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 crystalstrongly whereas a becomes constant. Thus it appears that longitudinal thermal expansion provides indica￾tions on the orientation of BSU and the degree of organization of fibre microstructure. 3.3. Mechanical behavior Mechanical properties measured at various tempera￾tures 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 rayon￾based 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 max￾imum (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 tem￾perature 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 con￾tribution 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 tempera￾tures 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