COMPOSITES SCIENCE AND TECHNOLOGY ELSEⅤIER Composites Science and Technology 62(2002)499-504 www.elsevier.com/locate/compscitech Thermomechanical properties of carbon fibres at high temperatures(up to 2000C) Cedric Sauder Jacques Lamon *, Rene paille Laboratoire des Composites Thermostructuraux, UMR 580/(CNRS-SNECMA-CEA-Universite Bordeaux 1) 3 allee de la boetie, 33600 Pessac. france Received 17 November 2000: accepted 19 July 2001 Abstract A high-temperature fibre-testing apparatus has been designed. It is dedicated to the determination of various properties at very high temperatures, including electrical conductivity, Youngs modulus, thermal expansion coeficient, strength. Test temperatures as high as 3000C can be applied to carbon fibres. two types of carbon fibres(a PAN-based and a Rayon-based fibre)have been investigated at temperatures up to 2000C. The measured properties are discussed with respect to microstructural features. C 2002 Elsevier Science Ltd. All rights reserved. Keywords: A. Carbon fibres: B. High-temperature properties; B. Thermomechanical properties: Electrical conductivity 1. ntroduction 2. Experimental procedure Carbon fibres represent a large part of the materials The available methods for fibre testing at high tem- ed in aeronautics and aerospace structures, and in the peratures exhibit various limitations. Two methods are reinforcement of composites(C/ brakes, etc. ) They essentially used: in the hot-grip technique, the whole of display a very wide range of thermal, electric and the fibre is exposed to a uniform temperature, whereas in mechanical properties: elastic moduli vary between 30 the cold grip technique only a short part of the fibre is at and 900 GPa, strength can be as high as 6 GPa the test temperature. Youngs modulus and strength data Reliable and accurate data for the mechanical prop-(tensile strength, oR, and statistical parameters) can be erties of carbon fibres and matrices are a prerequisite for measured by using the hot-grip method. The main lim the development of valid models of thermomechanical itation of this method lies in gripping. The use of a cera- behaviour of C/C composites that are based on micro- mic glue excludes tests at temperatures above 1500C mechanics and constituent properties. Very few data are The cold-grip method [3] exhibits several short com available in the literature for the properties of carbon ings. As a result of the presence of a large thermal gra- fibres and matrices at high temperatures [1, 2 dient along fibre, determination of true strain is Mechanical tests on fibres with diameter <7 um or uncertain. Moreover, the method of correcting fibre microcomposites with a diameter A30 um are very dif- elongation measurements is complex and inaccurate, so ficult. Difficulties are enhanced under high-temperature that results are obtained with a large uncertainty. Fur dition herme specimens are required (le The present paper proposes an experimental approach than 10 cm), experimental difficulties are enhanced for measuring the thermomechanical properties of car- bon fibres at temperatures up to 3000C. Temperature 2. Experimental device dependence of properties observed on two types of car bon fibres are discussed with respect to microstructure It is for all of the above reasons that a new for tensile tests at high temperatures was Novelty can be found in the technique of specimen heat sauder@ lcts. -bordeaux.fr (C. Sauder), ing, which takes advantage of the electric conductivity of lamon(@Icts. ul-bordeaux fr (J. Lamon), paler( @Icts. ul-bordeaux fr carbon fibres. An electric current is applied to the fibre. which allows temperature as high as 3000c to be 0266-3538/02/S. see front matter C 2002 Elsevier Science Ltd. All rights reserved. PII:S0266-3538(01)00140-3
