Composites hybrids

A relatively new fiber-reinforced composite is the hybrid, which is obtained by using two or more different kinds of fibers in a single matrix hybrids have a better all-around combination of properties than composites containing only a single fiber type. A variety 

The two different fibers may be combined in a number of ways, which will ultimately affect the overall properties. For example, the fibers may all be aligned and intimately mixed with one another, or laminations may be constructed consisting of layers, each of which consists of a single fiber type, alternating with one another. In virtually all hybrids, the properties are anisotropic. 

When hybrid composites are stressed in tension, failure is usually noncatastrophic (i.e., does not occur suddenly). The carbon fibers are the first to faO, at which time the load is transferred to the glass fibers. Upon failure of the glass fibers, the matrix phase must sustain the applied load. Eventual composite faUiue concius with that of the matrix phase. 

Principal applications for hybrid composites are hghtweight land, water, and air transport structural components, sporting goods, and hghtweight orthopedic components. 

To fabricate continuous fiber-reinforced plastics that meet design specifications, the fibers should be uniformly distributed within the plastic matrix and, in most instances, all oriented in virtually the same direction. This section discusses several techniques (pul-trusion, filament winding, and prepreg production processes) by which useful products of these materials are manufactured. 

A hybrid is generally considered to be a composite with two or more types of reinforcement, although there can also be a hybrid matrix [206]. In this chapter, the most common form of hybrid which is two types of fiber is considered. The hybrid effect is a term used to describe the apparent synergistic improvement of composite strength to a value more than that predicted by the rule of mixtures. However, negative effects have also been observed. A typical hybrid could be glass/carbon in a common matrix. The hybrid may be formed by alternate plies, interspersed tows or intermingled fibers. Alternatively, a hybrid could comprise a woven cloth with say, one fiber in the weft and the second fiber in the warp. Short and Summerscales [207] have reviewed hybrid composites. 

Considering equal fiber fractions of a unidirectional HM fiber/E-glass under axially applied tension, the stiffness of the hybrid Eh confirmed by experiment can be found from  

Proportion of carbon plies in glass/carbon hybrid laminate 

The hybrid effect has been studied [210] with carbon fibers and glass [211-217], carbon fibers and aramid [218 220], carbon fibers and PEEK [221] and carbon fibers and polyethylene [222-232]. 

The sandwich composite is a special form of hybrid and the sandwiched material itself may or may not be a composite. Hybrids can lower the cost, improve properties and enable composite properties to be tailored. 

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ARALL laminates, a family of hybrid composites consisting of aramid fibers bonded with epoxy between 0.3 mm thick aircraft ahoy sheets, were introduced in the 1980s (53). The laminates have lower density than even the new Al—Li ahoys and are greatly superior to monolithic aluminum sheet in resisting the growth of fatigue cracks. ARALL laminates have been specified for aircraft stmcture which is subjected to cycHc tension loads (see Laminates). 

A hybrid composite material is made up of 20% HS carbon fibres by weight and 30% E-glass fibres by weight in an epoxy matrix. If the density of the epoxy is 1300 kg/m and the data in Fig. 3.2 may be used for the fibres, calculate the density of the composite. 

E. Hybrid Composites Made of Natural Fibers and Glass or Carbon Fibers... 

Generally, the mechanical and physical properties of natural fiber-reinforced plastics only conditionally reach the characteristic values of glass fiber-reinforced systems. By using hybrid composites made of natural fibers and carbon fibers or natural fibers and glass fibers, the... 

Figure 21 Compression strength as dependent on the content of GRP in jute fiber-reinforced hybrid-composites [67J.

Composites containing more than one type of fiber are commonly known as hybrid composites. The term hy-... 

Wen and Wilkes [12] enlisted the names and types of most of the polymers employed for the preparation of hybrid composites using sol-gel technique. In the field of mbber, wide-scale research... 

There are various routes to synthesize rubber-based organic-inorganic hybrid composites through sol-gel process. These are mentioned in brief below. 

Dispersion of nanosilica within the mbber matrices usually generates optically transparent materials. All the ACM-silica and ENR-sihca hybrid composites are completely transparent up to 50 wt% of TEOS concentrations. EoUowing are the figures (Figure 3.9) which show the visual appearance of the representative hybrid nanocomposites. The logos over which the films (average film thickness 0.25 mm) are placed are clearly visible. 

Formation of optically transparent silicone rubber-silica hybrid composites has also been reported by Raj an and Sur [54]. 

