U.S. patent application number 10/472931 was filed with the patent office on 2004-05-20 for metal-composite laminates and a method for fabricating same.
Invention is credited to Hansson, Jan.
Application Number | 20040096674 10/472931 |
Document ID | / |
Family ID | 20283596 |
Filed Date | 2004-05-20 |
United States Patent
Application |
20040096674 |
Kind Code |
A1 |
Hansson, Jan |
May 20, 2004 |
Metal-composite laminates and a method for fabricating same
Abstract
This invention concerns a method for reducing the weight of
metal-composite laminates that consist of two or more metal foil
layers (1) and the polymeric binder layers (2) that hold these
metal foil layers together and contain fiber reinforcement (3)
designed in view of the intended area of application for the
product. The desired weight reduction is achieved according to the
invention in that at least parts of the fiber reinforcement (3) are
made from hollow fibers, i.e. consist of tubular fibers, each of
which contains at least one longitudinal internal hollow channel.
The invention also includes products fabricated in accordance with
said method.
Inventors: |
Hansson, Jan; (Linkoping,
SE) |
Correspondence
Address: |
SWIDLER BERLIN SHEREFF FRIEDMAN, LLP
3000 K STREET, NW
BOX IP
WASHINGTON
DC
20007
US
|
Family ID: |
20283596 |
Appl. No.: |
10/472931 |
Filed: |
September 26, 2003 |
PCT Filed: |
March 15, 2002 |
PCT NO: |
PCT/SE02/00496 |
Current U.S.
Class: |
428/457 ;
428/292.1 |
Current CPC
Class: |
B32B 27/38 20130101;
B32B 2363/00 20130101; Y10T 428/249924 20150401; B32B 15/01
20130101; B32B 15/08 20130101; B32B 2305/08 20130101; B32B 2311/00
20130101; B32B 2250/40 20130101; Y10T 428/31678 20150401; B32B 7/12
20130101; B32B 3/20 20130101 |
Class at
Publication: |
428/457 ;
428/292.1 |
International
Class: |
D04H 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 30, 2001 |
SE |
0101129-5 |
Claims
1. A method for reducing the weight of metal-composite laminates
that consist of two or more metal foil layers (1) and the polymeric
binder layers (2) that hold the metal foil layers together and
contain fiber reinforcement (3) designed in view of the intended
area of application for the product, characterized in that a fiber
material that consists at least in part of hollow fibers, i.e.
consists of tubular fibers, each of which contains at least one
longitudinal internal hollow channel, is chosen for making the
fiber reinforcements (3).
2. A metal-composite laminate of the type that contains at least
two metal layers (1) joined by means of fiber-reinforced polymeric
binder layers (2), characterized in that the binder-reinforcing
fiber material (3) consists at least in part of a hollow fiber
material, which means that each fiber has a tubular shape and
exhibits at least one throughpassing channel or opening extending
in its longitudinal direction.
3. A metal-composite laminate according to claim 2, characterized
in that the metal foil layers (1) included therein have a thickness
within the range from 0.1 to .ltoreq.1 mm, while each respective
polymeric layer (2), including the fiber reinforcement (3)
contained therein, has a thickness that never attains the thickness
of its respective adjacent metal layer (1).
4. A metal composite laminate according to claim 2 or 3,
characterized in that the reinforcement fibers (3) contains therein
consist at least in part of tubular carbon fibers.
5. A metal-composite laminate according to either of claims 2 or 4,
characterized in that the reinforcement fibers (3) contains therein
consist at least in part of tubular E- or S-glass fibers.
Description
[0001] This invention concerns a method for fabricating
fiber-reinforced metal-polymer laminates, referred to hereinafter
as metal-composite laminates, that exhibit an extremely
advantageous relationship between mechanical properties and
specific gravity. The invention also includes the laminates
fabricated in accordance with said method.
[0002] Laminates consisting of two or more metal layers or foils
joined by means of a composite layer in the form of a polymerized
binder and various types of fiber reinforcement have been tested in
many contexts where a need has been found to improve the fatigue
strength of the metallic base material. The strengths and weakness
of the metallic base material and the fiber-reinforced composites
offset one another. Metallic materials are weak at geometric
notches (stress concentrations) in connection with fluctuating
loads, while this is the strength of the composite; the composite
is conversely sensitive to geometric notches under static loads as
a result of its brittleness, while the metal is capable of plastic
deformation.
[0003] Reinforcements for metallic material structures that have
sustained cracking in service have consequently, to some extent,
already been subject to repair by, e.g. adhesively applying a
composite patch, since the composite is insensitive to fluctuating
loads and will thus relieve the area and prevent the cracking from
extending further.
