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Tensile and Compressive Properties of Epoxy Syntactic Foams Reinforced by Short Glass Fiber

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Tensile and Compressive Properties of Epoxy Syntactic Foams Reinforced by Short Glass Fiber Indian Journal of Engineering & Materials Sciences Vol. 24, August 2017, pp. 283-289 Tensile and compressive properties of epoxy syntactic foams reinforced by short glass fiber Wei Yu*, Hailong Xue & Meng Qian Key Laboratory of Mechanical Reliability for Heavy Equipments and Large Structures of Hebei Province, Yanshan University, Qinhuangdao 066004, China Received 22 April 2015; accepted 29 March 2017 The hollow glass microsphere/epoxy resin syntactic foams reinforced by short glass fibers are fabricated. The microsphere is constant 5% weight ratio to the epoxy resin matrix and the fibers with weight ratio to the resin matrix are 5%, 10%, 20% and 30%. Their mechanical properties are studied by uniaxial compression test and tension test. The compressive deformation morphology and tensile fracture surfaces of syntactic foams are investigated. It is obtained that the compressive and tensile strength of syntactic foams are enhanced by adding fibers, and the 10% fiber weight ratio is found to be much more efficient, which shows 70% and 49% higher compressive strength and tensile strength respectively than that of syntactic foams without fiber content. However, the strength decreases with further addition of glass fiber beyond 10% weight ratio. The reason of strength enhancements is discussed. The compressive and tensile moduli are also enhanced by adding fibers. The ductility of composites is found to decrease with larger fiber filling. Keywords : Syntactic foams, Epoxy, Hollow glass microsphere, Glass fiber The composite of hollow particle filled polymer is mechanical properties and thermal properties by called syntactic foams. Hollow particles are usually experiment. It is shown that the tensile strength, made up of glass, ceramic, materials. The epoxy resin, flexural strength and elastic modulus are enhanced by polyurethane, polyethylene, nylon, rubber, etc are adding fiber. Ferreira et al .20 presents the results of usually used as matrix. In recent years, the syntactic the addition of short fibres on the fatigue behaviour of foams attracted much attention by many scholars due syntactic foams. Their results show that the fatigue to its low weight, low moisture absorption, high strength more than 30% by the addition of small specific strength and good energy absorption 1-5, and percentages of glass or carbon fiber. Wang et al .22 widely applied in the machinery industry, investigated the flexural properties of syntactic foams transportation, construction, aerospace industry and reinforced by fiberglass mesh and short glass fiber. On deep-sea engineering 6-8. As two kinds of commonly the other hand, graphene platelets and nanofibers are used materials in the industry, the mechanical also used as reinforcements in these studies 7,24-28 . properties and modification of epoxy resin and Numerical method is also used to investigate the effect polyurethane have been widely studied by many of fiber reinforcement on properties of syntactic foams 29 . scholars 9-12 . Add higher volume fraction of hollow From the above research, the increase on particle can greatly reduce the density of syntactic mechanical properties of syntactic foams is not foams. However, the strength and stiffness of obvious for the lower contenting of glass fiber. With composites greatly decrease because of adding higher the increase of glass fiber filling amount, the volume fraction of hollow particle 10,11,13 . mechanical performance of syntactic foams increase. Many studies reported in literature show that However, how much glass fiber filled in syntactic adding fibers in syntactic foams is one of the methods foams is reasonable, which has yet to see literature of improving the mechanical properties 14-23 . report. Although the study of fiber reinforced epoxy Karthikeyan et al .15 observed that adding of chopped resin composite is more and the influence of fiber strand fibres into the syntactic foam system increased content on the composite mechanical properties is the flexural strength. Wouterson et al .18 studied the also analyzed, the fiber reinforced epoxy resin effect of fiber volume fraction and length on containing hollow glass microspheres composites, _____________ especially the fiber content is higher, has a little *Corresponding author (E-mail: [email protected] ) research. The interactions of the fiber and 284 INDIAN J. ENG. MATER. SCI., AUGUST 2017 microsphere have important effect on the performance compression specimens were Φ 19 mm × 20 mm, and of composites. Seeking a reasonable content of fibers for tensile tests were 40 mm × 10 mm × 6 mm, when the content of hollow glass microspheres and (Fig.1). Three specimens were tested in every series. fibers are higher is the purpose of this paper. In the The load rate of 1 mm/min was maintained for all the present