Reinforcement orientation

Equation (2.13) has also been used to predict the modulus of flake (platelet) composites containing planar oriented reinforcement for uniform arrays of flakes, Eq. (2.14), and for random overlap, Eq. (2.15) [10, 12, 14, 19]. Equations for the parameter u are somewhat different from those used for fibers, but thqr still contain the important parameters affecting the modulus of the composite, that is, aspect ratio, volume fraction, and flake/matrix modulus ratio. Equation (2.18) has also been used to predict the modulus of platelet-reinforced plastics [17, 21]. 

F rovides precisely oriented reinforcing filaments excellent strength-to-weight ratio good uniformity. 

The above fibre reinforcements are available in several forms that include almost parallel bundles of continuous filaments, either untwisted (rovings) or twisted (yarns), and short fibres (chopped) with a length of 3 mm to 50 mm (Keller, 2003). For use in pultrusion, fibre reinforcements can be worked to obtain textile products with several reinforcing directions. There are, therefore, several products available, either with randomly oriented fibres, which can be short (chopped strand mat) or continuous (continuous strand mat), or with oriented reinforcements (such as woven and non-woven fabrics, stitched fabrics, grids and meshes), which can be biaxial (0°/90° or -i-45°/-45°) or triaxial (0°/-i-45°/ 5°), the latter being considerably more expensive and less widely used in pultrusion. All these forms can be further combined to make complex textile products with continuous oriented fibres, together with randomly oriented short or continuous fibres. Figure 9.1 shows examples of forms of fibre reinforcement. 

The same conclusion could be drawn from Table 11.2, The randomly oriented reinforcement has a deleterious effect on both the modulus of elasticity (decrease of 10%), and the ultimate tensile strength, a, (decreases of 65%) when compared to the neat PP film. The crossply samples show a significant improvement in stiffness over neat PP of 44% on average, with an insignificant improvement in a. The uniaxial samples show a very good reinforcement effect, with nearly twice the modulus, E, at 3.43 GPa, and a 50% improvement in a at 42,5 MPa. 

Molar mass, chain orientation, reinforcement, rubber additions Tensile strength, toughness, impact resistance, fatigue resistance... 

Figure 11.21 The molecular composites concept utilizes a rod-shaped polymer dispersed in a random-coil-shaped polymer. When the rod-shaped chains are oriented, reinforced fibers can be made (38).

In contrast to conventional composites where fabrication of the composites involve multiple steps, some liquid crystalline composite structures with highly oriented reinforcing fibrous LCP phase can be produced in a single step. Because of this reason these blends are some time referred to as in situ composites (Kiss 1987). Beauty of such composite materials is that the mechanical properties of such composite materials can be tuned by controlling the addition of liquid crystalline... 

The mechanical capacity of polymers is often enhanced by the formation of composite structures composed of (1) oriented reinforcing imits, such as fibrils, fibers, or extended chain crystals and (2) the use of binding matrices of the same chemical structure [133]. An alternative that mediates improved mechanical performance while providing space for cellular invasion is the deposition of a bonelike mineral film on the interior pore surfaces of PLGA scaffolds (Fig. 8) [ 134,135]. This approach not only leads to increased compressive moduli, but also confers the scaffolds with osteoconductive characteristics and the ability to modulate proliferation and differentiation of multipotent stem cells [134-137]. 

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