effectiveness over a time duration. Each sample was retained for various periods from 0 to 9 weeks before proceeding to damage, allowed to self-heal for a 24-h duration in the atmospheric conditions and then permitted for flexural testing.
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900
Flexural strength (MPa)
800 700 600 500 400 300 200 100 F dam.
E 9 weeks
D 6 weeks
C 3 weeks
B 0 weeks
A undamaged
0
Figure 5.6 Flexural testing results [48].
Table 5.3 Flexural strength from the four-point bend flexural testing [48]. Sample type and conditions
Flexural strength (MPa)
Percentage of undamaged state
A/Undamaged
733
100
B/0 weeks stored, damaged, and repaired
682
93
C/3 weeks stored, damaged, and repaired
546
75
D/6 weeks stored, damaged, and repaired
574
78
E/9 weeks stored, damaged, and repaired
404
55
F/damaged
547
75
Williams et al. [52] investigated the flexural strength of T300/914 carbon fiber reinforced with epoxy resin and dispersed the filled hollow glass fibers into the polymer matrix composite. This research work studied the influence of the hollow fiber on the carbon fiber reinforced polymeric composite properties and also determined the self-healing efficiency under the quasi-static impact loading condition. Commercially available healing agent of Cytec Cycom 823 was employed for this investigation.
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Fig. 5.7 shows the intra-ply shear cracks in the composite material. They determined that the shear cracks’ thickness was 10 lm which was lesser than the delamination (30 lm) due to that a capillary action was produced to transport the healing agent into the fracture zone by the application of capillary force. Therefore through this crevice, healing agent is easily transported into the crack to repair this damage. Fig. 5.8 shows the load displacement plots that were drawn from the data of flexural testing. The curves represent the influence of fracture and healing agents on the flexural testing for the developed composites embedded with hollow fiber. The damaged sample under the flexural load appeared as an intermittent reduction in load and then failure was attained. It perhaps attributed to the growth of crack and delamination, which leads to reducing the load-bearing capacity of a composite.
Figure 5.7 Stopping of shear cracks by hollow fibre in the polymeric composite [52].
Undamaged
Damaged
Healed
900 800 700
Load (N)
600 500 400 300 200 100 0 0
2
4
6
8
Displacement (mm)
Figure 5.8 Load displacement curves for 70 lm spaced hollow fibre composite [52].
10
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Table 5.4 Results of flexural testing [52]. Type of sample/loading condition
Flexural strength (MPa) Plain composite
Composite with healing system
Undamaged sample
583.3
534.9
Damaged sample at 1700 N
538.6
527.3
Damaged sample at 2000 N
405
443.7
Healed sample at 1700 N
529
Healed sample at 2000 N
519.6
Figure 5.9 Optical micrograph of impact damaged composite [48].
On the other hand, the healed sample performs to repair the fracture sites, stopping the propagation of crack and thereby postponing the composite failure to a greater load level. It also shows a higher degree of closeness in-between the performance of healed and undamaged composite. Table 5.4 shows the flexural test data analysis for the 70-lm spaced fibers. It displays the largest reduction in the flexural strength of undamaged sample by 8%.
5.6
Impact testing
Fig. 5.9 shows a cross-sectional impact damaged composite including delamination, cracking of matrix, and fracture of hollow fiber. The induced damage is presented within or adjacent to the layers of hollow fiber layers and thereby generating the
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Self-Healing Composite Materials
Table 5.5 Results of impact testing [48]. Indentation force (N)
800
1000
1200
1400
1600
Impact energy (J)
0.25
0.43
0.62
0.80
1.13
96.14 83.31 Tensile strength (N/mm2)
100
75
50
25
0 Solid fiber
Hollow fiber
Figure 5.10 Tensile testing results [53].
circumstances for self-healing through healing agent within the hollow fibers. Table 5.5 shows that the results were observed from the impact testing machine. The fracture occured in the hollow fibers (0 and 90 layers) is permitted to mixing of hardener and healing agent and thus permits the beginning of healing process while at the same time stimulating penetration of cracks and delamination by capillary action. The main aspect is that the impact energy must be of a sufficient threshold value in order to break hollow fiber layers. This threshold value can be used for different applications by the overall self-healing layers within the stack of laminate.
5.7
Tensile testing
Balaji et al. [53] studied the influence of reinforcement on the mechanical properties of the developed polymer composites. The composite specimen were made by the hand layup technique individually with the E glass and hollow fibers. Low density of hollow fiber in comparison with E glass fiber decreases the whole weight of the composites. Fig. 5.10 shows the result of tensile strength from the ultimate tensile testing machine. It denoted that the hollow fiber embedded polymer composite reveals the tensile strength of 96.14 N/mm2 and was considerably higher than that of E glass fiber composite. Thus it was revealed that the hollow nature of hollow fiber offers higher contribution for improving the mechanical properties of the polymeric composites. Therefore from this result, it was concluded
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Figure 5.11 Compression samples after testing showing broom type failure mode [54].
that the composite with the reinforcement of hollow fiber shows potentially greater advantage than the conventional polymer composite in different engineering fields.
5.8
Compression testing
Hucker et al. [54] reported the mechanical performance of developed hollow fiber reinforced polymeric composites using compression testing. The compression strength of composites was measured using bespoke technique. A significant degree of scatter was noticed for the strength of compression of the different combinations of composites examined. But the suggested results identified that the significant enhancements for the compression strength of hollow fiber embedded composites were around 20% 25%. Fig. 5.11 shows the specimens after compression testing, which shows the broom-type failure mode. In the testing specimens, a small gauge section was allowed for a single measurement of compression strength. It was noticed that the dimensions of testing specimen [10.07 mm (width) 3 2.37 mm (thick)] should be made identical and thereby reduce the variations in the measuring load. The measured compression strength for each specimen is displayed in Table 5.6. Fig. 5.12 shows the specific compression strength of composites which notice the positive effect on the load-bearing capability. The specific compression strength seemed to enhance to a value 10% above the values for developed hollow fiber embedded composites (K2 5 22%) were examined. This value was perhaps further increased by the more reinforcement of fibers by 65%.
5.9
Summary
The research area of autonomic self-repairing healing materials has offered different processes to initiate the function of healing process to repair the damage in the
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Self-Healing Composite Materials
Table 5.6 Results of compression testing [54]. Type of specimen
Gross fiber volume
Density (kg/m3)
Compression strength (MPa)
Specific compression strength (m2/s2)
30/0
0.43
1641
757
0.46
30/25
0.48
1417
760
0.54
45/0
0.43
1573
855
0.54
45/25
0.45
1341
779
0.58
45/40
0.45
1249
665
0.53
60/0
0.45
1682
947
0.56
60/25
0.46
1441
860
0.6
60/50
0.46
1294
640
0.5
Figure 5.12 Specific compression strength result [54].
polymeric composites. In this chapter, a detailed and summarized report of this current research work related to the hollow fiber dispersion into the polymeric composite is provided.
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Further reading Aıssa B, Therriault D, Haddad E, Jamroz W. Self-healing materials systems: overview of major approaches and recent developed technologies. Adv Mater Sci Eng 2012;1 17. Sanada K, Itaya N, Shindo Y. Self-healing of interfacial debonding in fiber-reinforced polymers and effect of microstructure on strength recovery. Open Mech Eng J 2008;2:97 103.