EFFECT OF FIBER ORIENTATION ON THE MECHANICAL BEHAVIOR OF GLASS FIBER/EPOXY HYBRID NANOCOMPOSITES...

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International Journal of Mechanical Engineering and Technology (IJMET)

Volume 9, Issue 6, June 2018, pp. 383–401, Article ID: IJMET_09_06_044

Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=9&IType=6

ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication Scopus Indexed

EFFECT OF FIBER ORIENTATION ON THE

MECHANICAL BEHAVIOR OF GLASS

FIBER/EPOXY HYBRID NANOCOMPOSITES

CONTAINING MULTI WALLED CARBON

NANOTUBES AND GRAPHENE

Seshaiah.Turaka

Research Scholar, Department of Mechanical Engineering,

JNTUH College of Engineering (AUTONOMOUS), Kukatpally, Hyderabad, India

K. Vijaya Kumar Reddy

Professor, Department of Mechanical Engineering,

JNTUH College of Engineering (AUTONOMOUS), Kukatpally, Hyderabad, India

ABSTRACT

This paper deals with the influence of the lay-up configuration of glass fiber

reinforced epoxy matrix hybrid nanocomposites which are developed containing

multi-walled carbon nanotubes (MWCNTs) and graphene (GPN) to investigate

merged effect of nanoreinforcements on the mechanical performance of

nanocomposites. The accompanying laminates were produced by mechanical

ultrasonicator with compression molding for this study:[0°]s ,[90°]s ,[0°/90°]s and

[45°/45°]s oriented. Both the nanofillers were functionalized before incorporating

into epoxy matrix to promote interfacial interactions. The concentrations of both

MWCNTs and GPN filled in the reinforced glass epoxy matrix nanocomposites were

increased systematically, i.e. 0.1wt.%, 0.2wt.% and 0.3wt.% while composites

containing individual nano reinforcements were additionally manufactured for

comparison. The developed nanocomposites were characterized microstructurally by

scanning electron microscopy (SEM) and mechanically by tensile, flexural, and

compressive tests. Homogeneous dispersion of MWCNTs and GPN was observed

under SEM, which resulted in the revampment of mechanical properties of

nanocomposites. The [0°]s glass/epoxy hybrid nanocomposites containing 0.2wt.%

MWCNTs and 0.2wt.% GPN demonstrated 28.4% enhancement in tensile strength and

modulus revamped to 38.4%, respectively. Flexural strength and modulus likewise

demonstrated a rise of 84% and 64%, respectively. Compressive strength and modulus

likewise demonstrated a rise of 480% and 74%, respectively. Strikingly, fracture

strain likewise enhanced in both the tensile, flexural and Compressive testing. The

impact resistance enhanced to 237% demonstrating a significant revampment in the

toughness of hybrid nanocomposites.

Key words: E-glass fibre, MWCNTs, GPN, Mechanical properties, HR-SEM.

Seshaiah.Turaka and K. Vijaya Kumar Reddy


Cite this Article: Seshaiah.Turaka and K. Vijaya Kumar Reddy, Effect of Fiber

Orientation on the Mechanical Behavior of Glass Fiber/Epoxy Hybrid

Nanocomposites Containing Multi Walled Carbon Nanotubes and Graphene,

International Journal of Mechanical Engineering and Technology 9(6), 2018, pp.

383–401.

http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=9&IType=6

1. INTRODUCTION

The two allotropic forms of carbon, i.e. graphite and diamond, in nanometer size, i.e.

Graphene (GPN) and Multi Walled carbon nanotubes (MWCNTs), respectively have recently

attained much attention as reinforcing medium in polymer matrices[1-2].These tubular and

spherical structural types of carbon have appealing characteristics for use as

nanoreinforcements in a spread of polymeric substances to overcome their inherent limitations

and to develop a peculiar composition of composites with improved mechanical and

purposeful properties [3].

In contrast, GPN consists of with an average thickness of the 5-10 nm [4] are supplied in

varying sizes as much as 50 microns that have attracted attention as a promising candidate to

create new polymer-nano composites due to its excellent properties and ready availability of

its precursor, graphite. However, the inclusion of graphene (GPN) in epoxy has been proven

to enhance mechanical and electrical properties with respect to the un-reinforced epoxy [5-

10], thus showing promise for use of GNP-reinforced epoxy because of the matrix phase in a

fiber composite. The resulting GNP/carbon fiber/epoxy hybrid composite potentially show

upgrades in mechanical properties with respect to conventional carbon fiber/epoxy

composites. It's been demonstrated [6-10] that the effect of GPN on GNP/polymer composite

mechanical properties is administrated by the amount of GPN added to the polymer and the

dispersion of the GPN inside the polymer. Accordingly GPN have been successfully

incorporated in thermosetting (epoxy, phenolic, polyurethane etc.) and thermo polymers

