# Mechanical Properties of Natural Fiber Sandwich Composite: Effect of Core Layer

M Rajesh, T C Kanish

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M Rajesh, T C Kanish. Mechanical Properties of Natural Fiber Sandwich Composite: Effect of Core Layer. Mechanics, Materials Science & Engineering MMSE Journal. Open Access, 2017, 9, 10.2412/mmse.43.73.809. hal-01504687

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# Mechanical Properties of Natural Fiber Sandwich Composite: Effect of Core Layer

M. Rajesh¹, T.C. Kanish¹,ᵃ

1. School of Mechanical Engineering, VIT University, Vellore - 632014, India

a. tckanish@vit.ac.in

<figure><img src="image_2.png" /></figure>

DOI 10.2412/mmse.43.73.809 provided by [Seo4U.link](https://seo4U.link)

**Keywords:** natural fiber, weaving, mechanical properties, polymer.

**ABSTRACT.** In recent years, due to awareness of environmental system researchers are concentrated to developed natural fiber composite and replace with conventional material for low and medium load application. In this paper, an experimental investigations are made to analyse the mechanical properties on influence of core layers in sandwich composite. Three different weaving patterns are used as core layer namely plain, basket and twill. It has been fabricated by keeping stiff glass fabric as facing layer and relatively weak sisal natural fabric as core layer. The investigations made on sandwich composite reveals composite with plain woven sisal fabric as core layer gives higher flexural properties compared to composite with basket and twill woven fabric as core layer. Fracture surface of tensile and flexural specimens are analyzed using scanning electron microscope to understand the fracture behaviour of the sandwich composites.

**Introduction.** Last few decades, due to awareness of environmental and health issue, natural fiber based composites are recommended for industrial application, aerospace, automotive, civil, etc. [1]. Joshi et al. [2] analyzed the major advantages of natural fiber composite in automotive application and found that replace of light-weight natural fiber composites increases the fuel efficiency. Most of the researchers have reported the mechanical properties of natural fiber composite, by reinforcing them in short form random orientation in the matrix [3,4]. Major drawback associated with random oriented short fiber reinforcement in the polymer matrix is poor stress transfer due to amorphous nature which leads to fail composite early with lower strain rate. Alavudeen et al. [5] compared the mechanical properties of woven and short fiber reinforced banana/kenaf polyester composites. They found that woven composite enhances the mechanical properties of composites compared to composite with random oriented short fiber reinforcement. It is due to poor stress distribution in the random oriented composite under loading. Similar observation has been found by Sastra et al. [6]. They found that woven arengapinnata fiber-epoxy composite enhances the mechanical properties of composites compared to short fiber random oriented composites.

Even through woven natural fiber composites enhance the properties of composites compared to random oriented short fiber composite, it is important to improve the properties of composites for medium load application. For that, researchers are hybridized natural fiber with synthetic fiber. This enhances the properties of composites. Harish et al. [7] studied the mechanical properties of coir and glass epoxy composites. Results reveal that hybrid composite improves mechanical properties compared to individual coir and glass fiber reinforced composite. Prachayawarakorn et al. [8] investigated the mechanical properties of thermoplastic cassava starch composites by adding jute and kapok fibers. Reinforcement of fiber in the thermoplastic cassava enhances the mechanical properties of composites due to formation of new hydrogen bond. Ramesh et al. [9] analysed layering effect on
mechanical properties of glass-sisal-jute fiber. They found that mechanical properties of composites influenced by layer sequence.

Further to improve the properties of composite material, researchers suggest the sandwich composite by keeping stiff layer as skin, weak reinforcement as core layer to enhance the properties of composite material. From the above literature survey, it is notified that most of the researchers investigated natural fiber in the polymer matrix either short or continuous woven form. It is important to analyse the sandwich composite for different applications (car outer body). The present work analyse the effect of core layer on mechanical properties. For that three different woven sisal fabrics (plain, twill and basket) have been choose.

**Experimental details**

**1. Material used**

In this study glass and sisal fibers are used as reinforce material in woven form. Three different woven fabrics are used as core layer namely plain, basket and twill as shown in Fig. 1. Fibers which are used in the present work are purchased from local dealers and matrix material unsaturated isophthalic polyester resin and catalyst (Methyl Ethyl Ketone Peroxide) and an accelerator (cobalt naphthenate) are purchased from Vasavibala resins Ltd., Chennai, India.

