JEC COMPOSITES MAGAZINE - Issue #82 - July 2013 - 49

Tab. I: Beam variants tested in study
of applying uncured adhesive to
the beam’s flanges and setting
Part
the closure plate on top, then using Part
material
Name
SPR to mechanically join the parts,
which were then put into a hot-air
DP600 Steel (Baseline)
A
oven programmed to replicate an
5754 Aluminum
automotive BIW E-Coat/KTL
B
(Lightweight Metallic)
process (30 minutes at 180°C),
PA6-GF60 (Thermoplastic
which also cured the adhesive.
C

Composite)

Demonstrator part test development
While researchers had already used a
battery of ASTM- and ISO-type small-scale
laboratory tests to evaluate mechanical
performance of the composite material, they
decided to test steel, aluminium and composite beams side-by-side using custom test
protocols developed by the team to replicate
real-world automotive load cases. The first
was a quasi-static, three-point flexure test
that was similar to the type of loads seen in
an automotive side-impact crash. The test
was designed so the same section geometry
could be used for each beam while allowing
material thickness (Table I) to vary inward
from the fixed outer surface. A cylindrical
roller moving at speeds of 20 millimetres
per minute and with a maximum deflection
of 50mm was used. Researchers tested
two beams of each material and recorded a
variety of data including beam stiffness, load
at ultimate failure, energy-absorption rates
and failure modes.

Thickness (mm) & material
used for top-hat section

Thickness (mm) & material
used for closure plate

1,880

DP600 steel
(1.5)

DP600 steel
(1.5)

1,020

5754 aluminum
(2.5)

5754 aluminum
(2.5)

790

PA6-GF60 (11 Plies)
(3.0)

PA6-GF60 (11 Plies)
(3.0)

modes. As before, two samples were tested
for each type of beam, although one of the
composite beams slipped in the grips and
did not provide usable data.

Results and observations
Figure 2 shows specific (mass-normalised) stiffness and failure energy from
three-point bending tests of demonstrator
beams. All beams failed via progressive
local crushing under the central loading
point of the roller starting at moderately
low loads, which indicates beam stiffness
is a measure of resistance to bending and
local crushing. All three materials provided similar performance in terms of this
mixed-mode, flexure/crush. The composite
beam displayed both high toughness and
stiffness/strength, which led to enhanced
specific-energy absorption over the
metallic benchmark parts. Ductile steel
and aluminium beams displayed characteristic «V» shapes from local crushing, but

composite beams exhibited longitudinal
and transverse cracking from compressive
side-wall loading and tensile loading on the
upper beam surface.
In the dynamic axial crush test, both steel
and aluminium beams exhibited similar
failure modes and characteristic uniform
ductile folding. In contrast, the composite
beams displayed a combined primary
failure mode of progressive crush failure
in the composite with tearing along upper
top-hat radii, leading to formation of
large-scale fronds with some fragmentation, and a secondary failure mode along
the joint between the riv-bonded closure
plate and stamped top-hat section. The
damaged region of all beams was carefully
measured and used to calculate mass of
material destroyed/deformed in each test,
leading to the calculation of specific (massnormalized) energy absorption (SEA)
values for each beam. These SEA values
for each type of beam at both energy levels

Fig. 2: Specific stiffness and failure energy from 3-point bending tests of demonstrator beams

No82 July 2013 /

Feature Automotive

A second, dynamic test protocol (highspeed axial crush) was also developed by
the team – this time to simulate the type
of loads seen in an automotive frontal
crash. An instrumented spring-assist/dropweight tower was used at two different
energy levels: 4 kilojoules (equivalent to
a 133-kilogram impactor moving at ≈ 8
metres/second) and 8 kilojoules (equivalent to a 74-kilogram impactor moving at
14.6 metres/second). Beams were reduced
from 450mm to 375mm to stabilize the
crush column and prevent global buckling,
and failure initiators were cut into the end
of each beam face to ensure stable and
progressive crushing. Equipment measured
the test velocity at point of impact and
dynamic load throughout the event. Highspeed video was used to evaluate failure

Part weight
(g)

jec composites magazine 49
JEC COMPOSITES MAGAZINE - Issue #82 - July 2013

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #82 - July 2013