(polyethylene, polypropylene, polystyrene, nylon etc.) to fabricate composites [7]

CNTs are seamless hollow tubes of rolled up graphene sheets. An individual graphene

sheet forms a single walled carbon nanotube (SWCNT) while multiple graphene sheets

constitute a concentric multiwalled carbon nanotube (MWCNT). CNTs are generally

produced by chemical vapor deposition technique. This technique produces CNTs in

preponderance and usually used for the reinforcement in composite materials[11]. In any case,

with no driving force, as-grown CNTs do not disperse well in polymeric matrices and

therefore different processes have been developed to disperse CNTs in polymers including

ultrasonication, calendaring, ball milling, shear mixing and extrusion, together with the

physical and chemical functionalization techniques to increase the interfacial interactions

between CNTs and polymers. As an outcome, CNTs have been effectively incorporated in

different types of thermo and thermosetting polymers to produce their respective

composites[1,12-14].

In addition to CNTs and GPN, other forms of carbon, i.e. SWCNTs, MWCNTs,

nanoclays, nanorods, nanodiamonds, carbon nanofibers, graphene, graphene oxide and

graphite platelets and many other nanoreinforcements are used in thermo and thermosetting

polymers for a variety of mechanical, thermal, electrical and functional properties including

increased strength, enhanced toughness, electrical conductivity, shape memory effect, flame

resistivity, rheological behavior and electromagnetic filed absorption[15-26].

Effect of Fiber Orientation on the Mechanical Behavior of Glass Fiber/Epoxy Hybrid

Nanocomposites Containing Multi Walled Carbon Nanotubes and Graphene


Exclusively, CNTs and GPN have been utilized as a part of polymeric matrices,

especially, in epoxy for an assortment of purposes including the increased functional and

mechanical properties. In any case, their comprehensive combined effect has not yet been

explored up on the mechanical performance of the composites, next to the receptiveness of a

single report on polyvinyl alcohol composites containing SWCNTs and GPN wherein only

hardness and tensile modulus were reported [3,19].

The reports of polymeric composites containing individual CNTs and GPNs demonstrates

enhancement in mechanical properties [27–31]. For instance, improvement in tensile

properties has been appeared in epoxy matrix composites containing CNTs in restricted

quantities,i.e. up to 2.0 wt.% [32–35] and additionally in large quantities, i.e. up to 8.0 wt.%

[35]. The three sorts of CNTs, i.e. SWCNTs, DWCNTs and MWCNTs have all exhibited to

increase the tensile and modulus of composites [36,37]. Similarly, flexural properties of the

composites have additionally indicated rises with the addition of CNTs; for instance, 120%

improvement in flexural strength was seen in an investigation by including just 1 wt.%

MWCNTs in epoxy matrix [38]. Different investigations have additionally detailed the

enhancements in flexural strength and modulus of CNTs reinforced polymeric matrix

composites [38–40]

As of late, binary nanoreinforcements have been incorporated in hybrid fibre polymeric

matrices to build up a unique class of hybrid fibre nanocomposites [41]; the addition of

individual and two nanoreinforcements demonstrates distinctive impacts on the mechanical

and functional properties of composites. As section of the analyzed combinations of binary

nanoreinforcements in polymeric matrices are: CNTs-GNPs [41], CNTs- Carbon black [42],

CNTs-SiC [43], CNTs-Silica [44], CNTs-Copper [45].Utilizing these merges, the explored

functional and mechanical properties are electrical and thermal conductivities, dielectric and

microwave properties, depositary and defecit modulus, impact and fracture toughness, and

tensile, flexural and tribological properties.

In the present investigation, MWCNTs, GPN and MWCNTs/GPN have been incorporated

in various stacking sequence of glass fibre [0°]s, [90°]s, [0°/90°]s and [45°/45°]s reinforced

epoxy matrix in constrained amounts to guarantee their uniform dispersion in order to

accomplish the advantages of these three nanoreinforcements upon the mechanical

performance of glass fibre/epoxy matrix. Epoxy was particularly chosen because of its wide

applications in industries. Besides, epoxy resin offer low volume shrinkage amid curing and

can be utilized without solvent and discharges no by-products. In any case, in spite of these

attributes, the relatively weak mechanical properties of epoxy resins have confined its

utilization in numerous potential applications. MWCNTs and GPNs were particularly chosen

in blend with regards to the best of authors knowledge, this combinations has not been

utilized before in glass fibre/epoxy matrix in spite of the fact that reports on CNTs/epoxy and

