SAMPE Journal - March/April 2017 - 39
Feature Article
were damaged in a drop tower with
an impact energy of 16 J. Subsequent
to the premature damaging of the
specimens, a three point bending
test in dependence on DIN EN ISO
14125 was carried out. For the three
point bending test, the specimens
were cut to the dimensions 60 x 40 x
3 mm³. The width of the specimens
was increased in opposition to the
testing standard from 15 mm to 40
mm. This was necessary, because
the dimensions of the impacts were
larger than 15 mm. Normally, the
damage is not as large as the part.
Therefore, the width of the specimens
was increased to get specimens
which have a damaged area which
is smaller than the specimen's
width. Furthermore, the width of
the specimens is not influencing the
results. The flexural strength of the
parts is related to the area crosssection of the specimens. Moreover,
comparative
investigations
on
undamaged specimens with a width
of 15 mm and 40 mm show that
the flexural stresses have the same
values. In the three point bending
test, the same side of the specimen
was exposed to the load as it was
exposed to the impact.
Results
Analysis of the Flexural Properties
The selection of the textiles and
the process parameters of the 3D
Fiber Spraying were based on the
anisotropy of the flexural strength
of the RTM-parts with fiber sprayed
preforms. The results of the
investigation of the flexural strength
are illustrated in Figure 4.
The results show, that the average
flexural strength parallel to the
aspired fiber orientation of the noncrimped fabric part is 2.3% higher
than the flexural strength of the part
with a fiber sprayed preform. Due, to
the standard deviations, a significant
difference between both flexural
strengths could not be observed. The
standard deviation of the part with
the fiber sprayed preform is higher,
compared to both comparative parts.
During the fiber spraying process,
the amount of fibers, which are
SAMPE Journal, Volume 53, No. 2, March/April 2017
Figure 4. Influence of the preforming technology and fabrics on the flexural strength.
Figure 5. Influence of the preforming technology and fabrics on the flexural modulus.
orientated parallel or perpendicular
to the aspired fiber orientation, can
vary in a small range. Due to this
variation, the mechanical properties
vary in a wider range than the
mechanical properties of the parts
with non-crimped fabrics, because
the fiber orientation of non-crimped
fabrics is not subject to any variations
caused by the manufacturing
process. As mentioned above, the
part with a preform made from
chopped strands mats have no
adjusted fiber orientation. Parallel
and perpendicular to the aspired
fiber orientation means at these parts,
that the specimens are prepared
out of the parts in the production
direction of the textile (parallel) and
perpendicular to the production
direction. The results of the flexural
strength show, that the production
process of the chopped stands mats
causes a low orientation of the
fibers. The average flexural strength
of the part with fiber sprayed
preforms is 43% higher parallel to
the aspired fiber orientation than
the part with chopped strands mats.
Perpendicular to the aspired fiber
orientation, the flexural strength of
the fiber sprayed preforms is 40%
lower than the flexural strength of
the part with chopped strands mats.
The decrease of the flexural strength
perpendicular to the aspired fiber
orientation is less distinct at the noncrimped fabric part than at the fiber
sprayed part. This effect is noticeable
because the anisotropy of the parts
with non-crimped fabrics should be
at first approximation around 2 : 1
but the investigations show, that the
anisotropy is 1.6 : 1. A more detailed
discussion of this effect follows with
the discussion of the results of the
tensile properties (see Analysis of the
Tensile Properties that follow).
The trend from the flexural
strength can also be observed for the
flexural modulus (Figure 5).
The higher standard deviation
of the parts with fiber sprayed
preforms is even more distinctive at
the flexural modulus. The anisotropy
of the flexural modulus is overall
39
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