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Composites Science and Technology 67 (2007) 222–230

SCIENCE ANDTECHNOLOGY

Effect of fiber length on the wear resistance of short carbonfiber reinforced epoxy composites

Hui Zhang a,b, Zhong Zhang a,b,*, Klaus Friedrich b

a National Center for Nanoscience and Technology, China, No. 2, 1st North Street Zhongguancun, 100080 Beijing, Chinab Institute for Composite Materials, University of Kaiserslautern, 67663 Kaiserslautern, Germany

Received 1 August 2006; accepted 2 August 2006Available online 5 October 2006

Abstract

In this study, the influence of fiber length on tribological properties of short carbon fiber (SCF) reinforced epoxy composites was inves-tigated. Both a block-on-ring and a pin-on-disk apparatus were applied for the study of sliding performance of composite specimensagainst polished steel counterparts under dry conditions. It was found that composites with longer SCF (nominal length = 400 lm) exhib-ited better wear resistance than those with shorter SCF (nominal length = 90 lm), in both cases either with or without graphite flakes andTiO2 nanoparticles. This effect seemed to be more pronounced at higher contact pressures applied. Furthermore, the steady frictional coef-ficient and contact temperature were reduced slightly by longer fibers. The relationships among the frictional coefficient, the contact tem-perature and the wear rate were discussed under the support of scanning electron microscope observations of the worn surfaces.� 2006 Elsevier Ltd. All rights reserved.

Keywords: A. Carbon fibres; A. Short-fibre composites; A. Polymer-matrix composites (PMCs); D. Scanning electron microscopy (SEM); Wear Resis-tance

1. Introduction

Short carbon fibers are one of the most commonly usedreinforcements for improving mechanical and tribologicalperformance of polymers. Compared to continuous fibercomposites, short fiber reinforced polymers (SFRP) com-bine easier processability with low manufacturing cost.Therefore, in recent years the use of SFRP compositesgrows rapidly in many engineering applications, in particu-lar in automobile and mechanical engineering industry [1].Over the past several decades, numerous works have beendone to study the relationship between fiber length andmechanical performance of SFRP. Corresponding predic-tion models of stiffness, strength and impact properties

0266-3538/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.compscitech.2006.08.001

* Corresponding author. Address: National Center for Nanoscience andTechnology, China, No. 2, 1st North Street Zhongguancun, 100080Beijing, China. Tel.: +86 10 62652669; fax: +86 10 62650450.

E-mail address: zhong.zhang@nanoctr.cn (Z. Zhang).

have been also proposed by many researchers [2]. All theseinvestigations indicate that the fiber length is a crucialparameter in determining the mechanical performance ofSFRP [3–5]. In contrast, the understanding on the influenceof fiber length on wear and friction of composites is stillvery lacking, in comparison to other factors, such as fibervolume fraction, fiber orientation, and fiber type, whichhave been systematically investigated [6–8]. Friedrich [9]reported that the continuous fiber reinforced thermosettingseemed to be more effective on improving the abrasive wearresistance (against 70 lm Al2O3 particles). The longerfibers were damaged locally under wear against the abra-sive particles, and the rest of fibers still contributed to thewear resistance of those composites. Barkoula and Kar-ger-Kocsis [10] studied the erosive wear behavior of poly-propylene (PP) reinforced with glass fibers (2 and 10 mmin length, respectively). However, it was found out thatthe fiber length did not affect the erosive wear, especiallyat high impact angles. The mechanisms of fiber removal

H. Zhang et al. / Composites Science and Technology 67 (2007) 222–230 223

in the short fiber reinforced composites were similar tothose of the long fiber composites, especially when the per-pendicular erosion direction was considered.

The major subject of the present work was to evaluatethe influence of fiber length on the wear behavior of shortcarbon fiber reinforced epoxy (SCF/EP) composites underdry sliding conditions. The tribological tests were per-formed at various contact pressures, using both a block-on-ring (B-o-R) and a pin-on-disk (P-o-D) apparatus.The corresponding wear mechanisms were discussed onthe basis of the variation of tribological parameters andsupported with scanning electron microscope (SEM) wornsurfaces.