Thermomechanical properties of carbon fibres at high temperatures (up to 2000 C) Ce´dric Sauder, Jacques Lamon*, Rene´ Pailler Laboratoire des Composites Thermostructuraux, UMR 5801 (CNRS-SNECMA-CEA-Universite´ Bordeaux I), 3 alle´e de La Boe´tie, 33600 Pessac, France Received 17 November 2000; accepted 19 July 2001 Abstract A high-temperature fibre-testing apparatus has been designed. It is dedicated to the determination of various properties at very high temperatures, including electrical conductivity, Young’s modulus, thermal expansion coefficient, strength. Test temperatures as high as 3000 C can be applied to carbon fibres. Two types of carbon fibres (a PAN-based and a Rayon-based fibre) have been investigated at temperatures up to 2000 C. The measured properties are discussed with respect to microstructural features. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: A. Carbon fibres; B. High-temperature properties; B. Thermomechanical properties; Electrical conductivity 1. Introduction Carbon fibres represent a large part of the materials used in aeronautics and aerospace structures, and in the reinforcement of composites (C/C brakes, etc.) They display a very wide range of thermal, electric and mechanical properties: elastic moduli vary between 30 and 900 GPa, strength can be as high as 6 GPa. Reliable and accurate data for the mechanical properties of carbon fibres and matrices are a prerequisite for the development of valid models of thermomechanical behaviour of C/C composites that are based on micromechanics and constituent properties. Very few data are available in the literature for the properties of carbon fibres and matrices at high temperatures [1,2]. Mechanical tests on fibres with diameter 47 mm or microcomposites with a diameter 30 mm are very dif- ficult. Difficulties are enhanced under high-temperature conditions. The present paper proposes an experimental approach for measuring the thermomechanical properties of carbon fibres at temperatures up to 3000 C. Temperature dependence of properties observed on two types of carbon fibres are discussed with respect to microstructure. 2. Experimental procedure The available methods for fibre testing at high temperatures exhibit various limitations. Two methods are essentially used: in the hot-grip technique, the whole of the fibre is exposed to a uniform temperature, whereas in the cold grip technique only a short part of the fibre is at the test temperature. Young’s modulus and strength data (tensile strength, R, and statistical parameters) can be measured by using the hot-grip method. The main limitation of this method lies in gripping. The use of a ceramic glue excludes tests at temperatures above 1500 C. The cold-grip method [3] exhibits several short comings. As a result of the presence of a large thermal gradient along fibre, determination of true strain is uncertain. Moreover, the method of correcting fibre elongation measurements is complex and inaccurate, so that results are obtained with a large uncertainty. Furthermore, since long specimens are required (longer than 10 cm), experimental difficulties are enhanced. 2.1. Experimental device It is for all of the above reasons that a new apparatus for tensile tests at high temperatures was designed. Novelty can be found in the technique of specimen heating, which takes advantage of the electric conductivity of carbon fibres. An electric current is applied to the fibre, which allows temperature as high as 3000 C to be 0266-3538/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0266-3538(01)00140-3 Composites Science and Technology 62 (2002) 499–504 www.elsevier.com/locate/compscitech *Corresponding author. E-mail addresses: sauder@lcts.u-bordeaux.fr (C. Sauder), lamon@lcts.u-bordeaux.fr (J. Lamon), pailer@lcts.u-bordeaux.fr (R. Pailler).
