Page 328 - Engineered Interfaces in Fiber Reinforced Composites

Chapter 7. improvement of transverse fracture toughness with interjhce contra1 309

Table 7.4
Linear coefficients of thermal expansion (CTE) of fibers and matrix materials.

Fibers CTEs (x K-')

Carbon-PAN Based
HS XL = -0.5- -0.1
XT = 7-12
HM XL = -1.2- -0.5
XT = 7-12
Aramid
Kevlar 29 XL = -2.26
UT - 59
Kevlar 49 XL = -2
Cq = 59
Kevlar 149 XL = -1.49
XT = 59
Glass
E-glass 4.1-5.0
S-glass 5.6
Polyethylene
Spectra 900 G(L = -10.8
Boron (B-W) 4.8-8.3
A1203 3.5-8
SIC
scs 4.3-5.7
Nicalon 3.1-4.0
Steel (0.9% C) 12
Stainless steel (1 8-8) 11.6
Beryllium 11.6
Tungsten 4.5
Molybdenum 6.0

than other materials, and especially are at least one order of magnitude lower than
polymeric materials. Unidirectionally oriented fiber composites have two (or
sometimes three) CTEs: namely ctc~ and GT, in the longitudinal and transverse
directions, respectively. The expressions for the effective linear CTEs of unidirec-
tional fiber composites (Schapery, 1968) are derived based on the energy balance
method for transversely isotropic fibers, assuming that Poisson ratios of the
composite constituents were similar:

where the first subscripts, c, f and m refer to composite, fiber and matrix,
respectively, while the second subscripts L and T refer to the longitudinal and
transverse directions, respectively. For unidirectional fiber composite, the CTEs in
the longitudinal direction are normally lower than those in the transverse direction