SAMPE Journal - July/August 2022 - 68

FEATURE / INVESTIGATION ON MATERIAL EQUIVALENCY
material of the reinforcement
segment enables the automated
manufacturing of optimized
reinforcement architectures.
The ability to produce
geometrically complex, multimaterial
preforms expands
the automation envelope for
high performance composite
parts significantly. To unlock
this potential for aerospace
structures without the high
effort of complete component
recertification, this paper focuses on the question
on material equivalency and the provision of
dimensioning values for FPP laminates.
Design of the FPP Laminates
Generally, FPP laminates offer additional design
freedom, like choosing patch geometry (length,
thickness, width). In a basic UD design setup,
those parameters were already investigated
experimentally and numerically6,7
.
For complex loaded parts, FPP laminates
consist of multiple layers of fiber reinforced
material, usually with several principal fiber
orientations to support different load directions
within the laminate. Here, manufacturing
parameters like patch lay-up pattern, especially
regarding the overlap of two adjacent layers, are
adjustable parameters having influence on the
mechanical values of the laminate. Figure 2 shows
the three principal joining options for neighboring
reinforcement patches.
Butt joints offer the ideal material buildup
and usage. A deviating lay-up of the next
patch either leads to a gap or an overlap. For
aerospace laminates, as investigated in this
paper, manufacturing parameters should be set
in a way that lay-up deviations result in a gap, not
an overlap to avoid fiber undulation. The high
precision of a robot-based FPP process keeps the
lay-up deviations at a very low level (< 0.5 mm
Figure 2. Different deposition scenarios of neighbored
patches within one layer.
possible), so that effectively a laminate with butt
joints and without overlaps can be achieved during
production.
Regarding the arrangement of complete layers
relative to each other, FPP is based on a " sublayer "
approach. For every principal fiber orientation in
the laminate, at least two sublayers exist, meaning
two individual layers of the same orientation being
shifted longitudinally and laterally to each other
(see Figure 3).
In the common " FPP 2 " strategy, two sublayers
are stacked together, creating a sufficient overlap
of the individual patches to enable a force
transmission in the interface of the two sublayers.
As a setback, this lay-up strategy
results
in
layers with double thickness and thus in a rather
coarse distribution of layers within the laminate.
Alternatively, in the so called " FPP 1 " strategy,
the two or more sublayers are distributed over
the thickness of the laminate to achieve the same
stacking sequence like a conventional laminate
(see Figure 4).
An example of a quasi-isotropic lay-up [45/0/45/90]2s,
as investigated in this paper, is depicted in
Figure 5.
The aim of this paper is the investigation of
material equivalency on coupon level for patchbased
laminates compared to conventional ones.
Thus, FPP 1 is chosen for the experimental setup.
Figure 3. Lay-up of patch-based UD-layers.
68 | SAMPE JOURNAL | JULY AUGUST 2022
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SAMPE Journal - July/August 2022

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