2. Experimental

2.1. Materials and compounding

The matrix used was a bisphenol-A type epoxy resin(DER331, Dow), hardened by an amine-curing agent(HY2954, Dow). The average diameter of pitch-basedSCFs was around 14.5 lm, and the nominal fiber lengthsamounted to 90 lm (M-2007S) and 400 lm (M-207S),respectively, supplied by Kureha Germany. Graphite flakes(Superior 9039) with a size of 20 lm and TiO2 particle(Kronos 2310) with an average diameter of 300 nm wereapplied as additional fillers.

Two series of epoxy-based composites (series C and L)were prepared. In series C samples were reinforced onlyby SCFs of various lengths at same filler content of15 vol%, while samples of series L contained additionally5 vol% graphite flakes and 5 vol% nano-TiO2 particles.The compositions involved in this study are summarizedin Table 1. The composites were prepared in a vacuum dis-solver by mixing the epoxy resin with TiO2 particles, graph-ite flakes and SCFs in sequence (the first two fillers wereonly used for the series L as mentioned above). Taking intoaccount the possible breakage of fibers during mechanicalmixing, various processing parameters, i.e. stirring speedand time, were employed. In this way, we can obtain a

Table 1Compositions of short carbon fiber (SCF)/epoxy composites

Sampleno.

Filler volume content (%) Nominal lengthof SCF beforeprocessinga

Measured averagelength of SCFafter processing

Shortcarbonfiber

Graphite TiO2

C1 15 – – 90 67b

C2 15 – – 400 192b

C3 15 – – 400 236c

L1 15 5 5 90 –b,d

L2 15 5 5 400 –c,d

a Provided by the supplier, Kureha Company.b Processing parameters: 2000 rpm/30 min, at 70 �C.c Processing parameters: 1000 rpm/10 min, at 70 �C.d The fiber length is not measurable.

group of samples with same fiber volume content but differ-ent fiber length. (cf. Table 1). After mixing with the definiteamount of curing agent, a fraction of mixture was takenout for measuring the fiber length distribution, which willbe described in the next section. The rest was poured intoa rectangular aluminum mould for curing. The gel temper-ature applied was 70 �C for 8 h, and the final curing tem-perature amounted to 122 �C over a period of 16 h.

2.2. Fiber length distribution

In view of the oxidative reaction and the resulting damageof SCFs at high temperature, the measurement of the fiberlength distribution of the SCF reinforced composites cannotbe carried out through burning method in a muffle furnace,which is usually applied for short glass fiber (SGF) rein-forced composites [11]. Therefore, in the present study, thefollowing procedures were taken: (i) after mechanical disper-sion, the mixture of epoxy resin, curing agent and SCFs wasimmediately poured into a beaker with acetone; (ii) the epoxyresin and the curing agent were dissolved in the acetone,while the SCFs were deposited on the bottom of beaker;(iii) the SCFs were washed out many times with acetoneand then placed into an oven of 80 �C for drying; and (iv)the fiber lengths were measured by scanning electronicmicroscope (SEM). An average value of fiber length was cal-culated from at least 500 individual SCF for each composi-tion. It should be noted that this approach is not possiblefor the samples containing graphite flakes and TiO2, due tothe difficulty to separate SCFs from the deposits.

2.3. Mechanical properties

A Zwick universal testing machine was applied to investi-gate the flexural modulus and strength under a three-point-bending approach according to DIN-ISO-178. Specimenswere cut into a dimension of 100 · 10 · 4 mm3. The testspeed was kept constant at 1 mm/min. Five specimens ofeach composition were measured, and an average valuewas reported, with a standard error bar.

2.4. Wear test

In this study, the characterization of the wear behaviorof these composites was carried out on two tribometers,i.e. a block-on-ring (B-o-R) and a pin-on-disk (P-o-D)apparatus. Their configurations are schematically illus-trated in Fig. 1.

2.4.1. Block-on-ring test

For the B-o-R apparatus, a hardened and polished car-bon steel ring (German Standard 100 Cr6) having a diame-ter of 60 mm and initial surface roughness of 0.1 lm, servedas counterpart. The sliding speed was kept constant at 1 m/s, while the contact pressure was adjusted in a range of 0.5–5 MPa. The test duration was set to 20 h. All measurementswere performed at room temperature. The specific wear rate

Ring: Counterpart Steel 100Cr6 (DIN) Polished

Dead Weight Normal Force

Block Specimen

Dead Weight

Specimen: Composite Pin

Disk: Steel Counterpart

ϖ

Normal Force

16.5mm

Fig. 1. Schematic diagrams of: (a) block-on-ring and (b) pin-on-disk test apparatus.

