Epoxy-carbon composite shear strength

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].

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),...

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).

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). 

Two different polyacrylonitrile precursor carbon fibers, an A fiber of low tensile modulus and an HM fiber of intermediate tensile modulus were characterized both as to their surface chemical and morphological composition as well as to their behavior in an epoxy matrix under interfacial shear loading conditions. The fiber surfaces were in two conditions. Untreated fibers were used as they were obtained from the reactors and surface treated fibers had a surface oxidative treatment applied to them. Quantitative differences in surface chemistry as well as interfacial shear strength were measur-ed. 

Michelle Leali Costa, Sergio Fraseino M. de Almeida, Mirabel Cerqueira Rezende, The influence of porosity on the interlaminar shear strength of carbon/epoxy and earbon/bismaleimide fabrie laminates. Composites Science and Technology 61 (2001),... 

Figure 14.3. Contact angle of carbon fibers vs. interlaminar shear strength of epoxy composites. [Adapted, by permission from Tang L-G, Kardos J L, Polym. Composites, 18, No.l, 1997, 100-13.]...

If concrete removal is not required or supplementary reinforcing bars cannot be used, external reinforcement can be applied. For instance, steel bars may be encased in a shotcrete layer or steel plates may be bonded onto the concrete surface. Recently, the use of steel plates has been substituted by fibre-reinforced plastics (F. R.P.), that are composite materials with glass, aramide or carbon fibres embedded in a polymeric matrix (usually an epoxy system). F. R.P. are available in the form of laminates or sheets that are bonded to the concrete surface using an epoxy adhesive [11]. They are typically used to improve the flexural and shear strength or to provide confinement to concrete subjected to compression. The... 

The resin has good adhesion to glass and carbon fibers and shows a lower coefficient of thermal expansion than epoxies and most plastics. As a matrix resin in a carbon composite, PEAR is said to surpass epoxy (Hercules/Hexcel 3501-6) by 48% in tensile, compression, hot/wet, compression-after-impact, and other fiber-dominated properties. Shear strength (matrix-dominated property) is reported at 50% higher than epoxy at room temperature and up to 80% higher under hot-wet conditions. 

A unidirectional carbon fibre-epoxy laminate 3 mm thick is cut into a 10 mm wide strip and subjected to three-point bending with a span of 20 mm. Failure occurs by interlaminar splitting at a load of 2400 N. Calculate the interlaminar shear strength of the composite. 

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. 

Liu K, Piggott MR, Shear strength of polymers and fibre composites, Part 2 carbon/epoxy pultrusions, Composites, 26(12), 841-848, 1995. 

Figure 22.4 Interlaminar shear stress as a function of ply angle for Type I high modulus carbon fiber epoxy resin laminate tested in uniaxial tension in x-direction. The maximum interlaminar shear strength occurs at 0 = 35° and the stresses are zero at 0, 60 and 90°. Source Reprinted with permission from Pipes RB, Pagano NJ, Interlaminar shear stress in composite laminates under axial tension, J Composite Mater Sci, 13, 2131-2136, 1978. Copyright 1978, Sage Publications.

Donnet and coworkers [89-91] have studied adhesion between epoxy resins and carbon acid. The number of add groups on the fiber surface was used to neutralize strong addic groups such as carbo l and phenol. Sodium ethoxide was used to neutralize weaker addic groups such as hydro l and carbonyl. A direct correlation was found between the number of carboxylic add groups and the interlaminar shear strength of the composite (Figure 13). 

Fig. 6. Effect of surface treatment (degree of fibre treatment, DFT) on the mechanical performance of Type n carbon fibre epoxy composites. (1) Interlaminar shear strength of a unidirectional composite, (2) impact strength (3) notched tensile strength, of a...

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