Fibrous reinforcement structure for composite material part having a reduced thickness portion
A fiber structure reinforcing a composite material part woven as a single piece by multilayer weaving between plural first and second layers of yarns. The fiber structure includes a portion of decreasing thickness that presents: plural yarn withdrawal parts in surface continuity, with yarns interrupted from the first plural layers of yarns underlying the layer of yarns of the first plural layers of yarns situated in the surface of the structure; and plural yarn withdrawal parts in surface discontinuity, with yarns interrupted from the first plural layers of yarns situated at the surface of the structure, each interrupted yarn replaced in the surface of the structure by a yarn of a layer of yarns underlying the first plural layers of yarns. The yarns of the second plural layers of yarns situated in the surface of the fiber structure are continuous over at least the entire portion of decreasing thickness.
1. A fiber structure for reinforcing a composite material part, the structure being woven as a single piece by multilayer weaving between a first plurality of layers of yarns and a second plurality of layers of yarns, the fiber structure including at least one portion of decreasing thickness,
wherein, in the portion of decreasing thickness, the fiber structure includes at its surface:
one or more yarn withdrawal parts in surface continuity in each of which yarns are interrupted that belong to a layer of yarns of the first plurality of layers of yarns underlying the layer of yarns of the first plurality of layers of yarns situated at the surface of the structure; and
one or more yarn withdrawal parts in surface discontinuity in each of which yarns are interrupted in the layer of yarns of the first plurality of layers of yarns situated in the surface of the structure, each interrupted yarn being replaced in the surface of the structure by a yarn of a layer of yarns underlying the first plurality of layers of yarns; and
wherein the yarns of the layers of the second plurality of layers of yarns situated at the surface of the fiber structure are continuous over at least the entire portion of decreasing thickness.
2. A fiber structure according to claim 1 , wherein in each part in surface discontinuity, each interrupted yarn of the layer of the first plurality of layers of yarns is interlaced with at least one yarn of a layer of the second plurality of layers of yarns immediately before exiting the structure.
3. A structure according to claim 1 , wherein the fiber structure presents first and second outside faces extending in a longitudinal direction, and the yarn withdrawal parts present in the first face are longitudinally offset relative to the yarn withdrawal parts present in the second face.
4. A fiber structure according to claim 1 , wherein the portion of decreasing thickness presents, in a direction of the yarns of the first plurality of layers of yarns, a decreasing number of layers of yarns of the second plurality of layers of yarns, and wherein the fiber structure includes yarn withdrawal parts in surface discontinuity that are distributed as a function of a determined decrease in the number of layers of yarns of the second plurality of layers of yarns.
5. A composite material part comprising fiber reinforcement densified by a matrix, wherein the fiber reinforcement is formed by a fiber structure according to claim 1 .
6. A part according to claim 5 , constituting an aeroengine blade.
7. A turboprop comprising a plurality of blades according to claim 6 .
8. An aircraft comprising at least one turboprop according to claim 7 .
9. A method of fabricating a fiber structure for reinforcing a composite material part, the method comprising:
weaving as a single piece by multilayer weaving between a first plurality of layers of yarns and a second plurality of layers of yarns, the fiber structure including at least one portion of decreasing thickness;
wherein during the weaving of the portion of decreasing thickness, there are defined:
yarn withdrawal parts in surface continuity in each of which yarns of a layer of yarns of the first plurality of layers of yarns underlying the layer of yarns of the first plurality of layers of yarns situated at the surface of the structure are no longer woven with the yarns of the layers of the second plurality of layers of yarns; and
yarn withdrawal parts in surface discontinuity in each of which yarns of the layer of yarns of the first plurality of layers of yarns situated in the surface of the structure are no longer woven with the yarns of the layers of the second plurality of layers of yarns, yarns from a layer of yarns underlying the first plurality of layers of yarns being used to replace in the surface of the texture the yarns that are no longer woven as from the surface discontinuity part; and
wherein the yarns of the layers of the second plurality of layers of yarns situated at the surface of the fiber texture are continuous, at least over the entire portion of decreasing thickness.
10. A method according to claim 9 , wherein the yarns of the layer of the first plurality of layers of yarns that are no longer woven from the surface discontinuity part are interlaced with at least one yarn of a layer of the second plurality of layers of yarns immediately prior to exiting the structure.
11. A method according to claim 9 , wherein the fiber structure presents first and second outside faces extending in a longitudinal direction, and the yarn withdrawal parts present in the first face are longitudinally offset relative to the yarn withdrawal parts present in the second face.
12. A method according to claim 9 , wherein the portion of decreasing thickness presents, in a direction of the yarns of the first plurality of layers of yarns, a decreasing number of layers of yarns of the second plurality of layers of yarns, and the fiber structure includes yarn withdrawal parts in surface discontinuity that are distributed as a function of a determined decrease in the number of layers of yarns of the second plurality of layers of yarns.