The maximum bending moment that the ele-
reinforcement and eliminate almost all delamina-
ment can handle is related to the yield stress σ and
tions in the fabrication processes. The impreg-
the rail geometry, as follows:
nated reinforcements are called "prepegs." The
materials required for the fabrication process are
Mmax = (σ I/h)
(3)
shown in Table 2.
The glass fiber prepegs were then cut to length
where σ = yield stress
in both the longitudinal and transverse directions.
I = moment of inertia
There was no splicing of the reinforcement, so as
2h = thickness
to effect continuous strand reinforcement, thereby
maximizing strengths in both the warp and weft
Equating eq 2 and 3 and solving for eq l yields
directions. A surfacing veil consisting of a 170.1-g
(6-oz) C-glass mat was first laid down. This was
L = [ (8/w)(σ I/h) ]0.5
(4)
followed by a single layer of 510.3-g (18-oz) bidi-
From eq 4 it is obvious that longer beams can
rectional, stitched E-glass. Thereafter, different
be used if the I value can be increased by design.
layers of S-2 glass prepegs and E-glass fabric
prepegs were applied to build the thickness and
strength. The final two layers consisted of the
Test specimen fabrication
Materials considered for fabrication of the
bidirectional stitched E-glass and the surface veil
composite W-beam included both thermoplas-
of the C-glass mat.
tic and thermoset composites, including graph-
The number of layers and their orientations
ite-reinforced plastics, aramid-reinforced plastics,
were experimentally determined by reiterating
and fiberglass-reinforced epoxy, polyester, and
and running simultaneous tensile tests of the
vinyl ester. Because of cost considerations and
cured laminate coupons in the MTS testing
ease of fabrication, only glass-fiber-reinforced
machine and then fabricating the laminates. Fig-
polyester composite was chosen for specimen fab-
ure 16 shows the dimensions of the coupon
rication.
samples. A number of typical coupon test speci-
The costs of different fabrication processes,
mens after the test are shown in Figure 17a, and
including sheet molding, pultrusion and thermo-
an enlarged view of the typical fracture area is
forming, were examined. Since we needed a long,
shown in Figure 17b. Figure 18a gives the testing
constant cross-section product, the pultrusion
configuration of the test coupon, and Figure 18b
process was the most feasible option. To manufac-
shows a typical stress-strain curve from the ten-
ture the specimens, it was necessary to solicit the
sile test of one of the initial laminate designs. Note
cooperation of the pultrusion manufacturers to
design suitable dies and molds. Several pultru-
Table 2. Materials used for the FRP W-beam fabrica-
sion and molding companies were contacted and
tion.
designs were reviewed with them. Because of the
high cost of manufacturing the dies and tooling,
Resin:
MR12311 isophthalic polyester
the pultrusion process was abandoned. Instead,
Catalyst:
DDM 9 brand of methyl ethyl ketone peroxide
a vacuum bag technique using a mold made of
(MEKP)
existing steel W-beams was used. It was also
Glass fiber: C-glass, E-glass, and S-2 glass
decided that pigments and coatings would be pro-
The mechanical properties of the above materials, as declared by
vided on the FRP W-beams to give them a weath-
the suppliers:
ered zinc-coated look. The layup was also to be
Properties
Resin
E-Glass* S-Glass*
developed by the vendor, using the laminated
theory and their own design protocol, to achieve
Tensile modulus (psi 106)
0.5
4.3
6.4
Tensile strength (psi 103)
the goals of tensile strength (482.3 MPa, 70,000 psi)
10.0
105.0
123.0
Tensile modulus (psi 106)
0.5
4.3
6.4
and stiffness (E = 20.67 GPa, 3 million psi).
Tensile elongation (%):
2.4
--
--
For obtaining the highest strength in compos-
Flexural strength (psi 103)
18.0
142.0
100.0
ite laminates, the aim is always to maximize the
Flexural modulus (psi 106)
0.5
4.4
4.5
reinforcing glass fibers and minimize the matrix
Compressive strength (psi 103)
--
73.0
--
Compressive modulus (psi 106)
material. Before putting them into the W-beam
--
3.1
--
mold, all glass fiber fabrics were carefully impreg-
* Reinforcement: Matrix ratio = 60:40. Data supplied by manu-
nated with a measured amount of resin, which
facturer for unidirectional laminates.
helped to ensure uniform "wet-out" of the
SI conversion factor: 1 psi = 6.89 kPa
15
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