PART FOR PROTECTING THE LEADING EDGE OF A BLADE
The invention relates to a protection part used, for
example, for protecting the leading edge of a blade in a
turbomachine, a propeller blade, or a helicopter blade.
In the field of aviation, and more particularly in
the field of aircraft turbojets, reducing the weight of
the component parts of the turbojet is a perpetual
preoccupation.
Thus, blades have been developed for turbojet fans
or stators that are made of an organic-matrix composite
material (e.g. based on cyanate-ester, bismaleimide, or
epoxy resin), such that the blades are lighter in weight
than metal blades.
Nevertheless, the leading edges of such blades need
to be protected against erosion and possible impacts by
means of a protection part fitted to the leading edge.
Until now, such protection parts have been made of
titanium alloy of the TA6V type. That solution is
technically viable, since the alloy presents good
resistance to erosion and to impacts. Nevertheless, it
is found that the weight of such protection parts is
excessive.
An object of the invention is to propose protection
parts of lighter weight than prior art parts made of
titanium alloy, and that are strong enough to perform
their protection function.
To achieve this object, the invention provides a
protection part presenting an outer protection face and
characterized in that said outer face is made of an
aluminum alloy reinforced by particles of SiC, the SiC
particle content in said alloy lying in the range 15% to
40% by weight, and advantageously 15% to 30% by weight.
The density of SiC-reinforced aluminum alloys is
about 40% less than that of the titanium alloys that are
generally used. This results in a significant saving in
weight, and makes it possible amongst other things to
limit the stresses due to centrifugal forces acting on
the hubs of the blade-carrier disk. That makes it
possible to design disks that do not need to be so strong
and that are therefore lighter in weight, thereby further
reducing the weight of the turbojet.
The SiC particles serve to improve the strength of
the aluminum. At below 15% SiC, this strength is not
sufficient. Above 40% SiC, the alloy is too difficult to
form. Advantageously, the SiC content remains below 30%
in order to facilitate forming.
In a particular embodiment of the invention, the
part comprises at least two layers including an outer
layer and an inner layer, the outer layer being made of
said reinforced aluminum alloy and the inner layer being
made of an aluminum alloy that is optionally reinforced
with SiC particles, the content of SiC particles within
the layers increasing on going from the inner layer
towards the outer layer. Thus, mechanical strength
increases going from the inside towards the outside of
the part.
Using an aluminum alloy that is reinforced little or
not at all for the inner layer makes it easier to secure
said layer to the blade. This is particularly true when
the blade is made of organic-matrix composite material
(as opposed to metal-matrix composite material) and the
protection part is bonded thereto by adhesive. In
practice, in order to secure the protection part of the
invention, it is possible to use the same adhesives and
adhesive techniques that are already used for securing
protection parts made of TA6V titanium alloy. There is
therefore no need to develop adhesives that are specific
for the part of the invention.
The protection part of the invention has been
developed more particularly for fitting to a blade made
of composite material, and in particular an organicmatrix
composite material. Nevertheless, it could also
be fitted to a blade made of some other type of material.
The invention and its advantages can be better
understood on reading the following detailed description
which refers to the accompanying sheet of figures, in
which:
• Figure 1 is a perspective view of a blade showing
its cross-section, the blade having a protection part of
the invention fitted to its leading edge; and
• Figure 2 is a detail view on a larger scale of the
cross-section of the Figure 1 blade.
Figures 1 and 2 show the airfoil portion of a
turbomachine blade 1. The leading edge la of the blade 1
is covered by a protection part 3 of the invention.
The protection part 3 is substantially U-shaped in
section, enabling it to be placed astride the leading
edge la of the blade 1. The part 3 is made up of two
layers, an inner layer 5 and an outer layer 7. The outer
layer 7 is of aluminum alloy reinforced with particles of
SiC, while the inner layer 5 is made of the same aluminum
alloy, but is not reinforced with SiC. Preferably, for
aviation applications, an aluminum alloy of the 7000
series is selected.
