300 60 40 80 50 1 200 30 20 (sW)sninpow 0 60 卫 30 名 100 10 20 0 0 90 0 999 0 30 60 30 60 90 0 (a) 6(degrees) (b) 6(degrees) FIGURE 4.6 Variations of tensile modulus and tensile strength of a unidirectional carbon fiber-epoxy laminate with fiber orientation angle.(After Chamis,C.C.and Sinclair,J.H.,Mechanical behavior and fracture characteristics of off-axis fiber com- posites,II-Theory and comparisons,NASA Technical Paper 1082,1978.) laminate occurs at the fracture strain of 0 plies.The change in slope of the stress-strain curve at the knee can be reasonably predicted by assuming that all 90 plies have failed at the knee and can no longer contribute to the laminate modulus. Denoting the moduli of the 0 and 90 plies as E and E22,respectively,the initial (primary)modulus of the cross-ply laminate can be approximated as E=40 Eu+4 A A90 E22 (4.5) [o] [0/9o]ls Es Knee [90j ETt ELt FIGURE 4.7 Schematic tensile stress-strain diagram for a [0/90]s cross-plied laminate tested at =0 direction. 2007 by Taylor Francis Group,LLC.laminate occurs at the fracture strain of 08 plies. The change in slope of the stress–strain curve at the knee can be reasonably predicted by assuming that all 908 plies have failed at the knee and can no longer contribute to the laminate modulus. Denoting the moduli of the 08 and 908 plies as E11 and E22, respectively, the initial (primary) modulus of the cross-ply laminate can be approximated as E ¼ A0 A E11 þ A90 A E22, (4:5) 80 60 40 Strength (ksi) 20 0 40 30 20 10 0 0 0 30 60 90 100 200 300 60 90 q (degrees) q (degrees) 0 30 (a) (b) 0 10 20 Strength (MPa) Modulus (GPa) Modulus (Msi) 30 40 50 s q s 60 FIGURE 4.6 Variations of tensile modulus and tensile strength of a unidirectional carbon fiber–epoxy laminate with fiber orientation angle. (After Chamis, C.C. and Sinclair, J.H., Mechanical behavior and fracture characteristics of off-axis fiber com￾posites, II—Theory and comparisons, NASA Technical Paper 1082, 1978.) [90] [0] s sF sk [0/90]S Knee E eTt e Lt e ES FIGURE 4.7 Schematic tensile stress–strain diagram for a [0=90]S cross-plied laminate tested at u ¼ 08 direction.
2007 by Taylor & Francis Group, LLC