C. Sauder et al./ Composites Science and Technology 62(2002)499-504 eached, and a uniform temperature along the fibre to be apparatus. Fibre section was assumed to be circular. generated. Temperature in the fibre is measured by using This is true for the PAN-based fibre bichromatic pyrometer in the 1000-3000C range. In practice, temperatures in the 1200-3000oC range only 2.3. Experimental procedure are detected on fibres having a 7 um diameter. Since tests are performed under secondary vacuum (residual pres- 2.3.1. Measurement of electrical conductivity sure <10-3 Pa)there is a relationship between fibre The calibration curve established for temperature temperature and the electric power supplied as shown in determination(Fig. 1)allows determination of electrical Fig. l. As a consequence, temperature of fibre can be conductivity(a)at various temperatures easily derived from the electric power. placement of grips are measured by whose sensitivity is smaller than 0. 1 um. Fibre strain is o(Q2-1m-=I-L a sensor derived from grip displacement by using a compliance p RS calibration technique that allows deformation of load strain to be taken into account [4]. a technique of Where p=R S/L(resistivity), where R is the resistance direct measurement of fibre elongation is under devel- (R-UlL, U=tension, I=intensity ), S=sectional area opment. It is based upon optical extensometry and and L=fibre length. image analys A schematic diagram of the high temperature fibre 2.3.2. Measurement of thermal expansion testing apparatus is shown in Fig. 2. Alignment of grips Very few data on thermal expansion of carbon fibres is improved using internal and external devices. The are available at high temperatures [2, 5, 6]. The technique all the experimental data are recorded by a computer. onto the fibre (a few MPa). This stress is maintained constant during fibre heating through control of grip 2. 2. Materials and specimen preparation displacement. The displacement which is applied bal ances the longitudinal expansion of fibre induced by Two different carbon fibres were investigated: a heating. Such thermal expansion measurements are very rayon-base and a polyacrylonitrile-based fibre. Fibres easy and very accurate under computer controlled test- were tested either as-received or after treatment at 1600 ing conditions or 2200C. Fibres were fixed to graphite grips using a cement( C-34, UCAR). Batches of 20 specimens were 2.3.3. Mechanical behavior prepared, except for the tests at 1200, 1400 and 1800C Tensile tests were performed on those PAN-based and on the rayon-based fibres. rayon-based fibres which had been treated at 2200C Fibre diameter was measured before tests using laser The range of test temperatures could thus be increased diffractometry. The fibre was mounted on the testing from 1000 to 2200C, since mechanical properties of carbon fibres depend on the heating rate when the test temperature is higher than the treatment temperature Gauge length was 50 mm. The Youngs modulus was 口 estimated data 2400 3000 Fig. 1. Correlation between electrical power applied to the fibre and Fig. 2. Schematic diagram of the high temperature fibre testing appa- the temperature measured by using a pyromete atus
reached, and a uniform temperature along the fibre to be generated. Temperature in the fibre is measured by using a bichromatic pyrometer in the 1000–3000 C range. In practice, temperatures in the 1200–3000 C range only are detected on fibres having a 7 mm diameter. Since tests are performed under secondary vacuum (residual pressure <103 Pa) there is a relationship between fibre temperature and the electric power supplied as shown in Fig. 1. As a consequence, temperature of fibre can be easily derived from the electric power. Displacement of grips are measured by a sensor whose sensitivity is smaller than 0.1 mm. Fibre strain is derived from grip displacement by using a compliance calibration technique that allows deformation of load strain to be taken into account [4]. A technique of direct measurement of fibre elongation is under development. It is based upon optical extensometry and image analysis. A schematic diagram of the high temperature fibre testing apparatus is shown in Fig. 2. Alignment of grips is improved using internal and external devices. The load cells are located within the vacuum chamber and all the experimental data are recorded by a computer. 