Experimental and Numerical Investigation of Damping ... ijmte - cw.pdfTABLE 1 Physical properties of fibers Physical properties Jute Hemp Glass Density (g/cm3) 1.4 0.86 2.55 Diameter(mm)

Experimental and Numerical Investigation of Damping

Properties of Natural Fiber Reinforced Composites

Siddhesh Sawant1,Ashok Mache2

1Mechanical Engineering, Vishwakarma Institute of Information Technology, Kondhawa (Bk), Pune-

411048, India.

2Mechanical Engineering, Vishwakarma Institute of Information Technology, Kondhawa (Bk), Pune-

411048, India.

ABSTRACT

The importance of use of composite materials has been increasing consistently in various fields like mechanical,

civil and aerospace engineering etc. due to their good specific mechanical properties. Composites are known for

their high strength and stiffness with low weight. Most of the structural components are generally subjected to

dynamic loadings in their working life. Very often these components may have to perform in severe dynamic

environment where maximum damage results from resonant vibrations. Maximum amplitude of vibration must be in

the limited range for the safety of the structure. Hence, damping analysis has become very important to control the

vibration response and its amplitude. The present study involves experimental and numerical investigation of

damping properties of natural fiber reinforced composites and its hybrids i.e., jute/epoxy, hemp/epoxy, glass/epoxy,

glass/jute/epoxy, jute/glass/epoxy, aluminum/jute/epoxy and aluminum/glass/epoxy. Natural fibers are used to

fabricate fiber reinforced composites using hand lay-up method supported by compression molding machine.

Damping properties are determined by using half-power bandwidth method. Tensile strength and modulus of the

specimens are obtained experimentally. The experimental results of natural frequencies and damping ratio are

compared with numerical results obtained by using ANSYS R18.2.

Keywords: Composites, damping, FFT analyzer, frequency response function, half-power bandwidth

method, vibration.

.

International Journal of Management, Technology And Engineering

Volume 8, Issue IX, SEPTEMBER/2018

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1. INTRODUCTION

Natural fiber reinforced composites are widely used in the area of aerospace, automobile, sports equipments and

military sectors due to its multi-functional features like low density, biodegradability, high specific strength, fire

resistance, improved mechanical properties, resistance to corrosion and low cost when compared with artificial fiber

reinforced composites like glass, Kevlar, carbon fiber. The most commonly used plant fibers for reinforcement in

composite are sisal, jute, banana, Kenaf, Palmyra, hemp, coir, flax, ramie etc., which are best suited for low and

medium load engineering applications. It is important for an engineering material to have better energy dissipating

capability along with their stiffness and strength requirements. The composites are comparatively cheaper to

manufacture and have much higher surface finish. The use of composites has given more flexibility to design

engineers to modify the existing design or develop a new design. Composite material gives chance to designers and

engineers to increase material efficiency, therefore resulting in cost reduction and better utilization of resources.

Damping is the phenomenon by which mechanical energy is dissipated in dynamic system and it limits the resonant

amplitude of vibration. Damping is essential to study the dynamic characteristics of fiber reinforced composites.

Damping mechanisms in natural fiber composites differ entirely from those in conventional materials and energy

dissipation depends upon factors like viscoelastic nature of matrix and/or fiber, interphase, damage and viscoplastic

characteristics. Damping of a structure can be achieved by passive or active methods. A passive method uses the

inherent capacity of certain materials to absorb the vibration energy, thus providing passive energy dissipation. An

active method uses sensor and actuators to attain vibration sensing and activation to control the vibration in a real

time. However, fibers are the main factors controlling the properties of composites.

In particular, damping for materials with natural fiber is difficult to study due to their chemical constituents;

nevertheless it shows good damping characteristics due to their inherent porous nature. Many researchers have

investigated dynamic properties such as storage modulus, loss modulus and damping ratio of natural fiber rein-

forced composites. A. Mache et al. [1] studied the comparison of mechanical properties of jute-polyester composites

with hybrid jute-steel-polyester composites and summarized that hybridization is advantageous in terms of tensile

and flexural modulus, reducing the chances of brittle failure and arresting fall in tensile modulus due to moisture

absorption. Akash et al. [2] studied dynamic behavior of hybrid jute/sisal fiber reinforced polyester composites and

found that damping ratio of hybrid jute/sisal composites is higher than that of conventional composites and

monolithic materials i.e., 1.15 times jute laminate. C. Devalve and R. Pitchumani [3] contemplated damping

enhancement in fiber reinforced composite with addition of carbon nanotubes (CNT). Result shows that addition of