0 100 200 300 4000

5

10

15

20

25

30 C1,L=67μm

0 200 400 6000

2

4

6

8

10

Fiber Length [μm]

Fiber Length [μm]

Fiber Length [μm]

C2, L=192μm

0 200 400 6000

2

4

6

8

10

Fra

ctio

n [%

]

Fra

ctio

n [%

]

Fra

ctio

n [%

]

C3,L=236μm

a b

c

Fig. 2. Histograms of fiber length distribution after processing: (a) C1, (b) C2, and (c) C3.

224 H. Zhang et al. / Composites Science and Technology 67 (2007) 222–230

0 1 2 3 4 50

10

20

30

40

Ws

[10-7

mm

3 /N

m]

Contact Pressure [MPa]

C1C3

30L1L2

a

b

H. Zhang et al. / Composites Science and Technology 67 (2007) 222–230 225

Ws of the specimens was calculated according to the follow-ing equation:

W s ¼Dm

qF NL½mm3=N m� ð1Þ

where Dm is the specimen’s mass loss, q is the density of thespecimen, FN is the normal load applied on the specimenduring sliding, L is the total sliding distance. The averagevalue of Ws was calculated from at least six specimens.The inverse of the specific wear rate can be referred tothe wear resistance of the material.

2.4.2. Pin-on-disk test

For comparison purposes, parts of the wear tests werealso performed on P-o-D apparatus, according to ASTMD3702. The 100 Cr6 steel disk with an initial surface rough-ness of 0.2 lm was used as counterpart. The temperature ofthe disk was monitored by an iron–constantan thermocou-ple positioned on the edge of the disk, which was recordedas contact temperature. The frictional coefficient wasrecorded and calculated by a ratio between the tangentialforce and normal load. After test, the mass loss of the spec-imen was measured in order to calculate the specific wearrate [22]. At least three specimens of each composition weretested. Similarly, the specific wear rate Ws was also calcu-lated according to Eq. (1).

Table 2Mechanical properties of short carbon fiber/epoxy composites withvarious fiber lengths

Sampleno.

Density (g/cm3) Flexuralmodulus(GPa)

Flexuralstrength(MPa)

Elongation atbreak (%)

C1 1.209 ± 0.001 3.70 ± 0.15 95.1 ± 3.0 3.45 ± 0.09C2 1.205 ± 0.012 4.16 ± 0.18 106.3 ± 4.9 3.13 ± 0.21C3 1.206 ± 0.001 4.41 ± 0.35 107.8 ± 6.5 2.86 ± 0.11L1 1.393 ± 0.003 4.06 ± 0.12 80.7 ± 1.7 2.10 ± 0.06L2 1.392 ± 0.001 5.44 ± 0.20 101.5 ± 6.7 1.98 ± 0.10

50 100 150 200 250

5

10

15

20

Ws

[]

10-7 m

m3 /

Nm

Average Fiber Length [μm]

Contact Pressure= 1 MPa

Fig. 3. Influence of fiber length on the specific wear rate of epoxycomposites without graphite flakes and nano-TiO2 (series C) at the contactpressure of 1 MPa.

3. Results and discussion

3.1. Average fiber length

It is possible to measure the fiber length and their distri-bution by using a SEM as mentioned in Section 2.2. The

0 1 2 3 4 50

10

20

Ws

[10-7

mm

3 /N

m]

Contact Pressure [MPa]

Fig. 4. Influence of contact pressure on the specific wear rate of epoxycomposites: (a) without graphite flakes and nano-TiO2 (series C) and (b)with graphite flakes and nano-TiO2 (series L).

0

10

20

30

40

50

Ws[1

0-7 m

m3 /

Nm

]

Block on Ring Pin on Disk

Contact pressure=4MPa

1 C3C L3 L1

Fig. 5. Comparison of specific wear rates of epoxy composites measuredon block-on-ring and pin-on-disk apparatus at the contact pressure of4 MPa.

