Tensile Behavior of Hybrid Epoxy Composite Laminate Containing Carbon and Basalt Fibers

DOI 10.1515/secm-2013-0003 Sci Eng Compos Mater 2014; 21(2): 211–217

I.D.G. Ary Subagia and Yonjig Kim* Tensile behavior of hybrid epoxy composite laminate containing carbon and basalt fibers

Abstract: This paper investigated the effect of the incor- This is largely because of the good mechanical properties poration of basalt fibers on the tensile properties of car- and light structure of composite materials [7, 8]. Carbon bon fiber-reinforced epoxy laminates manufactured by fiber as reinforcement of polymeric matrix composite vacuum-assisted resin transfer molding. The purpose of presents several advantages such as high modulus, high this research was to design a carbon-basalt/epoxy hybrid strength and stiffness, good creep resistance, low density, composite material that is of low cost in production, is heat and flame resistance, and good compatibility with lightweight, and has good strength and stiffness. The ten- the epoxy matrix [9]. However, carbon fibers are relatively sile strength and stiffness of the hybrid laminates demon- brittle and very expensive [10]. Recently, glass fibers have strated a steady, linear decrease with an increase in basalt been recommended as one of the most popular reinforce- fiber content, but the fracture strain gradually increased ments that can hybridize carbon fiber-reinforced polymer together with the increase in the basalt layer content. In (CFRP). The principal advantages of glass fibers are low this study, the incorporation of basalt fibers into the car- cost, high tensile strength, high chemical resistance, and bon fiber-reinforced polymer (CFRP) showed lower tensile excellent insulating properties [11]. However, glass fibers strength than CFRP but has higher tensile strain. Further- also have several disadvantages, which include a rela- more, we found that the arrangement and enhancement tively low tensile modulus and high density, relatively low of basalt fiber into the CFRP significantly influence the fatigue resistance, and high hardness, which causes exces- mechanical properties of interply hybrid composites. sive wear on molding dies and cutting tools, although it has a low price. In addition, glass fiber is toxic [12]. Keywords: bonding; carbon fiber-reinforced plastic; In the past few years, with the increase in interest composites; tensile test; vacuum-assisted resin transfer regarding ecofriendly material, several types of fibers molding (VARTM). like organic and inorganic fibers were introduced to com- pounds with carbon fiber [13]. Recently, basalt fiber was introduced as a new type of reinforcing fiber [14, 15] that *Corresponding author: Yonjig Kim, Division of Mechanical Design is more competitive than glass fibers [16]. Basically, basalt Engineering, College of Engineering, Chonbuk National University, 567 Baekje-daero, Deokjin-gu, Jeonju, 561-756 South Korea, fibers are natural fibers that are produced from basalt e-mail: [email protected]; and Advanced Wind Power System volcanic rock by melting [10]. Good mechanical proper- Research Center, Chonbuk National University, Korea ties, noncombustibility, high resistance to temperature, I.D.G. Ary Subagia: Division of Mechanical Design Engineering, nontoxicity, and good chemical stability are the main College of Engineering, Chonbuk National University, 567 Baekje- advantages of basalt fiber. It is also economically and daero, Deokjin-gu, Jeonju, Korea; and Mechanical Engineering, Faculty of Udayana University, Denpasar, Bali, Indonesia environmentally viable [4, 14]. Several studies have shown the potential of basalt fibers as reinforcement materials to improve the properties of fiber-reinforced composites. The effect of temperature, adhesion time, and surface 1 Introduction treatment on the mechanical properties of thermoplas- tic basalt plastics were studied by Bashtannik et al. [17]. In recent years, hybrid composites have been increasingly Czigany et al. [18] studied the characteristics of basalt developed to improve the drawbacks of single-fiber com- fiber-reinforced hybrid polypropylene. Wei et al. [19] posites. Hybrid composites are materials consisting of two studied the tensile strength of basalt fiber with nano-SiO2- or more different fiber types, which act as reinforcement, epoxy coating. In their work, the incorporation of nano- and a polymer resin as matrix, which holds the fibers [1]. SiO2 coating increased the tensile properties of basalt fiber Recently, composite material has been applied to many compared to pure epoxy coating. Manikandan et al. [20] technological products like automotive and aerospace reported that basalt fiber-reinforced polymer (BFRP) has products [2], marine parts, sports equipment [3], windmill better mechanical properties compared with glass fiber- blades [4, 5], and lightweight construction materials [6]. reinforced polymer. Other studies have reported on the 212 I.D.G. Ary Subagia and Y. Kim: Tensile behavior of hybrid epoxy composite laminate containing carbon effect of nanoparticle addition to the mechanical properties of composites from carbon and basalt fiber [21] and different filler fibers [22–25]. However, very few studies have been carried out on the combination of carbon and basalt fiber laminates. In this work, we investigated the tensile properties of carbon- and basalt fiber-laminated composites, specifi- Figure 1 Schematic layout of VARTM: (1) bronze plate, (2) laminate fiber, (3) release films, (4) breather net, (5) vacuum tube, (6) plastic cally focusing on the effect of the number of basalt fiber bag, and (7) sealant tape. layers and arrangement position on the carbon fiber composite laminates. The aim of this work was to assess the suitability of basalt fiber as an effective competitor of glass injected into the impregnated preform at a pressure of -80 fiber for the reinforcement of composites. Tensile tests kPa using a vacuum pump (Airtech Ulvac G-100D, ULVAC were carried out. The failure surfaces of the composites Kiko Incorporated, Japan). The panel was then dried inside were analyzed by scanning electron microscopy (SEM). an oven at 65oC for at least 2 h. In this work, we laminated 10 layers of fibers in every panel, constituting about 62 wt% of the hybrid composite. The thickness of panels manufactured through VARTM was approximately 2 mm. The details 2 Experimental of the combination of the fibers are shown in Table 1.

