Shear strength of carbon fibers

Fig. 5.18. Comparison of shear strengths of carbon fiber-epoxy matrix composites determined from three dificrcnt test methods. Fiber surface conditions as in Fig. 5.17. After Drzal and Madhukar (1993).

Harding J, Dong L, Effect of strain rate on the interlaminar shear-strength of carbon-fiber-reinforced laminates, Composite Science Technology 51(3), 347-358, 1994. 

Table 9.12 Interfacial Shear Strength of Carbon Fiber/Epoxy by Various Test Methods...

The lap-shear strength of carbon-fiber composites bonded using an epoxy adhesive was increased by 45% with the addition of 5% of MWNT (Hsiao et al. 2003). However, the locus of failure was also altered - from interfacial for the control specimens to cohesive for the nanotube-modified materials. 

Fig. 19. Inlerfacial shear strengths of various fiber/matrix composites as a function of the work of adhesion as determined by IGC. 1, glass fiber-poly (ethylene) 2, carbon fiber-epoxy B 3, carbon fiber-epoxy A and 4, carbon fiber-PEEK. Redrawn from ref. [102].

Chuang, S.L. and Chu, N.J. (1990). Effect of polyamic acids on interfacial shear strength in carbon fiber/ aromatic thermoplastics. J. Appl. Polym. Sci. 41, 373-382. 

The SEM observations revealed that PAN based fibers failed by a buckling mechanism, whereas MP based fibers failed by shear. The TIOOO fiber exhibited the highest compressive failure strength and tensile strain to break. Compressive strengths of carbon fibers are related to the ability to absorb energy, as shown in Figures 20.20 and 20.21. 

Figure 20.26 Variation of longitudinal compressive strength of carbon fiber epoxy resin laminate with temperature showing transition from shear mode to buckling mode failure. Failure depends on the shear modulus of the matrix and shear strength of the fibers and a similar effect is observed with the uptake of water. Source Reprinted with permission from Ewins PD, Potter RT, Phil Trans R Soc London, A294, 507-517, 1980. Copyright 1980, The Royal Society of Chemistry.

Fan, Z., Santare, M. H. and Advani, S. G. (2008), Interlaminar shear strength of glass fiber reinforced epoxy composites enhanced with mnlti-walled carbon nanotnbes . Composites Part A Applied Science and Mamfacturing, 39(3), 540-554. 

Thermoplastic matrices may also be used with the microdrop method [58,61] A method to form thermoplastic matrix material microdrops in various fiber-thermoplastic systems has been reported by Gaur et al. [58]. They measured the interfacial shear strength of carbon and aramid fibers embedded in four thermoplastic resins polyetheretherketone (PEEK), polyphenylene sulfide (PPS),... 

Fig. 3.27. Effect of the interface shear strength on mechanical properties of carbon fiber-epoxy matrix composites ( ) tran.sverse tensile strength (A) maximum transverse tensile strain (O) transverse tensile modiilns. After Madhukar and Drzal (1991),...

In using Eq. (6.10) to predict / , of a given composite system it is important that the said failure mechanisms all exist. If any one mechanism is apparently absent the corresponding toughness term must be excluded from the / t equation. It is also worth emphasizing that / , varies linearly with reciprocal of the frictional shear strength of the interface, i.e. l/tf, with the lower limit of (1 — Ff)/fm when if approaches infinity. This relationship has been shown to apply to many carbon fiber polymer matrix composites (CFRPs) (Harris et al., 1971 Beaumont and Phillips,... 

Fig. 7.8. (a) Normalized impact fracture toughness and (b) interlaminar shear strength (ILSS) of carbon fiber-epoxy matrix composites as a function of glycidyl acrylate/methyl acrylate (GA/MA) interlayer... 

Fig, 7.16, Impact fracture toughness (O) and interlaminar shear strength (ILSS, ) of carbon fiber-epoxy matrix composites with varying number of nylon sheets as delamination promoters. After Havre (1977). 

An injection molded bar contains 20% by volume of short carbon fibers in a matrix of nylon 6,6. Take the tensile strengths of the carbon fibers and the nylon to be 3200 MPa and 70 MPa, respectively, and assume the shear strength of the carbon fiber-nylon interface to be 32 MPa. The tensile moduli of nylon 6,6 and carbon fibers are 2.7 GPa and 230 GPa, respectively. Assume that the fibers are all of length 400 p.m and diameter 6 p.m and are perfectly aligned along the axis of the bar. 

Fig. 15. The interfacial shear strength for coated fibers (C) versus uncoated carbon fibers in an epoxy matrix. The finish layer increases the shear strength by creation of a brittle interphase. From Drzal et al. 7S)...

Figure 6.17 shows that crystalline dimensions affect interlaminar shear strength. Crystalline dimensions on the surface of carbon fibers can be measured by Raman spectroscopy. The ratio of intensity of two bands (1355 and 1575 cm ) is proportional to the crystalline dimensions on the surface. The crystalline width increases considerably from 3 to over 12.5 nm when the temperature of manufacture of carbon fibers is increased from 1000 to 3000°C. The increase in band ratio correlates with an increase in interlaminar shear strength. 

Figure 6.17. Ratio of Raman peak intensities at 1355 and 1575 cm vs. interlaminar shear strength of composites containing carbon fibers of different origin. [Data from Tang L-G, Kardos J L, Polym. Composites, 18,No.l, 1997, 100-13.]...

Applications. The following uses of contact angle were reported in the literature surface energy of different sizes for fibers, correlation between contact angle of fiber and interlaminar shear strength of composite, effect of surface treatment of fillers for paints, the matrix-filler adhesion parameter for PS filled with CaCO, dispersion stability of PEO-modified kaolin particles, determination of contact angle of carbon fibers and its dependence on treatment, wettability of fiber sur-... 

Carbon/Aramid Fiber Sheet Jacketing Method. The application of carbon/aramid fiber sheet for the reinforcement of concrete pier is adopted when restricted conditions are present on site, such as no permit of sectional increase due to clearance limit or weight increase on the foundation. The sheet in longitudinal direction is effective to increase the flexural strength and the sheet in transverse direction acts as lateral reinforcement to raise the shear strength. Particularly the fiber sheet is concentrically bonded at the termination of longitudinal rebar at the mid-height. 

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