N. Oya, D.J. Johnson /Carbon 39(2001)635-645 Comparison of longitudinal modulus values in PAN-based carbon fibres Average modulus Compressive modul Tensile modulus (GPa) 210 T1000 M40 M60J and d, the kink bands usually developed into splitting had difference in of disorder, crystallite failure along the fibre axis. Such surface changes strongly porosity suggest local buckling of crystallites due to large needle- like pores in this type of fibre 3.3. Structure-compressive property relationships 3.3.1. 3. 2. Microstructure Fig. 9 shows the relationship between longitudinal compressive strength and intracrystalline disorder D. for Table 4 lists the structural parameters obtained from carbon fibres used in this work. HS fibres showed different /AXS study. Interlayer spacing d tracrystallite compressive strength with the same amount of disorder disorder D showed the same values for all HS fibres On Therefore, the differences of compressive strength in HS the other hand, both values declined with increase of fibre variants were probably due to another structural modulus level for HM fibres. Crystallite sizes in three difference. HM fibres showed higher compressive strength no size changes for HS fibres and significant increase for propagation with more disorder. HM fibres. As regards total porosity p, T300 showed the highest value among HS fibres. For HM fibres, the 3.3.2. Compressive strength vs. crystallite size porosity decreased with increase of modulus. From these Longitudinal compressive strength was compared with measurements, it was found that Hs fibres had only crystallite thickness Le in Fig. 10. HS fibres showed structural difference in the porosity, whereas HM fibres different compressive strength wit a Tensile modulus s Ratio of compressive modulus to tensile modulus Fig. 7. Comparison of longitudinal compressive and tensile moduli.N. Oya, D.J. Johnson / Carbon 39 (2001) 635 –645 641 Table 3 Comparison of longitudinal modulus values in PAN-based carbon fibres Average modulus Compressive modulus Tensile modulus (GPa) (GPa) (GPa) T300 158 106 210 T700S 218 199 237 T800H 215 124 306 T1000 270 246 294 M40J 277 219 335 M50J 343 256 430 M60J 409 283 535 and d, the kink bands usually developed into splitting had difference in respect of disorder, crystallite size, and failure along the fibre axis. Such surface changes strongly porosity. suggest local buckling of crystallites due to large needle￾like pores in this type of fibre. 3.3. Structure–compressive property relationships 3.3.1. Compressive strength vs. disorder region 3.2. Microstructure Fig. 9 shows the relationship between longitudinal compressive strength and intracrystallite disorder D for c Table 4 lists the structural parameters obtained from carbon fibres used in this work. HS fibres showed different WAXS study. Interlayer spacing d and intracrystallite compressive strength with the same amount of disorder. 002 disorder Dc showed the same values for all HS fibres. On Therefore, the differences of compressive strength in HS the other hand, both values declined with increase of fibre variants were probably due to another structural modulus level for HM fibres. Crystallite sizes in three difference. HM fibres showed higher compressive strength directions (L , L and L ) also exhibited similar trends; with increase of disorder amount, probably hindering crack c a' ai no size changes for HS fibres and significant increase for propagation with more disorder. HM fibres. As regards total % porosity p, T300 showed the highest value among HS fibres. For HM fibres, the 3.3.2. Compressive strength vs. crystallite size porosity decreased with increase of modulus. From these Longitudinal compressive strength was compared with measurements, it was found that HS fibres had only crystallite thickness L in Fig. 10. HS fibres showed c structural difference in the porosity, whereas HM fibres different compressive strength with almost the same Fig. 7. Comparison of longitudinal compressive and tensile moduli