GPNs/epoxy are available, as mentioned above and discussed about further beneath. The

composites were prepared by in situ polymerization subsequent to blending the

nanoreinforcements in epoxy utilizing ultrasonication technique to ensure their uniform

dispersion. So as to create solid collaborations of nanoreinforcements with the glass

fibre/epoxy matrix, MWCNTs and GPNs were functionalized. The tensile, flexural, and

compressive properties were measured in the present investigation and the morphology of the

developed composites was researched by scanning electron microscopy(SEM). The obtained

results were compared with the available data on MWCNTs/Glass fibre/epoxy and

GPNs/glass fibre/epoxy composite systems regarding relative mechanical improvements in

connection to the loadings of nanoreinforcements and the quality of their dispersion.



2. EXPERIMENTAL

2.1. Materials

MWCNTs were procured from United Nano Tech innovations Pvt Ltd, Bangalore, India. The

length of MWCNTs was 3~10 micron with the diameter of 12~15 nm; the purity level was

>97%. MWCNTs were acid-refluxed in 40 ml of 3:1 volume ratio of concentrated sulphuric

and nitric acids at 25 °C for 35 min (Fig.1a). The acid-treated MWCNTs were then washed

with distilled water, sonicated and centrifuged at 2500 rpm for 20 min [44] GPN were

provided by Bottom up Technologies Corporation, Jharkhand, India. The average GPN length

size was 5-10 micron with particle size thickness of 5–10 nm; the purity level was >

99%.GPN were air-oxidized at 440°C for 5 h to remove unwanted carbonaceous impurities

and then treated with UV/O3 cleaner (Jelight 144AX-220) emitting radiation of 28 μW/cm2

by low pressure mercury vapor grid lamp[11] (Fig.1b). Plain weave 200 gsm E-glass fiber

from Arun fabrics Pvt Ltd, Bangalore., The epoxy resin utilized in the present examination

was Araldite®LY 556 with a curing agent Aradur® HY 951.

Figure 1 Nanoreinforcements used in the glass reinforced epoxy matrix composites (a) MWCNTs and (b) GPN.

2.2. Manufacturing

For the manufacturing impact of the lay-up designs of glass fibre reinforced epoxy hybrid

nanocomposites, MWCNTs and GPN were dispersed in epoxy resin in ascertained amounts

and ultrasonicated for 4h at room temperature. Six glass/epoxy composites containing

individual 0.1-0.3wt.% MWCNTs and 0.1-0.3wt.% GPN, and three glass/epoxy composites

containing 0.1wt.%, 0.2wt.% and 0.3wt% of each one of MWCNTs and GPN were

manufactured. MWCNTs/GPN/epoxy(i.e. slurry of hybrid nanoreinforcement) blends were

degassed for 10 min after sonication before reinforced glass fabric. Curing agent was added to

the slurry of nano followed by mechanical blending. In parallel aluminum dies, which were

coated with polyvinyl alcohol before pouring. The coating procedure was performed to keep

away from the sticking of slurry of nanomixture to the die cavity and the simple expulsion of

the cured composites. After that slurry of hybrid nanomixtures were poured in between the

stacking sequence designs of (i) unidirectional at [0°]s, (ii) unidirectional at [90°]s (iii)

balanced and symmetrical laminate with a combination of [0°/90°]s layers; and (iv) angle ply

symmetric [45°/45°] glass fibre oriented then followed by compression molding to prepare

hybrid nano glass/epoxy composites. The molded glass/epoxy composite specimens were

dried for 24 h at room temperature and later expelled from the dies. Post-curing was

performed at 100 °C for 4 h in an electric oven. The size of the prepared composites plates

was 300 × 300 × 3 mm.

10µm 3µm

(a) (b)




2.3. Characterization

The fabricated composites were cut into required dimensions for tensile, flexural, and

compressive tests. ASTM standards of D3039, D790 and, D3410 were considered for tensile,

flexural and compressive tests and the dimensions of the specimen were 250 × 25 × 3 mm,

125×12.7×3 mm, and 140×15×3 mm respectively. Tensile tests were performed on a tensile

testing machine (Hydraulic Instron 3039) at a crosshead speed of 1.5 mm/min to acquire

tensile strength, tensile modulus and fracture strain in the composites. Flexural tests were

performed under three-point loading on a same testing machine at a crosshead speed of 1.5

mm/min to obtain flexural strength, flexural modulus and fracture strain and compressive

tests were performed on a same testing machine (Hydraulic Instron 3039) at a cross head

speed of 2mm/min to obtain compressive strength, compressive modulus and fracture strain

with the maximum load capacity of 100KN At minimum of five tests were performed for

each sort of composite system and for each sort of mechanical testing. High resolution

Scanning electron microscopy (HR-SEM) was performed on glass fibre reinforced containing

MWCNTs, GPNs and fractured surfaces of the composite specimens

3. RESULTS AND DISCUSSION

3.1. Microstructures of Composites

The morphology of the fractured surfaces of neat glass/epoxy composite and [0°]s, [90°]s,

[0°/90°]s, and [45°/45°]s glass fiber reinforced epoxy matrix along with MWCNTs and GPNs

nanocomposites were investigated utilizing SEM (Fig.2). An increase in the contents of

nanofillers can easily be observed in the images (Fig.2d, g and j) and a change in fracture

surface of the matrix was flat, and some cracks were seen in matrix side near the fibre-matrix

morphology of composites is visible in comparison to neat glass/epoxy composite because of

the agglomeration of MWCNTs, the matrix is absent on the fracture surface of

nanocomposites, and only bridging of some nanoparticles between the fibers is clear (Fig.2a).

The distribution of nanoreinforcements can be seen in Fig. 2d and f; no agglomerates of

MWCNTs or GPNs were found on the polished surfaces of the composites. The

functionalization of nanoreinforcements increased the adhesion of MWCNTs and GPNs with

the epoxy matrix; subsequently, it can be seen that nanoreinforcements were held firmly in the

epoxy matrix. Pullout phenomenon of MWCNTs is especially observable, which is an

indication of increased toughness. The firmly held nanoreinforcements along with their

uniform distribution without the presence of agglomerates foresee a significant effect of

MWCNTs and GPN on the mechanical performance of composites.



Fig.2.SEM images showing fractured surfaces of (a) neat glass/epoxy, (b) to (d)

glass/epoxy composites containing 0.1-0.3wt% MWCNTs, (e) to (g) glass/epoxy containing

0.1- 0.3wt.% GPN and (h) to (j) glass/epoxy containing 0.1-0.3wt.% MWCNTs/GPN. High

magnification SEM images of polished surfaces of glass/epoxy composites containing (c), (f)

0.2wt.% MWCNTs and 0.2wt.% GPN and (i) 0.2wt.% MWCNTs/ GPN, demonstrates the

uniform distribution of nanoreinforcements.




3.2. Mechanical properties of composites

3.2.1. Tensile Properties

Unidirectional neat glass/epoxy composite exhibits a tensile strength of 604.8 ± 5.5 MPa,

which increased to 624.3 ± 3.0 MPa (3.3% rise) by including 0.2wt.% MWCNTs-glass/epoxy

composite and 515.3 ± 3.7MPa (14% decrease) by incorporating 0.2wt.% GPN-glass/epoxy

composite. The consolidated inclusion of MWCNTs and GPN-glass/epoxy composite at the

fractions of 0.1wt.%, 0.2wt.% and 0.3wt.% each, additionally increasing the tensile strength

of composites, i.e., 612.2 ± 3.7 MPa, 774.8 ± 4.5 MPa and 259.1 ± 3.9 MPa (2%, 28%, rise

and 57% decrease), at [0°]s specimens respectively, when contrasted with other stacking

sequence lay-up i.e. [90°]s, [0°/90°]s and [45°/45°]s oriented nanocompsoites shown in

Fig.3a. Literature generally demonstrates a rising trend in tensile strength after incorporating

CNTs in different fibre/epoxy matrix composites however the extent of improvement varies

with the loading of CNTs in different investigations. For Instance, an increase in tensile

strength of carbon fibre/epoxy matrix was observed by adding CNTs in limited quantities, i.e.

1wt.% [41]; however, the extent of improvement (28%) was not considerable as compared to

that observed in the present study. Similarly, tensile strength increased in another study by

adding large quantities of MWCNTs, in neat epoxy composite i.e. up to 8.0wt.% but the

extent of improvement, i.e. 65% [46] and 80% [40] was not comparable in relation to the

quantity of MWCNTs used. In contrast, reports are also available which show no significant

effect upon tensile strength even after adding individual 0.2wt.% MWCNTs, 0.2wt% GPN-

glass/epoxy composite and binary nanoreinforcement of 0.2wt% MWCNT/GPN-glass/epoxy

composite [50].GPN are accounted for increasing the tensile strength of neat epoxy matrix

[8,9,10]; for instance, a 52.7% increase in tensile strength was seen in an investigation by

adding just up to 0.3 wt.% GPN [6,7].