2.2. Materials and specimen preparation Two different carbon fibres were investigated: a rayon-base and a polyacrylonitrile-based fibre. Fibres were tested either as-received or after treatment at 1600 or 2200 C. Fibres were fixed to graphite grips using a cement (C-34, UCAR). Batches of 20 specimens were prepared, except for the tests at 1200, 1400 and 1800 C on the rayon-based fibres. Fibre diameter was measured before tests using laser diffractometry. The fibre was mounted on the testing apparatus. Fibre section was assumed to be circular. This is true for the PAN-based fibre. 2.3. Experimental procedure 2.3.1. Measurement of electrical conductivity The calibration curve established for temperature determination (Fig. 1) allows determination of electrical conductivity () at various temperatures: ð1 m1 Þ ¼ 1 ¼ L R:S Where =R.S/L (resistivity), where R is the resistance (R=U/I, U=tension, I=intensity), S=sectional area and L=fibre length. 2.3.2. Measurement of thermal expansion Very few data on thermal expansion of carbon fibres are available at high temperatures [2,5,6]. The technique used here is very simple. A very low stress is applied onto the fibre (a few MPa). This stress is maintained constant during fibre heating through control of grip displacement. The displacement which is applied balances the longitudinal expansion of fibre induced by heating. Such thermal expansion measurements are very easy and very accurate under computer controlled testing conditions. 2.3.3. Mechanical behavior Tensile tests were performed on those PAN-based and rayon-based fibres which had been treated at 2200 C. The range of test temperatures could thus be increased from 1000 to 2200 C, since mechanical properties of carbon fibres depend on the heating rate when the test temperature is higher than the treatment temperature. Gauge length was 50 mm. The Young’s modulus was Fig. 1. Correlation between electrical power applied to the fibre and the temperature measured by using a pyrometer. Fig. 2. Schematic diagram of the high temperature fibre testing apparatus. 500 C. Sauder et al. / Composites Science and Technology 62 (2002) 499–504
C Sauder et al. / Composites Science and Technology 62(2002)499-50 determined under a 0. 2% strain. The statistical para- 3. 2. Longitudinal thermal expansion meters(Weibull modulus m and scale factor go) were estimated from the statistical distributions of strength In order to check the validity of measurements, the data using a linear regression technique [7] echnique was applied to a tungsten fibre having a 18 um diameter. Fig. 4 shows that the measured thermal expansions coincide with those values derived from the 3. Results and discussion coefficient of thermal expansion available in the litera- ture(SETARAM data) 3. 1. Electrical conductivity Thermal expansions at various temperatures are plot ted in Figs. 5 and 6. It can be noticed that the investi Electrical conductivity measured at various tempera- gated fibres exhibit different behaviors. Expansion of tures on the PAN-based and rayon-based fibres, that the PAN-based fibre is much smaller than that of the had been previously treated at 2200C, are plotted in rayon-based fibre. At temperatures close to ambient Fig 3a and b. The temperature dependence of electrical temperature, the PAN-based fibre contracts. This beha conductivity is typical for these fibres, since it can be vior is comparable to that displayed by graphite single noticed that electrical conductivity increases with tem- crystal. It is characterized by a negative coefficient of perature. This trend characterizes a semiconductor. thermal expansion at 20C. This behavior results from Although data at low temperatures were not deter- the fibre microstructure shown in Fig. 7 [8], which is not mined, it can be considered that this trend is pertinent isotropic but instead involves basal structural units to an extrinsic semiconductor. Indeed, at low tempera-(BSU) with a preferred orientation with respect to