Fiber structure woven as a single piece by 3D weaving and application to the manufacturing of composite material part

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 including a plurality of layers of warp 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 warp yarns and forming a second portion of the thickness of the fiber structure, the warp yarns being arranged in columns each of which includes warp yarns of the first portion and of the second portion;
• and
• in each plane of the fiber structure, a set of weft yarns interlinking the layers of warp yarns of the first portion and the layers of warp yarns of the second portion while leaving at least one non-interlinked zone separating the first and second portions over a portion of a dimension of the fiber structure in the weft direction from a first edge of the fiber structure to an end of non-interlinked zone, wherein:
• at least two first weft yarns interlink layers of warp yarns of the first portion of the fiber structure adjacent to the non-interlinked zone and layers of warp yarns of the second portion of the fiber structure beyond the non-interlinked zone;
• at least two second weft yarns interlink layers of warp yarns of the second portion of the fiber structure adjacent to the non-interlinked zone and layers of warp yarns of the first portion of the fiber structure beyond the non-interlinked zone;
• paths of the first weft yarns and paths of the second weft yarns cross over in a transition zone in a single pass extending in the fiber structure in the weft direction from the end of the non-interlinked zone;
• the transition zone extends in the weft direction over a distance that is greater than a pitch between adjacent warp columns;
• at least one warp yarn in the transition zone is free of interlinking with the first weft yarns and is free of interlinking with the second weft yarns;
• the first weft yarns interlink the layers of warp yarns of the second portion immediately after crossing through the transition zone in the weft direction, each weft yarn of the first weft yarns interlinking with a respective single layer of the warp yarns of the second portion between a section of the second portion adjacent to an end of the transition zone through which the first weft yarns cross and a second edge of the fiber structure in the weft direction such that the first weft yarns only extend in the weft direction between the first and second opposite surfaces, and the second weft yarns interlink the layers of warp yarns of the first portion immediately after crossing through the transition zone in the weft direction, each weft yarn of the second weft yarns interlinking with a respective single layer of the warp yarns of the first portion between a section of the first portion adjacent to an end of the transition zone through which the second weft yarns cross and the second edge of the fiber structure in the weft direction such that the second weft yarns only extend in the weft direction between the first and second opposite surfaces.