Indian Journal of Engineering & Materials Sciences Vol. 25, October 2018, pp. 425-431

Evaluation of tensile, flexural and impact properties on sisal/glass fiber reinforced polymer hybrid composites

S Ragunatha*, C Velmuruganb, T Kannana & S Thirugnanamc

aMechanical Engineering, SVS College of Engineering, Coimbatore 642 109, India bMechanical Engineering, Kumaraguru College of Engineering, Coimbatore 641 049, India cMechanical Engineering, Valliammai Engineering College, Kancheepuram 603 203, India

Received 29 July 2016; accepted 18 August 2017

The effective utilization of natural fibers is the main objective of the present research work. But natural fibers alone is not to meet the required strength properties. Hence, one more artificial material is to be added for obtaining required strength. The study undergone on sisal- glass fiber reinforced polymer composites, it is developed by heat compression moulding techniques and their mechanical properties such as tensile, flexural and impact strength are evaluated experimentally under the ASTM standards. The binding properties, internal crack and fiber alignments are examined by morphological test. It is observed that, the tensile strength of sisal/glass fiber composites produce 255.80 MPa. It is approximately same strength (260.10 MPa) of artificial fiber composites. Hence, the use of artificial fibers are minimized by addition of natural fiber which reduces cost of materials and utilization of natural resources. From the SEM test, fiber misalignments are over loading of fibers on composites leads decline in strength. The moisture and wax content of natural fiber may decrease hardness value (23.0 RHN).

Keywords: Hybrid composites, Unsaturated polyester, Sisal fiber, Glass fiber, Strength analysis

The composite is one of the most developed fields in engineering and science; hence it should have much more mechanical, chemical and physical properties than the conventional materials via high strength to weight ratio, impact strength, durability, stiffness and toughness.1-5 The wide availability of natural fiber has encouraged the development of natural fiber composites. Hence, global development depends on effective utilization of recourses such as natural materials and its products. But the natural materials don’t need the help of researchers such as strength, flexibility, durability and so on. Composite refers to a material system which is composed of discrete constituent (reinforcement) distributed in a continuous phase (matrix) and which derives its distinguishing characteristics from the properties of its constituents, from the geometry and architecture as well as the properties of the boundaries (interfaces) between different constituents.6-9 Hence, now a-days the developers concentrate to produce artificial materials to meet the requirements, but it may affect the environment and create some natural issues, to overcome. The specimens are

prepared by glass fiber and epoxy resin along with natural fiber materials.

The important advantages of natural fibers, such as low density, appropriate stiffness, highly disposable, renewable, recyclable and biodegradable. Banana fiber in combination with glass has proved to be excellent for making cost effective composite materials.10 An effort to utilize the advantages offered by renewable resources for the development of bio-composite materials based on bio-epoxy resin and natural fibers such as Agave sisalana; Musa sepientum; Hibiscus sabdariffa and its application in bone grafting substitutes.11 Increasing concern about global warming and depleting petroleum reserves have made scientists to focus more on the use of natural fibres such as bagasse, coir, sisal, jute etc.12

In fabrication of composite change in proposition of epoxy which pre-dominantly improves its mechanical properties. Natural fibers with the epoxy matrices results in lower density, weight, and cost, accompanied with physical, mechanical, and thermal properties extensively increased and are used for manufacturing of high-performance automotive, aerospace products.13

The effect of fiber twist on the tensile properties of sisal fibers. It was concluded that dimension and

——————— *Corresponding author (E-mail: ragunathsundaram@gmail.com)

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mechanical properties of single sisal fiber were changed after the twisting process. Untwisted sisal fiber presented a higher tensile strength than thetwisted fiber due to the fracture of the fiber cell wall. But the tensile modulus showed higher values after being twisted since the tensile strain.14 The structural equation modeling, a second-generation multivariate analysis technique that determines the degree to which a theoretical model is supported by the sample data. It is concluded that a newly developed or existing psychological instruments and to examine the possibility of complex. It provides an overview of structural equation modeling and steps for conducting SEM analysis.15

