The invention relates to a method of needling a fiber layer, and in particular to fabricating a fiber preform by using needling to bond a fiber layer to an underlying fiber structure.
Needling methods are known for fabricating fiber preforms made up of a plurality of fiber layers in a stack. In such methods, the fiber layers are stacked in succession on a needling table and they are needled by the action of a needling head. When a fiber layer is struck by the needling head, the layer is bonded with the underlying layer(s). Once the set of fiber layers has been stacked and needled, the resulting fiber preform can be densified by a matrix in order to form a part made of composite material.
The mechanical characteristics of the final part nevertheless depend on the needling actually performed within the fiber preform.
The present invention seeks to improve the mechanical properties of parts made of composite material including fiber reinforcement formed by needling.
To this end, in a first aspect, the invention proposes a method of needling a fiber layer, the method comprising at least:
During the shift step, the needles of the needling head are shifted relative to the fiber layer. As a result, during the second needling step, the needles do not penetrate into the holes formed during the first needling step. As a result, a fiber layer is obtained in which the needling is more uniform. This makes it possible to obtain better introduction of the matrix material while the part is being formed, and thus to improve its mechanical properties. The fact that the needles do not penetrate into the same holes also makes it possible to reduce the risk of damaging the fiber layer during needling.
In an implementation, the movement in translation performed during the first needling step takes place along a movement axis, and the shift direction is not perpendicular to the movement axis. In particular, the shift direction is parallel to the movement axis.
In a variant, the movement in translation during the first needling step is performed along a movement axis, and the shift direction is perpendicular to the movement axis.
In an implementation, the movement in translation during the first needling step is performed in a first direction of advance, and the movement in translation during the second needling step is performed in a second direction of advance, opposite to the first direction of advance.
In an implementation, the fiber layer is moved in translation along a movement axis during each of the first and second needling steps, and the position of the needling head along the movement axis is stationary during each of the first and second needling steps.
In an implementation, during each of the first and second needling steps, stages of movement in translation along the movement axis alternate with stages of stopping movement along that axis, with the fiber layer being needled by the needling head during the stages of stopping.
Performing needling during the stages of stopping serves advantageously to reduce shear in the fiber layer during needling and to further improve the mechanical properties of the part.
In an implementation, the needling head is held stationary and the fiber layer is moved through the distance d along the shift direction during the shift step.
In an implementation, the coefficient x lies in the range 0.1 to 0.9, e.g. in the range 0.2 to 0.8, e.g. in the range 0.3 to 0.7, or indeed in the range 0.4 to 0.6.
The present invention also provides a method of fabricating a needled multilayer fiber preform including at least one fiber layer bonded to an underlying fiber structure by needling by performing a method as described above.
The present invention also provides a method of fabricating a composite material part comprising at least the following steps:
Other characteristics and advantages of the invention appear from the following description of particular implementations of the invention given as non-limiting examples, and with reference to the accompanying drawings, in which:
The conduct of a first implementation of a needling method of the invention is described initially with reference to
In general manner, a needling machine 100 is used that comprises a needling head 110 having needles 111 and a support carrying a fiber layer 10 for needling, which support is constituted in this example by a table 120.
In order to perform the needling, the needling head 110 may be moved vertically above the table 120, i.e. along the direction Z shown in the figures. The needling head 110 moves both downwards and upwards along the vertical direction Z, as represented by double-headed arrow 112. The needling head 110 is thus driven with reciprocating vertical motion (i.e. back-and-forth motion) relative to the table 120. The needling head 110 carries a determined number of needles 111 that are provided with barbs, hooks, or forks for taking hold of fibers in the fiber layer 10 and transferring them through said layer. In known manner, these needles 111 are arranged in a plurality of rows of needles, these rows being visible in
The table 120 extends in horizontal directions X and Y perpendicular to the direction Z (see
With reference to
The situation shown has only one fiber layer that is needled by performing the method of the invention. Naturally, in a variant, it would be possible to position a fiber layer on an underlying fiber structure and then to perform a needling method of the invention in order to bond the fiber layer 10 to the fiber structure. Under such circumstances, the needling serves to cause the fibers of the fiber layer 10 to penetrate into the underlying fiber structure in order to provide bonding between those two elements.
Thereafter, after the first needling step, a shift step is performed for shifting the fiber layer 10 relative to the needling head 110. The purpose of this shift step is to ensure that the needles 111 do not pass once more through the holes 11a during the second needling step.
