Page 223 - Mechanics Analysis Composite Materials

208 Mechanics and analysis of composite materials
Because the fibers of the fill yarns are orthogonal to the loading direction, we can
take Ef =El, where E2 is the transverse modulus of a unidirectional composite.
Compliance of the warp yam can be decomposed into two parts corresponding to tl
and t2 in Fig. 4.80, i.e.,
-+-,
2tl +t2 - - 2tl t2
E\y E1 E,

where, E1 is the longitudinal modulus of a unidirectional composite, while E, can be
determined with the aid of the first equation of Eqs. (4.76) if we change (b for a,i.e.,

(4.166)

The final result is as follows:

For example, consider a glass fabric with the following parameters: a = 12",
t2 = 2tl. Taking elastic constants of a unidirectional material from Table 3.5 we get
for the fabric composite Ea = 23.5 GPa. For comparison, a cross-ply [0"/90"]
laminate made of the same material has E = 36.5 GPa. Thus, the modulus of a
woven structure is by 37% less than the modulus of the same material but reinforced
with straight fibers. Typical mechanical characteristics of fabric composites are
listed in Table 4.4.

Table 4.4
Typical properties of fabric composites.

Property Glass fabric-epoxy Aramid fabric-epoxy Carbon fabric-epoxy
Fiber volume fraction 0.43 0.46 0.45
Density (g/cm3) 1.85 I .25 I .40
Longitudinal modulus (GPa) 26 34 70
Transverse modulus (GPa) 22 34 70
Shear modulus (GPa) 7.2 5.6 5.8
Poisson's ratio 0.13 0.15 0.09
Longitudinal tensile strength 400 600 860
(MPa)
Longitudinal compressive 350 150 560
strength (MPa)
Transverse tensile strength 380 500 850
(MPa)
Transverse compressive strength 280 150 560
(MPa)
In-plane shear strength (MPa) 45 44 150