The variations of impact strength and compressive strength of unsaturated polyester based on sisal/glass hybrid composites with fiber loading. It is concluded that no significant improvement in impact strength of the sisal/glass hybrid composites has been observed by these treatments, whereas a marginal increase in compressive strength of these hybrid composites has been observed.16 Analysis on sisal-epoxy composites prepared with different fiber weight fractions. It concluded that an enhancement of 110% in optimally treated fiber tensile property resulted in improvement of composite mechanical properties like compression, tensile, inter laminar shear stress and energy absorption. The composite mechanical properties have improved to different degrees.17 Natural fiber composites based on sisal and its hybrid composites with polyester as resin matrix. Increasing the sisal fiber content resulted in a reduction in the hardness and flexural properties. It is addressed that properties were found to increase with alkali treated fabrics used in composite. The properties of polyester composites are found to be better than those of sisal polyester composites.18

The structural features were revealed by the scanning electron microscopy (SEM). SEM micrographs of impact fractured and worn surfaces clearly demonstrate the interfacial adhesion between fiber and matrixes.19 Tensile strength of the composite specimen increased for

approximately 25% of weight fraction of the fibers and hybrid combination of ridge guard and sisal fiber is 65% increase in the tensile strength.20 Tensile, flexural and impact strength of the composites are investigated in the process of mechanical characterization. Glass fiber on top and bottom layers of the laminate improves its surface finish and strength.21 Glass/sisal fibers were combined in the same matrix (unsaturated polyester) to make hybrid composites and the tensile and flexural properties are studied. It is also observed that the chalk powder quantity increases tensile and flexural properties decreases.22

From the above literature review, the glass fiber is added with sisal fiber to make a hybrid composites by compression moulding techniques. The mechanical properties such as tensile, flexural, impact strength and hardness number on developed fiber reinforced polymer composites are evaluated. Experimental Procedure

Materials and fabrication The natural fibers such as sisal fiber available from

Tamilnadu Agriculture University, Coimbatore dist., Tamilnadu, India. The sisal fiber is taken as a continuous form (long fiber) to obtain high aspect ratio (fiber length to diameter ratio). The high aspect ratio produces high tensile strength on composite.23

Hence, the continuous form of fiber are used to obtain a lamina. The chemical24 and mechanical25 properties are presented in the Tables 1 and 2, respectively.

To increasing the hardness and impact strength, the woven type E glass fibers are oriented in a layer formto above and below of sisal fibers and produce a laminate. At the time of fabrication of composite, the LY 556 epoxy resin is used as a binding agent for binding a laminate. In addition, for faster curing of this process, a HardenerHY 951 is used as catalyst. The binding material and catalyst are taken in the ratio of 10:1. The artificial materials which are used in fabrication of fiber reinforced polymer composites are obtained from Praga Industries Pvt. Ltd, Coimbatore dist., Tamilnadu, India.

Table 1 — Average chemical composition of selected sisal fiber

Description (%) Cellulose Hemicellulose Lignin Pectin Wax Ash Moisture

Sisal fiber 65.8 12.0 9.9 0.8 0.3 4.2 10.0

Table 2 — Mechanical properties of selected fibers

Description Density (g/cm3) Elongation (%) Tensile strength (MPa) Young’s modulus (GPa) Specific modulus (GPa)

Sisal fiber 1.3-1.6 1.9-15 400-700 8.5-40 6.5-30.8

E glass fiber 2.5 2.5-3.0 2000-3500 70.0 26.9

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The fiber reinforced polymer composite are developed by 40% of reinforcement materials (sisal and glass fiber) are loaded with 60% of matrix material (polymer). The more addition of reinforcements on composites leads to decline in strength.26 The four different volume percentile combination of fibers are attempted in a 40% of reinforcement materials. The volume percentage of selected materials are presented on Table 3.