[0004] By combining the positive properties of the metal and the
composite, it has been possible to produce metal-composite
laminates that have begun to be used to an ever-increasing extent
in aviation and aerospace technology, where they have been
replacing more and more metal structures for a number of years,
since these laminates can provide products with better strength
properties at lower weight, even though they also entail a higher
price. These laminates generally consist of two, three or more
metal layers held together by polymeric binder layers, which are
usually reinforced with some type of fiber material such as glass,
aramid or carbon fiber. Various types of polymers have been used as
binders for this purpose; thermoplastics may have dominated
initially, but today different types of epoxides are generally more
prevalent.
[0005] One such metal-composite laminate that is commonly used in
the aviation industry is known as GLARE.RTM., which refers
primarily to thin aluminum plates and fiberglass prepreg, thus
providing a material that performs well under repeated stresses,
and in which cracks grow slowly.
[0006] Because it has proven possible to produce metal-composite
laminates with such advantageous properties, a great deal of work
has been done in recent years to further improve these materials.
As a result, there is a fairly large number of patents in this
field.
[0007] For example, EP 001 3146 describes a metal-composite
laminate consisting of two thin metal surface layers joined by
means of an adhesive layer of thermoplastic, wherein the adhesive
layer may also contain filler material such as glass fiber.
However, this laminate, which is described as being intended
primarily for making different types of panels for the automotive
industry, is unsuitable for use at high temperature, since the
adhesive consists of a thermoplastic; the glass fiber added to the
adhesive layer is at the same time assumed to consist of short,
unattached fibers so as to yield a material that is sufficiently
deformable for the intended purpose, but these fibers fail, because
of their short common length, to give the laminate the improved
properties that would be desirable for many other applications.
[0008] DE 2,642,882 describes an armor material consist of at least
one steel plate coated with multiple layers of a /sic/thermoplastic
polyamide and aramid fibers.
[0009] U.S. Pat. No. 4,035,694 concerns an electrically conductive
metal layer coated with polymeric binder and a non-woven material
containing aromatic polyamide fibers, among others. However, this
laminate is intended for use in making printed circuits, and was
never intended to absorb heavy mechanical loads.
[0010] GB 1,303,301 describes a metal-composite material consisting
of multiple metal layers joined together by means of
fiber-reinforced plastic material, where the fiber material is said
to potentially consist of carbon and/or glass fibers. Major
emphasis is placed in this patent on how the fibers are oriented,
and the patent thus also includes a description of a device for
stretching the fibers in each particular direction.
[0011] Finally, U.S. Pat. No. 3,321,019 describes a helicopter
rotor propeller that is partly reinforced with aluminum plates and
fiberglass fabric. The patent thus does not actually describe a
generally applicable material, but rather a specific product.
[0012] U.S. Pat. No. 4,489,123 also describes a metal-composite
laminate of thin aluminum layers and a composite layer containing
continuous fibers of aramid or carbon fibers, plus a polymeric
thermoplastic binder. The aluminum layer incorporated in the
laminate is said to measure from 0.1 to less than 1 mm in
thickness, while the fiber material according to claim 1 must
consist of an aromatic polyamide fiber containing
poly-paraphenylene terephthalamide yarn in long lengths and with a
stiffness of 50,000-250,000 Mpa. These broad limits with respect to
fiber rigidity naturally raise certain questions as to what is
actually intended, and whether any aramid fibers exist that cover
this entire range. On the other band, claim 15 cites limits of
100,000 to 150,000, which indicates that carbon fiber is intended.
Carbon fiber is also cited in the abstract on page 1 of the patent,
but not in the claims. (E-glass with ca. 70,000 Mpa and S-glass
with ca. 85,000 Mpa would thus fall within the limits set forth in
claim 1, assuming that the chemical definition in claim 1 could be
considered to include these products). The most specific attribute
of the laminate defined in this patent otherwise appears to be that
the metal layers incorporated in the laminate would, in a
completely unloaded laminate, be subjected to a certain compressive
force, while the polymeric layer would simultaneously be subjected
to a tensile or ductile load.
[0013] U.S. Pat. No. 4,500,589 describes the same product as U.S.
Pat. No. 4,489,123, with the difference that, from the same
starting materials, a product is produced that is free of the
intrinsic prestresses that characterize the product according to
U.S. Pat. No. 4,500,589.
[0014] U.S. Pat. No. 5,039,671 further describes a variant of
essentially the same product as the two products described above,
but with the difference that the fiber material in the laminate is
replaced with so-called S-glass, whose modulus of elasticity is
given to be 80,000-100,000 Mpa, and whose elongation at break is
4-6%. According to the patent, the S-glass fiber gives much better
"blunt notch strength", which refers to the static strength of the
material with a geometric notch such as, e.g. a hole.
