(57) The invention relates to combinations of filaments having substantially different
damping responses to mechanical vibrations in a matrix, the filaments having good
damping properties being present in an amount of about 30 to 50% by volume of the
total quantity of filaments. The filaments having high damping properties are in particular
filaments made of polyethylene of ultrahigh molecular weight and the filaments having
low damping properties are glass fibers or carbon fibers. The composite articles
produced from the filaments, which are embedded in a matrix, in particular a matrix
made of epoxy resin, are preferably suitable for producing skis, hockey sticks, tennis
rackets, robot arms, machine housings, angling rods, competition bows or the like.
[0001] The present invention relates to a combination of filaments having substantially
different damping responses to mechanical vibrations in a matrix.
[0002] With many structural parts incorporating composite materials which are reinforced
with fibers or filaments, the situations under load incured cause incidental vi brations
or oscillations of high frequency. These vibrations or oscillations are generally
undesirable, since they lead to premature fatiguing of the material or have an adverse
effect on the performance characteristics of the structure. There are existing composite
materials composed of graphite, glass and Kevlar fibers and filaments embedded in
a matrix in order to have a positive effect on the damping properties of structural
parts. Nonetheless, structural parts which are produced in this known manner are subject
to undesirable vibrations or oscillations. In addition, composite materials based
on graphite, glass and Kevlar fibers or filaments are expensive.
[0003] It is an object of the present invention to provide a composite material of high
strength combined, at the same time, with good internal damping.
[0004] This object is achieved according to the invention by combinations of filaments
having substantially different damping responses to mechanical vibrations, preferably
filaments having high internal damping and consisting of highly drawn filaments of
polymers having ultrahigh molecular weight and high tensile strengths and also moduli
and filaments of low internal damping, for example glass fibers or carbon fibers,
being embedded in a matrix made preferably of epoxy resin. Other suitable materials
for the matrix are unsaturated polyester, polyethylene, vinyl or thermoplastics.
[0005] The filaments of high internal damping have preferably been produced by the gel
process with subsequent drawing to high draw ratios. In a preferred embodiment, the
filaments of high internal damping consist of polymers having an ultrahigh molecular
weight of more than 600,000 g/mol (weight average of molecular weight), in particular
polyolefins.
[0006] Replacing a portion of the filaments of low internal damping with filaments of high
internal damping and made in particular of a polyethylene of ultrahigh molecular weight
gives a hybrid structure which, depending on the proportion of filaments of high
internal damping, is adaptable to the purposes required. Preferably, the filaments
of high internal damping are present in a proportion from 30 to 50% by volume of the
total quantity of filaments in the composite material or combination.
[0007] A gel process whereby the filaments of high internal damping are preferably produced
is described for example in GB-A-2,042,414 and -2,051,667 and also in DE Offenlegungsschrift
3,724,434 and comprises essentially dissolving the particular polymer used for filament
production in a solvent, molding the solution at a temperature above the dissolving
temperature of the polymer into a filament, cooling the filament, for gelling, down
to a temperature below the dissolving temperature and drawing the filament with solvent
removal. The polymer used for producing the filaments of high internal damping can
be of any desired type, for example polyolefins, polyesters, polyamides, as also polyacrylonitrile,
polyvinyl alcohol, polyvinyl chloride etc.
[0008] Preferably, the filaments of high internal damping consist of polymers of ultrahigh
molecular weight, in particular polyolefins, particular preference being given to
polyethylenes, in particular linear polyethylenes. These polyethylenes may contain
minor amounts, preferably not more than 5 mol-%, of one or more other alkenes copolymerizable
therewith, such as propylene, butylene, pentene, hexene, 4-methylpentene, octene etc.
and have 1 to 10, in particular 2 to 6, methyl or ethyl groups per 1,000 carbon atoms.
It is also possible to use other polyolefins, for example polypropylene homopolymers
and copolymers. Furthermore, the polyolefins used may also contain minor amounts of
one or more other polymers, in particular alkene-1 polymers.
[0009] Preferably, the filaments of high internal damping have an oscillation damping factor
of more than 20 . 10⁻³. Filaments made of polyethylene of ultrahigh molecular weight
have an internal damping factor of more than 100 . 10⁻³.