2.1 Materials 2.3 Tensile test and characterization In the present study, we used plain woven carbon fiber (C120-3K; fabric weight = 200 ± 10 g/m2; fabric In the present study, tensile tests were performed to thickness = 0.25 ± 0.02 mm) purchased from Hyun Dai determine the stress-strain behavior of each composite Fiber Co. Ltd. (Korea), and plain woven basalt fiber (carbon-basalt fibers/epoxy) in accordance with ASTM D (EcoB4 F210; fabric weight = 210 ± 10 g/m2; fabric thick- 638 [28]. Five dog-bone-type specimens were cut for each ness = 0.19 ± 0.20 mm) provided by Secotech (Korea). composite panel using water-jet machining (see Figure The resin matrix used was a modified bisphenol 2). The tensile tests were performed in a universal testing A epoxy resin (HTC-667C; specific gravity = 1.16 ± 0.02; machine (Unitect-M, R&B Research and Business, Korea) viscosity = 1.2 ± 0.5 kg/m.s) with a modified aliphatic amine at a constant crosshead speed of 2.0 mm/min at room tem- hardener and was supplied by Jet Korea Co. (Korea). perature. The strain was measured through an extensometer with a gage length of 50 mm (Extensometer model 3542-0200-50-ST, Epsilon Tech. Corp, WY, USA). The failed 2.2 Composite fabrication surface characterization of each specimen was investigated and analyzed using SEM. Microscopic analyses were The panels of laminates were manufactured by a vacuum- assisted resin transfer molding (VARTM) process. VARTM is an adaptation of the resin transfer molding (RTM) process Table 1 Properties of CFRP, BFRP, and hybrid composite with different numbers and arrangement positions of basalt fiber into that exploits vacuum pressure of < 101.32500 kPa to draw the carbon fiber/epoxy. off resin to the impregnate preforms. VARTM presents many benefits in composite fabrication such as low cost, Sample Sample Number of fibers Basalt fiber low void contents, and stable product thickness [22, 26, 27]. code fraction (wt%) CF BF The schematic of the present VARTM process is shown in Figure 1. In this work, a bronze plate with dimensions of CFRP C 10 0 62 BFRP B – 10 61.9 300 mm × 300 mm was prepared and oiled with a liquid wax C B C B1 9 1 6.19 (for safe release) on the top of plate. Sealant tape was then 4 1 5 C4B2C4 B2 8 2 12.4 placed around the plate. The carbon and basalt fibers were C3B3C4 B3 7 3 18.6 both cut with a dimension of 250 mm × 250 mm and arranged C3B4C3 B4 6 4 24.8 on the mold according to the laminate design. Next, epoxy C2B5C3 B5 5 5 30.9 B C B BC 6 4 24.8 resin with a hardener mixture ratio of 5:1 after degassing in 2 6 2 C B C B C CB 6 4 24.8 vacuum desiccators (at -70 cmHg for 40 min), was directly 2 2 2 2 2 I.D.G. Ary Subagia and Y. Kim: Tensile behavior of hybrid epoxy composite laminate containing carbon 213

Table 2 Mechanical properties of CFRP, BFRP, and hybrid composites with different contents of basalt fiber into the carbon fiber/epoxy laminate.

Hybrid Tensile strength Young’s modulus Tensile code σ (MPa) E (GPa) strain ε

CFRP 687 65 1.062 B1 630 60 1.07 Schematic of dog-bone-type specimen for tensile test. Figure 2 B2 602 55 1.095 B3 558 50 1.1 B4 536 45 1.14 performed aiming to recognize the failure mode of each B5 502 40 1.2 hybrid composite. BFRP 402 18 2.2

contrast, the tensile strength of the composites with the 3 Results and discussion basalt fiber has values slightly lower than that of CFRP but much higher than BFRP (see Figure 3). In other words, 3.1 Tensile properties the enhancement depending on the content of basalt fiber has a significant impact on the ultimate strength, elastic Figure 3 illustrates the typical stress-strain curves modulus, and strain of the composite laminate. As a result obtained from the tensile test for each laminate, and of basalt reinforcement in CFRP, the interply hybrid com- Table 2 gives the summary of the mechanical properties. posites could take more strain before incurring failure Here, the basalt fabric layers were placed between carbon [1, 29]. fabric layers (i.e., B1–B5). It can be directly noticed that Figure 4 shows photographic images of the failed the behaviors of each laminate all showed a linear trend. samples after the tensile test. The laminate with only one The slope of the stress-strain curves demonstrated a layer of basalt fiber in CFRP (Figure 4A) showed a brittle proportional decrease with the increase in the number mode of failure. However, the damage modes of compos- of basalt fibers in the composite laminates. However, ite laminates B2, B3, B4, and B5 (Figure 4B–D) demon- the tensile strain showed an increasing trend with the strated many dispersed failure fibers. B4, with four plies increase in the number of basalt fabric layers. This signi- of basalt fiber, incurred flat damage on carbon layers after fies that at the highest number of basalt layers, i.e., B5, the the tensile test and disperse fiber failure on the basalt composite laminate showed the highest tensile strain. In layer (Figure 4D), which means that the interply hybrid composites can take more strain before failure under tensile loading. Similar results were also reported by other research groups [30, 31] when they investigated the behavior of FRP and hybrid FRP. From Table 2, the results of the mechanical properties depending on the basalt content show a linearly decreasing tensile strength and Young’s modulus values of the hybrid composites with the increase in the number of basalt layers. This signifies that the incorporation of basalt fiber significantly affected the tensile behavior of hybrid composites. However, an increase of basalt fibers also raises the strain behavior of hybrid composite. Here, we can make the approximate relations for the tensile strength and the Young’s modulus of the interply hybrid composites as a function of the number of basalt fiber layers, x. It has been derived as follows:

σH = -37x+687 (MPa) (1) Figure 3 Stress-strain curves of CFRP, BFRP, and hybrid composites with different numbers of basalt fiber layers. EH = -5x+64 (MPa) (2) 214 I.D.G. Ary Subagia and Y. Kim: Tensile behavior of hybrid epoxy composite laminate containing carbon

C D

Figure 4 Optical images of failed hybrid composite under tensile loading: (A) B1, (B) B2, (C) B3, (D) B4, and (E) B5.

3.2 Hybridization effect the outermost layer and the carbon layer in the innermost layers showed an increase in tensile properties of the com- To investigate whether the arrangement of basalt fibers posite compared to B4. Figure 5 shows the stress-strain in the hybrid composite laminate has some effect on its curves of hybrid composite for B4, BC, and CB. Here, the tensile properties, we tested several types of specimens hybrid composite with basalt layers placed in the exterior that have different arrangements, i.e., BC, CB, and B4 (see of BC has higher tensile strength and strain compared with Table 3). In all cases, the specimens were made by using the carbon layers placed in the exterior of B4. The tensile four and six plies of basalt and carbon fibers, respec- strength values of hybrid composite were about 571 and tively. In the present study, placing the basalt fibers in 536 MPa for hybrid composites BC and B4, respectively. At the same time, the Young’s modulus of BC was about Table 3 Effect of the positioning of basalt or carbon fiber in the 49.5 GPa, which was higher than that of B4 (∼47 GPa). hybrid epoxy laminate. Furthermore, the hybrid composite with dispersed stacks of basalt layers between the carbon layers, i.e., CB, had a Hybrid Tensile strength Young’s modulus Tensile tensile strength and Young’s modulus of about 556 MPa code σ (MPa) E (GPa) strain ε and 47.5 GPa, respectively, which were lower compared B4 536 45 1.14 with that of BC, but higher than that of B4 (see Table 3). BC 571 49.5 1.15 The tensile strains of hybrid composites of B4, BC, and CB CB 556 47.5 1.17 have almost similar values (Table 3). This result indicates I.D.G. Ary Subagia and Y. Kim: Tensile behavior of hybrid epoxy composite laminate containing carbon 215