Comparable to tensile strength, the tensile modulus of the unidirectional glass hybrid

nanocomposites[0°]s additionally increased by the inclusion of individual nanoreinforcements

(MWCNTs,GPN) in glass/epoxy composite at a stacking of 0.2wt.% each, i.e. 14.5 ± 0.4 GPa

and 18.3 ± 0.1 GPa, respectively, in comparison to neat glass/epoxy composite, i.e. 13.2 ± 0.2

GPa exhibiting a rise of 9.8% and 38%. The consolidated effect of MWCNTs and GPN-

glass/epoxy composite likewise exhibits a rise in the tensile modulus values, i.e. 14.3 ± 0.4

GPa, 16.4 ± 0.3 GPa and 14.9 ± 0.3 GPa; at the loading points of 0.1wt.%, 0.2wt.% and 0.3

wt.% each indicating a rise of 8.3%, 24% and 12.8% individually, when compared with other

orientations of glass/epoxy nanocomposite shown in Fig.3b. Literature generally for the most

part a rising trend is observed in tensile modulus of neat epoxy matrix composites by

including CNTs [39,40];for instance,the elastic modulus increased continuously in composites

containing coiled CNTs [47] and SWCNTs, DWCNTs and MWCNTs, both un-treated and

NH2-treated, increased the tensile modulus of epoxy matrix composites [41,42]. In a riveting

examinations, 0.5wt.% MWCNTs were incorporated in epoxy matrix with various matrix

stiffness values by varying the quantity of curing agent; it was discovered that the effect of

MWCNTs was noteworthy in ductile matrix which gradually diminished with an increase in

the stiffness of the matrix [48]. The incorporation of 0.3wt.% GPN in epoxy matrix has

likewise brought about enhancing the tensile modulus of epoxy matrix composites however

further loadings of GPN switched the rising pattern [18].In contrast, a reverse pattern is

additionally seen in different investigations where elastic modulus diminished ceaselessly in

epoxy matrix composites by including CNTs [49,50] and reports are additionally accessible,

which demonstrate no significant improvement in tensile modulus even after the loading of

SWCNTs at 0.1wt.% [51] and MWCNTs up to 1wt.% [38]. In an alternate study, the



expansion of MWCNTs increased the tensile modulus more than GPN when incorporated in

the same loadings [48], as additionally observed in the present investigation.

A comparative pattern was observed elsewhere; however, maximum tensile modulus was

observed at 0.2wt.% MWCNTs/GPN-glass/epoxy composite, which at that point diminished

continuously up to 0.3 wt.% MWCNTs/GPN [12,13]

In addition to the increase of tensile strength and modulus of the composites the fracture

strain is also increased by including 0.2wt.% MWCNTs-glass/epoxy composite, i.e. 8.2 ± 0.2

(6.36% rise) in comparison to neat glass/epoxy, i.e. 5.0 ± 0.1,which is an indication of

enhanced ductility and toughness of the composites at [0°]s. However, fracture strain

diminished in composites containing 0.1wt.% GPN-glass/epoxy composite, i.e. 3.1 ± 0.1

demonstrating a fall of 3.8%. The incorporation of both nanoreinforcements, i.e. MWCNTs

and GPN in glass/epoxy composite at the fractions of 0.1wt.% ,0.2wt% and 0.3wt.% each,

however, it demonstrates a rising pattern, i.e. 5.34 ± 0.1, 9.3 ± 0.2 and 5.54 ± 0.1 however it is

not exceptionally significant and demonstrating a rise of 1.64% and 8.56% and 1.05% but

loading of 0.2wt.% to each filler demonstrated an value of 6.52 ± 0.25,which is a 30% rise in

fracture strain (Fig. 3c).




Figure 3 Tensile properties of nanocomposites in comparison to neat epoxy (a) tensile strength (b)

tensile modulus and (c) fracture strain.

Both increasing [49] and diminishing [10] patterns have been accounted for the fracture

strain in the wake of incorporating MWCNTs and GPNs in polymeric matrices. For instance,

an increase in fracture strain was observed by adding 1wt.% MWCNTs [38] and in another

investigation, surprisingly, the rise of fracture strain up to 20% was seen in epoxy matrix

composites containing 8.0wt.% MWCNTs, which increased persistently from ~9% in neat

epoxy specimens [50]. In the present investigation, the most astounding fracture strain of

unidirectional glass/epoxy[0°]s composites containing MWCNTs increased while composites

containing GPN demonstrated a decrease at [90°]s. The composites containing both

nanofillers (MWCNTs/GPN) in [0°]s, glass/epoxy composite demonstrated rise in the fracture

strain values despite the presence of GPN.

