N. Oya, D.J. Johnson /Carbon 39(2001)635-645 B Compressive strength ■ Tensile strength 40 045 0.29 T300T70sT800HT100M40J M50J M60J Ratio of compressive strength to tensile strength Fig. 5. Comparison of longitudinal compressive and tensile strengths. tensile modulus except for T700S and T1000 fibres. These to form the smooth surface. Therefore, it is not appropriate two fibres exhibited higher compressive moduli presumab- to directly compare the compressive moduli of T700S and ly due to the epoxy-sizing effect Since the modulus was T1000 here with other non-sized fibres based on the flexure of fibres, the results were extremely ensitive to the surface state. It is known that non-sized 3.1.3. Longitudinal compressive failure aspect carbon fibres generally show a rugosity including distinct In-situ SEM observations were also attempted for flaws on the lateral surface. In such a case, the estimated compressed single carbon fibres For HS fibres, there was modulus from the buckling test could be lowered because no significant surface cha lange during compression until the fibre is likely to be bent at parts with reduced diameter. catastrophic failure. On the contrary, for HM fibres(pai On the other hand, the sized fibres may give higher ticularly for M60d), kink bands appeared on the surface modulus since the defects are covered with the sizing ager shown in Fig. 8a and b. Subsequently, as shown in Fig. g 0 100 00 600 Fig. 6. Change of average modulus against sample gauge length(T300)640 N. Oya, D.J. Johnson / Carbon 39 (2001) 635 –645 Fig. 5. Comparison of longitudinal compressive and tensile strengths. tensile modulus except for T700S and T1000 fibres. These to form the smooth surface. Therefore, it is not appropriate two fibres exhibited higher compressive moduli presumab- to directly compare the compressive moduli of T700S and ly due to the epoxy-sizing effect. Since the modulus was T1000 here with other non-sized fibres. based on the flexure of fibres, the results were extremely sensitive to the surface state. It is known that non-sized 3.1.3. Longitudinal compressive failure aspect carbon fibres generally show a rugosity including distinct In-situ SEM observations were also attempted for flaws on the lateral surface. In such a case, the estimated compressed single carbon fibres. For HS fibres, there was modulus from the buckling test could be lowered because no significant surface change during compression until the fibre is likely to be bent at parts with reduced diameter. catastrophic failure. On the contrary, for HM fibres (par￾On the other hand, the sized fibres may give higher ticularly for M60J), kink bands appeared on the surface as modulus since the defects are covered with the sizing agent shown in Fig. 8a and b. Subsequently, as shown in Fig. 8c Fig. 6. Change of average modulus against sample gauge length (T300)