CNT increases damping by 133%. P. Sature and A. Mache [4] investigated mechanical properties and water

absorption study of jute fiber, hemp fiber, jute-hemp fiber, and jute-hemp-glass fiber reinforced composites and

found that hybridization of jute with hemp and jute-hemp with the glass fiber improves the mechanical properties

and can be considered as potential replacement to glass fiber. V. Allien et al. [5] presented investigation on free

vibration analysis of laminated chopped glass fiber reinforced polyester (CGRP) resin composite with two, four and

six layers. Result indicates that natural frequency of six layers CGRP composite material is more than two and four

layers CGRP composite material. A. Mache et al. [6] studied the effect of strain rate on mechanical response of jute-



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polyester composites and observed that there is significant effect of strain rate on stress-strain curves as tensile and

compressive failure strength increases with respect to increasing strain rate. M. Rajesh [7] studied influence of

surface pre-treatment with sodium hydroxide and hybridization effect of natural fiber on flexural test and free

vibration behavior. It is found that chemical treatment improves the mechanical and free vibration properties of

polymer composites due to the enhancement of interfacial bond between fiber and matrix as the result of chemical

treatment. J. Alexander and B. Augustine [8] studied damping characteristics of unidirectional [UD], woven fabrics

of basalt fiber and glass fiber at various end condition and observed that natural frequency of woven fabric

composite is higher than UD composite. Also, laminate with fixed-fixed end conditions are having high natural

frequency than cantilever and simply supported end condition. A. Erklig, M. Bulut [9] studied influence of borax

filler on vibration response of S-glass/epoxy composite laminates and found that the sample with 5 mass % of borax

filler has maximum damping ratio and loss modulus. K. Kumar et al. [10] analyzed sisal fiber (SFPC) and banana

fiber (BFPC) under the influence of fiber length and weight percentage. It is observed that an increase in fiber

content increases mechanical and damping properties. S. Chavan and M. Joshi [11] investigated vibration of

glass/epoxy composite in fix-free boundary condition and found that natural frequency increases with increase in

aspect ratio and no. of layers.

Many researchers have developed various solutions to analyze the dynamic performance of laminated

composites. Though experimental investigations on woven fabric composite laminated structures are not received

much attention. Therefore, the aim of this study is to compare damping properties of natural fiber reinforced

composites and its hybrid.

Nomenclature

FFT Fast Fourier Transform

FRF Frequency Response Function

2. EXPERIMENTAL DETAILS

2.1 Materials

Woven jute fiber, hemp fiber, glass fiber and aluminium sheet are used as reinforced materials and commercially

available epoxy 520 and PAM-hardener as a matrix material.



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TABLE 1 Physical properties of fibers

Physical properties

Jute

Hemp

Glass

Density (g/cm3)

1.4

0.86

2.55

Diameter(mm)

0.017

0.066

0.02

Tensile strength(MPa)

108

250

1950

Young’s modulus(GPa)

3.42

11

72

2.2 Fabrication of Laminates

The composite laminates are prepared by hand lay-up technique supported with compression moulding machine.

The laminate of size 300mm x 300mm x 3mm was made. Firstly, Epoxy resin-520 was mixed with PAM-hardener

in the ratio 10:1 by weight. Fibers are impregnated with resin and arranged one over the other with different stacking

sequence. Then, put whole assembly under rectangular mould plates and compressed the given structure to obtain

desire thickness. The laminate is then allowed to cure for next 24 hours at room temperature. Spacers are used

during the manufacturing to obtain uniform thickness. The manufacturing laminates are labelled as jute/epoxy

laminate (J/E), hemp/epoxy (H/E), glass/epoxy (G/E), glass/jute/epoxy (G/J/E), jute/glass/epoxy (J/G/E),

aluminium/jute/epoxy (Al/J/E) and aluminium/glass/epoxy (Al/G/E).

Fig. 1.Compression moulding machine

2.3 Tensile Testing

The composite materials fabricated are cut into required dimension using wire cutting machine. The tensile test

specimen is prepared according to the ASTM D3039 standard and tensile testing is carried out using the Universal

Testing Machine (UTM) (Model No-STS248) with an accuracy of ±1%. The UTM cross head speed is maintained at

1 mm/min. The capacity of the machine is 100kN. The testing process involves placing the test specimen in the



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testing machine and applying tension to it until it fractures. During the application of tension, the elongation of the

gauge section is recorded against the applied force. The experiments are repeated for several times and the average

values are used for discussion.

