Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention concerns a ski staff composed of two or
more fibre courses, the fibres of which have been bonded together
with a hardening compound~
Particularly in competitive skiing the light weight of the ski
staff has an essèntial significance because in the first place
the staff has to be carried in the hand and secondly it has to
be accelerated from ~ero velocity to a considerable velocity.
It is therefore obvious that in the case of the ski staff light
weight is even more significant than in that of the ski, which
glides along the trail most of the distance traversed. It is ; ;~
nowadays possible to make ski staffs which are light in view of
their strength, e.g. of light metal and reinforced plastic, ~ ;
which is most commonly known as a combination of glass fibres ~
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and epoxy or polyester resin. Up to date, however, with fibre~
reinforced staffs no results decisively superior to those
obtained with metal staffs have been achieved because one has
not understood to utilize fully the orientation and arrangement
of the fibres and the possibility of combining different fibre
types. Replacement or admixing of glass fibre with carbon fibre,
` which has greater strength, for instance does not in
itself produce the desired result.
The object of the invention is to accomplish a fibre staff of a
new type which may be made lighter than staffs of prior art
without resulting detriment to strength or rigidity, and wherein
the increase of cost compared with a conventional glass fibxe
staff can be kept within reasonable bounds considering the
~ advantages gained.
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This object is achieved b~ means of the invention mainly in that
one fibre course consists of glass fibres transversal to the staff
and wound around, and another fibre course consists of carbon
fibre longitudinal to the staff or of both carbon and glass
fibres, both courses being bonded to each other.
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As a result o~ the use of light and s-trong carbon fibres the
staff according to the invention will be substantially lighter
than any staff of prior art.
~n essential feature of the invention is howe~er the way in which
the manner of joining according to the invention the carbon fibre
and the glass fibre endows the s~aff with the desired character-
istics. It is well known that carbon fibre has a tensile strength
and a modulus of elasticity considerably higher than the cor-
responding values of glass fibre, and therefore its disposition
as longitudinal fibre already in itself results in a very strong
and rigid staff, and a rigidity equivalent to that of glass
fibre structures is achieved with a far less fibre quantity.
However, the elastic elongation of carbon fibre is low and
therefore the rigid staEf is subject to rupture under a
relatively low bending already unless it is possible to increase
the permissible deflection of the staff in the elastic range by
some new means. An opportunity hereto is indeed aforded by
expedients which aim to influence the oval transformation
tendency of the cross section which is associated with bending.
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Oval transformation taking place too easily leads to buckling of
the staff and to rupture by buckling even before the stress in
the longitudinal reinforcement has reached the permissible limit,
and it follows that counteriaction of the oval transformation
tendency, which is implemented in the present invention by the
aid of transversally wound fibres, is indispensable. But an
i excessively rigid transversal reinforcement leads, expressly in
a staff containing carbon fibres as its longitudinal reinforce-
ment, to an abrupt ruptur~ event without any worthwhile oval
transformation. Therefore carbon fibre, which has a high
modulus of el~sticity, is not appropriate for use as transversal
reinforcement, whereas glass fibre, with its lower modulus of
elasticity is paxticularly well adapted to this purpose especially
in a staff having carbon Fibres as its longitudinal reinforcement.
Glass fibre used as transversal reinforcement permits an oval
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txansformation of the staff in such amount that for the staff
an optimized elastic deflection is obtained without incurring
in the longitudinal carbon fibres a stress which would rise up to
the ultimate stress limit.
The invention is described in the following more closely, with
reference to the attached drawinq, wherein:-
Fig. 1 presents a staff according to a first embodiment of the
invention, in cross section and vertical section,
Fig. 2 presents a staff according to a second embodiment of the
invention, in cross section and vertical section, and
Fig. 3 presents a staff according to a third embodiment of the
invention, in cross section and vertical section.
In the embodiment of Fig. 1 the tubular staff consists of an
inner glass fibre course 1 and an outer carbon fibre course 2. ~-
The staff has been made in that around a so-called core glass
fibre filaments have been wound, either in a uniform fibre layer ~-
or as a helical fibre bundle, ~he interstices being filled with
resin. Generally considered the last-mentioned alternative
implies that, viewed in vertical section, the distribution of the
glass fibres displays concentrations and rarefactions. In the
same manufacturing step, immediately upon the winding of the
glass fibres, follows the drawing of carbon fibres longitudina~ly
to the staff~ This may be done in a way well-known in the art by
pulling carbon fibres, which have been wetted with a hardening
compound, through an annular, compressing nozzle. The carbon
fibres may appropriately be drawn under a pre-stress and in the
next step a tape is wound upon the staff that has been formed,
which tape binds and presses the fibres and resin together until
sufficient hardening has taken place so that the encircling
tape ma~ be removed. The manufacturing may be arranged to take
place in a continuous process, in which case after the tape ~ -~
winding step cross cutting of the tube thus formed to desired
lengths is undertaken, and curing of the resin.
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In the embodiment of Fig. 2 there is innermost a longitudinal
carbon fibre course 2' and upon this a transversal glass fibre
course 1' has been wound. Upon this moreover a longitudinal
glass fibre course 3 has been drawn. By means of the location
and choice of material of the longitudinal fibre layers 2' and 3
an essential addi~ional advantage of the invention is gained
owing to the fact that with the carbon fibres, which have a
higher modulus of elasticity/ substantially closer to the core
of the staff and the lower modulus of elasticity glass fibres
on the surface of the staff, greater uniformity is obtained in
the distribution o~ stresses between the longitudinal fibre
layers 2' and 3.
In the embodiment of Fig. 3 the two innermost layers have been
formed in the same way as the staff of Fig. 1. Additionally, upon
the carbon fibre course 2 another transversal glass fibre course
1" has been wound, and upon this even further one longitudinal
glass fibre layer 3 has been drawn. In this embodiment the
buckling of the carbon fibre course 2 is efficiently prevented
and accordingly its high tensile strength can be efficiently
utilized. Sufficient strength and rigidity of the staff have
been achieved with a comparatively low amount of carbon fibres
and it has been possible to use a relatively large quanti~y of
the less expensive glass fibre. This notwithstanding the staff
is substantially lighter than any staff of prior art having
comparable strength and rigidity characteristics. When the
longitudinal carbon fibre layer 2 is located closer to the
core o~ the staff than the longitudinal glass fibre course 3 a
more uniform distribution of stresses between the longitudinal
fibre layers is achieved in the same manner as in the embodiment
of Fig. 2.
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