Page 93 - 3D Fibre Reinforced Polymer Composites
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82 30 Fibre Reinforced Polymer Composites
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Y
Y
Figure 4.8 Element array model (a) unit cell, (b) division and idealisation in z-x and z-y
planes (Naik and Ganesh, 1992)
Consider the unit cell shown in Figure 4.6, we assume that the undulation and cross-
sectional shape of each individual yarn is known. Both yarns are treated as transversely
isotropic unidirectional composites, for which the engineering constants can be
measured or evaluated from the local fibre volume fraction and fibre and matrix
properties. There exist a number of closed-form approximations for evaluating the
properties of unidirectional composites (Hill 1965; Hashin 1979; Christensen 1990;
Aboudi, 1991;). For example, Chamis (1984) proposed the following equations for the
engineering constants:
