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Development and characterization of carbon-carbon composite for aircraft brake pad usingpreformed yarn method

by

P. Naik, M. Ibrahim, A.O. Surendranathan and M. A.Mujeebu

reprinted from

WORLD JOURNALOF ENGINEERING

VOLUME 8 NUMBER 3 2011

MULTI-SCIENCE PUBLISHING COMPANY LTD.

1. IntroductionCarbon-carbon (CC) composites are composed of

carbon fibers in a carbon matrix. They arelightweight materials that can perform structurally atextreme temperatures and have superior thermalshock, toughness, ablation, and high-speed frictionproperties. CC components have been emerged in

Development and characterization of carbon-carbon composite for aircraft brake pad using

preformed yarn method

P. Naik1, M. Ibrahim1,*, A.O. Surendranathan2

and M. A. Mujeebu3

1Department of Mechanical Engineering, Anjuman Engineering College,Bhatkal, Karnaka, S. India.

2Department of Metallurgical and Materials Engineering, National Institute of TechnologyKarnataka, Surathkal, Karnataka, S. India.

3School of Mechanical Engineering, Universiti Sains Malaysia, Engineering Campus,14300 Nibong Tebal, Penang, Malaysia

[email protected]

(Received 10 June 2010; accepted 6 March 2011)

Abstract

This paper presents the synthesizing of carbon-carbon (CC) composites by preformed yarn(PY) method, by varying the percentage of carbon fiber volume. The PY used is carbon fiberbundle surrounded by coke and pitch which is enclosed in nylon-6. Three types of samples withfiber weight fractions of 30%, 40% and 50% respectively, are fabricated and tested. In each case,the PY is chopped and filled into a die of required shape and hot pressed at 600°C to get thecarbonized composite. To obtain the graphitic structure, the specimen is heat treated at 1800°Cfollowed by soaking for two hours. Further, one cycle pitch impregnation is done by hot isostaticpressing, to eliminate the voids. The characteristics such as hardness, compressive strength, creep,density and oxidation resistance are studied. It is observed that, as the carbon fiber percentageincreases the properties also improved, provided sintering is done at fairly higher temperatures.The superiority of the new class of CC composites made by the proposed PY technique over thoseobtained by the conventional methods is also demonstrated.

Key words: Composites, Hot isostatic pressing, Creep

World Journal of

EngineeringWorld Journal of Engineering 8(3) (2011) 259-266

response to sustained aerospace and defense needs(Sheehan et al., 1994). However, the extremelyhigh price of CC composite due to productioncharacteristics made it difficult to the industrialapplication. In 1991, Institute of ProductionTechnology of Tokyo University in Japan developedinnovative Preformed Yarn (PY) technology, which

ISSN:1708-5284

260 P. Naik et al./World Journal of Engineering 8(3) (2011) 259-266

improved manufacturing process drastically fromexisting infiltration method and resulted in reductionof manufacturing cost. Substantial investigationshave been carried out and are still underway, on thedevelopment and characterization of CC composites.A comprehensive review on all those works is beyondthe scope of this article; however, few works whichare related to the current study are summarized here.

A CC composite coil spring was manufactured byNagao et al. (1998), using PY method. A bundle ofcarbon fibers was included in a matrix composed ofpitch coke, mesophase pitch and scaled coke, andcoated with polypropylene, resulting in a preformed-yarn. Two kinds of carbon fiber, filament yarn orspun yarn, were used for reinforcement. Thepreformed-yarn was wound spirally around a metalcore, and this was formed into a CC coil spring by hotpress forming. The spring manufactured by PYmethod using spun yarn showed a higher springconstant than that obtained using filament yarn.Subsequently, they (Nagao et al., 1998; Chacko et al.,2009) applied similar technique to fabricateunidirectional carbon–carbon (UD-CC) composite.Density, porosity, flexural strength and modulus ofthe resulting UD-CC composite test pieces weremeasured and found to be superior by a factor of about1.3 than the UD-CC composites manufactured byconventional methods. Hatta et al. (1999) examinedthe high-temperature oxidation behavior of bare andSiC-coated CC composites. Their measurements werefocused on the effect of oxygen partial pressure onthe oxidation behavior and the transition temperaturebetween the passive and active oxidation regimes.