FIGURE 3.8 Scanning electron microscopic (SEM) pictures of acrylic mbber (ACM)-silica hybrid composites (a) synthesized from 50 wt% tetraethoxysilane (TEOS) and (b) synthesized from 10 parts of precipitated silica. (From Bandyopadhyay, A., Bhowmick, A.K., and De Sarkar, M., J. Appl Polym. Sci., 93, 2579, 2004. Courtesy of Wiley InterScience.)... 

Different characteristics of solvents seriously affect the sol-gel reaction in solution. This in turn influences the physico-mechanical properties of the resultant rubber-silica hybrid composites. Bandyopadhyay et al. [34,35] have carried out extensive research on stmcture-property correlation in sol-gel-derived rubber-sihca hybrid nanocomposites in different solvents with both chemically interactive (ENR) and noninteractive (ACM) mbber matrices. Figure 3.12 demonstrates the morphology of representative ACM-sihca and ENR-sihca hybrid composites prepared from various solvents. In all the instances, the concentration of TEOS (45 wt%), TEOS/H2O mole ratio (1 2), pH (1.5), and the gelling temperature (ambient condition) were kept unchanged. 

FIGURE 3.12 Morphology of mbber-silica hybrid composites synthesized from solution process using different solvents (a) and (b) are the scanning electron microscopic (SEM) pictures of acrylic rubber (ACM)-silica hybrid composites prepared from THF (T) and ethyl acetate (EAc) (E) and (c) and (d) are the transmission electron microscopic (TEM) pictures of epoxidized natural rubber (ENR)-siUca hybrid composites synthesized from THF and chloroform (CH). (From Bandyopadhyay, A., De Sarkar, M., and Bhowmick, A.K., J. Appl. Polym. Sci., 95, 1418, 2005 and Bandyopadhyay, A., De Sarkar, M., and Bhowmick, A.K., J. Mater. Sci., 40, 53, 2005. Courtesy of Wiley InterScience and Springer, respectively.)... 

AND GELATION TEMPERATURE ON STRUCTURE AND PROPERTIES OF THE HYBRID COMPOSITES... 

Tian et al. [56] have studied poly(G-caprolactone)-silica and Sengupta et al. [57] have investigated nylon 66-silica hybrid systems and have observed that the phase separation started when Si/H20 mole ratio is increased above 2 and the resultant hybrid films become opaque. Gao [11] has reported similar observations on sol-gel-derived ionomeric polyethylene-silica system. A wide range of literatures is not available on this topic of mbber-silica hybrid nanocomposites, though Bandyopadhyay et al. [34,35] have reported the hybrid formation with different TEOS/H2O mole ratios from ACM and ENR and also demonstrated detailed structure-property correlation in these systems. The hybrids have been prepared with 1 1, 1 2, 1 4, 1 6, 1 8, and 1 10 TEOS/H2O mole ratios. Figure 3.14 shows the morphology of the ACM-silica hybrid composites prepared from different TEOS/H2O mole ratios. 

Figure 3.17 shows the mechanical properties of the ACM-silica and ENR-silica hybrid composites synthesized from various pH, reproduced from the data reported by Bandyopadhyay et al. [36]. As morphology indicates, all the samples prepared within the pH range 1.0-2.0 are transparent, contain nanosilica particles, and are superior in tensile strength and modulus... 

FIGURE 3.16 Morphology and visual appearance of acrylic rubber (ACM)-silica and epoxidized natural rubber (ENR)-silica hybrid composites prepared from different pH ranges (a) transmission electron microscopic (TEM) picture of ACM-siUca in pH 1.0-2.0, (b) scanning electron microscopic (SEM) picture of ACM-siUca in pH 5.0-6.0, (c) SEM image of ACM-siUca in pH 9.0-10.0, (d) TEM picture of ENR-silica in pH... 

An attempt has also been made for qualitative estimation of the interaction at the rubber-silica interfaces. This has been accomplished by recording the solution viscosity of the precursor sols of these hybrid composites continuously for five days, with an interval of 24 h in the course of in situ silica generation. Figure 3.21 shows the result. 

Tan, X.C.,Tian, Y.X., Cai, P.X. andZou, X.Y. (2005) Glucose biosensor based on glucose oxidase immobilized in sol—gel chitosan/silica hybrid composite film on Prussian blue modified glass carbon electrode. Analytical and Bioanalytical Chemistry, 381, 500-507. 

X.C. Tan, MJ. Li, RX. Cai, LJ. Luo, and X.Y. Zou, An amperometric cholesterol biosensor based on multiwalled carbon nanotubes and organically modified sol-gel/chitosan hybrid composite film. Anal. Biochem. 337, 111-120 (2005). 

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