Table 3Frictional coefficient and contact temperature of epoxy composites with/without graphite flakes and nano-TiO2 measured by a pin-on-diskapparatus at a contact pressure of 4 MPa

Sample no. Average frictionalcoefficient

Average contacttemperature (�C)

C1 0.673 ± 0.03 90.1 ± 0.4C3 0.654 ± 0.01 87.7 ± 2.1L1 0.219 ± 0.001 36.6 ± 0.3L2 0.244 ± 0.009 39.9 ± 0.5

226 H. Zhang et al. / Composites Science and Technology 67 (2007) 222–230

average fiber lengths of the series C are given in Table 1,and the histograms of the fiber length distribution are pre-sented in Fig. 2. For the series C, i.e. sample without graph-ite flakes and nano-TiO2, it is obvious that the average fiberlength after mechanical mixing was reduced more or less.The longer the nominal fiber length was, the higher wasthe level of fiber breakage. One possible explanation couldbe that, as compared to shorter fibers, the mixture of resinswith longer fibers had a much higher viscosity, which maylead to severe fiber attrition during mixing. Moreover,longer SCFs usually had more structural flaws on their sur-faces, at which the fiber breakage was easy to occur [12].Besides, in the case of the same fiber nominal length, theprocessing condition affected their final length consider-ably. As shown in Table 1, a mild processing condition,i.e. low stirring speed and short dispersion time, led to lessdamage of the carbon fibers, due to a reduced attritionbetween fibers, when comparing sample C2 with C3. Forthe series L, i.e. samples with graphite flakes and nano-TiO2, the fiber length could not be measured directlythrough the method mentioned earlier, but one can stilldetermine the relative fiber length from the mechanicalproperties of the composites, which will be discussed inthe following sections.

0 5 10 15 20

0.2

0.3

0.4

0.5

0.6

0.7

0.8 Contact Pressure = 4 MPa

Sliding Time [hour]

Fri

ctio

nal

Co

effi

cien

t

C1, μ=0.673 C3, μ=0.654 L1, μ=0.244 L2, μ=0.219

C1

C3

L1 L2

0 5 10 15 2030

40

50

60

70

80

90

100Contact Pressure = 4 MPa

Co

nta

ct T

emp

erat

ure

[oC

]

Sliding Time [hour]

C1, T=90.1oC C3, T=87.7o

C

L1, T=39.9oC L2, T=36.6oC

C1

C3

L1L2

a

b

Fig. 6. Typical wear curves of epoxy composites with/without graphiteflakes and nano-TiO2 at the contact pressure of 4 MPa: (a) frictionalcoefficient and (b) contact temperature.

3.2. Mechanical properties

The mechanical properties of all specimens are summa-rized in Table 2. Firstly, it can be seen that the densityfluctuation of all samples was very small, indicating thatboth the longer and the shorter SCFs were homogenouslydistributed in the epoxy resin under the processing condi-tions applied. Note that the average fiber length in the pres-ent case was shorter than the critical fiber length (refer to

Fig. 7. Worn surfaces of epoxy composites without graphite flakes andnano-TiO2 at the contact pressure of 1 MPa: (a) C1 and (b) C3.

H. Zhang et al. / Composites Science and Technology 67 (2007) 222–230 227

the values in the literatures [13,14]). Within the range of crit-ical fiber length, a longer fiber length usually corresponds toa higher stiffness of the composite, and vice versa [15]. Thishas been also confirmed here. For example, the flexuralmodulus of the series C increased monotonously, whenthe average fiber length increased from 67 to 236 lm(Tables 1 and 2). Similarly, for the series L, it can be inferredfrom their flexural modulus that the sample L2 should havea longer average fiber length than L1. With this conclusion,one can further discuss the effects of fiber length on the wearperformance.

3.3. Tribological behavior

3.3.1. Wear rate, using block-on-ring configuration

Fig. 3 illustrates the wear rate of the series C as a func-tion of average fiber length. Tests were performed at a stan-dard sliding condition of 1 m/s and 1 MPa. As expected,the fiber length had an obvious influence on the wear resis-tance. When the average fiber length increased from 67 to

Fig. 8. Worn surfaces of epoxy composites without graphite flakes and n

236 lm, the wear resistance was improved by nearly threetimes, i.e. the wear rate was significantly reduced.