Ogasawara and Ishikawa (2001) studied thermalresponse and oxidation behavior of commercialmetal silicon-infiltrated carbon/carbon composites(MICMATTM; Si-CC) in a high-enthalpy convectiveenvironment using an arc jet facility (an arc windtunnel). Composite specimens were put into asupersonic plasma air stream having a gas enthalpyof 12.7–18.8 MJ/kg for 50–600s. Excellent oxidationresistance was obtained by the formation of a porousSiC layer at the surface of the composite. Goto et al.(2003) examined the tensile fatigue behavior of across-ply CC laminate at room temperature.Tension–tension cyclic fatigue tests were conductedunder load control at a sinusoidal frequency of 10 Hzto obtain stress–fracture cycles (S–N) relationship.The residual tensile strength of specimens thatsurvived fatigue loading was enhanced with increasein fatigue cycles and applied stress. Formation of

micro-cracks at the fiber–matrix interfaces wasobserved during fatigue loading. Experiments onmeasurement of tensile strength of CC compositesmade by PY method was reported by Aya et al.(2004) and Hatta et al. (2001, 2004a). Tensilefracture behavior of CC composites with 0°/90°laminations were examined by Hatta et al. (2004b)by using double end-notched specimens. In theirexperiment, the volume fractions of the 0°– and 90°–layers were systematically varied to observe thevariation of fracture patterns as a function of theshear strength. Fatigue behaviors of unidirectionallyreinforced (UD), symmetric cross-ply laminated(CP) and symmetric quasi-isotropically laminated(QI) CCs were examined by Goto et al. (2005).

In the present study, an attempt is made tointroduce the PY method in India, to synthesize CCcomposites for aerospace brake pad application.Moreover, as far as the authors are aware,manufacturing of CC composite by varying thepercentage of fiber content has not been reported sofar. The PY developed in the current study is carbonfiber bundle surrounded by coke and pitch which isenclosed in Nylon-6; three types of samples withfiber weight percentages of 30%, 40% and 50%respectively, are fabricated. The PY is subjected tohot pressing at 600°C followed by heat treatment at1800°C. Subsequently, in order to eliminate thevoids, one cycle pitch impregnation is performedon the samples, by hot isostatic pressing.Characterization of the specimens is then carriedout in terms of hardness, compressive strength,creep, density, and oxidation resistance.

2. Materials and methods

2.1. Preparation of CC compositeThe materials used in the manufacture of

carbon-carbon composites are: 1) Carbon fiber asreinforcement. Table. 1 gives the properties of carbonfiber which was fabricated by controlled pyrolysis

Table 1. Properties of carbon fiber (de Villoria et al., 2006) (Mark Tech India Pvt. Ltd., India)

Diameter 7 µmLength of the fiber 5–6 mDensity 1.8g/ccTensile strength 124 MPaYoung’s modulus 230 GPaElongation 1.5%

P. Naik et al./World Journal of Engineering 8(3) (2011) 259-266 261

of an organic fiber precursor (Polyacrylonitrile,known as PAN, is the commonly used precursor; 2)Pitch, coke and nylon-6 as matrix materials,supplied by DRDO (Defense Research andDevelopment Organization) Hyderabad, India.Three different samples of CC composite withdifferent carbon fiber content such as 30%, 40% and50% weight fractions are prepared; the compositionsof the samples are given in Table 5. The PY ischopped and filled into a die of size 15 × 2 × 2 cmmade of ally steel, and hot pressed at around 600°Cusing a 10 ton capacity press, to get the composite.At this stage, the composite is only carbonized, butactually needed is graphitic structure which isobtained by heat treatment at 1800°C followed bysoaking for two hours. The voids are then eliminatedby one cycle pitch impregnation by hot isostaticpressing. The CC composites are prepared accordingto the flowchart shown in Figure 1.

2.2. Experimental procedureThe Brinnel hardness test, Compression test,

Oxidation test, Creep test and density test areconducted on the CC composites of differentcarbon fiber content (specimens 1, 2 and 3).Microstructure of CC composites is also studiedby using both optical and scanning electronmicroscopes (SEM). For the hardness test, initiallythe samples are cut as per the ASTME 10 and areplaced in the Brinell testing machine. In thecompression test, the samples are cut according tothe SACMA standards (SACMA SRM 6 which ismainly used for compressive properties oforiented cross-plied-fiber resin composites) beforebeing placed in the compression testing machine(Fig. 2). The experimental setup for oxidation test (Fig. 3) consisted of TGA machine (EXSTAR−6300, Nanotechnology Inc.) with a platinumcrucible used for placing the samples and an airsupply cylinder (Nitrogen) connected to thefurnace inside which the samples are placed tocreate an inert atmosphere. The compositesamples are placed in the form of powder. Thewhole system is PID controlled and is directlyconnected to the computer.

