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Abstract This paper presents experimental investigations onimpact resistance of glass fiber-reinforced epoxy nano composites.

The laminates are prepared using 6 layers of glass woven roving

mates of 610gsm and nano clay content varied from 0%, 1%, 3% and

5% by weight with respect to matrix material. The composite panels

were submitted to low-velocity impact tests with energy of 18 J. The

methodology used for the impact test is based on the ASTM D3029

standard. During these impact tests, the time-histories, Peak load and

energy at maxi load were recorded by load cell. The incorporation of

1% and 3% of nanoclay lead to more stiffness and higher energy

absorption. Damages produced on the front and back surfaces ofimpact were also observed and compared neat epoxy laminates.

Keywords Composites, Glass fibre, Low velocity impact,Nanoclay

I. INTRODUCTIONLASS fiber reinforced composites are widely used in the

aviation and automotive industry due to their

advantageous characteristics, mainly weight reduction,

which is one of the most important design parameters for such

applications. Due to completely different material

specifications between metals and composites, the impact

behavior of structures made by these materials is inherentlydifferent. Metals show visible damage caused by impact

mainly on the surface of structures, while damage is hidden

inside composite structure especially when subjected to low

velocity impact [1]. Luo et al. [2] the damage in composite

structures resulting from impact events is one of the most

important aspects to be considered in the design and

applications of composite materials. Abrate [3] also made a

comprehensive review of all the literature available from 1989

to the present to give the view of latest developments in the

study on low velocity impact of composite material. He

observed that damage induced by impact consisted of fiber

breakage, matrix cracking and delamination. The damage

induced by low energy impact is often a complex mixtureconsisting of interlaminar fracture (delamination), intralaminar

fracture (transverse matrix cracking and debonding between

F. A.Thiagarajan, Department of Mechanical Engineering, Pondicherry

Engineering College, Puduherry-605014, India. (corresponding author phone:

+919092608765; fax: (0413) 2655101; e-mail: thiagu_ami@yahoo.co.in).

S. K.Palaniradja, Department of Mechanical Engineering, Pondicherry

Engineering College, Puduherry-605014, India. (e-mail:

palaniradja72@pec.edu).

T. M. Saravanan, Department of Mechanical Engineering, V.R.S College

of Engineering and Technology, Arasur-607107, India. (e-mail:

ultimate_saro@yahoo.co.in).

fibre and matrix) and fibre fracture. The effects of impactor

mass and velocity on damage in woven fabric composites were

studied by Cantwell and Morton [4] have documented efforts

over the past two decades specifically to understand the

behavior of laminated composite structures under transient

loading conditions. These efforts were (1) to identify and

characterize the relevant failure mechanisms, (2) to understand

their interactions, and (3) to be able to predict the extent of

damage within a given composite system under a set of

specified loading conditions. The impact event itself is also

defined by many variables such as impactor and targetgeometries, impact speed and energy [5]. Naik et al. [6] found

that for a given incident impact energy, the damage tolerance

of plain weave E-glassepoxy laminates is higher for low-

mass, high-velocity combinations and lower for low-velocity,

high-mass combinations. Sonparote and Lakkad [7] used

glasscarbon hybrids with various proportions of glass and

carbon fiber volume contents and determined flexural, impact

and interlaminar properties. Nano particles make a better inter

phase property than the fibers in which the inter phase

properties affects the damping character of a composite. The

nanocomposites containing organoclay have been further

employed as the matrix material to produce hybrid

nanoclay/fibre reinforced polymer composites that possessimprove the mechanical and fracture properties [8], [9]. From

the literature it has been found that nanoclay provides better

properties to the composite and clay filled composites show

competitive mechanical and vibration damping properties to

fiber reinforced composites.

This paper focus on the effect of nanoclay dispersed into an

epoxy/fiber glass composite and its influence on impact

response at low-velocity impact tests. Square laminates of size

150 mm were subjected to low-velocity impact loading using

an instrumented falling dart impact testing system at energy

level of 18J, four samples were tested. Details of the impact

response in terms of key impact parameters like peak load and

absorbed energy were studied.