Fig. 4 presents the influence of the contact pressure onthe wear rate of both series C and L, i.e. with/withoutgraphite flakes and nano-TiO2. Firstly, it is clear that theaddition of graphite flakes and nano-TiO2 can improvethe wear resistance of all samples significantly. It is wellknown that, owing to their layer structure [16], the graphiteflakes can be easily separated by shear force during slidingand form a transfer film on the counterpart, which caneffectively reduce both frictional coefficient and thusimprove the wear resistance [17]. On the other hand, thewear-reduction effects of nanoparticles in polymer havebeen thoroughly investigated recently as reviewed byZhang and Friedrich [18]. The corresponding mechanisms,such as enhancing the mechanical properties of matrix,improving the bonding strength between transfer film andcounterface, as well as reducing friction coefficient causedby the rolling effect of fine particles, have been reported[19–22].

ano-TiO2 at the contact pressure of 5 MPa: (a, b) C1 and (c, d) C3.

228 H. Zhang et al. / Composites Science and Technology 67 (2007) 222–230

Concerning the effect of fiber length, in both cases, i.e.either with or without graphite flakes and nano-TiO2, thelonger fiber composites exhibited always a better wearresistance than the shorter ones, as shown in Fig. 4. Theeffect, especially for the series L, seemed to be more pro-nounced at higher contact pressures. In fact, at a contactpressure of 5 MPa, macro-cracks and fracture can be rec-ognized on the worn surfaces of the shorter fiber compos-ites, while it was rarely observed for the longer ones. Thisreflected that the longer fiber composites possessed a higherload-carrying capacity, which was probably ascribed totheir better stiffness and strength (Table 2).

3.3.2. Comparison of wear rates, measured on block-on-ringand pin-on-disk configurations

In order to compare the effect of fiber length on the wearperformance of composites under different test configura-tions, partial experiments were also conducted on a P-o-Dapparatus. A constant sliding speed of 1 m/s and a contactpressure of 4 MPa were applied in the case of the P-o-Dstudy. Fig. 5 presents a comparison of the specific wear ratesdetermined by the two apparatuses. Because wear proper-ties are not intrinsic material parameters but are sensitiveto the condition applied [9], it is easy to understand the dif-ference of Ws obtained with the two tribometers at the samepv-condition. In spite of that, a parallel tendency wasobserved on both tribometers, i.e. the longer fiber compos-ites more or less performed better wear resistance than theshorter ones.

Fig. 9. Worn surfaces of epoxy composites with graphite flakes and nano-TiO2 at the contact pressure of 1 MPa: (a) L1 and (b) L2.

3.3.3. Frictional coefficient and contact temperature,

measured on pin-on-disk configuration

The dependency of frictional coefficient and contacttemperature on sliding time is given in Fig. 6. For all sam-ples, unsteady-state sliding processes, the so-called run-ning-in periods, took place at the initial stages. Duringthe running-in period, the frictional coefficient for the seriesC rose sharply until a steady-state level was reached. Whilefor the series L, the frictional coefficient ran through a peakat first, and then dropped quickly to a stable and low value,which reflected the formation of a graphite transfer film,which has been reported in details by others [17]. Theserunning-in periods lasted about 2–2.5 h. In the presentwork, only steady-state results were used to calculate theaverage values of frictional coefficient and contact temper-ature, as given in Fig. 6 and Table 3. The fiber length wasfound to have notable influence on the frictional coeffi-cients of the studied samples after running-in periods. Asit can be seen from Fig. 6a, the longer fibers could reducethe frictional coefficient slightly in comparison to shorterones (to be discussed in the next section). Correspondingly,a slight reduction in the contact temperature was alsoobserved in the case of longer fiber samples (Fig. 6b). Apossible explanation for the slight reduction of the contacttemperature is that the longer SCF might contribute to ahigher thermal conductivity than the shorter ones.