The each of above volume percentage of materials are fabricated by heat compression moulding techniques with the dimension of 300*200*10 mm3. Initaily a prepared resin is applied in and around the moulding box. In before, the mould box is clean and dried. The continous sisal fiber is arranged in the direction of length (0°-orientation) with the epoxy resin for good adhesive properties and better strength.27 The random orientated shot sisal fiber with epoxy resin is improved in tensile strength.30 The woven type glass fiber is located around the fibers to form a lamina. The above number of lamina are binded together to form a composite laminate. By the way of formulate, adesired volume fraction is atttained. Finally, the above setup is kept under pressure of 500 psi with 95°C for 60 min for curring the developed fiber reinforced composites. Figures 1-4 clearly explained from fiber to composite specimen. Mechanical testing

Tension test The fabricated fiber reinforced polymer composites

are shaped with the required dimension by saw cutter and edge preparation is done by emery sheet for tensile test. The test specimen is prepared according to the ASTM D 3039. The gauge length and cross head speed are obtained from the ASTM standards. The specimen is mounted in between the jaws and it is subjected to under tension. The test sample is loaded in the direction of fiber length, until the fracture takes place. At the same time the reading is noted as a function of increasing in length. The measurement of tensile strength are taken parallel to fiber length. Obtained very precision result on tension test, the same procedure is repeated for four times of

Table 3 – Composition of developed composites

Designation Description Sisal fiber (vol%) E glass fiber (vol%) Epoxy resin (vol%)

4S6E 40% Sisal-60% Epoxy 40 -- Remaining 4G6E 40% Glass-60% Epoxy -- 40 Remaining 2S2G6E 20% Sisal – 20% Glass – 60% Epoxy 20 20 Remaining 1S3G6E 10% Sisal-30%Glass -60 % Epoxy 10 30 Remaining

Fig. 1 — Extracted and dry sisal fiber

Fig. 2 — Preparation of composites

Fig. 3 — Compression moulding

Fig. 4 — Developed composites

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same test samples. Finally, the average value are taken in an account.

Flexural test A three point flexural test is commonly conducted

on a fiber composite. At present, the flexural test of fabricated specimen is carried out under the ASTM B 790-03 standards. The test specimen is placed in between two supports and it is loaded at center, until the failure takes on composite specimen. The results of flexural strength are noted. The same procedure is followed for four times and finally mean value is reported.

Impact test According to ASTM D 256 standards, the impact

test samples are prepared. The prepared sample are placed on Izod machine. The pendulum allows to sticks the specimen which are loaded in tester. The noted result is the function of energy, which is required to break the specimen. It is used to measure the yield properties of fiber reinforced polymer composites. To avoid the manual error, minimum four testings are taken and average reading is finalized. Hardness test

The hardness test on fabricated fiber composites are carried by Rockwell hardness number under the ASTM 2210-86 standards. The L scale tester is used to measure hardness value of composite specimen under the applied load of 60 kg with 0.25’’ ball indenter. The test samples are placed on moving jaw and it will be loaded for 10s in an ambient conditions. Finally, the load is released gradually and corresponding reading is noticed. The same test was carried by four times on test samples. The mean value of results are consider as an exact hardness number. Results and Discussion

The mechanical properties namely tensile strength, flexural strength, impact strength and hardness value of fabricated fiber reinforced polymer composites are experimentally evaluated. The average results of each test are given Table 4.

The obtained results from the tensile test of fabricated fiber reinforced polymer composites are presented in Fig. 5. The result indicated that, the glass fiber composite (4G6E) specimen have better tensile strength than the other composition of specimen. But at the same time, sisal fiber loaded with glass fiber composite (2S2G6E) have almost same strength (2% of deviation takes place). The sisal fiber alone produce a very minimum strength (185.50 MPa), but the considerable amount of strength increased with the proper mixing ratio of sisal and glass fiber. The tensile strength of 232.20 MPa and 255.80 MPa are obtained by the addition of 10%, 20% volume of sisal fiber with glass fiber. The overloading of sisal fiber on composite produces less strength due to weak interfacial bond increased between fiber and matrix materials.28,29 It clearly shows that the addition of natural fiber with artificial fiber materials produces a better result then uses of natural fiber alone. By the way, the natural fiber composites are effectively used in tensile applications.

The flexural strength of various mixing composition of composites are loaded in Fig. 6. The glass fiber composite (4G6E) have more strength as compared to other composites specimen. At meanwhile, the same strength produced on sisal fiber added glass fiber composites (2S2G6E). The 1S3G6E composites are capable of carrying a flexural load of 4.19 kN whereas 2S2G6E composites are capable of taking a flexural load up to 4.36 kN, a very minimum

Fig. 5 — Tensile strength

Table 4 – Mechanical properties of fiber reinforced polymer composites

Test samples Tensile strength, MPa

Elongation, %

Flexural strength, MPa

Flexural load, kN

Impact strength, J/mm2

Hardness number, RHN

4S6E 185.50 3.01 155.50 2.88 2.44 23.0 4G6E 260.10 4.25 235.10 5.12 2.32 85.5

2S2G6E 255.80 3.72 200.80 4.36 2.52 75.5 1S3G6E 232.20 3.47 192.20 4.19 2.48 36.5

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amount of deviation takes place as compare to maximum load carrying capacity of glass fiber composites. It is clearly shows that, sisal fiber composites have very low load carrying capacity (2.88 kN) as compared to other composites.31 The same strength variation produced in tension test of fabricated composites.

For analyzing the impact properties of composite specimen, the test samples are undergone an impact test and the average result of each composition are shown in Fig. 7. The impact strength of sisal added glass fiber composite produce better result than the glass fiber composites. Those impact strength result is entirely differ from the other strength. During the test, the sisal fiber is not pullout easily as compare to glass fiber. So more energy is required to break the fabricate specimens (2.52 J/mm2). The long fiber usage on developed composites produce high impact strength. At the same time short fiber is not producing that much strength.30 Hence, the sisal content added with

glass fiber (2S2G6E) composites are more suitable for impact strength applications.

From Fig. 8, the glass fiber composite have higher hardness value than other fiber loaded composites. The glass fiber alone composite have more mechanical properties than the other composition of composite. This higher value produces by interfacial bond strength between the glass fiber and epoxy resin. If the sisal loaded fiber is not having that much adhesive properties with polymer materials. The furthermore addition of sisal fiber decline its value, because of its water molecules more present in the natural fiber than glass fiber. SEM Analysis

The interfacial bonding and nature of the fibers on composites are investigated through scanning electron morphological (SEM) analysis. The SEM test conducted on fabricated fiber reinforced polymer composite specimens (Fig. 9). In SEM image, contains mostly fiber misalignments (voids 0° orientation) fiber pullout, uneven fiber loading, fiber breakage and internal crack are observed on composite. The successful completion of tensile test, the specimen under gone SEM observations. The specimens are fractured due to fiber pullout (Fig. 3) and weak interfacial bonding on composites.9 The uneven distribution of fibers on composites (Fig. 1) the mechanical properties may varied in results.

Due to the poor adhesion of fibers were not properly bonded with resin, also the un-mixture fiber were noticed and hence, it lead to propagated while in testing.32 For obtaining the better bond between the fibers and also reduction in fiber pullout gives the maximum withstand capacity.

Fig. 6 — Flexural strength

Fig. 7 — Impact strength of fabricated specimens

Fig. 8 — Hardness number of fabricated specimens

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Conclusions The mechanical properties of sisal/glass fiber

reinforced epoxy matrix based composites were investigated. The tensile strength, flexural strength, impact strength and hardness are analyzed as a function of fiber content. Based on the experimental results, the following conclusions are drawn:

(i) From the investigation, the addition of sisal fiber with glass fiber composites produces good tensile strength (255.80 MPa). Hence, it is more suitable for tensile application.

(ii) The impact strength of fiber loaded composite (2S2G6E) gives more strength (2.52 J/mm2) than the artificial fiber (2.32 J/mm2).

(iii) It is clearly noticed that the addition of fiber happens in strength as it follows 2S2G6E > 1S3G6E > 4S6E > 4G6E. Hence, the addition of fiber with glass fiber is essential for producing better strength on impact.

(iv) It is clearly noticed that the sisal fiber alone is not produced a considerable strength. But, at the same time, a significant improvement on strength when it is loaded with glass fiber. Hence, the natural fiber is used in mechanical application with the addition of glass fiber.

(v) By the experimental work, it is proved that the natural fiber composites are produced a artificial fiber strength.

(vi) The interfacial bonding, fiber cracking, misalignment of fibers are observed on developed composites by SEM analysis which is effected on its strength.

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Fig. 9 — SEM analysis of fabricated specimens

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