3.2.2. Flexural Properties

Similar to tensile properties, the addition of nanoreinforcements increased the flexural

properties of in [00]s glass/epoxy. Neat glass/epoxy demonstrated the flexural strength of

129.5 ± 6.2 MPa, which increased to 654.6 ± 5.0 MPa (80% rise) by including 0.2wt.%

MWCNT- glass/epoxy and 598.2 ± 4.5 MPa by addition of 0.2wt.% GPN-glass/epoxy

exhibits a rise in the flexural strength, i.e. (78.42%). (Fig. 4a). The addition of both nanofillers

at 0.1wt.%, 0.2wt.% and 0.3wt.% each, in any case, it increases the values, i.e. 593.4 ± 7.2

MPa, 682 ± 8.5 ± 4.0 MPa, 350 ± 5.2 MPa indicating a rise of 79%, 81% and 64%,

respectively. Insignificant increase in flexural strength was observed in an alternate study on

epoxy matrix composites containing 2.3wt.% halloysite nanotubes [52]. However, up to 120%

change in flexural strength was observed in another investigation by including 1wt.%

MWCNTs in epoxy matrix which diminished to 100% by increasing the MWCNTs substance

to 2wt.% [43]. Rather than utilizing high loadings of nanoreinforcements, the flexural strength

also increased after including low contents of MWCNTs [44] and GPNs [17] individually in

epoxy matrix, i.e. 0.4wt.% and 0.1wt.%, respectively.

The flexural modulus likewise enhanced with the addition of MWCNTs and GPN in [0°]s

glass/epoxy individually at 0.2wt.%, i.e. 25 ± 0.8 GPa and 23 ± 0.8 GPa in contrast with neat

glass/epoxy, i.e. 9 ± 0.1 GPa demonstrating a rise of 64% and 60% respectively (Fig. 4b).



The addition of both MWCNTs and GPN in the [0°]s glass/epoxy at 0.1wt.%, 0.2wt.%

and 0.3 wt.% loadings resulted in the increased flexural modulus values, i.e. 22.1 ± 0.1 GPa,

30.7 ±0. 4 GPa and 10.2 ± 0.2 GPa, which demonstrate a rise of 59%, 70% and 10%,

respectively. The incorporation of MWCNTs and GPN in various stacking sequence lay-up of

90°, 0°/90° and 45°/45° glass/epoxy matrix has demonstrated for the most part an increase in

flexural modulus in small fractions; however, the pattern reverses after increasing the content

of nanoreinforcements. For instance, in an investigation flexural modulus increased with the

addition of 0.1wt.% MWCNTs in epoxy that diminished significantly by increasing the

MWCNTs content up to 0.35wt.% in the epoxy [45]. In another examination, flexural

modulus is accounted for a similar pattern, i.e. sharp increment after including ~0.5wt.%

MWCNTs followed by a decrease when their content was increased to 3.5wt.% in epoxy

matrix [46].




Figure 4 Flexural properties of nanocomposites in comparison to neat epoxy (a) flexural strength

(b) flexural modulus and (c) fracture strain.

The maximum fracture strain in flexural testing increased when 0.2wt.% MWCNTs and

0.2 wt% GPN were included in unidirectional glass/epoxy composite [0°]s, i.e. 6.2 ± 0.15%, a

(244.4 % rise), 6.5 ± 0.11% ( 261.1% rise) when compared with neat glass/epoxy 1.8 ± 0.1%

yet GPNs affected adversely and reduced the flexural strain, i.e. 1.5 ± 0.15 (27.7% fall). The

binary addition of MWCNTs and GPN in glass/epoxy composite at 0.2wt.% and 0.1wt.%

each resulted in modest increase in flexural strain, 6.1 ± 0.18 (238.8% rise) and 7.2 ± 0.16

(300% rise).However, composites containing 0.2 wt.% MWCNTs and GPN each,

demonstrated a significant rise, i.e. 5.6 ± 0.19% (211% rise), as shown in Fig. 4c. The

addition of 0.4 wt.% MWCNTs had demonstrated the increase in flexural strain [44] at the

effect of GPN on the flexural strain isn't accessible in literature.