II. EXPERIMENTAL PROCEDURES

A. Nanocomposites synthesis

The materials used for this investigation is nanoclay, epoxy

resin and E- glass fiber. The epoxy system was made of

Diglycidyl ether of Bisphenol-A in the trade name of LY 556

and the curing agent is Tri-ethylene tetra amine of HY 951

bought from Hunstman Inc. The nanoclay used in this research

was organic modified montmorillonite bought from Southern

Clay Inc in the trade of Garamite-1958, while the glass fiber

Impact behavior of Nano composite laminates

under low velocities

A.Thiagarajan, K.Palaniradja and M.Saravanan

G

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has a woven roving mat (WRM) with density of 610 gsm. The

amount of nanoclay exfoliated into the epoxy system, in

weight of 1%, 3% and 5% respectively. The nanocomposite

synthesis is carry out by two different steps, in the first step the

nano clay is mixed with epoxy resin then exfoliation process

can be done by high shear mixing with the help of laboratory

stirrer. Then 10% of hardener was mixed with the epoxy resin-

clay mixture by weight. The nanocomposites laminates is

prepared by hand lay-up techniques. The laminate was cut into150 mm x 150 mm square specimen for drop weight impact

test.

B. Falling Drop Weight impact Test

The impact resistance on the nano composites laminate is

performed by falling drop weight. The laminates were fixed

horizontally on the drop-weight fixture and drop height in

these experiments was 750 mm, thus giving impact energy of

18 J. The energy was calculated using the equation E = mgh,

where E is the impact energy, m is the mass of the impactor, g

is the acceleration due to gravity, and h is the drop height. The

impactor was made up of hardened steel, and their shapes were

cylindrical with hemispherical nose. The impactor was

attached to the circular discs of mass of 2.5 kg, which were

dropped. Falling weight impact test equipment setup is shown

in Fig. 1. The dart material used was steel. Standard equipment

is used in order to collect and store the signal from a load cell

positioned in the proximity of the head of the dart.

Fig.1 Falling weight impact testing machine

III. RESULTS AND DISCUSSION

A.Microstructure of nanocomposites

Scanning electron microcoscope (SEM) is a straight forward

technique to visualize the dispersion of nanoparticles within

matrix and to study the structure of nanocomposites

(intercalation/exfoliation). SEM pictures of Epoxy/ nanoclay

were represented in Fig. 2. A homogeneous dispersion of

nanoparticles is clearly visible, although some small

agglomerates present in the matrix medium. Fig. 2(a) shows

that the dispersion of nanoclay in the matrix is random and

uniformly dispersed throughout the matrix. Epoxy with 5 %

nanoclay at lower magnification shows agglomerated structure

and the dispersion of the agglomerated particles throughout the

matrix. This agglomerated structure shows that at higher

concentration the nanoclay dispersion is difficult in the matrix

medium.

(a)

(b)

Fig. 2 SEM micrographs of (a) 3 and (b) 5% nanoclay

B. Impact response

To be able to understand the impact response of nano

composites low velocity impact tests were performed. The

energies employed were enough to cause damage ranging from

a barely visible delamination and perforation. Loadtime

curves from the impact testing are shown in Fig. 4. These show

that the time the striker was in contact with the impacted

specimens is longer for 3 % of nanoclay sample. When the test

coupons were subjected to energy of 18J, the forcetime curve

was linear up to the laminates fail. The peak load values for 0,

1, 3 and 5 % nanoclay reinforced specimens were 1478, 1520,

2200 and 1335 N respectively (Fig. 3).

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Fig. 3 Load vs Nanoclay contents

(a)

(c)

Fig. 4 Load vs Time (a) neat epoxy, (b) 1, (c) 3 and (d) 5 %nanoclay

Absorbed energy is the energy at the peak load deducted

from the total energy. As the composite materials are brittle in

nature, it is assumed here that the energy up to the peak load is

absorbed through elastic deformation and all the energy that is

absorbed beyond that is assumed to be absorbed through the

creation of damages [9]. The absorbed energy for 0 .1, 3 and 5

% was 16, 16.85, 18.25 and 15 J; the absorbed energy was

linearly increase with the addition of nanoclay contents Fig. 5.

