FREE VIBRATION OF DAMAGED AND UNDAMAGED HYBRIDCFRP … · 2017-08-24 · The experimental apparatus...

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International Journal of Mechanical Engineering and Technology (IJMET)Volume 8, Issue 8, August 2017, pp.

Available online at http://www.iaeme.com/IJME

ISSN Print: 0976-6340 and ISSN Online: 0976

© IAEME Publication

FREE VIBRATION

UNDAMAGED HYBRIDCFRP

COMPOSITE LAMINATES

Devendiran.S, Manivannan K, VenkatesanK, Arun Tom

School of Mechanical Engineering,

ABSTRACT

The paper deals with the experimental testing and the theoretical analysis of

damaged and undamaged CFRP/GFRP with rec

The reason to vary their composition is to study their nature under various loading

conditions. The experimental apparatus used conducts dynamic test uses

accelerometers to detect the frequency of vibration when excit

hammer. Damages in the laminates under study are due to the rectangular notches

created in the laminates at varying distances along the transverse axis of the beam.

This will help us to study its influence on the material and geometrica

hybrid material of varying compositions. A theoretical model and a FEM model to be

designed for validation with the necessary assumptions. The values of frequencies

obtained through theoretical methods are compared and validated with the

obtained from the experimental and the FEM models.

by 32% and 27% for cantilever and hinged specimens for tested laminates of CFRP

(75%)/GFRP(25%) that of CFRP(50%)/GFRP(50%).The differences between

theoretical and experimental frequency values for the first the difference in percent

between the values of the frequency approximately 2.7% on average for D4

(75%)/GFRP(25%).

Keywords: CFRP, GFRP, frequency, rectangular notches.

Cite this Article: Free Vibration of Dam

Composite Laminates, International Journal of Mechanical Engineering and

Technology 8(8), 2017, pp. 349

http://www.iaeme.com/IJME

1. INTRODUCTION

In the recent decades, fiber reinforced composites (GFRP/CFRP) have been used extensively

for aerospace and other applications due

stiffness. Various researchers used for their investigation

tension, compression and impact loading conditions

the theoretical analysis. Glass fiber reinforced plastic (FRP) composite are potential materials for

IJMET/index.asp 349 [email protected]

International Journal of Mechanical Engineering and Technology (IJMET) 2017, pp. 349–360, Article ID: IJMET_08_08_039

http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=8

6340 and ISSN Online: 0976-6359

Scopus Indexed

FREE VIBRATIONOF DAMAGED AND

UNDAMAGED HYBRIDCFRP/GFRP

COMPOSITE LAMINATES

Manivannan K, VenkatesanK, Arun Tom Mathew, Abhijeet Thakur, and

Ashish Chauhan V

Engineering, VIT University, VIT-Vellore, Tamil Nadu


damaged and undamaged CFRP/GFRP with rectangular notches under free vibration.



accelerometers to detect the frequency of vibration when excited manually using a



This will help us to study its influence on the material and geometrical property of the



obtained through theoretical methods are compared and validated with the

obtained from the experimental and the FEM models. Frequency values is decreased



erimental frequency values for the first the difference in percent

between the values of the frequency approximately 2.7% on average for D4

CFRP, GFRP, frequency, rectangular notches.

Free Vibration of Damaged and Undamaged Hybrid cfrp/Gfrp

International Journal of Mechanical Engineering and

8(8), 2017, pp. 349–360.

aeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=8

reinforced composites (GFRP/CFRP) have been used extensively

and other applications due to their high strength towards weight ratio

Various researchers used for their investigation to predict their failures during

pression and impact loading conditions using with the experimental testing and

lass fiber reinforced plastic (FRP) composite are potential materials for

[email protected]

T&VType=8&IType=8

OF DAMAGED AND

/GFRP

Mathew, Abhijeet Thakur, and

Tamil Nadu. India.


tangular notches under free vibration.



ed manually using a



l property of the



obtained through theoretical methods are compared and validated with the results

Frequency values is decreased



erimental frequency values for the first the difference in percent

between the values of the frequency approximately 2.7% on average for D4:CFRP

aged and Undamaged Hybrid cfrp/Gfrp

International Journal of Mechanical Engineering and

asp?JType=IJMET&VType=8&IType=8

reinforced composites (GFRP/CFRP) have been used extensively

towards weight ratio and

to predict their failures during

with the experimental testing and

lass fiber reinforced plastic (FRP) composite are potential materials for

Devendiran.S, Manivannan K, Venkatesank, Arun Tom Mathew, Abhijeet Thakur, and Ashish