**2. Preparation of Composites**

In this study hand-lay-up technique has been adopted to fabricate the sandwich composites. For that, initially matrix material has been prepared using unsaturated polyester resin, catalyst and accelerator with weight ratio of 10:1:1. Mould has been fabricated using stainless steel with a size of 300 mm×300 mm×4mm. Further top and bottom portion of the mould is covered by stiff parallel steel plate. Initially known amount of matrix mixture is poured into mould cavity, followed by stiff glass fiber is placed over poured resin. Further small amount of resin has been poured over layer. Followed by natural fiber core layer is layered then stiff glass fiber mat has been placed as skin layer. At last, remaining amount of matrix mixture is poured in the mould cavity. Later top portion of mould cavity is coved by stiff parallel pate. In order to achieve uniform compression, 60 kg weight has been placed over the mould cavity for 5 hours. After allowing five hour curing composite laminates are removed from mould cavity and sized according to ASTM standard for tensile and flexural test. For tensile test ASTM D-638 standard has been used. For that specimens are prepared dog-bone shape with dimension of 127 mm×18 mm. For flexural test ASTM D-790 has been followed. Specimens are prepared with a dimension of 127mm×12.7mm×4mm. Fig. 2 depict the schematic diagram of sandwich composites fabricated in the study.

<figure><img src="image_3.png" /><figcaption>Fig. 1. Schematic diagram of sisal fiber mat used in the study. a) plain, b) basket, c) twill.</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>Fig. 2. Schematic diagram of sandwich composite fabricated in the study.</figcaption></figure>

### 3. Material Characterization

The surface morphology studies have been carried out on tensile and flexural fracture specimen to understand the interfacial bonding between fiber and matrix, and fiber pull out. This has been done using Hitachi-S3400 Scanning Electron Microscopy (SEM) at 20KV accelerating voltage.

**Results and Discussion.** Table 1 shows the influence of core layer on tensile and flexural properties of sandwich composites. One can observed from Table 1 is, nature of weaving pattern influence on mechanical properties. The results reveal that sandwich composite with basket core layer enhances the tensile properties of composites. It is due to high load carry capacity of basket weave fabric carries more load. In the case of basket weave type, gap between two yarn in the warp and weft direction is low, this reduces the stress concentration between warp and weft direction. Also yarn crimp in the warp and weft direction is always less while in the plain weave it is high. This leads to poor stress transfer. In the case of twill weave, movement of yarn in the warp direction is diagonal in nature. This also one reason, tensile properties of sandwich composite with twill core between basket core and plain core. From the tensile properties, it can be concluded that tensile modulus of sandwich composite with basket core is always higher than plain and twill core. This increases the resistance against deformation during tensile load. From the Table 1, it is observed that percentage variation of tensile properties for basket core sandwich composite always higher than flexural variation. Tensile strength of basket core sandwich composite is 14% and 9% higher than sandwich composites with plain and twill core.

<table><caption>Table 1. Mechanical properties of sandwich composites.</caption><thead><tr><th rowspan="3">Sandwich composite</th><th colspan="2">Tensile properties</th><th colspan="2">Flexural properties</th></tr><tr><th>Tensile strength</th><th>Tensile modulus</th><th>Flexural strength</th><th>Flexural modulus</th></tr><tr><th>(MPa)</th><th>(GPa)</th><th>(MPa)</th><th>(GPa)</th></tr></thead><tbody><tr><td>Plain core</td><td>38.28±4.08</td><td>1.40±0.16</td><td>72.08±5.42</td><td>1.51±0.56</td></tr><tr><td>Basket core</td><td>44.35±3.18</td><td>1.48±0.38</td><td>66.54±4.65</td><td>1.50±0.35</td></tr><tr><td>Twill core</td><td>40.12±1.11</td><td>1.45±0.21</td><td>68.34±9.33</td><td>1.49±0.52</td></tr></tbody></table>

In the case of flexural properties, plain core sandwich composite gives higher flexural properties compared with basket and twill core. It is due to the effects of core against flexural load. In the case of plain core, composite gives more resistance against shear and bending. Higher amount of matrix material in the core layer also influences on flexural properties. This higher amount matrix has
viscous nature; this enhances the properties of composites. Percentage variation of plain core is 4% and 8% higher than twill and basket core.

