ment of any 0 or 90 fiber layer with a 45 layer
W-beam made of ductile metals deforms plasti-
within the given thickness would have reduced
cally, involving crystalline slip or molecular slid-
the tensile strength from the desirable 413.4 MPa
ing, which are thermally activated processes. In
(60,000 psi). The energy absorbed by this mate-
contrast, in FRP composites made from fibers and
rial in tensile fracture is due almost entirely to
resins that are brittle, the energy is absorbed by a
the microfracture process. In flexural loading the
large number of different microcracking pro-
FRP W-beam produced much more deflection
cesses, which are controlled by the properties of
before failure than the 2.82-mm- (0.111-in.-) thick
the fibers and resins and the geometrical arrange-
steel beam. Despite the local catastrophic failure
ment of the fibers. In fact, the specific absorption
at the crest, the FRP W-beam regained its shape
energies are probably significantly larger in many
after removal of the load, while the postyield defor-
fiber-reinforced polymer composites than those
mation of the steel beam was sustained. Thus, in
observed in ductile metals or plastics.
installations of the FRP W-beam, the replacement
The key to developing a large amount of
could be delayed or deferred for some time with-
energy absorption is to design the composite W-
out impairing the performance of the guardrail
beam with constituents arranged in such a man-
system seriously, but in case of the steel W-beam
ner that progressive crushing occurs. The crush
immediate replacement is necessary for maintain-
would be expected to move at approximately a
ing the safety of the system.
constant load equal to the residual load and also
Laboratory tests in both slow, flexural loading
at the same velocity dictated by the deceleration
on the corrugated surface of the FRP W-beam and
rate of the errant vehicle. The aim is to achieve
drop testing of weight on the plane surface of the
extensive microfracturing of the matrix and par-
FRP beams show a dramatic difference in the
tial failure of the fibers by breakage and pull-out,
energy absorption characteristics between the
so that sufficient residual load is sustained to
steel and the FRP composites. Upon impact, the
guide the errant vehicle to its previous course.
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