In 5% laminates the energy value drops to 15 J. Several

authors have reported that as the nano weight fraction increase,

the wettability of fibre with resin decreases and weak

interfacial bonding potentially occurs.

(b)

(d)

Fig. 5 Absorbed energy vs Nanoclay content

C. Damage evaluation

The fragmentation characteristics of fiber reinforced epoxy

nano composite collapsed very seriously with both fiber cracks

and separation from matrix. Fig. 6 represents the damaged

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specimens of neat and nanoclay at the energy of 18 J. For 0 %

specimens, there is an approximately 12 mm round

.

Fig. 6 Front and back face of impacted samples

damaged in the front face and approximately 30 mm round

damaged area in the back face and debonding occur on the

surface. While, for 1% sample a round damage found in front

face which is approximately 10 mm and back face damage is20 mm and full penetration is not occur. For sample 3% and 5

% specimen there is an approximately 10 mm round damaged

in the front face and approximately 15 mm round damaged

area in the back face.

Apart from 3% and 5 % nanoclay specimens, all other

specimens exhibit extensive matrix cracking, debonding,

delamination and fibre breakage in the middle of their face.

The impactor did not penetrate on the specimens for 3 and 5 %

of nanoclay. The reason is that the stiffness of these

composites laminate is greater than the 0 % specimen. It is

evident that for these nanoclay specimens, the damage area is

reduced and the specimen is not perforated fully on back face.

From the experimental result it shows that the nanoclaysamples sustain maximum load and good damage resistance.

IV.CONCLUSION

The nanocomposites laminate was successfully prepared

and the impact response was observed using drop weight

impact test. The effect of nanoclay addition to fiber

glass/epoxy nano composites was investigated. Scanning

electron microscopy observation proven that the 3% of

nanoclay is fully exfoliated structures and uniformly dispersed

into the epoxy system. Low velocity impact test was performed

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with the energy of 18 J. From the results, the following

conclusions can be highlighted.

i. Incorporation of nanoclay into the matrix loweredthe impact damage size compared with neat epoxy

laminates.

ii. With up to 3 wt% of nanoclay in the matrix, theimpact resistances of the laminate were improved

in term of higher load and energy absorption.

iii. From the stiffness point of view, an averageincrease of 32.8% was observed with the additionof the 3 % of nanoclay. The results show the

addition of clay improves the impact strength and

also controls the damage of the laminate.

iv. The weak fiber/matrix interfacial bonding andagglomeration was the reason for this reduction of

impact strength for 5% nanoclay sample.

REFERENCES

[1] WJ. Cantwell and J. Morton. The impact resistance of compositematerials a review. Compos Struct, Vol. 22(5), 1991, pp.347362.

[2] K. Luo, E.R. Green and C.J. Morrison. Impact damage analysis ofcomposite plates.Int J Impact Egg, Vol. 22(5), 1999, Pp. 435447.

[3] S. Abrate. Impact on laminated composite materials. Appl Mech Rev ,Vol. 44(4), 1991, pp. 155190.

[4] WJ .Cantwell and J. Morton. Geometrical effects in the low velocityresponse of CFRP. Compos Struct, Vol. 1, 1989, pp. 3960.

[5] AP. Christoforou. Impact dynamics and damage in compositestructures. Compos Struct, Vol. 52, 2001, pp. 181188.

[6] NK. Naik, SV. Borade, H. Arya, M. Sailendra and SV. Prabhu.Experimental studies on impact behaviour of Woven fabric composites

effect of impact parameter. J Reinf Plast Compos. Vol. 21(15), 2002,pp. 13471362.

[7] PW .Sonparote and SC. Lakkad. Mechanical properties of carbon/glass fibre reinforced hybrids. Fiber Sci Technol, Vol.16, 1982

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[8] JF. Timmerman, B. Hayes and JC. Seferis. Nanoclay reinforcementeffects on the cryogenic micro cracking of carbon fiber/epoxy

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