the tures, conduction is governed by impurities(extrinsic fibre axis. This organized microstructure contrasts with conductivity), whereas at high temperatures the thermal the one of rayon-based fibre. Fig. 6 also shows that energy is sufficient to induce electronic transitions(strip treatment influences the fibre respon of valence B V. strip of conduction B.C. ) This is the This phenomenon can be attributed to successive domain of intrinsic conductivity for this type of carbon changes in the fibre microstructure. As the treatment microstructure. The energy gap(AE=EcEv) can b temperature increases, the BSU tend to be oriented determined by using the following equation parallel to the fibres axis, which would increase the coherent domains in X-ray diffraction(XRD). On the a=Cexp(-△E/2k contrary, the behavior and the microstructure of the rayon based fibres do not change when the treatment temperature is increased AE=0.12 and 0. 18ev were obtained respectively for the Expansion of graphite single crystal is shown in PAN-based and the rayon based fibres. These values are Fig. 8 [9. It can be noticed that for both fibres, long itudinal thermal expansion results from a combination 10.6 10.5 120 103 11,7 116 10 11,5 0.0 2,0 0,0 2,0 3,0 1「T(101 1「T(10 Fig. 3. Electrical resistivity vs temperature for a PAN-based (a)and a rayon based(b)fibre
determined under a 0.2% strain. The statistical parameters (Weibull modulus m and scale factor 0) were estimated from the statistical distributions of strength data using a linear regression technique [7]. 3. Results and discussion 3.1. Electrical conductivity Electrical conductivity measured at various temperatures on the PAN-based and rayon-based fibres, that had been previously treated at 2200 C, are plotted in Fig. 3a and b. The temperature dependence of electrical conductivity is typical for these fibres, since it can be noticed that electrical conductivity increases with temperature. This trend characterizes a semiconductor. Although data at low temperatures were not determined, it can be considered that this trend is pertinent to an extrinsic semiconductor. Indeed, at low temperatures, conduction is governed by impurities (extrinsic conductivity), whereas at high temperatures the thermal energy is sufficient to induce electronic transitions (strip of valence B.V.!strip of conduction B.C.). This is the domain of intrinsic conductivity for this type of carbon microstructure. The energy gap (E=Ec–Ev) can be determined by using the following equation: ¼ CexpðE=2kTÞ E=0.12 and 0.18ev were obtained respectively for the PAN-based and the rayon based fibres. These values are quite small. 3.2. Longitudinal thermal expansion In order to check the validity of measurements, the technique was applied to a tungsten fibre having a 18 mm diameter. Fig. 4 shows that the measured thermal expansions coincide with those values derived from the coefficient of thermal expansion available in the literature (SETARAM data). Thermal expansions at various temperatures are plotted in Figs. 5 and 6. It can be noticed that the investigated fibres exhibit different behaviors. Expansion of the PAN-based fibre is much smaller than that of the rayon-based fibre. At temperatures close to ambient temperature, the PAN-based fibre contracts. This behavior is comparable to that displayed by graphite single crystal. It is characterized by a negative coefficient of thermal expansion at 20 C. This behavior results from the fibre microstructure shown in Fig. 7 [8], which is not isotropic but instead involves basal structural units (BSU) with a preferred orientation with respect to the fibre axis. This organized microstructure contrasts with the one of rayon-based fibre. Fig. 6 also shows that treatment influences the fibre response. This phenomenon can be attributed to successive changes in the fibre microstructure. As the treatment temperature increases, the BSU tend to be oriented parallel to the fibres axis, which would increase the coherent domains in X-ray diffraction (XRD). On the contrary, the behavior and the microstructure of the rayon based fibres do not change when the treatment temperature is increased. Expansion of graphite single crystal is shown in Fig. 8 [9]. It can be noticed that for both fibres, longitudinal thermal expansion results from a combination Fig. 3. Electrical resistivity vs temperature for a PAN-based (a) and a rayon based (b) fibre. C. Sauder et al. / Composites Science and Technology 62 (2002) 499–504 501
