Note: Descriptions are shown in the official language in which they were submitted.
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SANDWIC»I ELEMENTS AND THE USE THEREOF
Field of the Invention
The invention relates to sandwich elements with at least one predetermined
breaking-point at which the sandwich element breaks in the event of an impact
and also to their use in the automotive field.
Background of the Invention
Sandwich elements can be employed, for example, in the automotive field as
roof,
bonnet, tailgate, door or floor-panel modules and also as load floors, rear
parcel
shelves or interior-trim components; an advantage in this connection is their
high
flexural rigidity with, at the same time, low area weight in comparison with
structural elements of massive construction. In particular, structural
elements that
extend predominantly in a plane display high rigidity and strength values when
loaded in that plane. However, in many structural elements these high strength
values in the plane are disadvantageous.
For example, in the case of load floors of automobiles it car. happen that the
load
floors do not break in the event of a rear-end crash but pass on the energy of
the
crash to the passenger compartment and the occupants. This entails a high
potential exposure to danger.
The load floors currently on the market are therefore provided, if necessary,
with
notches or slits. Such predetermined breaking-points weaken the load floors in
the
event of an accident. However, at the same time the load floors also always
lose a
large proportion of their flexural rigidity and flexural strength and diminish
the
working load.
Designs with articulations (hinges) in the load floors, at which the load
floor
collapses in the event of a crash, are possible but are technically very
elaborate.
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Split load floors also exist. In this case it is disadvantageous that under
unfavorable loading conditions the entire load rests on only one subsegment.
This
requires an additional high flexural rigidity of the individual segments.
S
Furthermore, by virtue of special structural bearing elements it can be
ensured that
the Ioad floors rotate into a harmless position in the event of an accident.
But such
very elaborate measures cannot be implemented in every vehicle.
I O Summary of the Invention
The present invention therefore provides constructional elements that exhibit,
on
the one hand, a low weight and, on the other hand, a high flexural rigidity
and
flexural strength and that, in addition, in the event of an accident (a
crash., in
particular a rear-end crash) do not transmit the energy of the crash into the
I5 passenger cell and hence endanger the occupants.
This is achieved by the introduction of at least one predetermined breaking-
point
into a sandwich element, whereby in the event of a rear-end collision the
sandwich
element breaks at the predetermined breaking-point, so that the energy of the
crash
20 is not transmitted (reduced strength of the sandwich element in the plane),
whereas the flexural strength and flexural rigidity under working load remain
unchanged.
These and other advantages and benefits of the present invention will be
apparent
2S from the Detailed Description of the Invention herein below.
Detailed Description of the Invention
The present invention will now be described for purposes of illustration and
not
limitation.
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The present invention provides a sandwich element with at least one
predetermined breaking-point, the sandwich element made of
a) a core layer, preferably constructed from at least one ply, and
b) two exterior outer layers firmly connected to the core Layer, which are
preferably each constructed from at least one ply,
c) optionally, one or more adhesive layers disposed between the core layer and
the exterior layers,
wherein at least one delamination means is included in at Least a portion of
the
sandwich element on a first (tension) side of the sandwich element, and
wherein
the delamination means is disposed between the exterior layer located on the
first
(tension) side and the core layer or contained in the outermost third of the
core
layer on the first (tension) side of the sandwich element.
The first (tension) side is that side of the sandwich element that is
subjected to
tensile stresses in the event of a flexural Load.
For the exterior layers in the present invention, use may be made of fibrous
materials that are interspersed with plastics (such as, for example,
polycarbonates,
polyamides, polyurethanes, polyesters, polypropylene, polyethylene, polyvinyl
chloride, polystyrene, polymethyl methacrylate,
acrylonitrile/butadiene/styrene
copolymers and blends thereof, epoxy resins, in particular polyurethane
resin),
such as glass-fiber mats, glass-fiber fleeces, glass-fiber random layers,
glass-fiber
cloth, cut or ground glass fibers and mineral fibers, natural-fiber mats,
natural-
fber knitted fabric, cut natural fibers and also fibrous mats, fibrous fleeces
and
fibrous knitted fabric based on polymer fibers, carbon fibers or aramide
fibers and
also mixtures thereof. Plastics such as, for example, polycarbonates,
polyamides,
polyurethanes, polyesters, polyethers, copolymers, polypropylene,
polyethylene,
polyvitryl chloride, polystyrene, polymethyl methacrylate,
acrylonitrile/butadiene/styrene copolymers and blends thereof can also be
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employed. Furthermore, metal sheets, plastic sheets, wood panels or wood
veneers can be employed. Glass-fiber mats with polyurethane resin applied to
them preferably find application in the present invention.
As a core layer, thermoformable and also thermosetting polyurethane and thermo-
plastic foamed materials, paper honeycombs, metal honeycombs or plastic
honeycombs with honeycomb or corrugated structure may preferably be employed
in the present invention.