[0010] The filaments of high internal damping and of low internal damping are preferably
embedded in a plastic matrix, made in particular of epoxy resin, polyester, polyethylene
or the like. In a preferred embodiment, the filaments of low internal damping are
arranged around the filaments of high internal damping.
[0011] The combination of fibers of high internal damping and fibers of low internal damping
in a matrix improves the dynamic behavior of the composition as a consequence of the
high damping capacity of the filaments, made for example of polyethylene of ultrahigh
molecular weight, and as a consequence of the high energy absorption by the filament/matrix
interface, in particular if the filaments consist of a polyethylene of ultrahigh molecular
weight and matrix of epoxy resin. The composite materials made of filaments of high
internal damping, filaments of low internal damping and a matrix in which the filaments
are embedded are preferably suitable for producing skis, hockey sticks, tennis rackets,
arms for industrial robots, machine housings, angling rods, competition bows or the
like. In the composite material the polyethylene filaments of ultrahigh molecular
weight are preferably covered with glass fibers. In the event of oscillations this
prevents the polyethylene fibers from emerging and projecting out of the matrix. Moreover,
the composite article can be covered with a nonwoven to produce a smooth surface.
Examples:
[0012]
1. A vibration test (RES ME 87 0037 MT-AC) at frequencies from 100 to 310 Hz revealed
the following damping factors for fibers embedded in an epoxy matrix:
Carbon fibers in epoxy matrix: damping factor
3 . 10⁻³
Glass fibers in epoxy matrix: damping factor
6 . 10⁻³
Kevlar fibers in epoxy matrix: damping factor
10 . 10⁻³
Fibers made of PE of ultrahigh molecular weight in epoxy matrix: damping factor
20 . 10⁻³
2. Torsion damping test (RVD no. 00 00 33).
The test specimens were hybrid structures composed of glass fibers and fibers made
of PE of ultrahigh molecular weight in an epoxy matrix and composed of glass fibers
in a epoxy matrix.
[0013]
Temperature T (°C) |
Proportion of glass fibers |
Proportion of PE fibers |
tan |
0° |
76% |
0% |
0.9 x 10⁻² |
35% |
41% |
2.8 x 10⁻² |
20° |
76% |
0% |
1.2 x 10⁻² |
35% |
41% |
4.0 x 10⁻² |
40° |
76% |
0% |
2.4 x 10⁻² |
35% |
41% |
5.8 x 10⁻² |
[0014] It has been found that the damping of the hybrid structure is 2.5 to 3 times better
than the internal damping of glass fibers in an epoxy matrix.
1. A combination of filaments having substantially different damping responses to
mechanical vibrations in a matrix.
2. A combination as claimed in claim 1, wherein the filaments are present in the form
of yarns, fabrics, blends and/or nonwovens.
3. A combination as claimed in claim 1 or 2, wherein the bulk of the filaments consists
of filaments of low internal damping.
4. A combination as claimed in any one of claims 1 to 3, wherein the filaments of
high internal damping account for 30 to 50% by volume of the total quantity of filaments.
5. A combination as claimed in any one of claims 1 to 4, wherein the filaments of
high internal damping consist of highly drawn filaments of polymers having a high
molecular weight and high tensile strengths and also moduli.
6. A combination as claimed in claim 5, wherein the filaments have been produced by
the gel process and subsequent drawing to high draw ratios.
7. A combination as claimed in any one of claims 1 to 6, wherein the filaments of
high internal damping consist of polymers having an ultrahigh molecular weight of
more than 600,000 g/mol (weight average of molecular weight), in particular polyolefins.
8. A combination as claimed in any one of claims 1 to 7, wherein the filaments of
low internal damping are glass fibers or carbon fibers and have an internal damping
factor of less than 10 . 10⁻³.
9. A combination as claimed in any one of claims 1 to 8, wherein the matrix in which
the filaments are embedded comprises a plastics material.
10. A combination as claimed in claim 9, wherein the plastics material is polyester,
epoxy, polyethylene or the like.
11. A combination as claimed in any one of claims 1 to 10, wherein the filaments of
low internal damping are arranged around the filaments of high internal damping.
12. Use of a combination as claimed in any one of claims 1 to 11 for producing composite
materials for skis, hockey sticks, tennis rackets, robot arms, machine housings,
angling rods, competition bows or the like.