study, the syntactic foams with 5% hollow testing. The compressive deformation set as glass microsphere mass fraction and with four kinds 50% strain. of glass fiber weight ratio in the range of 5%-30% are prepared. The influence of glass fiber contents on Results and Discussion mechanical properties of composites are studied by Figure 2 shows the deformation morphology of tensile and compressive experiments. syntactic foams after compression. It is observed that all the cylindrical specimens present the shape of Experimental Procedure drum after compression because of the friction between specimen and the pressure head. The Materials specimens without fiber or with low fiber content Hollow glass microsphere with bulk density of 0.11 3 have not obvious cracks on the surface by applying g/cm , crushing strength of 3-5 MPa and average 50% strain. It indicates that the specimens are still diameter of 60 µm were used as the lightweight filler. not completely destroyed. There are small cracks on Glass fiber with average length of 106 µm and the surface of syntactic foams with 10% fiber average diameter of 13 µm were used as reinforcing weight ratio. However, there are obvious large phase, and its original yarn breaking strength is not oblique cracks in the specimens which fiber less than 0.28 N/Tex. Hollow glass microsphere and contenting more than 10%. It is similar to that of glass fiber were supplied by Qinhuang Hollow cast iron cylinder specimen compression damage. It Glass Microsphere Co., LTD, China. The epoxy indicated that the composites with a lot of fiber resin contents have brittle characteristics. The reason is (E-44) and hardener polyamide (650#) were the brittle fracture of microspheres and fibers. In supplied by Langfang Norsun Chemical Industry addition, it can be seen from the Fig.2, the heights Co., LTD. of specimens are different, because of the different resilient rate of specimen. The resilient rate Material processing and testing decrease with the increasing of fiber content. In this paper, hollow glass microspheres are added The compressive and tensile stress-strain curves in 10% weight ratio of the epoxy resin as well as are shown in Fig. 3. It is observed that the hardener in all syntactic foams. The short glass fibers are added in the range of 5-30% weight ratio of the Table 1 — Material composition resin matrix. The unreinforced syntactic foams are Specimen Epoxy resin Hollow glass Glass fiber Density ρ/ also fabricated for comparison. Table 1 shows the No. matrix (g) microsphere (g) (g) (g·cm -3) design proposal and the density. The specimen 1 200 10 0 0.927 preparation process is as follows. Firstly, the epoxy 2 200 10 10 0.940 resin and hardener were heated respectively in a water 3 200 10 20 0.955 4 200 10 40 0.991 bath pot at 80°C to be fully diluted. Then, the glass 5 200 10 60 1.003 fiber were firstly added to the epoxy resin and stirred for 20 min to disperse the fibers fully. After that, the hollow glass microspheres were added and stirred additional 20 min. Then, the sufficient diluted hardener was slowly mixed and stirred fully. And then, the slurry was transferred to tabular and Fig. 1 — Schemes of tensile specimens cylindrical plastic moulds. Finally, the specimens were cured at 40°C for 24 h and post-cured at 80°C for 2 h. Compressive and tensile tests were conducted in a universal testing machine (WDW3100, Changchun China) at room temperature. The dimensions for Fig. 2 — Deformation morphology of compressive specimens YU et al .: EPOXY SYNTACTIC FOAMS REINFORCED BY SHORT GLASS FIBER 285 Fig. 3 — Stress-strain curves of syntactic foam s (a) compression Fig. 4 — The strength and modulus versus the fiber weight ratio and (b) tension The results indicate that the addition of fibers compressive stress-stain curves show the same decreases the ductility of the syntactic foams. trend, (see Fig. 3a). The first stage of the curves is Figure 3(b) also shows that the tensile properties of the elastic stage. The yield stage is begin when the syntactic foams with 10% fiber weight ratio is strain is about 4.5%, then the curves down slowly better than the others, and the tensile fracture strain and then slowly rising within a larger strain range. is about 5%. It indicates that adding short glass The stress-strain curves rise faster when the strain fiber with 10% weight ratio can effectively enhance are beyond 25%. The figure is also shows that the the tensile properties of syntactic foams, and have position of all the curves of fiber reinforced syntactic little effect on its ductility. foams are higher than that of plain syntactic foams. It Figure 4 shows the relationship of the strength indicates that the mechanical properties of syntactic and modulus versus the fiber weight ratio. In most foams had obvious enhancement by adding short glass cases, the three data points of a same proportion are fibers. However, the three curves of syntactic foams close in addition to the individual specimen. From with fiber weight ratio 10%, 20% and 30% are close, Fig.
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