C Sauder et al./ Composites Science and Technology 62(2002 )499-504 0,70 0,50 古 0,00 10001200 Temperature(C) Fig. 7. Structure of an ex-PAN fibre [8] Fig 4. Longitudinal thermal expansion at various temperature for a tungsten fibre(d=18 um) 0. 3 expansion coefficient for 1600/C treated fibre a expansion coefficient for 2200C treated fibre_.'p Experimental points g cal fit 100o Temperature(K) Fig. 5. Longitudinal thermal expansion at various temperatures for a PAN-based fibre 0.8 1 o untreated fibre strain Experimental points 8 - 1600C treated fibre strain 20 Theoretical fit 1600C treated fibre expansion coefficient 6 1000 3000 2200C treated fibre expansion Temperature(K sion⑨9 of thermal expansions of single crystal in the transverse and in the longitudinal directions. Indeed if orientation of BsU was parallel to fibre axis, the expansion of fibre would be close to that indicated by aa. However, at temperatures above 1000C the coefficient of thermal expansion still increases, which suggests that bsU are 4008001200160020002400 not perfectly oriented parallel to fibre axis and that ac Fig. 6. Longitudinal thermal expansion at various temperatures a governs thermal expansion in the longitudinal direction This phenomenon is particularly significant at tempera rayon-based fibre tures above 1000C. At these temperature ae increases
of thermal expansions of single crystal in the transverse and in the longitudinal directions. Indeed, if orientation of BSU was parallel to fibre axis, the expansion of fibre would be close to that indicated by a. However, at temperatures above 1000 C the coefficient of thermal expansion still increases, which suggests that BSU are not perfectly oriented parallel to fibre axis and that c governs thermal expansion in the longitudinal direction. This phenomenon is particularly significant at temperatures above 1000 C. At these temperature c increases Fig. 4. Longitudinal thermal expansion at various temperature for a tungsten fibre (d=18 mm). Fig. 5. Longitudinal thermal expansion at various temperatures for a PAN-based fibre. Fig. 6. Longitudinal thermal expansion at various temperatures for a rayon-based fibre. Fig. 7. Structure of an ex-PAN fibre [8]. Fig. 8. Bulk graphite thermal expansion [9]. 502 C. Sauder et al. / Composites Science and Technology 62 (2002) 499–504
C Sauder et al./ Composites Science and Technology 62(2002 )499-504 Table I Mechanical properties at various temperatures Temperature PAN-based fibre Rayon-based fibre E/Eo (%) OR(MPa) ER(%) m ao(MPa) E/Eo(%) OR(MPa) ER(%) Oo (MPa) 2107(405)b0.71(0.13)5.1660 719(157) 5(0.4)2292(410) 77(0.5)2401(540) 95700.8)2386(507)08500.18)54810 89.50.6)825(116)2.680.36)NDND 6(1.6)2359(520)0910.23) 832(1.0)821(114)541(1.75)7.9 818(1.7)2857(611)1.53(0. 4(1.0)605(72) 695(1.8)2348(443)3.71(1.84)5.9850 527(1.7)371(39)12.7(6,1)10200 b(Standard deviation a different trend is observed for the strength oR (Fig. 9). For both fibres or increases slightly when the temperature increases to 1600C. This phenomenon may result from a reduction in flaw severity associated with internal stress relaxation 2100 At temperatures>1600C, fibres exhibit a different behavior. For the rayon-based fibre, the strength -BPAN-based decrease is large whereas the strength scatter narrows (Table 1). For the PAN-based fibre, or reaches a max imum (2850 MPa) at 1800C and then decreases to a value close to that measured at room temperature. The origin of this phenomenon has not been elucidated yet This will require specific analyses that fall out of the scope of this paper 0200400600800100012001400160018002000 Finally, the statistical parameters(Weibull modulus Temperature enC m and scale factor ao) indicate that flaw population in Fig 9. Youngs modulus and tensile strength at various temperatures the PAN-based fibre is not influenced by temperature. for a PAN-based fibre and a rayon-based fibre On the