3.2.3. Compressive Properties

Similar to tensile and flexural properties, neat glass/epoxy composite demonstrated a

compressive strength of 14.6 ± 4.12MPa (Fig.5 a),which increased to 80.1 ± 3 (448% rise) by

including 0.2 wt.% MWCNTs in glass/epoxy composite and 85.8 ± 0.6 MPa (487% rise) by

the expansion of 0.2wt.% GPN in glass/epoxy composite. The effect of the incorporation of

low content of MWCNTs in glass/epoxy matrix is more articulated in comparison with

GPN/glass/epoxy matrix. Literature demonstrates the comparative outcomes when an

comparison of increase in compressive strength is drawn between polymeric matrix

composites containing GPN [7,8,9] and MWCNTs [50,51]; the influence of SWCNTs [3,50]

is much more significant than MWCNTs. The combined effect of MWCNTs and GPN at a

loading of 0.2wt.% each likewise demonstrated a rise in the compressive strength value, i.e.

84.6 ± 2.6 MPa (479 % rise), which is higher than the solitary effect of MWCNTs and not as

much as the individual influence of GPN on compressive strength. Additional rise in the

contents of MWCNTs and GPN in glass/epoxy matrix, i.e. 0.1wt.% to 0.3wt.% each,

increased the hardness of composites, i.e. 45.4 ± 1.7 MPa (210% rise),80.3 ± 0.2MPa (450%

rise) and 14.9 ± 2.7 MPa(20% rise).The extent of improvement in the compressive strength of

epoxy matrix composites is tantamount with literature in similar concentrations of

nanoreinforcements [49]. Both MWCNTs and GPN are accounted for increase the



compressive strength of epoxy matrix composites when incorporated independently in

constrained amounts, i.e. 0.1wt.% [52].

The Compressive modulus likewise enhanced with the addition of MWCNTs and GPN in

glass/epoxy individually at 0.2wt.%, i.e. 18.4 ± 0.5 GPa and 14.5 ± 0.3 GPa in comparison to

neat glass/epoxy, i.e. 10.2 ± 0.4 GPa demonstrating the rises of 74% and 39% respectively

(Fig. 5b). The addition of both MWCNTs and GPN in the glass/epoxy at 0.1wt.%, 0.2wt.%

and 0.3 wt.% loadings also resulted in increased compressive modulus values, i.e. 11.3 ± 0.3

GPa,12.5 ± 0.2 GPa and 7.5 ± 0.6 GPa, which exhibits a rise of 10.%, 22% rise and 26% fall,

respectively. The incorporation of MWCNTs and GPN in glass/epoxy matrix has for the most

part demonstrated an increase in the flexural modulus in small fractions; however, the pattern

reverses after increasing the content of nanoreinforcements. For instance, in an examination

compressive modulus increased with the addition of 0.1wt.% MWCNTs in epoxy that

diminished significantly by increasing the MWCNTs and GPN content up to 0.35wt.% in the

epoxy [7,34]. In another examination, compressive modulus is accounted for a similar pattern,

i.e. sharp increment subsequent to adding ~0.3 wt.% MWCNTs and GPN followed by a

decrease when their content was increased to 3.5wt.% in epoxy matrix [8,42].

The maximum fracture strain in compressive testing increased when 0.2wt.% MWCNTs

and 0.2wt% GPN were included in unidirectional glass/epoxy composite [0°]s, i.e. 3.8 ±

0.14%, a (125.4 % rise), 1.5 ± 0.11( 261.1% rise) when compared with neat glass/epoxy 0.28

± 0.1% however GPN were affected adversely and diminished the flexural strain, i.e. 1.5 ±

0.15% (27.7% fall). The binary addition of MWCNTs and GPN in glass/epoxy composite at

0.2wt.% and 0.1wt.% each resulted in modest increase in flexural strain, 6.1 ± 0.18 (238.8%

rise) and 7.2 ± 0.16 (300% rise).However, composites containing 0.2wt.% MWCNTs and

GPN each, demonstrated a significant rise, i.e. 5.6 ± 0.19 (211% rise), as shown in Fig. 5c.

The addition of 0.4wt.% MWCNTs has just demonstrated the increase in flexural strain [44]

however the effect of GPN on the flexural strain isn't accessible in literature.




Figure 5 Compressive properties of nanocomposites in comparison to neat glass epoxy (a) flexural

strength (b) flexural modulus and (c) fracture strain.

The change in the fracture morphology of composites due to the incorporation of

nanoreinforcements seems to be conceivable reason of increased toughening effect. The

roughness of the fractured nanocomposites increased significantly (Fig. 6) in comparison to

the fractured surface of neat glass/ epoxy composite (Fig. 2a). Neat glass/epoxy composite

showed a typical brittle fracture, i.e. smooth surface, while the rough surface was observed in

composites due to the phenomena of shear yielding and deformation of epoxy between the

reinforcements, as also observed elsewhere [13]. The fracture morphology also shows the

appearance of crazing due to nanoreinforcements, which limits the propagation of cracks and

increases the strength of the composites [10].



