Carbon fibre-reinforced epoxy laminate

Yang and Chou " have shown schematically the change in these moduli, E and E, for a carbon fibre-reinforced epoxy laminate with a range of fibre architectures, but the same fibre volume fraction of 60% (Fig. 1.3). Such a diagram provides a good starting point for the discussion of textile-reinforced composites. The cross-ply composite has... 

Figure 8.15 Dependence of the delamination resistance under quasi-static mode I loading for carbon-fibre-reinforced epoxy (IM7/977-2) on test temperature (after sufficient conditioning) for two laminate thicknesses [113] with increasing temperatures, the delamination resistance is increasing.

In this chapter, the characteristics of air explosions are briefly described and various blast protection paradigms are discussed. The blast behaviour of plain composites and multilayered structures are then discussed. Plain composites typically comprise polymeric resins with a fibre reinforcement, such as carbon fibre-reinforced epoxy resins. Multilayered systems include composite sandwich stmctures and hybrid composite-metal structures, known as fibre-metal laminates (FMLs). 

Fig. 8.22. Modified Goodman diagram showing fatigue stress amplitude required to cause failure in 10 cycles as a function of mean stress for two carbon-fibre reinforced epoxy resin materials (a) unidirectionally reinforced, stressed parallel to fibres, and (b) cross-plied laminate, with 45% of plies parallel to stress, and 55% transverse. Fibre volume fraction 60% (after R. Tetlow).

Considering first the engine unit. Rolls Royce use a significant range of substrates in their bonded components. These include large quantities of sheet aluminium and much smaller quantities of titanium and stainless steel, large quantities of carbon-epoxy laminates and small quantities of fibre-reinforced bismaleimide laminates and aluminium and Nomex honeycomb. 

There are now commercially available a large range of laminated plastics materials. Resins used include the phenolics, the aminoplastics, polyesters, epoxies, silicones and the furane resins, whilst reinforcements may be of paper, cotton fibre, other organic fibres, asbestos, carbon fibre or glass fibre. Of these the phenolics were the first to achieve commercial significance and they are still of considerable importance. 

Thermal decomposition of the matrix material offers a simple way of recovering the relatively expensive reinforcing fibres from a fibre-reinforced laminate. The epoxy resin matrix was made to decompose by thermal treatment in air or nitrogen, this treatment allowing the carbon fibres to be recovered without damage. 

Fibre-reinforced polymers (FRP) rebars, usually made of an epoxy matrix reinforced with carbon or aramide fibres, have also been proposed both as prestressing wires and reinforcement. Nevertheless, they are not discussed here, because these applications are still in the experimental phase and there is a lack of experience on their durability. In fact, while they are not affected by electrochemical corrosion typical of metals, they are not immune to other types of degradation. FRP are also used in the form of laminates or sheets as externally bonded reinforcement in the rehabilitation of damaged structures this application will be addressed in Chapter 19. 

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... 

Small deviations from the intended fibre orientation within a nominally unidirectional ply can reduce the mechanical strength and stiffness of continuous fibre laminates considerably, especially with aramid reinforcement. Wisnom [6] has investigated the reduction in strength caused by misalignment of unidirectional carbon fibres in XAS/914 carbon/epoxy... 

First, the effects of outdoor use on structural reinforced plastics such as glass/polyester or carbon/epoxy laminates are confined to the surface and do not often involve a serious threat to their structural integrity, unless perhaps there is a reduction in impact strength as a result of surface cracking. Fortunately carbon is a well-known UV absorber and therefore the fibres act as a good stabiUzer. The problems are mainly cosmetic. 

Sloan and Talbot [113] reported a study of the anodic exposure of autoclave-cured 30-ply unidirectional AS-4/3501-5a carbon epoxy laminates in unaerated 0.5 M pH 7 sodium chloride at ambient temperature, against a platinum counter electrode. Crack formation was observed at potentials above 600 mV (SCE) at currents as low as 1 pAcm. Discoloration (yellowish brown) of the electrolyte was observed at potentials above 900 mV with both the carbon/Pt and Pt/Pt electrode systems. The reinforcement fibres... 

Maximization of the load-bearing behaviour of these tubes can be achieved by external reinforcement, consisting of composites (see Fig. 10.5). In the experiments a woven fabric of fibreglass, as well as of carbon fibre, was used, which was laminated with epoxy resin. Static load tests have proved that the new material has significant better characteristics than normal wood, especially if the weight is taken into consideration. Within the areas of connections failures could be observed, which can be avoided by partial fortification of the reinforcement [30,31]. 

The increases in through-the-thickness reinforcement achieved by NCFs have been demonstrated by a number of authors. For example. Backhouse et aV compared the ease of delaminating polyester stitched 0/ 45 carbon fibre NCF with equivalent carbon fibre/epoxy UD laminates. There were large increases, some 140%, in the measured... 

The repair laminate was assumed to be reinforced with a bidirectional carbon fibre woven fabric with equal number of tows by weight in the weft and warp direction. The matrix was assumed to be epoxy. The laminate properties used for the FEA simulation were calculated using mle-of-mixtures (Daniel and Ishai, 1995), assuming a fibre volume fraction of 40%. The laminate elastic properties are given in Table 11.2. To calculate the repair thickness, the composite allowable strain (sc) was limited to 0.3%, selected as a number in between the two extremes (0.25% and 0.40%) proposed by ASME PCC-2 and also equal to the allowable strain for a class 2 repair with a 10 year lifetime. 

FIGURE 9.3 Comparison between the predicted and measured final failure stresses for (07+45°/90°) AS4/3501-6 carbon-fiber/epoxy laminates subject to biaxial loads (Test Case No 6-range of biaxial stress ratios). (Reprinted from Failure Criteria in Fibre Reinforced Polymer Composites The World-Wide Failure Exercise, Hinton, M. J., A. S. Kaddour, and R D. Soden, eds., Elsevier, London, 2004, with permission from Elsevier.)... 

---