3.3.4. SEM observation of worn surfaces

The wear mechanisms of SCF reinforced epoxy compos-ites can be furthermore analyzed by using SEM observa-tions of the worn surfaces. As shown in Fig. 7, nosignificant difference can be recognized on the worn sur-faces under lower contact pressure (1 MPa) for the seriesC, although the worn surfaces of the longer fiber compos-ites (Fig. 7b) look a bit smoother than those of the shorterones (Fig. 7a). However, the difference became obvious athigher contact pressures, e.g., 5 MPa. As given in Fig. 8,the shorter fiber composites had a much rougher worn sur-face (Fig. 8a and b) in comparison to the longer ones(Fig. 8c and d), at both lower and higher magnifications.

It is generally accepted that the wear behavior of shortfiber-reinforced composites is dominated by the processof fiber peeling-off, which typically occurs following suchsequential stages: fiber thinning, fiber cracking and fiberremoval [9]. Fiber peeling-off plays a key role, especiallyat high-pressure condition. This was also confirmed inour case. As an example for the shorter fiber composite

H. Zhang et al. / Composites Science and Technology 67 (2007) 222–230 229

C1, a large amount of fibers was peeled-off from the matrixdue to the strong interactions between mating surfaces athigher contact pressure (cf. Fig. 8a). As indicated byarrows in Fig. 8a, the peeled-off fibers were approximately100 lm in length, which was roughly in accordance withthe average fiber length of composite C1. It seems thatthe strong frictional force may ‘‘dig out’’ the individualfibers directly without obvious breakage. Due to the fiberpeeling-off effect, a great number of cavities remained onthe worn surfaces (Fig. 8b). By the lack of support and pro-tection of the fibers, the matrix was subjected to moreintensive micro-ploughing and micro-cutting attacks bysteel asperities, so that more wear of the matrix couldoccur. Moreover, the lots of peeled-off fibers could tempo-rarily act as three body abrasives [9], leading to an increasein the wear rate and the frictional coefficient. By contrast,the wear process was some difficult for the longer fibercomposite C3. Due to the greater length, the peeling-offof the whole fibers from matrix would not occur so easily.This resulted in more fiber thinning, followed by fiber

Fig. 10. Worn surfaces of epoxy composites with graphite flakes andnano-TiO2 at the contact pressure of 5 MPa: (a) L1 and (b) L2.

breakage (cf. Fig. 8c and d). Parts of them were finally sep-arated from the wear surface, whereas the rest remainedembedded in the wear surface and could still contributeto the wear resistance of the composites for certain time.Probably due to this reason, the worn surface became rel-atively smooth, and consequently, the frictional coefficientbetween the mating surfaces and the wear rate dropped tosome extent, as shown before. Although the peeled-offfibers finally took part in the wear process acting as thirdbody abrasives, their contribution was relatively smaller,when compared to the shorter fiber composites.

For the series L, similar phenomena could be found. Asshown in Figs. 9 and 10, the longer fiber composite L2 hadalways much smoother worn surfaces than the shorter one,L1. In our case the rougher worn surfaces always corre-sponded to the lower wear resistance. The fiber peeling-off was more obvious for L1 than for L2 (cf. Fig. 10aand b), supporting the fact again that shorter fibers wereeasier to be removed from the matrix than the longer onesat higher contact pressure.

4. Conclusions

In this study, the influence of fiber length on the tribo-logical properties of short carbon fiber (SCF) reinforcedepoxy composites was investigated, using both a B-o-Rand a P-o-D test configurations. Based on the experimentalresults, the following conclusions can be drawn:

1. The longer SCF composites exhibited better wear resis-tance in comparison to the shorter ones in both cases,either with or without graphite flakes and nano-TiO2.This effect seemed to be more pronounced at higher con-tact pressures.

2. In terms of SEM observations of worn surfaces, thelonger SCFs were more difficult to be peeled-off fromthe matrix, even at higher contact pressure. Accordingly,the worn surface became relatively smooth. This effectfurther caused a slight decrease in the frictional coeffi-cient and contact temperature. All these factors in turncontributed positively to the wear resistance of the com-posites. In addition, the enhanced load-carrying capac-ity of the longer SCF reinforced composites could befavorable to the improved wear resistance, especiallyat higher contact pressures.

Acknowledgements

This project was partly supported by the German Re-search Foundation (DFG FR675/45-1). Z. Zhang is gratefulto the Alexander von Humboldt Foundation for his SofjaKovalevskaja Award, financed by the German Federal Min-istry of Education and Research within the German Gov-ernment’s investment in the future program. Thanks arealso due to Kureha Company (Germany), which kindly sup-plied us with the short carbon fibers of various lengths.