Figure 6 SEM images of fracture morphology in hybrid nanocomposites containing e-glass

fibre/epoxy composite after the incorporation of 0.2wt.%MWCNTs and 0.2wt.%GPN. The images

show rougher surfaces compared to the fractured surface of neat glass/epoxy composite in Fig. 2a.

The toughening mechanisms introduced by incorporating MWCNTs and GPN may be the

pullout of nanoreinforcements, glass fibre reinforcement/ epoxy matrix debonding, crack

deflection, and MWCNTs bridging. A model has been shown in Fig. 7 demonstrating the

presence of MWCNTs and GPN in the glass/epoxy matrix, both individually and combined.

The presence of MWCNTs and GPN is expected to initiate toughening mechanisms in

glass/epoxy matrix, as shown in Fig. 8, where an advancing crack is deflected numerous times

because of MWCNTs and GPN. In the wake of the crack, the crack bridging effect because of

MWCNTs is also shown. Pulled out MWCNTs are also visible in the crack; this phenomenon

happens takes place after the debonding of MWCNTs from the matrix material. All these

toughening mechanisms are probably to be the possible conceivable reasons for an increase in

the tensile and flexural strength of the composites especially the impact resistance. Fig. 9 a

and b demonstrate the presence of pull out and bridging phenomena (arrowed) in

nanocomposites, respectively, because of MWCNTs; the hauled out phenomena strengthens

in composites containing increased amounts of MWCNTs, as can be witnessed and compared

in composites containing 0.1wt.% and 0.3wt.% MWCNTs in Fig. 9c and d. The crack

development is all by account limited because of the bridging of MWCNTs (Fig. 9b)

( (




Figure 7 Models of glass/epoxy matrix hybrid nanocomposites (a) without reinforcements and

containing (b) MWCNTs (c) GPN and (d) MWCNTs and GPN.

Figure 8 Model of glass/epoxy matrix hybrid nanocomposite showing the propagation of crack

through epoxy matrix and the interaction of crack with MWCNTs and GPN producing toughening

mechanisms including crack deflection, MWCNTs bridging and MWCNTs pullout.



Figure 9. Toughening mechanisms introduced in hybrid nanocomposites (a) MWCNTs pullout (b)

MWCNTs bridging; pullout phenomenon in composites containing (c) 0.1wt.% MWCNTs and

0.1wt.% GPN, and (d) 0.2wt.% MWCNTs and 0.2wt.% GPN.

4. CONCLUSIONS

The individual and combined effect of MWCNTs and GPN on the mechanical properties of

various stacking sequences lay-up glass/epoxy [0°]s,[90°]s, 0°/90°]s and [45°/45°]s matrix

hybrid nanocomposites has been investigated. To ensure uniform dispersion of

nanoreinforcements and optimum bonding with the [0°]s glass/epoxy hybrid nanocomposite,

MWCNTs and GPN were functionalized before their incorporation into epoxy resin. The

contents of each of MWCNTs and GPN were increased from 0.1wt.% to 0.3wt.% while the

glass/epoxy composites containing individual reinforcement were also fabricated for

comparison. Mechanical testing of the composites containing 0.2wt.% MWCNTs/[0°]s

glass/epoxy composite and 0.2wt.% GPN/[0°]s glass demonstrated an increase in tensile

(28.4%) flexural (84%) and compressive (480%) strengths along with tensile (38%) flexural

(64%) and Compressive(74% ) moduli in comparison to neat glass/epoxy composite; fracture

strain increased in both the tensile, flexural and compressive testing. Uniform dispersion of

MWCNTs and GPN were observed in SEM images without the presence of their

agglomerates. The increase in mechanical properties of the composites can be related with the

uniform dispersion of nanofillers and their strong interfacial adhesion with the epoxy matrix.

ACKNOWLEDGMENT

The authors gratefully acknowledge the technical support of the manufacturing of Hybrid nan

reinforced glass/epoxy composites and Experimental Testing's Facilities, Composite




Technology Centre for Composites, Aerospace Engineering Department, Indian Institute of

Technology, Madras, India.

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EFFECT OF FIBER ORIENTATION ON THE MECHANICAL BEHAVIOR OF GLASS FIBER/EPOXY HYBRID NANOCOMPOSITES...

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