contrary, the flaw population seems to become more homogeneous in the rayon-based fibre as tem- perature increases, since m increased from 5 to 10 when the temperature was increased from 24 to 2000C. strongly whereas aa becomes constant. Thus it appears that longitudinal thermal expansion provides indica tions on the orientation of bsu and the degree of 4. Conclusions organization of fibre microstructure The high temperature fibre testing apparatus that was 33. Mechanical behavior developed allowed determination of a large variety of carbon fibre properties at temperatures up to 2000C: mechanical properties measured at various tempera- electrical conductivity, longitudinal thermal expansion tures are summarized in Table 1. The elastic modulus of Young,'s modulus and strength Tests at temperatures both fibres exhibits the same trend(Fig 9). The elastic high as 3000 C can be performed modulus is quite constant at temperatures 1000C, Temperature dependence of thermal expansion and then it decreases steeply at temperatures >1000C. mechanical properties reflected the preponderant con- This phenomenon is more significant for the rayon- tribution of microstructure of fibres to their properties based fibre. A similar phenomenon has been previously (a/, E, oR, m, ao). In those PAN-based fibres, "BSU reported for a Thornel 50 fibre [10]. It may be attributed tend to be oriented parallel to fibre axis. These fibres are to an increase in anharmonic vibrations that would lead less sensitive to temperature than the rayon-based to plastic deformations and a reduced linear elastic fibres. Besides, PAN-based fibres contract at tempera behavior. This phenomenon becomes less significant as tures close to ambient temperature. This behavior is BSU are oriented parallel to fibre axis. close to that displayed by graphite single crystal
strongly whereas a becomes constant. Thus it appears that longitudinal thermal expansion provides indications on the orientation of BSU and the degree of organization of fibre microstructure. 3.3. Mechanical behavior Mechanical properties measured at various temperatures are summarized in Table 1. The elastic modulus of both fibres exhibits the same trend (Fig. 9). The elastic modulus is quite constant at temperatures 41000 C, then it decreases steeply at temperatures >1000 C. This phenomenon is more significant for the rayonbased fibre. A similar phenomenon has been previously reported for a Thornel 50 fibre [10]. It may be attributed to an increase in anharmonic vibrations that would lead to plastic deformations and a reduced linear elastic behavior. This phenomenon becomes less significant as BSU are oriented parallel to fibre axis. A different trend is observed for the strength R (Fig. 9). For both fibres R increases slightly when the temperature increases to 1600 C. This phenomenon may result from a reduction in flaw severity associated with internal stress relaxation. At temperatures >1600 C, fibres exhibit a different behavior. For the rayon-based fibre, the strength decrease is large whereas the strength scatter narrows (Table 1). For the PAN-based fibre, R reaches a maximum (2850 MPa) at 1800 C and then decreases to a value close to that measured at room temperature. The origin of this phenomenon has not been elucidated yet. This will require specific analyses that fall out of the scope of this paper. Finally, the statistical parameters (Weibull modulus m and scale factor o) indicate that flaw population in the PAN-based fibre is not influenced by temperature. On the contrary, the flaw population seems to become more homogeneous in the rayon-based fibre as temperature increases, since m increased from 5 to 10 when the temperature was increased from 24 to 2000 C. 4. Conclusions The high temperature fibre testing apparatus that was developed allowed determination of a large variety of carbon fibre properties at temperatures up to 2000 C: electrical conductivity, longitudinal thermal expansion, Young’s modulus and strength. Tests at temperatures as high as 3000 C can be performed. Temperature dependence of thermal expansion and mechanical properties reflected the preponderant contribution of microstructure of fibres to