Chauhan V

http://www.iaeme.com/IJMET/index.asp 350 [email protected]

designing weight efficient armor systems and combat vehicles [1].The fiber damage behavior

plays an important role in the laminated composites failure analysis, damage accumulation model

was proposed to take fiber post-failure behavior into account. By comparing finite element results

with experimental data, we proved that the fiber damage accumulation parameter is a material

constant and a fiber [2]. The free vibration analysis of a laminated beam with notched, while

modeling the mathematical model in ANSYS and MATLAB, is studied with delamination using a

layer wise theory. Equations of motion are derived from the Hamilton's principle, and a finite

element method is developed to formulate the problem. The obtained numerical results are

compared with various theories addressing the effects of the lamination angle, location, size and

number of delamination on vibration frequencies of delaminated beams. It is found that a layer

wise approach is adequate for vibration analysis of delaminated composites [3].The blast

resistance of unidirectional fiber reinforced composites is proposed that the energy dissipation due

to the cracking of the matrix is minimal compared to removal of bonding or delamination. The

result shows the preliminary information on composite structure’s design for maximizing the

energy absorption and hence increasing structure’s resistance to blast loads [4].The free vibration

analysis of composite beam is proposed with overlapping delamination. As in free vibration

analysis of composite beams with overlapping delamination, the analytical methods have been

solved without repelling to the numerical approximations while the Euler-Bernoulli beam models

have been assumed [5]. Vibration analysis of delaminated composite beams and plates using

higher-order finite element is proposed. The assumptions for the lower and upper laminate

bindings of the natural frequencies of the delaminated beams are identified as free and fully

constrained deformity of deformed laminas. The result proves that the longer delamination

influences the natural frequency changes in the beam while researching on various sample

structures [6].

The modeling of impact induced delamination of woven fiber reinforced composites with

contact/cohesive laws is proposed. The model predicts partial delamination during

compressive shock loading above a certain threshold due to local shear and mode coupling.

By contrast, the experimental result shows a total loss of spall strength of the woven

composite during compression. Reason for the discrepancy is that the response of the woven

composite certainly be three dimensional that of two dimensional plane strain analyses. The

effect of various parameters under three dimensional loading may be more pronounced to de-

laminate the composite during compression. Also, the analyses show that it may berequired to

re-evaluate the concept of pull back velocity as a measure of spall strength in the case of

heterogeneous materials like GRP composites. It has been found above that the pullback

velocity is higher corresponding to a lower delamination stress [7]. The mechanical fractures

and micro-fracture behaviors of flat braided composites with a circular hole is proposed. It is

reported that damage at the specimen depends on the properties of the interface between fiber

bundles and also confirmed to concentrate around a hole, whereas in the other specimen it is

observed that the damage depended on properties of continuously oriented fiber bundle [8].On

the other hand, vibration analysis of composite elements is a convenient, non-destructive

assessment method [9–10].

From the detailed literature study, it is observed that the carbon fiber and glass fibers are

found in marine constructions, aerospace and it brings the need for proper validation of such

composite laminates. The damages in composite laminates such as debonding, delaminating,

porosity in the laminates, cracks in fibers makes them a complicated process in studying their

failure behaviors, so the future scope lays in the validation of damaged and undamaged

carbon and glass fiber reinforced polymers in various ratios. The variation in composition is

to check properties of the materials and their ability to meet the application standards. Based

on their properties it can be validated for other applications which will reduce the cost to a

considerable extent. Owing to the research scope in the validation of damaged (circular

holes/rectangular notches) composite materials such as carbon fiber and glass fiber reinforced

Free Vibration of Damaged and Undamaged Hybrid cfrp/Gfrp Composite Laminates


polymers, the following have be studied: to study the behavior of the composite materials

with and without the rectangular notches, to derive the governing equation of composite

laminate structures, to design and analyze the FEM model of the laminate using ANSYS

15.0, to manufacture and experimentally deduce the frequencies for various modes of

vibration The comparison of the aforementioned results has to be validated.