Naturally, the protection part may have more than
two layers, with the content of SiC particles in each
layer increasing going from the inside towards the
outside. Thus, in an embodiment not shown, the
protection part is made of four layers Cl, C2, C3, and C4
with the SiC content in the inner layer Cl being zero,
about 10% by weight in C2, about 20% in C3, and about 30%
in the outer layer C4.
In order to assemble the layers of the protection
part to one another, various techniques can be used.
Advantageously, use is made of co-extrusion or of
roll-bonding, which two techniques work well with
aluminum alloys, whether or not they are reinforced with
SiC.
Co-extrusion consists in causing a bar of nonreinforced
aluminum alloy surrounded by a sleeve of SiCreinforced
aluminum alloy to pass through a die (a
reduction cone). The compression forces and the heating
generated by friction between the two materials at their
interface, ensure that the two materials become
intimately bonded. This produces a bar with a core of
non-reinforced aluminum alloy and a covering of SiCreinforced
aluminum alloy. The bar obtained in this way
can subsequently be formed, e.g. by stamping.
Roll-bonding consists in pressing together a
plurality of aluminum alloy plates either hot or cold in
order to bond them to one another. In order to obtain a
protection part 3 as shown in Figure 1 having two layers
5 and 7, an SiC-reinforced aluminum alloy plate is
pressed against a plate of non-reinforced aluminum alloy.
As a general rule, two cylindrical rollers are used with
the plates being cause to pass between them. Thereafter,
the final plate is formed (to take up a U-shape), e.g. by
forging or by stamping.
Once the protection part 3 has been formed, it is
bonded to the leading edge la of the blade 1.
In order to make said sleeve or said plate of SiCreinforced
aluminum alloy, use is made of conventional
powder-metallurgy techniques, consisting in mixing an
aluminum alloy powder with an SiC powder, and in
densifying the powder mixture, e.g. by sintering, so as
to give it the desired shape.
The blade 1 is the airfoil portion of a blade or a
vane in a turbomachine. More particularly, it may form
part of a fan blade or of a stator vane for a turbojet.
The airfoil portion of a blade is the portion surmounting
the blade root, while the blade root is the portion used
for securing the blade to the remainder of the
turbomachine.
When the blade 1 is a fan blade, it can be made by
injecting resin on a fiber preform. The fiber preform
and the resin then respectively constitute the fiber
reinforcement and the matrix of the resulting composite
material. The fiber preform may be obtained in
particular by weaving and various known methods of
injecting resin onto a fiber preform can be used,
including the resin transfer molding (RTM) method.
The blade 1 could also be a propeller blade or a
helicopter blade.

CLAIMS
1. A protection part presenting an outer protection face,
and characterized in that said outer face is made of an
aluminum alloy reinforced by particles of SiC, the SiC
particle content in said alloy lying in the range 15% to
40% by weight.
2. A protection part according to claim 1, characterized
in that the content of SiC particles in said alloy lies
in the range 15% to 30% by weight.
3. A protection part according to claim 1 or claim 2,
characterized in that it comprises at least two layers,
including an outer layer (7) and an inner layer (5), the
outer layer being made of said reinforced aluminum alloy
and the inner layer being made of an aluminum alloy that
is optionally reinforced with SiC particles, the content
of SiC particles in the layers increasing from the inner
layer to the outer layer.
4. A protection part according to any preceding claim,
characterized in that it comprises at least two layers
(5, 7), and in that the layers are assembled together by
co-extrusion or by roll-bonding.
5. A protection part according to any preceding claim,
characterized in that it presents a section that is
substantially U-shaped.
6. A protection part for protecting the leading edge (la)
of a blade (1), according to any preceding claim.
7. A method for protecting the leading edge (la) of a
blade (1) , in particular a turbomachine blade or vane, a
helicopter blade, or a propeller blade, using a
protection part according to any preceding claim.

.8. An assembly comprising a blade (1) presenting- a leading edge (la) and a protection part (3) according to any one of claims 1 to 6, fitted onto the leading edge (la) in order to protect it.
9. An assembly according to claim 8, characterized in
that said protection part (3) is bonded on the leading
edge (la) by adhesive.
10. An assembly according to claim 8 or claim 9,
characterized in that the blade (1) is made of an
organic-matrix composite material.