M. Shioya, M. Nakatani/ Composites Science and Technology 60(2000)219-229 1.0 2.5 8 看20 感06 2∽ 1.5 0.4 方1.0 0.2 E8g 00.51.01.52.02.5 0051.01.5202.5 Tensile stress /GPa Compressive strength from Fig. 8. Probability, F, that compressive fracture occurs at stress level, micro-compression test / GPa o, for(O)X5 and(o)T4 fibres. Solid lines show relations of Eq (2) pression test of carbon fibre/ th determined with axial com- Fig. 10. Reduced co pressive strength determined with micro-compression test for (O) 2.5 pitch-and(o) PAN-based carbon fibres 2.0 It is considered that the larger reduced compressive trength than the compressive strength of bare fibres, is obtained owing to the ability of the surrounding matrix 方方15 to prevent lateral displacements of the fibres at the fracture points. In the case of bare fibres, the fibres split into pieces after the carbon layers in the fibres are 1.0 buckled at the critical load, accompanying lateral dis- placements. On the other hand, in the case of the com- the alignment of the fibres can be 0.5 maintained even though the carbon layers in the fibres are buckled. Thus, the compressive load can be trans mitted through the damaged region, beyond the fracture 00.51.01.52.02.5 load of the bare fibres It is considered that the selection of the matrix resin Compressive strength from has an important influence on the reduced compressive micro-compression test /GPa strength. The variation of the axial compressive strength nal composites with the properties etermined with micro-compression test for(O) pitch-and(O)PAN. the matrix can be predicted by Rosen's model [18]. In directional composites is limited by the buckling stress of the component fibres supported elastically by the strands using the matrix resin with a tensile modulus of matrix, where buckling of the fibres occurs in either the 3.0 GPa. The reduced compressive strength is almost in shear or the extension mode. In the shear mode, the proportion to the compressive strength determined with fibres buckle into sinusoidal wave forms with coincident the micro-compression test as shown in Fig. 10. The phases so that the buckled fibres can be superimposed ratio of the reduced compressive strength against the with each other by translation in the transverse direc compressive strength determined with the micro-com- tion of the composite. In this case, the matrix between pression test is 1. 15. Therefore, if a stiff resin was used the fibres is deformed in shear In the extension mode, for the matrix, the compressive strength of the fibres are the phases of adjacent waves differ by I so that the sufficiently utilized in the compressive strength of uni- tensile and compressive deformations of the matrix, in directional composites. the transverse direction of the composite, take placestrands using the matrix resin with a tensile modulus of 3.0 GPa. The reduced compressive strength is almost in proportion to the compressive strength determined with the micro-compression test as shown in Fig. 10. The ratio of the reduced compressive strength against the compressive strength determined with the micro-com￾pression test is 1.15. Therefore, if a sti€ resin was used for the matrix, the compressive strength of the ®bres are suciently utilized in the compressive strength of uni￾directional composites. It is considered that the larger reduced compressive strength than the compressive strength of bare ®bres, is obtained owing to the ability of the surrounding matrix to prevent lateral displacements of the ®bres at the fracture points. In the case of bare ®bres, the ®bres split into pieces after the carbon layers in the ®bres are buckled at the critical load, accompanying lateral dis￾placements. On the other hand, in the case of the com￾posite strand, the alignment of the ®bres can be maintained even though the carbon layers in the ®bres are buckled. Thus, the compressive load can be trans￾mitted through the damaged region, beyond the fracture load of the bare ®bres. It is considered that the selection of the matrix resin has an important in¯uence on the reduced compressive strength. The variation of the axial compressive strength of the unidirectional composites with the properties of the matrix can be predicted by Rosen's model [18]. In his model, the axial compressive strength of the uni￾directional composites is limited by the buckling stress of the component ®bres supported elastically by the matrix, where buckling of the ®bres occurs in either the shear or the extension mode. In the shear mode, the ®bres buckle into sinusoidal wave forms with coincident phases so that the buckled ®bres can be superimposed with each other by translation in the transverse direc￾tion of the composite. In this case, the matrix between the ®bres is deformed in shear. In the extension mode, the phases of adjacent waves di€er by  so that the tensile and compressive deformations of the matrix, in the transverse direction of the composite, take place Fig. 9. Compressive strength determined with recoil test versus that determined with micro-compression test for (*) pitch- and (*) PAN￾based carbon ®bres. Fig. 10. Reduced compressive strength determined with axial com￾pression test of carbon ®bre/epoxy-A composite strands versus com￾pressive strength determined with micro-compression test for (*) pitch- and (*) PAN-based carbon ®bres. Fig. 8. Probability, F, that compressive fracture occurs at stress level, , for (*) X5 and (*) T4 ®bres. Solid lines show relations of Eq. (2). 226 M. Shioya, M. Nakatani / Composites Science and Technology 60 (2000) 219±229