2.4 Modal Analysis

A cantilever rectangular plate of composite material is shown in Fig. 2. The specimen is clamped on test fixture at

one end and accelerometer is attached to the other end of specimen. The structure is excited by tapping free end of

specimen. A signal is recorded by unidirectional piezoelectric accelerometer. Four channelled FFT analyzer is used

to obtain relation of amplitude and frequency with time i.e. frequency response function (FRF). FRF is used to

calculate damping ratio by using half power bandwidth method.

Fig. 2. Modal analysis by FFT analyzer

1. Piezoelectric accelerometer, 2. Four-channel FFT analyzer, 3. Damping response displayed on screen,

4. Canti-lever beam support.

4

3

1

2



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2.5. Half-power Bandwidth Method

Fig. 3.Half-power bandwidth method

This method is based on curve of frequency response function (FRF) obtained from model analysis. Bandwidth is

defined as the width of the frequency response curve when magnitude is 1/√2 times the peak value i.e. represented

by point 1 in Fig. 3. If we draw a horizontal line at 1/√2 times the peak value, it will intersect the curve at two points

and gives corresponding values of frequencies i.e. ω1 and ω2. Then, damping ratio can be determined from

bandwidth using the expression;

(1)

Where, = Natural frequency corresponds to point 1.

2.6. Euler-Bernoulli Equation

The experimental results of natural frequency are compared with theoretical results using by Euler-Bernoulli beam

theory. The expression of natural frequency is given by equation;

(2)

where, E- Young’s modulus of beam (Pa), I- Moment of area (m2), ρ- Density of beam (m4), A-Cross sectional

area of beam (m2), L- Length of beam (m)

2.7 Logarithmic Decrement Method

One of the methods which is used to measure the damping ratio of an under damped system is the log decrement

method. In this system, vibration amplitude exponentially decays over time and natural log of amplitudes of any two



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successive peaks is called the logarithmic decrement. Logarithmic decrement can be calculated by equation (3);

(3)

Where, = Logarithmic decrement, A0= Maximum amplitude of first cycle, A =Maximum amplitude of nth cycle

Damping ratio can be obtained using logarithmic decrement by equation (4);

(4)

2.8 Etching Treatment for Aluminum

Sulphuric acid (H2SO4) A.R grade (Specific gravity=1.84) and ferric sulphate Fe2 (SO4)3 4H2O is used to make

solution. Solution is prepared by dissolving 122.5 g ferric sulphate Fe2 (SO4)3 4H2O and 0.185 liter of concentrated

sulphuric acid (H2SO4) in enough water to make a liter of Solution [12] and aluminum plates are dipped inside it.

The aluminum plates are immersed in this solution at 65 oC for 8 min. and then used to make laminates.

3. RESULT AND DISCUSSION

3.1 Tensile Testing

The different composite specimen samples are tested in the universal testing machine (UTM) and the samples are

left to break till the ultimate tensile strength occurs. Stress–strain curve is plotted for the determination of ultimate

tensile strength and elastic modulus.



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Fig. 4. Stress vs. Strain curve for different composites under consideration.

The results indicated that aluminum/glass/epoxy specimen gives better tensile strength then the other composites

under consideration. Aluminum/glass/epoxy has maximum tensile strength of 168.693MPa. The tensile strength of

glass/epoxy, jute/glass/epoxy, glass/jute/epoxy; hemp/epoxy, jute epoxy and jute/aluminum/epoxy composite

laminates are 158.44, 106.98, 61.46, 33.10, 48.27 and 38.54 respectively. The significant improvement in tensile

strength has been recorded due to hybridization. Hybridization of jute with glass fiber increases the tensile strength

of pure jute by 121%. As the composite materials are orthotropic in nature, the tensile testing of specimen was done

in longitudinal (L) and transverse (T) directions.

Fig. 5.Comparison of tensile strength for different composites.



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3.2 Vibration Analysis

Fig. 6. Frequency response curve obtained from modal analysis.

Vibration testing has been carried out on all composites under consideration. The composite specimen is clamped as

cantilever beam and modal analysis is carried out. The frequency response curve is obtained directly from the

software itself (RT Pro Photon 6.34.9104). Fig. 6 shows (Amplitude vs. Time) curve that represents exponential

decay of amplitude with time after disturbance and (Amplitude vs. Frequency) curve represents resonant frequency

of vibration. These results are validated numerically by ANSYS R18.2 shown in Fig. 7. Glass/jute/epoxy has

maximum natural frequency of 38.75Hz. Fig. 8 shows comparison of natural frequency for different composites.