Table 2.Compositions of preformed yarn (Sheehan et al., 1994)

Matrix

Specimen Type of PY Wt% Binder ratio Wt% Cf Wt% Sleeve Wt%

1 PY-B75 35 75 30 352 PY-B60 35 60 40 253 PY-B50 35 50 50 15

Coke and pitch binder

Carbon fiber

Sleeve forming

Chopped yarn

C-C composite

Nylon (Sleeve)

Hot press + heat treatment

Preformed yarn (PY)

Fig. 1. Flow chart for CC preparation. Fig. 2. The compression testing set-up.


The creep test is conducted on the compositesamples which are initially heat treated at 1800° Cand soaked for 2 hours and then theses samples arefitted in an impression creep test set up. The machine(Fig. 4) consists of a superalloy cage with two rigidframes-one fixed to the base & other free to move.The former has an indenter of about 1.08 mmdiameter and latter has a seat to hold test specimenexactly below the indenter. The setup also consists oflever arm on which a known weight can be placed ina pan attached to its end, and connected by frameswhich are free to move. Depth of the indentationwhich is the displacement of the indenter sensed

through the movement of the pull rod is measured byLVDT with an accuracy of about (±0.001 mm) and atimer is used to measure the time in seconds withrespect to the displacement in mm. The wholeexperiments are carried out at room temperature.

3. Results and discussion

3.1. Hardness testThe variation of hardness with carbon fiber

content is shown in Figure 5. Carbon fiber is a brittlematerial. It is well established that, as the carboncomponent increases in a particular structuralcomponent the material gains brittle property, and asthe brittleness increases the hardness also increases.Accordingly, Figure 5 clearly suggests that theincrease in composition of carbon fiber increases thehardness of the CC composite.

3.2. Compression testAs strength and hardness are proportional to each

other, the increase in the hardness increases theability to withstand higher loads. The result ofcompression test is shown in Figure 6 which showsthat the increase in the addition of carbon fiberincreases the strength, which obviously increasesload carrying capacity.

Fig. 3. Oxidation experiment set-up.

Fig. 4. Creep testing set-up.

60

50

40

30

20

10

30 40 50Fiber content, %wt

Brin

ell h

ardn

ess

num

ber

0

Fig. 5. Hardness vs % carbon fiber content.

70

30 40 50Fiber content, %wt

Com

pres

sion

ste

ngth

, MP

a

50

686664626058565452

Fig. 6. Compressive strength vs % carbon fiber content.


3.3. Creep test Figures 7, 8 and 9 show the plots of Strain v/s time

for samples 1, 2 and 3 respectively. It is understoodthe creep rate increases with increase in temperatureand the composition of carbon fiber. This is becauseof poor interfacial bond between the carbon fiber andcarbon matrix, as also revealed by the SEM analysis.

3.4. Density The densities of the composites are found and

are given in the Table 3. It is known that thedensity of carbon fiber is higher than that of matrixmaterials. Table 3 shows that the increase in thecarbon fiber composition increases the density ofthe material, and hence its weight. However, as faras its suitability for aerospace application is

concerned, the increase in weight is still within theacceptable limit.

4. Oxidation testOxidation test is carried out by placing the

composite sample in the form of powder inthermogravimetry experimental setup and directgraph is obtained. Plots of DTG (ug/min) vs.Temperature, DTA uV vs. Temperature and TG mgvs. Temperature, for specimens 1, 2 and 3 are shownin Figures 10, 11 and 12 respectively. A sharper dropin a nitrogen atmosphere indicates that a more drasticthermal decomposition reaction takes place and thatCC composites decompose more rapidly in air thanin nitrogen. The more rapid the pyrolysis, the greater

Table 3.Densities of specimens 1, 2 and 3

Specimen Composition Density, (gm/cc)

1 30% Cf + matrix material 1.552 40% Cf +matrix material 1.603 50% Cf + matrix material 1.65

Time, sec

0.160.140.120.1

0.080.060.040.02

00 1000 2000 3000

Str

ain,

mm

8 kg (200°C)

8 kg (200°C)

8 kg Room temp.

6 kg Room temp.