their properties (//, E, R, m, 0). In those PAN-based fibres, ‘‘BSU’’ tend to be oriented parallel to fibre axis. These fibres are less sensitive to temperature than the rayon-based fibres. Besides, PAN-based fibres contract at temperatures close to ambient temperature. This behavior is close to that displayed by graphite single crystal. Table 1 Mechanical properties at various temperatures Temperature C PAN-based fibre Rayon-based fibre E/E0 (%) R (MPa) "R (%) m 0 a (MPa) E/E0 (%) R (MPa) "R (%) m 0*(MPa) 24 100 2107 (405)b 0.71 (0.13) 5.1 660 1 719 (157) 2.16 (0.45) 5.1 230 1000 98.5 (0.4) 2292 (410) 0.80 (0.14) 6.5 950 96.6 (0.4) 789 (103) 2.39 (0.31) 8.3 390 1200 97.7 (0.5) 2401 (540) 0.86 (0.18) 5.2 890 94.6 (0.4) 756 (118) 2.32 (0.38) ND ND 1400 95.7 (0.8) 2386 (507) 0.85 (0.18) 5.4 810 89.5 (0.6) 825 (116) 2.68 (0.36) ND ND 1600 91.6 (1.6) 2359 (520) 0.91 (0.23) 5.4 800 83.2 (1.0) 821 (114) 5.41 (1.75) 7.9 390 1800 81.8 (1.7) 2857 (611) 1.53 (0.44) 5.6 1020 69.4 (1.0) 605 (72) 12 (6.7) ND ND 2000 69.5 (1.8) 2348 (443) 3.71 (1.84) 5.9 850 52.7 (1.7) 371 (39) 12.7 (6,1) 10 200 a Vo= 1 mm3 . b ( ) Standard deviation. Fig. 9. Young’s modulus and tensile strength at various temperatures for a PAN-based fibre and a rayon-based fibre. C. Sauder et al. / Composites Science and Technology 62 (2002) 499–504 503
C Sauder et al. Composites Science and Technology 62(2002)499-504 References ceramique monofilamentaires, These Universite de bordeaux I [1 Tanabe Y, Yasuda E, Bunsell AR. The strength of pitch-based [6 Dresselhaus MS, Dresselhaus G, Sugihara K, Spain IL, Gold arbon fibre at high temperature. J Mater Sci 1991: 26(6): berg HA. Graphite Fibres and filaments, 1988. 1601-4 [7 Lissart N. Lamon J. Statistical analysis of failure of SiC fibres in 2 Trinquecoste M. Carlier JL. Derre A, Delhaes P. Chadeyron P. the presence of bimodal flaw populations. J Mater Sci 1997: 32 temperature thermal and mechanica 6107-17 tensile carbon single filaments. Carbon 1996: 34(7): 923-9 [8 Guigon M. Oberlin A, Desarmot G. Microtexture and structure B Bunsell AR, Hearle JwS. Hunter RD. An apparatus for fatigue. of some high tensile trength, PAN-based carbon fibres. Fibre Sci testing of fibres. J. Phys. E: Scientific Instruments 1971; 4: 868. Technol 1984: 20: 55 4 Chi-Tang Li, Langley NR. Improvement in fibre testing of high- [9 Morgan wC. Thermal expansion coefficients of graphite crystals. 02-C-204. [0 Rowe CR, Lowe DL. High temperature properties of carbon Villeneuve J. Etude de la dilatation thermique et du comporte. fibres. extended Abstracts of the 13th Biennal conference on ment thermomecanique en traction et torsion de quelques fibres carbon, Irvine, CA, 1977. p. 170
References [1] Tanabe Y, Yasuda E, Bunsell AR. The strength of pitch-based carbon fibre at high temperature. J Mater Sci 1991;26(6): 1601–4. [2] Trinquecoste M, Carlier JL, Derre´ A, Delhae`s P, Chadeyron P. High temperature thermal and mechanical properties of high tensile carbon single filaments. Carbon 1996;34(7):923–9. [3] Bunsell AR, Hearle JWS, Hunter RD. An apparatus for fatiguetesting of fibres. J. Phys, E: Scientific Instruments 1971;4:868. [4] Chi-Tang Li, Langley NR. Improvement in fibre testing of highmodulus single-filament materials. J Am Ceram Soc 1985;68(8): C-202–C-204. [5] Villeneuve J. Etude de la dilatation thermique et du comportement thermome´canique en traction et torsion de quelques fibres ce´ramiques monofilamentaires, The`se Universite´ de Bordeaux I, 1991. [6] Dresselhaus MS., Dresselhaus G, Sugihara K, Spain IL, Goldberg HA. Graphite Fibres and filaments, 1988. [7] Lissart N, Lamon J. Statistical analysis of failure of SiC fibres in the presence of bimodal flaw populations. J Mater Sci 1997;32: 6107–17. [8] Guigon M, Oberlin A, Desarmot G. Microtexture and structure of some high tensile trength, PAN-based carbon fibres. Fibre Sci Technol 1984;20:55. [9] Morgan WC. Thermal expansion coefficients of graphite crystals. Carbon 1972;10:73. [10] Rowe CR, Lowe DL. High temperature properties of carbon fibres, extended Abstracts of the 13th Biennal conference on carbon, Irvine, CA, 1977. p. 170. 504 C. Sauder et al. / Composites Science and Technology 62 (2002) 499–504
