Modulus continued fiber

Tensile modulus Continuous fibers Eq. no. Continuous ribbons (tapes) of high aspect ratio Eq. no. 

We will see in Section 5.4.2 that the elastic modulus of a unidirectional, continuous-fiber-reinforced composite depends on whether the composite is tested along the direction of fiber orientation (parallel) or normal to the fiber direction (transverse). In fact, the elastic modulus parallel to the fibers, Ei, is given by Eq. (1.62), whereas the transverse modulus, 2, is given by Eq. (1.63). Consider a composite material that consists of 40% (by volume) continuous, uniaxially aligned, glass fibers (Ef =16 GPa) in a polyester matrix (Em = 3 GPa). 

Note the similarity of this relationship to the equation of mixing given at the beginning of this section by Eq. (5.82). The factor /Si is called the fiber length correction factor, and it corrects the fiber modulus for the shortness of the fibers. It is plotted in Figure 5.95 as a function of the product na. When na becomes very large, fii approaches one, as is expected since this limit is the case of continuous fibers, and Eq. (5.110) reduces to Eq. (5.82). When na falls below about 10, Pi is significantly less than one. 

Assume that the conductivity of a undirectional, continuous fiber-reinforced composite is a summation effect just like elastic modulus and tensile strength that is, an equation analogous to Eq. (5.88) can be used to describe the conductivity in the axial direction, and one analogous to (5.92) can be used for the transverse direction, where the modulus is replaced with the corresponding conductivity of the fiber and matrix phase. Perform the following calculations for an aluminum matrix composite reinforced with 40 vol% continuous, unidirectional AI2O3 fibers. Use average conductivity values from Appendix 8. 

Filament winding (FW) is a fabrication technique for forming reinforced plastic parts of high strength/modulus and lightweight. It is made possible by exploiting the remarkable strength properties of their continuous fibers or filaments encased in a matrix of a resinous material. For this process, the reinforcement consists of filamentous non-metallic or metallic materials processed either in fibrous or tape forms.488 489... 

Amoco has developed a family of ultra high modulus continuous graphite fibers and preforms with axial thermal conductivity to llOOW/mK. The extremely high thermal conductivity is a direct result of an extremely high degree of crystallinity during carbonization of the mesophase pitch precursor fiber. Table... 

The properties of PAN fibers ( 10 pm diameter) are very dependent on the final heat treatment temperature (HTT). Tensile strength reaches a maximum (3.5 GPa) at a HTT of around 1500°C, and then decreases, while Young s modulus continues to... 

Figure 18.20 shows the effect of continuous and long glass fiber concentration on the tensile properties of a pultruded element. The continuous fiber increases tensile more than does long glass fiber. Similarly, flexural modulus and impact strength increase more as the continuous fiber concentration is increased. ... 

Equations such as Equation 3.144 give satisfactory agreement with the measured values of strength and modulus for polyester composites reinforced with chopped strands of glass fibers. These strength and modulus values are only about 20%-25% of those achieved by reinforcement with continuous fibers. 

As we have seen, the presence of fibers in the matrix has the effect of stiffening and strengthening it. The tensile deformation behavior of fiber-reinforced composites depends largely on the direction of the applied stress in relation to the orientation of the fibers, as illustrated in Figure 3.48. The maximum strength and modulus are achieved with unidirectional fiber reinforcement when the stress is aligned with the fibers (0°), but there is no enhancement of matrix properties when the stress is applied perpendicular to the fibers. With random orientation of fibers the properties of the composite are approximately the same in all directions, but the strength and modulus are somewhat less than for the continuous-fiber reinforcement. 

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