Fiber structure woven as a single piece by 3D weaving, and an application thereof to fabricating a composite material part

1. A fiber structure woven as a single piece by three-dimensional weaving, the fiber structure having first and second opposite surfaces and comprising:

a first portion having a plurality of layers of weft yarns and forming a first portion of a thickness of the fiber structure between the first and second opposite surfaces;

a second portion including a plurality of layers of weft yarns and forming a second portion of the thickness of the fiber structure, the weft yarns being arranged in columns each of which includes weft yarns of the first portion and of the second portion; and

in each plane of the fiber structure, a set of warp yarns interlinking the layers of weft yarns of the first portion and the layers of weft yarns of the second portion while leaving at least one non-interlinked zone separating the first and second portions over a portion of the dimension of the fiber structure in the warp direction from a first edge of the fiber structure to an end of non-interlinked zone, wherein:

at least two first warp yarns interlink layers of weft yarns of the first portion of the fiber structure adjacent to the non-interlinked zone and layers of weft yarns of the second portion of the fiber structure beyond the non-interlinked zone;

at least two second warp yarns interlink layers of weft yarns of the second portion of the fiber structure adjacent to the non-interlinked zone and layers of weft yarns of the first portion of the fiber structure beyond the non-interlinked zone;

paths of the first warp yarns and paths of the second warp yarns cross over in a transition zone in a single pass extending in the fiber structure in the warp direction from the end of the non-interlinked zone;

the transition zone extends in the warp direction over a distance that is greater than a pitch between adjacent weft columns;

at least one weft yarn in the transition zone is free of interlinking with the first warp yarns and is free of interlinking with the second warp yarns; and

the first warp yarns interlink the layers of weft yarns of the second portion immediately after crossing through the transition zone in the warp direction, each warp yarn of the first warp yarns interlinking with a respective single layer of the weft yarns of the second portion between a section of the second portion adjacent to an end of the transition zone through which the first warp yarns cross and a second edge of the fiber structure in the warp direction such that the first warp yarns only extending in the warp direction between the first and second opposite side, and the second warp yarns interlink the layers of weft yarns of the first portion immediately after crossing through the transition zone in the warp direction, each warp yarn of the second warp yarns interlinking with a respective single layer of the weft yarns of the first portion between a section of the first portion adjacent to an end of the transition zone through which the second warp yarns cross and the second edge of the fiber structure in the warp direction such that the second warp yarns only extend in the warp direction between the first and second opposite surfaces.

2. The fiber structure according to claim 1 , wherein a plurality of first warp yarns and a plurality of second warp yarns follow similar paths between ends in the warp direction of the transition zone.

3. The fiber structure according to claim 1 , wherein a plurality of first warp yarns and a plurality of second warp yarns follow similar paths that are mutually offset in the warp direction in the transition zone.

4. The fiber structure according to claim 1 , wherein outer layers of weft yarns adjacent to the first and second opposite surfaces of the fiber structure are woven with the same warp yarns extending continuously over an entire dimension of the fiber structure in the warp direction.

5. The fiber structure according to claim 1 , wherein, in at least one of the first and second portions of the fiber structure, the weft yarns of the outer layers of weft yarns adjacent to a surface of the fiber structure are woven with the same warp yarns having paths that cross over at a location corresponding substantially to that of the transition zone.

6. The fiber structure according to claim 1 , comprising at least two non-interlinked zones separating the first and second portions over a portion of the dimension of the fiber structure in the warp direction from opposite edges of the fiber structure as far as respective ends of non-interlinked zones.

7. The fiber structure according to claim 1 , wherein the thickness of the fiber structure is constant.

8. The fiber structure according to claim 1 , wherein the first and second opposite surfaces of the fiber structure each has a satin weave beyond the transition zone in the warp direction.