Page 88 - 3D Fibre Reinforced Polymer Composites

Micromechanics Models for Mechanical Properties 77
determined. It is clear a combination of iso-strain and iso-stress conditions are used in
the bridging model. The bridging model is considered to be applicable to satin weave
with n,24.

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N
N

Figure 4.5 Bridging model (Ishikawa and Chou, 1982b)

Ishikawa and Chou (1982b) applied the “bridging model” to investigate the linear
elastic properties of woven fabrics and non-linear behaviour due to the initial failure of
the fabrics. It was reported that the elastic stiffness and knee stress in satin weave
composites were higher than those in plain weave composites due to the presence of
bridging regions in the weaving pattern. The fibre undulation model and bridging
model were applied to analyse the non-linear elastic behaviour of fabric composites
(Ishikawa and Chou, 1983b), coupling with the non-linear constitutive relation
developed by Hahn and Tsai (1973). However, only the undulation and continuity of
yams along the loading direction were considered, and the yarn undulation in the
transverse direction and its actual cross-sectional geometry were neglected.
Ishikawa and his colleagues (1 985) conducted experiments to verify the theoretical
predictions obtained in their previous work. In these experimental tests, the maximum
strain level of ~OOXIO-~ was chosen. The materials used were plain weave and 8-harness
satin fabric composites of carbodepoxy. It was found that for plain weave composites,
the elastic moduii increases with the laminate ply number but levels out at about 8-ply
thickness. The ratio of ply thickness to thread width (i.e., Mu) is also a very important
parameter, which strongly affects the elastic moduli of plain weave composites. In-