Surface morphology studies on the fractured test specimens are carried out using scanning electron microscope to understand the failure mechanism. Fig. 3a shows the tensile fracture surface of plain core sandwich composites. It reveals plain core damages the matrix due to the poor stress transfer. This reduces the interfacial adhesion between fiber and matrix. Fig. 3b shows flexural fracture surface of twill core sandwich composites. It reveals twill core layer damages the matrix due to non-uniform stress distribution between fiber and matric. It is due to diagonal nature of yarn movement in the warp direction creates non-uniform stress distribution. This leads to fail composite early. Fig. 3c reveals plain core transfer stress effectively on flexural load. It shows uniform matrix surface near fiber reinforcement. This indicates plain core increases the adhesion between fiber and matrix. Similar observation has been seen from Fig. 3d. It reveals basket core transfer stress uniformly from fiber to matrix. This eliminates the matrix damage.

<figure><img src="image_5.png" /><figcaption>Fig. 3. SEM micro structure of fracture surface. a) Tensile fracture surface of sandwich composite with plain core, b) Flexural fracture surface of sandwich composite with twill core, c) Flexural fracture surface of sandwich composite with plain core, d) Tensile fracture surface of sandwich composite with basket core.</figcaption></figure>

**Summary.** Influence of core layer of glass-sisal natural fiber sandwich composites on mechanical properties [tensile and flexural properties] have been investigated. Results depict that nature of weaving pattern affects the mechanical properties of sandwich composites effectively. Sandwich composite with basket core has higher tensile properties compared to plain core while twill core sandwich composite in between. It is due to less interlace between two yarns in the warp and weft direction. This reduces the stress concentration between two yarns during loading. Sandwich composite with plain core enhances the flexural properties of composites. It is due to higher amount of matrix in between skin layer and higher resistance against shear and bending gives better properties.

**References**

[1] Z. Dashtizadeh, K. Abdan, M. Jawaid, M.A. Khan, M. Behmanesh, M. Dashtizadeh, C. Francisco, M. Ishak, Effect of Chemical Treatment on Kenaf Single Fiber and Bio-Phenolic Resin Regarding its Tensile and Interfacial Shear Stress, Middle-East Journal of Scientific Research. 2016, 24(9), 2685-92.
[2] S.V. Joshi, L.T. Drzal, A.K. Mohanty, S. Arora, Are natural fiber composites environmentally superior to glass fiber reinforced composites? Composites Part A: Applied Science and Manufacturing, 2004, 35(3), 371 - 376.

[3] T.P. Sathishkumar, P. Navaneethakrishnan, S. Shankar, Tensile and flexural properties of snake grass natural fiber reinforced isophthalic polyester composites, Composites Science and Technology, 2012, 72(10), 1183-1190.

[4] P.V. Joseph, K. Joseph, S. Thomas, Effect of processing variables on the mechanical properties of sisal-fiber-reinforced polypropylene composites. Composites Science and Technology 1999, 59(11), 1625-1640.

[5] A. Alavudeen, N. Rajini, S. Karthikeyan, M. Thiruchitrambalam, N. Venkateshwaren, Mechanical properties of banana/kenaf fiber-reinforced hybrid polyester composites: Effect of woven fabric and random orientation. Materials and Design, 2015, 66, 246-257.

[6] H.Y. Sastra, J.P. Siregar, S.M. Sapuan, M.M. Hamdan, Tensile properties of Arenga pinnata fiber-reinforced epoxy composites. Polymer-Plastics Technology and Engineering, 2006, 45(1), 149-155.

[7] S. Harish, D.P. Michael, A. Bensely, D.M. Lal, A. Rajadurai, Mechanical property evaluation of natural fiber coir composite, Materials Characterization, 2009, 60(1), 44-49.

[8] J. Prachayawarakorn, S. Chaiwatyothin, S. Mueangta, A. Hanchana, Effect of jute and kapok fibers on properties of thermoplastic cassava starch composites, Materials and Design, 2013, 47, 309-315.

[9] M. Ramesh, K. Palanikumar K, K.H. Reddy, Mechanical property evaluation of sisal-jute-glass fiber reinforced polyester composites, Composites Part B: Engineering, 2013, 48, 1-9.

Cite the paper

M. Rajesh, T.C. Kanish (2017). *Mechanical Properties of Natural Fiber Sandwich Composite: Effect of Core Layer*. Mechanics, Materials Science & Engineering, Vol 9. Doi 10.2412/mmse.43.73.809