M. Shioya, M. Nakatani/Composites Science and Technology 60(2000)219-229 3 后2 0.5mm 0 0 200 400600 800 Tensile modulus /GPa Fg.6.(口,■) Tensile and(O.●) compressive strength versus tensile modulus for(口,O) pitch- and(■,●) PAN-based carbon fibres Compressive strength was determined with micro-compression test. 2.5 22a0 0.5mm 20 1.5 ① 1.0 0.5 0DD 25 20 00 0.5mm Cross-section area/nm Fig. 5. SEM images of (a)X5/epoxy.A, (b)T4/epoxy.A and(c)H4 pressive strength determined with epoxy.A composite strands after axial compression bending test. versus average area of microvoid cross-section perpendicular to fibre axis, S,, for(O)pitch- and(O)PAN-based carbon fibres. Solid line shows relation of Eq (1)for a=3.2. If there is an energy dissipation during the recoil pro- cess due to damping in the fibre and at the fixed end of back into strain energy uniformly over the entire cross- the fibre, the compressive stress applied to the fibre section. In this case, the recoil test underestimates the becomes lower than the pretensioning stress. Thus, the compressive strength of the fibre. The obtained ratio of recoil test overestimates the compressive strength of the 0. 74 indicates the occurrence of flexural fracture fibre. If. on the other hand. flexural deformation takes place during the recoil process, the compressive stress is 3.4. Compressive strength determined with the axial not distributed uniformly in the cross-section. That is, compression test of the composite stran the compressive stress at the concave side of the fibre becomes larger as compared with the compressive stress The reduced compressive strength of the carbon fibres which will arise when the kinetic energy is transformed was determined by the compression tests of the compositeIf there is an energy dissipation during the recoil pro￾cess due to damping in the ®bre and at the ®xed end of the ®bre, the compressive stress applied to the ®bre becomes lower than the pretensioning stress. Thus, the recoil test overestimates the compressive strength of the ®bre. If, on the other hand, ¯exural deformation takes place during the recoil process, the compressive stress is not distributed uniformly in the cross-section. That is, the compressive stress at the concave side of the ®bre becomes larger as compared with the compressive stress which will arise when the kinetic energy is transformed back into strain energy uniformly over the entire cross￾section. In this case, the recoil test underestimates the compressive strength of the ®bre. The obtained ratio of 0.74 indicates the occurrence of ¯exural fracture. 3.4. Compressive strength determined with the axial compression test of the composite strand The reduced compressive strength of the carbon ®bres was determined by the compression tests of the composite Fig. 5. SEM images of (a) X5/epoxy-A, (b) T4/epoxy-A and (c) H4/ epoxy-A composite strands after axial compression bending test. Fig. 6. (&,&) Tensile and (*, *) compressive strength versus tensile modulus for (&, *) pitch- and (&, *) PAN-based carbon ®bres. Compressive strength was determined with micro-compression test. Fig. 7. Compressive strength determined with micro-compression test versus average area of microvoid cross-section perpendicular to ®bre axis, S3, for (*) pitch- and (*) PAN-based carbon ®bres. Solid line shows relation of Eq. (1) for  ˆ 3:2. M. Shioya, M. Nakatani / Composites Science and Technology 60 (2000) 219±229 225