In the example shown, the fiber layer 10 is shifted in the shift direction DD, which in this example is parallel to the movement axis X. In the example shown, the fiber layer is shifted through a distance d that is substantially equal to 0.5p, where p corresponds to the distance between two consecutive needles 111 along the shift direction DD (or the axis X). In the situation shown diagrammatically in
Thereafter, the second needling step is performed with the fiber layer 10 in the second position at the beginning of the second needling step. During the second needling step, the fiber layer 10 is moved in translation along the movement axis X in a second direction of advance D2. In the presently-considered example, the position of the needling head 110 along the directions X and Y remains unchanged during the second needling step. In this example, the needling head 110 is driven solely with reciprocating motion transversely relative to the fiber layer 10 during the second needling step. In this example, the needling head 110 is driven solely with go-and-return motion vertically along the direction Z during the second needling step. Nevertheless, in a variant, it would be possible to keep the fiber layer 10 stationary and to move the needling head 110 in translation during the second needling step.
In the example shown, it should be observed that the second direction of advance D2 is opposite to the first direction of advance D1. In this example, the fiber layer 10 is moved in translation along the same movement axis X as during the first needling step, but in an opposite direction of advance D2. The example shown thus relates to a “go-and-return” needling method during which the fiber layer 10 is subjected to the first needling step in the go direction and is subjected to the second needling step in the return direction.
Other variants are possible for moving the fiber layer during the second needling step. By way of example, at the end of the first needling step, it would be possible in the
During the second needling step, the needles 111 penetrate into the fiber layer 10 and form a second set of holes 11b therein. The speed of advance of the fiber layer 10, or of the needling head if it is the needling head that moves, may be identical during the first and second needling steps. The frequency with which the needles 111 impact against the fiber layer 10 may be identical during the first and second needling steps. Two holes 11b of the second set following each other along the movement axis X are spaced apart at the pitch p.
After the second needling step and on moving along the movement axis X, the fiber layer presents holes 11a of the first set alternating with holes 11b of the second set. During the second needling step, because the shift step has been performed, the needles 111 carried by the needling head 110 do not impact into the holes 11a of the first set. This produces the fiber layer shown in
During each of the first and second needling steps, stages of moving in translation along the movement axis may alternate with the stages of stopping along that axis, with the fiber layer being needled by the needling head during the stages of stopping. Under such circumstances, the movement in translation performed during the first and second needling steps is performed incrementally. The needling is advantageously performed solely during stages of stopping. During each of the first and second needling steps, it is possible to alternate between stages of moving the fiber layer in translation along the movement axis and stages of stopping the fiber layer, with needling being performed during these stages of stopping. During each of the first and second needling steps, it is also possible to alternate between stages of moving the needling head in translation along the movement axis and stages of stopping the needling head in its movement along the movement axis, with needling being performed during these stages of stopping. The invention also relates to the variant in which movement is performed continuously during the needling step. The needles of the needling head may also be of elongate shape so as to give them flexibility for limiting shear in the fiber layer.
The above-described example relates to needling a single fiber layer. It would not go beyond the ambit of the invention for the fiber layer that is needled by the method of the invention to be positioned on an underlying fiber structure. The fiber structure could comprise one or more fiber layers, e.g. connected together by needling. When the fiber layer is positioned on a fiber structure, the needling that is performed enables the fibers of the fiber layer 10 to penetrate into the underlying fiber structure, thereby bonding together the fiber layer and that structure. This produces a fiber preform that is to form the fiber reinforcement of a composite material part that is to be obtained.
Once a fiber layer has been needled by the method of the invention, a second fiber layer may be positioned thereon. Thereafter, the second fiber layer can be needled by the method of the invention in order to be connected to the underlying first fiber layer. The table 120 may be moved down a step in order to control the depth to which the needles penetrate into the first and second fiber layers. The method may be repeated by stacking at least one third fiber layer on the first and second fiber layers.
The above description with reference to
Specifically,
It is possible to form a fiber preform for a part made of composite material by performing the needling method as described above. Once the preform has been obtained, a matrix can be formed in the pores of that preform in a manner that is itself known. The matrix densifying the fiber preform may be organic, ceramic, or made of carbon. It is possible to envisage various known methods for forming a matrix, such as for example injecting a liquid polymer followed by applying heat treatment thereto in order to cross-link it, and possibly also to pyrolize it, thereby forming the matrix. It is also possible to use a method of densification by a gaseous technique in which the matrix is formed by infiltration using a precursor in the gaseous state.
The resulting part made of composite material may be a valve body or a valve needle.
The term “lying in the range . . . to . . . ” should be understood as including the bounds.
Number | Date | Country | Kind |
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1751829 | Mar 2017 | FR | national |