2. EXPERIMENTAL PROCEDURE

The CFRP/GFRP of various proportions of laminates is shown in Figure 1. The fabricated

hybrid laminates are subjected to the experimental analysis of vibration using tensile tests

according to ASTM D-3039/D3039M-08 standards. CFRP/GFRP laminate specimens are used

for analyzing the non-damaged and damage composites. The dimensions of composites are

shown in Figure 2.

Figure 1 Composition of materials a) CFRP 25%, GFRP 75%, b) CFRP 50%, GFRP 50%, c) CFRP

75%, GFRP 25%

Figure 2 Types of damaged-composites (D.C) in CFRP-GFRP laminate of 3 different proportions

The distance between the two end hinges of the CFRP/GFRP laminate specimen measured

350 mm. The fabricated composites for testing are shown in Figure 3 and 4, respectively. In

the dynamic tests the CFRP/GFRP laminate was stressed at equi-distances of 10 mm from one

end to the end of the laminate, via an impact hammer. Piezoelectric accelerometer was placed

at the midpoint of the beam and at the regular intervals of 30mm. The experimental setup is


Chauhan V


shown in Figure 5. A set of 10 hits were made from either ends of the beam and the average

value was acquired by a measurement system capable of extracting frequency values by

transformed signals in frequency domain using the Fast Fourier Transform (FFT) technique

and the integrated software. The CFRP-GFRP beam was initially tested in an undamaged

condition. The frequency response functions envelope for recorded frequency values in the

range 0–1500 Hz for the undamaged CFRP-GFRP laminate with the accelerometer in the

midpoint of the beam. Flowchart of the methodology approached is shown in Figure 6.

Figure 3 CFRP-GFRP manufactured specimens

Figure 4 Damaged specimens with notches

Figure 5 Vibration test rig used for conducting the experiment



Figure 6 Flowchart of the methodology approached

3. RESULTS AND DISCUSSIONS

3.1 Vibration data for undamaged composite laminates

The fabricated hybrid composite laminates with various proportion of samples was subjected

to an experimental analysis of vibration and its results are shown in Tables 1-6, respectively.

The values of frequency for first three modes of free vibration during experimental analysis

along with damping coefficient are tabulated. From Tables 1-6, it may be noted that first three

frequencies values obtained during experimental analysis are sufficient to compare that of

analytical and finite element analysis considering the CFRP/GFRP laminate for hinged and

fixed plate. From the Tables 1-6, it is observed that frequency is decreased by 32% (for first

mode shape)for one end fixed and 27% (for first mode shape) for both end fixed for tested

laminates of CFRP(75%)/GFRP(25%) that of CFRP(50%)/GFRP(50%). In intermediate

laminates shows higher frequency values and damping factor for CFRP (25%)/GFRP(70%).


Chauhan V


Table 1 Frequency for CFRP 50% and GFRP 50% specimen- One end fixed

Table 2 Frequency for CFRP 50% and GFRP 50% specimen- Both end fixed







3.2 Vibration data for damaged composite laminates

The experimental analysis of vibration on damaged CFRP/GFRP laminates was subjected to

rectangular shaped notching for two different typologies D (1-4). The rectangular notch is

located for CFRP/GFRP laminates along two different distances along the axis of the notches

in the midsection of the laminate: 45mm–75 mm (Fig. 2).The fabricated hybrid composite

laminates results are shown in Tables 7-12, respectively. It is observed from the test results in

Tables 7-12 that the frequency values reduced for three modes of vibration with increasing the

damage on the fabricated hybrid laminates. It is also noted that the located damage influences

the variation of frequencies comparatively to mode shapes. The frequency value increases for

both end fixed that of one end fixed for tested laminates. The value is low for CFRP

(75%)/GFRP(25%) for damaged composite 8x5mm at 45 mm distances from the centerline.

Furthermore, the obtained experimental frequency values for first mode on an undamaged

beam is compared to that of damaged beam, a maximum variation can be observed. Variation

remains contained between 5% and 7% for damage located in proximity of the CFRP

(75%)/GFRP(25%) laminate’s median line.