flat features. Figure 7 shows the SEM images of cross sec- tions of the failed tensile specimens. B4 (Figure 7A) shows few carbon fiber-matrix debonding and basalt fiber shows damage in dispersed failures. In the hybrid composite BC (Figure 7B), there are some carbon fiber pullouts, debonding, and fiber-matrix delamination. Some longitudi- nal delaminations also occurred in basalt layers. In this case, the interfaces between carbon fiber and basalt fiber were delaminated caused by the effect of residual stress between the layers during tensile loading. At present, the carbon layers failed in a flat manner and basalt layers failed in a rumpled manner. This is due to the fact that carbon fiber is brittle and basalt fiber is relatively ductile. In the hybrid composite, with an alternatively sequenced manner (Figure 7C), some rumpled failures occurring on the basalt layer, causing delamination between the carbon layer and basalt layers, were observed, as similarly Figure 5 Stress-strain curves of the hybrid composites with differ- attempted by Wei et al. [19]. This made its tensile strength ent stacking varieties: B4, BC, and CB under tensile loading. lower than that of other hybrid composite arrangements, even though the strain on this arrangement was a little that the variation of the basalt-reinforcing position has a higher (see Table 3). This phenomenon is attributed to the major effect on the tensile strength and Young’s modulus brittle failure of carbon fibers, where the specimen broke of this type of hybrid composite. Tensile strength and through all layers with an abundant rupture [32]. Young’s modulus of BC are higher than that of B4 by 6.5% and 5.3%, respectively. 4 Conclusions

3.3 Fracture characterization In this study, the effect of the position and contents of basalt fiber on the tensile properties of carbon-basalt/ Figures 6 and 7 show the SEM images of the fractured sur- epoxy hybrid composite, which was prepared by faces of the present samples after the tensile test. Figure 6A VARTM, has been examined. The increase in the number shows cross-sectional damage of the BFRP, which shows of basalt fiber layers stacked in between carbon fiber rumpled failure features, whereas in Figure 6B, we can layers led to a decrease in tensile strength and Young’s observe that the CFRP failed via a tensile mode failing by modulus but an increase in tensile strain of the hybrid

Figure 6 Low- and high-magnification SEM images for the cross section of the fracture surface of the hybrid composites: (A) BFRP and (B) CFRP. 216 I.D.G. Ary Subagia and Y. Kim: Tensile behavior of hybrid epoxy composite laminate containing carbon

A A’

B B’

C C’

Figure 7 Low- and high-magnification SEM images for the cross section of the fracture surface of the hybrid composites: (A-A’) B4, (B-B’) BC, and (C-C’) CB.

composites. The results suggest the possible control the hybrid composite leads to the variation of the frac- and balance of the tensile properties of the interply ture mechanism of the composite under tensile loading. hybrid composite laminates by controlling the number For B4 and CB, the delamination between carbon and of basalt fiber layers. The tensile properties of carbon- basalt occurred before the fracture of reinforcing fibers, basalt/epoxy hybrid composite depended on the basalt whereas for BC, the delamination occurred after the fiber position. Here, the BC composite, wherein carbon carbon layer had broken. fiber layers were inserted between basalt layers, had the highest tensile strength and Young’s modulus. The Acknowledgments: This research was supported by the change in the type of arrangement of the basalt fiber in Basic Science Research Program through the National I.D.G. Ary Subagia and Y. Kim: Tensile behavior of hybrid epoxy composite laminate containing carbon 217

Research Foundation of Korea (NRF) funded by the Minis- Ph.D. program at Chonbuk National University in South try of Education, Science and Technology (2010-0022359). Korea. I.D.G. Ary Subagia acknowledges the support from the Degree General High Education (DGHE) postgraduate Received January 3, 2013; accepted June 23, 2013; previously pub- abroad scholarship of the Republic of Indonesia for his lished online August 8, 2013

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