Fig. 7. Strain v/s time for specimen 1.

Time, sec

0.160.18

0.140.120.1

0.080.060.040.02

00 2000 4000

Str

ain,

mm

8 kg (200°C)

8 kg (200°C)

8 kg Room temp.

6 kg Room temp.


0.140.16

0.120.1

0.080.060.040.02

00 20001000 3000

Time, sec

Str

ain,

mm

8 kg (200°C)

8 kg (200°C)

8 kg Room temp.

6 kg Room temp.


200.0

0.0

100.0

−100.0

−200.0

−300.0

−400.0

−500.0

70.00

60.00

50.00

40.00

30.00

20.00

10.00

0.00

3.500

3.000

2.500

2.000

1.500

1.000

100 200 300 400 500Temp cel

600 700 800 900 1000

DT

G u

g/m

in

DT

A u

V

TG

mg

Fig. 10. Specimen 1: 30% carbon fiber.

Temp cel

200.0

0.0

100.0

−100.0

−200.0

−300.0

−400.0

45.00

40.00

35.00

25.00

30.00

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10.00

15.00

5.00

0.00

3.800

3.600

3.400

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3.000

2.800

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2.000

1.800

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100 200 300 400 500 600 700 800 900 1000

DT

G u

g/m

in

DT

A u

V

TG

mg



the amount of volatiles generated. Dynamic TGexperiments are conducted in a nitrogen flow atheating rate from 0.5 to 15°C/min. The graphsshow that as temperature increases material lossincreases owing to the enhanced oxidation. Weightloss in specimen 1 is 2.564 mg, in specimen 2 is 2.2 mg and in specimen 3 is 2.15 mg. It is also clearthat as carbon fiber percentage increases material loss

decreases. Hence it is concluded that increase incarbon fiber percentage in CC composite decreasesthe oxidation.

5. Optical micrographsThe Microstructures of material 1, 2 and 3 under

500X magnification is shown in the Figure 13. Itshows the distribution of short carbon fibers. It can beseen that the gap between each fiber reduces as %composition of carbon fiber increases.

Figures 14, 15 and 16 show the SEMphotographs of specimens 1, 2 and 3 for differentmagnification. It is clear that the distributions ofcarbon fibers in the specimens are perfect. Theinterfacial bond between the carbon fibers and thecarbon matrix is not good; hence the properties ofthe materials are much less than the theoreticalvalues. This is because of the low sinteringtemperature (1800°C); if high sinteringtemperature is applied (above 2300°C), theinterfacial bond becomes perfect and better resultswould be expected.

0.800

0.000

0.200

0.400

0.600

−0.400

−0.200

−0.800

−0.600

−1.000

−1.200

DT

G u

g/m

in

30.00

25.00

20.00

15.00

10.00

5.00

0.00

DT

A u

V3.800

3.600

3.400

3.200

3.000

2.800

2.600

2.400

2.200

2.000

1.800

1.600

TG

mg

Temp cel

100 200 300 400 500 600 700 800 900 1000


Fig. 13. Microstructures of specimens 1, 2 and 3 at 500X.

SEI5kV × 2,000 10 µm 0045 13 62

Fig. 14. SEM photograph of specimen 1 at different magnifications.


6. ConclusionThe PY method is successfully employed to

produce the CC composites for aircraft brake pad.The properties of CC composites are dependent onfiber content and fiber orientation. Unlike polymermatrices, carbon matrices contribute significantlyto the ultimate properties of the composites,especially in the case of pitch and CVD-derivedcarbon matrices. CC composites are a family of materials with choice of variation in fiber andmatrix architecture, structure, microstructure,mechanical, thermal and physical properties etc.Hence these provide high performance materialsfor application in a number of sectors. From thehardness test and compression test, it is observedthat as carbon fiber fraction increases the material properties also increases; however, theseproperties are much less than the theoreticalvalues because of low sintering temperature. Thecreep rate increases with addition of carbon fibercomposition; this is because of imperfect bond

between the carbon fibers with carbon matrix, asunderstood from the SEM photographs. When theimprovements in physical and mechanicalproperties are taken into consideration, theincrease in density due to the addition of carbonfiber is not so alarming, and hence acceptable foraerospace applications. A major drawback of CCcomposite is lack of oxidation resistance. Asimportant solution to this problem, the presentstudy reveals that the oxidation resistance can beincreased by increasing the percentage of carbon fibers.

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