Carbon Fibers unidirectional strength

Fig. 12. (a) The variation of the tensile strength of unidirectional carbon-fiber-reinforced epoxy resin as a function of the fiber volume fraction, (b) The variation of the tensile strength of unidirectional carbon-fiber-reinforced epoxy resin as a function of the fiber volume fraction for low fiber volume... 

Fig. 7.25. Impacl fracture toughness (O) and interlaminar shear strength (ILSS, ) of unidirectional carbon fiber-epoxy matrix composites as a function of expanding monomer (spiro) content. After Lim...

Effect of through-the-thickness stitches on flexural strength and Mode I interlaminar fracture toughness of carbon fiber-epoxy matrix composites manufactured using unidirectional prepregs". 

Figure 5.122 Strength chart for a (0, 9) unidirectional carbon-fiber-reinforced epoxy laminate composite. Reprinted, by permission, from N. G. McCrum, C. P. Buckley, and C. B. BucknaU, Principles of Polymer Engineering, 2nd ed., p. 408. Copyright 1997 by Oxford University Press.

Piezoresistivity [66] was observed in cement matrix composites with 2.6-7.4 vol% unidirectional continuous carbon fibers. The dc electrical resistance in the fiber direction increased upon tensile loading in the same direction, such that the effect was mostly reversible when the stress was below that required for the tensile modulus to decrease. The gage factor was up to 60. The resistance increase was due to the degradation of the interface of the fiber and matrix, which was mostly reversible. Above the stress at which the modulus started to decrease, the resistance abruptly increased with stress/strain, due to fiber breakage. The tensile strength and modulus of the composites were 88% and 84%, respectively, of the calculated values based on the rule of mixtures. 

Unidirectional carbon fiber reinforced SiC/C composites were fabricated by Tani et al [213] using reaction bonding. The prepreg for the composites was prepared by the filament winding method, with a mixed slurry of phenolic resin, sihcon powder and ethyl alcohol, then die pressed at 130°C and sintered in Ar. The formation of SiC took place through a reaction between the carbon from the pyrolyzed phenolic resin and the silicon powder above a temperature of about 1320°C and was completed by 1420°C. The bulk density of the composites was about 1.7 gcm. The average flexural strength of the composites with a Si/C ratio of 0.2, 0.4 and 1 was about 310, 250 and 150 MPa respectively. 

Figure 17.52 The angular dependence of fracture strength of a cfrp unidirectional Type I carbon fiber lamina Vf=0.5). Source Reprinted from Chamis CC, Sinclair JH, Exp Mech, 17, 339-346, 1977 and Tsai-Hill criterion presented by Hull, Hull D, Clyne DW, Cambridge University Press, Cambridge, 1996.

Cui WC, Wisnom MR, Jones M, Effect of specimen size on interlaminar shear strength of unidirectional carbon fiber-epoxy. Composites Eng, 4(3), 299-307, 1994. 

Wisnom MR, The effect of specimen size on the bending strength of unidirectional carbon fiber-epoxy, Composite Structures, 18(1), A1-G3, 1991. 

Tani and Shobu [256] fabricated unidirectional carbon fiber reinforced SiC composites with a polymer pyrolysed and reaction bonded SiC matrix. In spite of a low density of about 1.85 mgm , the flexural strength of the composites was about 530 MPa. Addition of polymer decreased the open porosity and increased the elastic modulus of the composites. 

Key words matrix, strength, stiffness, composite, carbon fibers, Kevlar fibers, glass fibers, unidirectional fabrics, woven fabrics, stitched fabrics. 

Carbon fiber reinforcements enhance the modulus and strength of a plastic and reduce the density and thermal coefficient of expansion. They also lower the coefficient of friction and provide excellent resistance to most environmental exposure conditions and chemicals. The properties of the final composite are very much dependent on the degree of orientation of the fibers within the resin matrix. When the fibers are in complete aligmnent (e.g., unidirectional or all fibers are at an orientation of 0°), the properties of the composite are more affected by the fiber than if the fibers are randomly aligned. 

Continuous or unidirectional carbon fibers generally render the composites with high mechanical strength and stiffness. Thermoset resins are widely used as matrix materials... 

Most carbon fibers are in the form of continuous filaments with a diameter averaging 10 They are applied unidirectionally (0°) by the processing techniques of filament winding and tape layup described in Ref. 2. Such unidirectional systems have the highest property-translation efficiency, i.e., the fraction of fiber properties translated Into the composite. On the other hand, they have low interlaminate strength because of the lack of fibers in the thickness direction. 

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