As a delamination means, means having a decoupling effect (loosening the
adhesion between exterior Layer and core layer or weakening the core layer on
the
tension side), which are introduced either (a) in situ in the course of
manufacture
of the sandwich elements or (b) subsequently, may preferably be disposed
between the exterior layers and the core layer.
I5
Suitable materials in case (a) include, but are not limited to, paper,
cardboard,
plastic foils and sheets or sheet-metal foils and plates, textile, plastic or
metal foils
provided with adhesive layers on one side, wood panels or wood veneers,
impermeable textiles or naturally or synthetically based woven fabrics as well
as
solid or liquid films acting as separating agents as well as adhesive-free or
coupling-agent-free zones. Where use is made of adhesive layers, an adhesive-
free zone, for example, may act as delamination means. An adhesive-free zone
or
a zone with low adhesion or without adhesion can be produced by a delamination
means which was inserted during the manufacture of the sandwich element being
removed.
Suitable in case (b) are subsequent, mechanical or thermal, locally limited
separation, such as sawing, cutting, splitting or losing, of the core layer
and of the
exterior layer on the tension side, so that a zone without adhesion is formed.
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The decoupling is more preferably obtained by means of delamination means that
are described in case (a).
The sandwich elements according to the present invention may fmd particular
application in the automotive field as roof modules, bonnets, tailgate
modules,
door modules or floor-panel modules, more particularly as load floors, rear
parcel
shelves or interior-trim components.
The flexural strength is the limit of the flexural load, the exceeding of
which
results in failure of the structural element.
The flexural rigidity is the resistance of a structural element to flexure.
The invention will be elucidated in more detail on the basis of the following
Examples.
Examples
In Comparative Example l, a compression test was carried out in the plane of
the
sheet (crash direction) on samples without predetermined breaking-point, and
in
Example 2, on samples with predetermined breaking-points according to the
invention. In Comparative Example 3, the flexural rigidity and flexural
strength
were determined on samples without predetermined breaking-point, and in
Example 4, on samples with predetermined breaking-point according to the
invention. Examples 5 and 6 show, on the basis of compression tests, how the
breaking behavior can be controlled by modification of the type and geometry
of
the predetermined breaking-point according to the invention.
Initial materials:
Polyol 1: polyether polyol with an OH-value of 865, prepared by addition
of propylene oxide onto trimethylolpropane as initiator.
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Polyol 2: polyether polyol with an OH-value of 1000, prepared by
addition of propylene oxide onto trimethylolpropane as initiator.
Polyol 3: polyether polyol with an OH-value of 42, prepared by addition
of 86 % propylene oxide and I4 % ethylene oxide onto
propylene glycol as initiator.
Polyisocya.nate: polymeric MDI with an isocyanate content of 31.5 wt.%
(DESIVIODUR 44V20L, Bayer AG).
Stabilizer: silicone stabilizer POL~'URAX SR242, Osi Crompton Witco
Specialities, Frankfurt.
Catalyst: amine catalyst THANCAT AN10, Air Products GmbH,
Hattingen.
Dyestuff: BAYDUR Schwarzpaste DN, Bayer AG, Leverkusen.
Polyurethane
formulation
1:
Polyol 1 30 parts by
weight
Polyol 2 20 parts by
weight
Polyol 3 33 parts by
weight
catalyst 2.8 parts by
weight
stabilizer 1.3 parts by
weight
acetic acid 0.3 parts by
weight
dyestuff 3.3 parts by
weight
polyisocyanate 140 parts by
weight
The polyol mixture formed from Polyols 1 to 3 has an average OH-value of
568 mg KOH/g.
Comparative Example 1 (compression test on samples without predetermined
breaking-point)
Onto a flat core layer made of a paper honeycomb of corrugated-board type 5/5
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having a thickness of 20 mm and an area weight of 1,600 g/m2 there were placed
on both sides chopped glass-fiber mats having an area weight of 450 g/mZ which
were treated at room temperature by spraying on 450 g/m2 of polyurethane
formulation 1. This sandwich element was introduced into a flat tool heated to
130°C and subsequently press-molded to a thickness of 19.4 mm. After a
pressing-time of 180 sec., the tool was opened and the finished sandwich
element
was taken out. The size of this sandwich element amounted to about 1,000 mm x
1,000 mm.
Three rectangular samples having a size of 400 mm x 180 mm (length x width)
were sawn out of the sandwich element which was produced in this way, the
longer edge of the sample being at right angles to the course of the paper
corrugations of the core layer. These samples were subj ected to pressure
uniaxially over the front faces in a universal tension/compression testing
machine
at a speed of 5 mm/min. The compressive stress consequently acted in the plane
of the sheet in the direction of the longer dimension o.f the sample. The
forces
resulting in failure of the samples amounted to 14,173 N, 14,093 N and 15,928
N
(mean value: 14,731 N).
