JEC COMPOSITES MAGAZINE - Issue #101 - November/December 2015 - 45

beams, shells
or membranes,
where trusses and
membranes have no
bending stiffness.
In a first step, the
shear behaviour is
analyzed using two
picture-frame tests
with a different
fixation for the test
specimens. Afterwards, simulations
of the picture-frame
Fig. 1: Picture-frame tests: pins (left), clamps (right)
tests are performed
in Abaqus/Explicit to compare the different FE models with experimental results of the dry fabric reinforcement for the discrete
approaches and, additionally, at the forming temperature of PA6
for the *Fabric model to show their accuracy. The simulation effort
is also an important selection criterion, especially for larger parts
made of FRTs.
Finally, a sensitivity study of a FE model that was selected beforehand is performed. The study is performed for a double-dome
forming analysis. The double-dome geometry is a deep drawing
part provided by the Ford Motor Company for a forming benchmark [14].

Material characterization
The forming simulation of fibre-reinforced thermoplastics requires
the determination of the material's behaviour at the forming temperature of the thermoplastic matrix.
In this work, the shear behaviour of fibre-reinforced thermoplas(a)

tics and dry fabrics is tested with different picture-frame tests.
The investigated material is a glass fibre-reinforced polyamide 6
(PA6) with one or three layers of twill fabric and dry twill fabric,
respectively.
Picture-frame test
Figure 1 shows the picture-frame test devices. The frame on the
left side has pins to hold the specimen during the test procedure;
the other frame has clamps to fasten the whole border area of the
sheets. The latter is integrated into a thermal chamber to perform
shear tests above the melting temperature of the thermoplastic for
impregnated sheets. The dry fabrics were tested with both frames.
Figure 2a and 2b show the results of the picture-frame test with
clamps for the reinforced PA6 with one (Figure 2a) and three
(Figure 2b) fabric layers. The sheets made of glass and PA6 are
tested at 260°C, the melting temperature of PA6 is about 230°C.
The results show that there is a significant difference in tensile
forces between three specimens for each test. Furthermore, the
highest tensile force identified for specimens with one fabric
layer is equal to the lowest tensile force identified for specimens
with three fabric layers. One would expect that three fabric layers would need about three times as much shear force.
The picture-frame test with clamps and glass/PA6 is not
reproducible for the tested amount of specimens. One reason
could be a variation in the fibre angles of the sheets due to the
manufacturing process of these semi-finished parts. The angles
between the fibres in the warp and weft direction should be
90° and they should be parallel to the clamps of the frame. FE
simulations of the picture-frame test show that a rotation of the
fibres of about 0.5° doubles the tensile forces of the pictureframe test (Figure 2c).
(b)

Fig. 2: Picture-frame test: glass/PA6, 3
layers (a), Picture-frame test: glass/PA6,
1 layer (b), Simulation of picture-frame
test, rotation of fibres (c), Picture-frame
test: dry fabric (d), Picture-frame test:
experimental results for validation of FE
models (e)

(c)

(d)

No101 November - December 2015 /

(e)

jec composites magazine 45

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #101 - November/December 2015