M. Shioya, M. Nakatani/Composites Science and Technology 60(2000)219-229 specimens with a very small gage length and for adjust- plates prepared by curing these epoxy resins are shown ing the fibre and loading axes. It is beneficial, therefore, in Table 2. These values were determined according to to know the compatibility of various test results so that JIS K7113 [12] using a strain rate of 0.01 min-l.The a relatively simple method can be selected as a supple- tensile modulus was determined in the strain range from mental method, if a large number of fibres are to be 0.001 to 0.02 evaluated The composite strands with a circular cross-section In the present study, axial compressive strengths of vere prepared as follows. A carbon fibre tow was pitch- and polyacrylonitrile(PAN)-based carbon fibres soaked in liquid epoxy resin and passed through a die were determined by means of the micro-compression with an appropriate diameter to adjust the fibre volume and recoil tests on single fibres Axial compression and fraction For X7, X5 and N3 fibres, two fibre tows were axial compression bending tests [ll] were also carried combined before passing through the die. The resin out on unidirectional composite strands. A comparison impregnated carbon fibre tow was wound on a frame was made between the compressive strength values and cured in an air circulating oven. For the epoxy-A determined with these test methods resin, the resin impregnated tow was left for 18 h before curing in order to evaporate methyl ethyl ketone 2. Experimental 2. Materials Pitch- and polyacrylonitrile(PAN)-based carbon fibres with characteristics shown in Table I were used for the experiments. The tensile properties in this table are the values shown by the producers. These pitch-and PAN-based carbon fibres revealed different textures in the cross-section cut with a blade. The X7.X5 and n3 fibres had a pleat-like texture extending radially from the center of the cross-section as shown in Fig. 1 (a) This pleat-like texture was more distinctively developed a 5 um for the X7 and X5 fibres as compared with the N3 fibre which had lower tensile modulus. on the other hand he H4 and T4 fibres had no characteristic cross-section texture as shown in Fig. I(b) As the matrix of the unidirectional composite strand of carbon fibres, three types of epoxy resins named epoxy-A, B and C were used. These were the mixtures of diglycidyl ether of bisphenol A-type epoxy resin(Epi kote 828, Yuka Shell Epoxy), difunctional diluent (YED 205, Yuka Shell Epoxy), methylnadic acid anh dride, benzyldimethylamine and methyl ethyl ketone by the weight ratios of 100: 0: 90: 2.5: 15 for epoxy-A 20:80:100:4.75:0 for epoxy-Band0:100:100:4.75:0for epoxy-C. The cure conditions were 2 h at 110.C and additionally I h at 150C for epoxy-A, and 3 h at 140oC 5 um for epoxy-B and C. The tensile properties of the resin Fig 1. SEM images of cross-section of (a)X5 and (b) T4 fibres Table I Characteristics of carbon fibres Fibre Precursor material Number of filaments per tow Density/g cm Tensile properties Petroleum pitch 9.8 Petroleum pitch 1200 14 PAN 12.000specimens with a very small gage length and for adjust￾ing the ®bre and loading axes. It is bene®cial, therefore, to know the compatibility of various test results so that a relatively simple method can be selected as a supple￾mental method, if a large number of ®bres are to be evaluated. In the present study, axial compressive strengths of pitch- and polyacrylonitrile(PAN)-based carbon ®bres were determined by means of the micro-compression and recoil tests on single ®bres. Axial compression and axial compression bending tests [11] were also carried out on unidirectional composite strands. A comparison was made between the compressive strength values determined with these test methods. 2. Experimental 2.1. Materials Pitch- and polyacrylonitrile(PAN)-based carbon ®bres with characteristics shown in Table 1 were used for the experiments. The tensile properties in this table are the values shown by the producers. These pitch- and PAN-based carbon ®bres revealed di€erent textures in the cross-section cut with a blade. The X7, X5 and N3 ®bres had a pleat-like texture extending radially from the center of the cross-section as shown in Fig. 1(a). This pleat-like texture was more distinctively developed for the X7 and X5 ®bres as compared with the N3 ®bre which had lower tensile modulus. On the other hand, the H4 and T4 ®bres had no characteristic cross-section texture as shown in Fig. 1(b). As the matrix of the unidirectional composite strands of carbon ®bres, three types of epoxy resins named epoxy-A, B and C were used. These were the mixtures of diglycidyl ether of bisphenol A-type epoxy resin (Epi￾kote 828, Yuka Shell Epoxy), difunctional diluent (YED 205, Yuka Shell Epoxy), methylnadic acid anhy￾dride, benzyldimethylamine and methyl ethyl ketone by the weight ratios of 100:0:90:2.5:15 for epoxy-A, 20:80:100:4.75:0 for epoxy-B and 0:100:100:4.75:0 for epoxy-C. The cure conditions were 2 h at 110C and additionally 1 h at 150C for epoxy-A, and 3 h at 140C for epoxy-B and C. The tensile properties of the resin plates prepared by curing these epoxy resins are shown in Table 2. These values were determined according to JIS K7113 [12] using a strain rate of 0.01 minÿ1 . The tensile modulus was determined in the strain range from 0.001 to 0.02. The composite strands with a circular cross-section were prepared as follows. A carbon ®bre tow was soaked in liquid epoxy resin and passed through a die with an appropriate diameter to adjust the ®bre volume fraction. For X7, X5 and N3 ®bres, two ®bre tows were combined before passing through the die. The resin impregnated carbon ®bre tow was wound on a frame and cured in an air circulating oven. For the epoxy-A resin, the resin impregnated tow was left for 18 h before curing in order to evaporate methyl ethyl ketone. Table 1 Characteristics of carbon ®bres Fibre Precursor material Number of ®laments per tow Diameter/mm Density/g cmÿ3 Tensile properties Modulus/GPa Strength/GPa X7 Petroleum pitch 4,000 9.8 2.16 720 3.6 X5 Petroleum pitch 4,000 10.1 2.14 520 3.6 N3 Coal pitch 3,000 10.3 2.00 296 3.4 H4 PAN 12,000 6.4 1.80 392 4.4 T4 PAN 12,000 6.8 1.80 235 4.9 Fig. 1. SEM images of cross-section of (a) X5 and (b) T4 ®bres. 220 M. Shioya, M. Nakatani / Composites Science and Technology 60 (2000) 219±229