Note: Descriptions are shown in the official language in which they were submitted.
CA 022~860 1998-11-23
TUBULARELEMENTSINCOMPOSITEMATERIALSOBTAINEDBYWINDING
ANUNBALANCED-WEAVEFABRICONACOMPRESSIBLEMANDREL
Numerous structural elements, in particular piles, posts
or masts, are made from steel and, as a consequence, suffer
from disadvantages such as:
a) their significant weight and, in certain cases, the
resultant problems in placing them;
b) their tendency to corrode due to the effects of air,
water or the soil.
c) the cost of their maintenance.
In an attempt to overcome these disadvantages, such
structural elements have been made from aluminium or
composite materials. Regarding such structural elements in
composite materials, the technique that is generally employed
consists in winding filaments of rovings.
Structural elements such as piles, posts or masts should
not only have good breaking strength characteristics but also
be highly rigid when subject to movements which tend to bend
them. To achieve this, it is necessarily for the composite
structure to take full advantage, firstly, of the tensile
breaking and compressional strength of the fibers and,
secondly, of the flexural modulus of the reinforcing fibers.
Thus, the major portion of the latter should be placed along
the axis of the pile, post or mast.
According to the invention, elongated structures such as
piles, posts, masts, beams, are produced by winding,
preferably helically, thermosetting-resin-impregnated glass
fabric impregnated with a a heat-setting resin such as an
epoxy, polyester, or vinyl ester resin.
According to the invention, these fabrics have an
unbalanced weave, in other words have a higher percentage of
filaments in the fill or woof than in the warp. Additionally,
their weave makes angular deformability possible thereby
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CA 022~860 1998-11-23
making it possible, according to the invention, to place the
fill or woof filaments parallel to the X- X~ axis of the
structure.
The originality of the design of these high bending-
strength composite tubes of the invention will become clearfrom the description and corresponding technical
justification.
According to the invention, a tube is produced by
helically winding a glass fabric in which the ratio warp/woof
is unbalanced, with c>t, where c is the percentage of the
fiber placed in the warp and t is the percentage of fiber
placed in the woof. The preferred values are between 10 and
25~ for c and between 90 and 75~ for t; this figure for
modularity makes it possible, as a function of
diameter/thickness ratio, to ensure good resistance against
radial buckling.
According to the invention, the tube is built up from
successive layers provided by forward and return helical
winding. On the forward runs, helical winding is done at an
angle of B1 = (90 ~ - a) with respect to the longitudinal
axis and on the return run with an angle of B2 = (90~ + a) .
According to the invention, helical winding is preferably
carried out while giving the fabric an oblique slope of angle
a (see FIG 1) so that the fill or woof 1 is parallel to the
longitudinal axis of the tube, the warp 2 having an angle a
with respect to the circumferential plane 3; this arrangement
improves flexural modulus.
According to the invention, each layer is wound
preferably by partially overlapping (see 6) successive turns
4, 5 (see FIG 2). To avoid local excess thickness the width
of offset 1 between two successive turns is such that
L
~ = _
n
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CA 022~860 1998-11-23
where L is the width of the layer and n is an integer >
1.
Without departing from the invention, helically winding
is performed either with individual widths abuting as
indicated by reference 7 in FIG 3, or with alternating
individual widths (see FIG 4). The individual widths 8 and 9
are placed during the first outward run. The individual
widths 10 and 11 are placed during the first return run; the
widths 12 and 13 during the second outward run. This latter
type of winding improves resistance to inter-layer shear
stress.
According to the invention, where winding is done with
the turns abuting, the successive layers are preferably
offset in order to decrease the effect of discontinuity
brought about by the individual widths. For example, in the
case of a helical winding with abuting individual widths of
width L and a number of layers q, the position of each layer
(outward + return run) is offset by a space of width K such
that
K = _
m
where m is an integer > 1 and if possible with
m
r being an integer (see FIG 5).
The individual widths 14 ,15, 16 are the widths for the
first outward run and the individual widths 17,18 and 19 are
the widths for the second outward run.
Even though the preferred fabric is a glass fabric it is
possible, without a departing from the scope of the
invention, to employ fabrics in carbon, aramide, or high
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CA 022~860 1998-11-23
strength polyethylene. It is also possible to employ hybrid
fabrics, for example glass plus carbon.
Without departing from the invention, the fabrics can be
pre-impregnated with heat-setting resin.
Without departing from the invention, the fabrics
employed can be pre-impregnated with thermoplastic resin.
Without departing from the invention, the fabrics can be
wound at the same time as a thermoplastic film and
impregnated by melting plus compression.
Where it is desired to produce structural elements such
as piles, posts or masts which are of considerable thickness,
including cylindrical portions and having an unbalanced fiber
reinforcement along the X-X~ axis of the structural element,
the presence of significant forces tending to clamp the
composite structure against the mandrel, after
polymerization, has been observed; this phenomenon can make
it difficult to remove the element from the mandrel and can
create micro-cracking in the structure.
In order to avoid these major disadvantages, according to
the invention, a smooth layer of a compressible material is
placed on the mandrel after which the glass fabric is wound
onto this compressible mandrel.
According to the invention, the characteristics of
compressability of the material will be such that it only
shows a slight deformability under the limited force of
winding the fabric and it will absorb the contraction of the
composite structure and only transmit a slight clamping force
to the mandrel, thereby facilitating removal therefrom. The
material chosen should have a low coefficient of friction.
According to the invention, the material is preferably a
closed-cell polyethylene foam with a smooth polished skin.
Without departing from the invention, another material
having the above characteristics can be used, for example a
flexible polyurethane foam.
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CA 022~860 1998-11-23
According to the invention, in order to facilitate
removal from the mandrel and preserve the internal surface
state of the tube, the foam should be coated with a terpane
film.
In the presence of flexural forces operating in a
priviledged radial direction, oblong-shaped tubes are
provided (see FIG 6). This type of tube can for example be
employed in the construction of breakwaters.
Without departing from the invention, the tube can have a
sandwich structure (see FIG 7) constituted by two concentric
tubes 20, 21 obtained by means of the invention and separated
by a wall 22 in a material which is rigid in compression such
as a rigid foam, a honeycomb structure, balsa, and so on.
This makes it possible to make the tubes lighter and improves
rigidity.
Without departing from the invention, in order to improve
rigidity in the presence of bending forces acting along a
preferred axis, the inner tube can be cylindrical and the
outer tube oblong.
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