Maximum damping ratio has observed for hemp/epoxy laminate. Also, hybrid jute/glass/epoxy laminate has higher

damping ratio than pure glass. The experimental results of damping ratio obtained from half-power bandwidth

method are compared with theoretical results obtained from logarithmic decrement method. Fig. 9 shows

comparison of damping ratio for different composites. The vibration testing of composites are tested for different

length i.e. 200mm, 230mm, 250mm. and it is observed that as length of the laminate increases, damping ratio

increases and natural frequency decreases.



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Fig. 7.Vibration analysis of aluminium/glass/epoxy composite laminate by ANSYR18.

Fig. 8.Comparison of natural frequency for different composites.



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Fig. 9. Comparison of damping ratio for different composites.

4. CONCLUSION

Tensile, damping and vibration characteristics of jute/epoxy laminate (J/E), hemp/epoxy (H/E), glass/epoxy (G/E),

glass/jute/epoxy (G/J/E), jute/glass/epoxy (J/G/E), aluminum/jute/epoxy (Al/J/E) and aluminum/glass/epoxy

(Al/G/E) composites are examined. Damping characteristics of the composite samples are determined by FFT

Analyzer. The main conclusions from this study can be summarized as follows;

It has been observed that the theoretical calculations of natural frequency and damping ratio matched

with experimental calculation very well for the cantilever structural beam with maximum errors of

27%.

Aluminium/glass/epoxy composite laminate has maximum tensile strength and can hold strength up to

168.693 MPa.

Tensile strength of composites is strongly affected by hybridization. Jute/glass/epoxy hybrid composite has

tensile strength of 106.98MPa which is higher than pure hemp and jute.

Hemp/epoxy laminate possesses highest damping capacity and has maximum damping ratio of 0.1025.

It has been observed that as length of the laminate increases, damping ratio increases and natural frequency

decreases.

This experimental damping analysis has explored to predict the dynamic behavior of composites in order to

design panels or other similar structure and to develop high performance materials for building and



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construction, railways, automobiles, aerospace, biomedical etc. Also, the applications of such high damping

materials may eliminate special energy absorbers.

REFERENCES

1. Anindya Deb, Sumitesh Das, Ashok Mache and Rokesh Laishram, A study on mechanical behaviors of jute

polyster composites, ELSEVIER, Procedia Engineering 173 (2017) 631-638.

2. Akash. D. A, Thyagaraj. N. R, Sudev. L. J, Experimental Study of Dynamic Behavior of Hybrid Jute/Sisal Fiber

Reinforced Polyester Composites, International Journal of Science and Engineering Applications Volume 2

Issue 8, 2013, ISSN-2319-7560.

3. C. Devalve, R. Pitchumani, ELEVIER, CARBON 63, (2013) 71-83.

4. Pradip Sature and Ashok Mache, Mechanical Characterization and Water Absorption Studies on Jute/Hemp

Reinforced Hybrid Composites, American Journal of Materials Science 2015, 5(3C): 133-139.

5. Vipin Allien, Hemantha Kumar and Vijay Desai, An investigation on characteristics and free vibration analysis

of laminated chopped glass fiber reinforced polyester resin composite, ARPN Journal of engineering and

applied sciences, vol. 11, no. 18, september 2016 issn 1819-6608.

6. A.Mache , A Deb , and C. Chou , "Effect of Strain Rate on Mechanical Responses of Jute-Polyester

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reinforced hybrid polymer composite beam, ELSEVIER, Procedia Engineering 144 ( 2016 ) 1055 – 1059.

8. J. Alexander and B. S. M. Augustine, Free Vibration and Damping Characteristics of GFRP and BFRP

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DOI: 10.17485/ijst/2015/v8i12/54208, June 2015.

9. Ahmet Erklig, Mehmet Bulut,"The Influence of Borax Filler Addition on Damping and Vibration Response of

Sglass/epoxy Composite Laminates”, Proceedings of the World Congress on Civil, Structural, and

Environmental Engineering, Paper No. ICSENM 113, CSEE-2016.

10. K. Senthil Kumar, I. Siva , P. Jeyaraj J.T. Winowlin Jappes c, S.C. Amico , N. Rajin, Synergy of fiber length

and content on free vibration and damping behavior of natural fiber reinforced polyester composite beams,

ELSEVIER, Materials and Design (2014),pp379-386.

11. S. S. Chavan, M. M. Joshi, Study on Vibration Analysis of Composite Plate, Technical Research Organisation

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Experimental and Numerical Investigation of Damping ... ijmte - cw.pdfTABLE 1 Physical properties of fibers Physical properties Jute Hemp Glass Density (g/cm3) 1.4 0.86 2.55 Diameter(mm)