Table 7 Frequency for damaged CFRP 50% and GFRP 50% specimen-One end fixed

Table 8 Frequency for damaged CFRP 50% and GFRP 50% specimen- Both end fixed


Chauhan V


Table 9 Frequency for damaged CFRP 25% and GFRP 75% specimen- One end fixed




3.2 Frequency values for damaged laminate by FE analysis

Finite element analysis for damaged and undamaged CFRP/GFRP is carried using

computational software of ANSYS 15.0 and Hyperworks. SHELL 181 is used as an element

and meshed modelis shown in Figure 7. The element has 4 nodes and each node contributes to

6 degrees of freedom (3 transverse and 3 rotations). It is best applicable for composite

material, sandwich or shell structures. The element follows the theoretical assumptions of

First-Order Shear Deformation Theory (FSDT) for solving the finite element models. Modal

analysis is done to find out the various mode shapes of the specimen and their respective

frequencies. The algorithm used in ANSYS is Block Lanczos method for calculation. The

generated mode shapes for first three for one end hinged and both end fixed are shown in

Figure 8. Whilst the experimental setup is done using vibration test simulator which will

transpond the frequency acquired by hammering a specimen fixed on a rigid table, either



cantilever or simply supported beam. The accelerometer fixed on the specimen will help in

the transmission of signals from the specimen to the digital read out. Mathematical

formulation of the specimen can be framed using many theories such as the harmonic

analysis, Classic-laminated-plate-theory, First-order-shear-deformation-theory, and Higher-

Order-Theory. In this research proceeding, H-O-T is used since it is more accurate compared

to the FSDT or CLPT. In this, the boundary conditions as specified in the theory are

considered. The theoretical model adopted appears capable of giving vibration response in

sufficiently agreement with experimental behavior: the differences of frequency values for the

first mode.

Figure 7 Geometry modeled using SHELL 181 in 3D a) Undamaged b) Damaged with boundary

conditions

Table 13 Comparative results of undamaged specimen from FEM and experimental

a a


Chauhan V


Figure 8 Mode 1, 2 and 3 for specimen with one end fixed (a) and both ends fixed (b)

Table 14 comparing the results of damaged – composite (D.C-4 as shown in Figure 2) specimen from

FEM and Experimental test



Figure 9 Frequency data from experimental vs. FEM for varying composition ratios of undamaged

CFRP:GFRP with one end fixed.

Figure 10 Frequency data from experimental test vs. FEM results for varying composition ratios of

undamaged CFRP:GFRP with both ends fixed.

In Table 13 and 14 the frequency values obtained by finite element analysis are compared

with the experimental data; the difference in percent between the values of the frequency

approximately 2.7% on average. This confirming the validity of the modeling adopted for

plate elements. Figure 9 shows that the fluctuation appears at the mode shapes 2-3 and the

Figure 10 shows that the frequencies change at mode 2. The experimental results for first two

composition ratios did not match with the modal frequencies of the specimens with 3:1

composition ratio because of the reduction in the glass fiber reinforced polymer.

4. CONCLUSION

Experimental vibration tests on undamaged and damaged hybrid CFRP/GFRP laminates by

rectangular notches on double side at different locations has been carried out in research

laboratory on cantilever and simply supported specimens. The hybrid material proposed with

varying combinations of 1:1 (CFRP (50%)/GFRP(55%)), 1:3 (CFRP (25%)/GFRP(75%) and

3:1(CFRP (75%)/GFRP(25%)). The frequency values obtained during experimental results

has been compared to that of finite elements and analytical modeling of hybrid laminate. The

following are the main results obtained:


Chauhan V


• Experimental analysis of free vibration of CFRP/GFRP laminates is beneficial for

evaluating the damage of different proportion of hybrid laminates.

• Frequency values is decreased by 32% and 27% for cantilever and hinged specimens

for tested laminates of CFRP (75%)/GFRP(25%) that of CFRP(50%)/GFRP(50%).

• The theoretical model and analytical solution are permits useful for describing

damaged hybird laminates under free vibration with adequate approximation.

• The differences between theoretical and experimental frequency values for the first the

difference in percent between the values of the frequency approximately 2.7% on

average for D4:CFRP (75%)/GFRP(25%).

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FREE VIBRATION OF DAMAGED AND UNDAMAGED HYBRIDCFRP … · 2017-08-24 · The experimental apparatus...

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