230 H. Zhang et al. / Composites Science and Technology 67 (2007) 222–230

References

[1] Chou TW. Microstructural design of fiber composites. CambridgeUniversity Press; 1992. p. 169–230 [chapter 4].

[2] Du SY, Wang B. Meso-mechanics of composites. China SciencePress; 1998. p. 118–60 [chapter 4].

[3] Thomason JL, Vlug MA. Influence of fiber length and concentrationon the properties of glass fiber reinforced polypropylene: 1. Tensileand flexural modulus. Composites A 1996;27:477–84.

[4] Thomason JL, Vlug MA, Schipper G, Krikor HGLT. Influence offiber length and concentration on the properties of glass fiberreinforced polypropylene: 3. Strength and strain at failure. Compos-ites A 1996;27:1075–84.

[5] Thomason JL, Vlug MA. Influence of fiber length and concentrationon the properties of glass fiber reinforced polypropylene: 4. Impactproperties. Composites A 1997;28:277–88.

[6] Hollander AE, Lancaster JK. An application of topographicalanalysis to the wear of polymer. Wear 1973;25:155–70.

[7] Lancaster JK. Dry bearings: a survey of materials and factorsaffecting their performance. Tribology 1973;12:219–51.

[8] Voss H, Friedrich K. On the wear behaviour of short-fiber-reinforcedPEEK composites. Wear 1987;116:1–18.

[9] Friedrich K. Wear of reinforced polymers by different abrasivecounterparts. In: Friedrich K, editor. Friction and wear of polymercomposites. Amsterdam, The Netherlands: Elsevier; 1986. p. 233–87.

[10] Barkoula NM, Karger-Kocsis J. Effect of fiber content and relativefiber orientation on the solid particle erosion of GF/PP composites.Wear 2002;252:80–7.

[11] Vu-Khanh T, Denault J, Habib P, Low A. The effect of injectionmoulding on the mechanical behaviour of long-fiber reinforced PBT/PET blends. Compos Sci Technol 1991;40:423–35.

[12] Petry M. Diploma work: Mechanical, superficial and interfacialcharacterisation of carbon fibers and carbon fiber/VEUH composites.University of Kaiserslautern; 2000. p. 20–1.

[13] Netravali AN, Li ZF, Sachse W, Wu HF. Determination of fiber/matrix interfacial shear strength by an acoustic emission technique. JMater Sci 1991;26:6631–8.

[14] Fjeldly A, Olsen T, Rysjedal JH, Berg JE. Influence of the fibersurface treatment and hot-wet environment on the mechanicalbehaviour of carbon/epoxy composites. Composites A 2001;32:373–8.

[15] Robinson IM, Robinson JM. Review the influence of fiber aspectratio on the deformation of discontinuous fiber reinforced compos-ites. J Mater Sci 1994;29:4663–77.

[16] Dresselhaus MS, Dresselhaus G, Eklund PC. Science of fullerenesand carbon nanotubes. Academic Press, Inc; 1996. p. 18–9 [chapter 2].

[17] Srivastava VK, Pathak JP. Friction and wear properties of bushingbearing of graphite filled short glass composites in dry sliding. Wear1996;197:145–50.

[18] Zhang Z, Friedrich K. Tribological characteristics of micro- andnanoparticle filled polymer composites. In: Friedrich K, Fakirov S,Zhang Z, editors. Polymer composites – from nano- to macro-scale.Springer; 2005. p. 169–85 [chapter 10].

[19] Friedrich K. Particle dental composites under sliding wear conditions.J Mater Sci: Mater Med 1993;4:266–72.

[20] Bahadur S. The development of transfer layer and their role inpolymer tribology. Wear 2000;245:92–9.

[21] Zhang Z, Breidt C, Chang L, Haupert F, Friedrich K. Enhancementof the wear resistance of epoxy: short carbon fiber, graphite, PTFEand nano-TiO2. Composites A 2004;35:1385–92.

[22] Chang L, Zhang Z, Breidt C, Friedrich K. Tribological properties ofepoxy nanocomposites: I. Enhancement of the wear resistance bynano-TiO2 particles. Wear 2005;258:141–8.