N. Oya, D.J. Johnson /Carbon 39(2001)635-645 639 1.0 04 200 ge length(um) Fig 3. Change of longitudinal compressive strength against sample gauge length(L, axially compressed; L, buckled samples he sample did not easily show typical buckling Comparison of longitudinal strength values in PAN-based carbon slipped due to the low frictional for fibres he fibre and the cantilever before the buckling load was reached. In other words, the sample showed a strength slippage before the clamped-simple support buckling (GPa) (GPa) Pa) occurred and the modulus had been underestimated with 1.8(16.9 5.3(21.4) Table 3 lists average, compressive and tensile moduli of T800H 23(146 each fibre. Average modulus was calculated using the 28(18.8) 7. 1(193) critical buckling load obtained with sufficiently long gauge 8(13.0) 49(125) lengths to eliminate any effect of different buckling modes 4.3(13.0) Fig. 7 shows a comparison of longitudinal compressive M60J 35(14.1) and tensile moduli in carbon fibres Compressive modulus Coefficient of variation(%)in parentheses. was generally lower than tensile modulus; <50% of the 3.0 8 Direct method ■ Recoil method g2.0 15 T300T700sT800HT1000M40M50JM60J Fig. 4. Comparison of direct and recoil compressive strengthsN. Oya, D.J. Johnson / Carbon 39 (2001) 635 –645 639 Fig. 3. Change of longitudinal compressive strength against sample gauge length (h, axially compressed; j, buckled samples). Table 2 length, the sample did not easily show typical buckling Comparison of longitudinal strength values in PAN-based carbon because its end slipped due to the low frictional force fibres between the fibre and the cantilever before the buckling Compressive Recoil Tensile load was reached. In other words, the sample showed a strength strength strength slippage before the ‘clamped-simple support’ buckling (GPa) (GPa) (GPa) occurred and the modulus had been underestimated with a short gauge lengths. T300 1.8 (16.9) 1.0 3.5 (12.6) T700S 2.4 (15.6) 1.6 5.3 (21.4) Table 3 lists average, compressive and tensile moduli of T800H 2.3 (14.6) 1.6 6.4 (14.8) each fibre. Average modulus was calculated using the T1000 2.8 (18.8) 2.2 7.1 (19.3) critical buckling load obtained with sufficiently long gauge M40J 1.8 (13.0) 1.0 4.9 (12.5) lengths to eliminate any effect of different buckling modes. M50J 1.3 (15.5) 0.7 4.3 (13.0) Fig. 7 shows a comparison of longitudinal compressive M60J 1.0 (13.9) 0.5 3.5 (14.1) and tensile moduli in carbon fibres. Compressive modulus a Coefficient of variation (%) in parentheses. was generally lower than tensile modulus; |50% of the Fig. 4. Comparison of direct and recoil compressive strengths