[0015] A great deal has thus been accomplished in the field of
metal-composite laminates, and the material types each have their
familiar areas of application within which their higher price in
comparison with pure metals is clearly justified.
[0016] However, demands in terms of performance are constantly
increasing in the field of aviation and aerospace, insofar as
purely physical aircraft performance is advancing in the military
sphere, while the civilian sphere is concerned mainly with the need
to improve product profitability. Because the heaviest costs in
civil aviation are fuel costs, the aim there is to reduce the costs
per air kilometer and kilogram. For this reason, efforts are
continuously underway to produce aircraft materials that are
lighter but do not diminish performance, while at the same time
avoiding increases in material costs beyond acceptable levels.
[0017] We have now found that, simply by making small changes in
the essentially well established current technology, it is possible
to produce metal-composite laminates that have essentially the same
strength and other mechanical properties as current products, but
are 5% or more lighter. Given that, as noted above, fuel costs
comprise the largest single operating cost in civil aviation, a
weight reduction of 5% in, e.g. the fuselage panels offers clear
advantages, since each kilo of weight saved in the airplane itself
can be replaced with an equal weight of paying cargo.
[0018] The basic idea behind the invention is that at least a part
of the fiber material used to reinforce the metal composite must
consist of hollow fiber, which refers here to a fiber material in
which each fiber exhibits one or more longitudinal and
throughpassing channels, i.e. each fiber has a tubular shape. On
the other hand, the chemical composition of the hollow fiber is not
critical to the invention per se. The base material in the hollow
fiber can thus consist of any of the previously known types of
fiber materials used for corresponding purposes, but it could also
consist of an entirely new type of fiber material that is currently
unknown, subject however to the condition that it meets the
necessary requirements in terms of stiffness and breaking strength,
and exhibits satisfactory adhesion to relevant binders.
[0019] Replacing the previously used homogenous fiber material with
hollow fiber material yields a weight savings equivalent to the
volume of fiber material that, in the hollow fiber, consists of the
longitudinal channels in the fiber, while the advantages of the
tubular shape over homogenous rods in terms of flexural rigidity,
etc. are at the same time fully realized.
[0020] One advantage in this context is that certain hollow fiber
materials that could be used when the invention is put into
practical use are already available on the market, and most of
these existing hollow fiber materials have not currently found any
major uses other than in certain special applications. The hollow
fiber materials that have found the largest market today are of the
textile types used as thermal insulation in sleeping bags and
thermal garments. Certain hollow polymeric fibers are used
commercially to separate gases by exploiting osmotic pressure
differences. Hollow carbon fibers have also been produced
experimentally for the purpose of increasing the pressure
resistance of products made from them, but hollow carbon fibers do
not appear to have found any broader applications. Hollow S-glass
fiber is also commercially available under the name HOLLEX.RTM.,
but this fiber, which has good dielectric properties, is currently
used mainly in the construction of radomes.
[0021] As noted above, the hollow fibers that characterize the
invention can be made from a number of different base materials
that are used for similar purposes in the form of homogenous
fibers, while all the previous binders that could conceivably have
been used to produce composites can, at the same time, also be used
in realizing the invention. However, in the preponderance of cases,
binders of the epoxy type would be preferable over, e.g.
thermoplastics, just as fiber reinforcements consisting at least in
part of glass fiber may be expected to yield the highest quality
metal-composite laminates.
[0022] Just as the choice of chemical composition for the fiber
material and the binder component may be made freely, so too is the
type of metal foils used in the finished product also not critical.
However, since the invention mainly concerns, in terms of its
result, a method for reducing the weight of the final product, we
may well expect that aluminum, aluminum alloys and titanium or
titanium alloys will predominate as the most suitable metal foil
materials. It may also be worth noting in this context that
finished products fabricated according to the invention will,
despite multiple layers of both metal and composite, often be of a
thickness that falls within the range of from less than 1 mm to 2-3
mm. As is the case with other similar materials, the composite
layers, i.e. the binder plus the fiber reinforcement, are generally
thinner than the metal foils.
[0023] The invention is illustrated in a purely general way in the
accompanying FIGURE, which shows an oblique projection of a piece
of material fabricated according to the invention, and is defined
in the subsequent claims.
[0024] In the laminate shown in the FIG. 1 designates the metal
foil layers, 2 the binders and 3 the reinforcements in the form of
hollow fiber material, which can be arranged in a manner that is
known per se in the form of a fabric, or as endless fiber loops
that are stretched randomly or in extremely well-ordered,
predetermined courses.
* * * * *