Example 2 (compression test on samples with predetermined breaking-point)
A delamination means made of an aluminum strip coated with adhesive on one
side, manufactured by Beiersdorf AG, brand TESA, designation TESAMETAL
4500, was applied onto a core layer as described above. The delamination means
was cut to a width of 15 rnm and a length of 1,000 mm. and was stuck onto one
side parallel to the course of the paper corrugations in the middle of the
core layer.
Then there were placed on both sides chopped glass-fiber mats having an area
weight of 450 g/m2 which were treated at room temperature by spraying.on
450 g/m2 of polyurethane formulation 1. This sandwich element was introduced
into a flat tool heated to 130°C and subsequently press-molded to a
thickness of
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1
19.4 mm. After a pressing-time of 180 sec., the tool was opened and the
finished
sandwich element was taken out. The size of this sandwich element amounted to
about 1,000 mm x 1,000 mm. Then three rectangular samples with a size of
400 mm x 180 mm were sawn-out of the sheet, the longer edge of the sample
being at right angles to the course of the paper corrugations of the core
layer. The
samples were sawn out in such a way that the delamination means was located in
the middle of the samples. With the exception of the delamination means, these
samples were produced so as to be identical to those from Comparative Example
1.
The compression testing was effected in a manner analogous to Comparative
Example 1. The forces (breaking-loads) resulting in failure of the samples
amounted to 5,622 N, 5,106 N and 5,777 N (mean value: 5,502 N).
By virtue of the predetermined breaking-point in Example 2, the mean value of
the
breaking-load in comparison with sandwich elements without predetermined
breaking-point (Comparative Example I) was reduced to 37 %.
Comparative Example 3 (flexural test on samples without predetermined
breaking-point)
Five samples each having a length of 240 mm and a width of 60 mm were taken
from the sandwich element described in Comparative Example I . The orientation
of the corrugated honeycomb was at right angles to the length of the sample.
The
flexural test was carned out in accordance with DIN 53293. Effective flexural-
rigidity values of 80.6 x 106 Nmm2, 82.1 x 106 Nmm2, 72.1 x 106 Nmm2, 75.4 x
106 Nmm2 and 77.5 x 106 Nmm2 (mean value: 77.5 x 106 Nmm2) were
ascertained. The forces in the case of failure amounted to 853.6 N, 826.4 N,
828.7 N, 845.4 N and 820.6 N (mean value 834.9 N).
Example 4 (flexural test on samples with predetermined breaking-point)
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Five samples each having a length of 240 mm and a width of 60 mm were taken
from the sandwich element described in Example 2. The orientation of the
corrugated honeycomb was at right angles to the length of the sample, the
delamination means was located in the middle of the sample. The flexural test
was carried out in accordance with DIN 53293. The samples were inserted into.
the testing device in such a way that the delamination means was located on
the
tension side of the samples. Effective flexural-rigidity values of 84.3 x 106
NmmZ, 76.1 x 106 Nmm2, 74.6 x 106 Nmm2, 79.2 x 106 Nmm2 and 72.3 x 106
Nmm2 (mean value: 77.3 x 106 Nmm2) were ascertained. The forces in the case of
failure amounted to 875.2 N, 864.8 N, 872.2 N, 849.1 N and 867.7 N (mean value
865.8 N).
In the case of an arrangement of the delamination means on the first (tension)
side
of the sandwich element, the effective flexural rigidity with and without
delamination means did not change within the limits of the statistical
variation of
the measured values. The forces resulting in failure of the samples in the
case
with delamination means (Example 4) did not lie below the values for the case
without delamination means (Comparative Example 3).
Example 5 (compression test on samples with predetermined breaking-point)
In a manner analogous to Example 2, compression tests were carried out with
the
same delamination means (TESAMETAL 4500), this time cut to a width of
35 mm. The forces (breaking-loads) resulting in failure of the samples
amounted
to 1,838 N, 1,654 N and 1,735 N (mean value 1,742 N).
Example 6 (compression test on samples with predetermined breaking-point)
In a manner analogous to Example 2, compression tests were carried out with
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another delamination means (adhesive tape manufactured by Beiersdorf AG,
brand TESA, designation 4304; strip of paper coated with adhesive on one
side).
The delamination means was cut to a width of 35 mm. The forces (breaking-
loads) resulting in failure of the .samples amounted to x,146 N, 5,374 N and
4,712 N (mean value 5,077 N).
Although the invention has been described in detail in the foregoing for the
purpose
of illustration, it is to be understood that such detail is solely for that
purpose and
that variations can be made therein by those skilled in the art without
departing from
the spirit and scope of the invention except as it may be limited by the
appended
claims.
