Fiber structure and a composite material part incorporating such a structure
A fiber structure includes a plurality of weft layers and of warp layers interlinked by multilayer three-dimensional weaving, the fiber structure having at least first and second portions that are adjacent in the warp direction, the first portion presenting, in a direction perpendicular to the warp and weft directions, a thickness that is greater than the thickness of the second portion, wherein the first portion has at its core at least one fiber fabric obtained by three-dimensional weaving of warp yarns and weft yarns in the form of a Mock Leno weave grid, the at least one fabric being present between two skins present at the surface of the first portion and being linked to the skins by warp yarns belonging to the skins that are locally deflected into the fabric.
1. A fiber structure comprising a plurality of weft layers and of warp layers interlinked by multilayer three-dimensional weaving, the fiber structure having at least first and second portions that are adjacent in the warp direction, the first portion presenting, in a direction perpendicular to the warp and weft directions, a thickness that is greater than the thickness of the second portion, wherein the first portion has at its core at least one fiber fabric obtained by three-dimensional weaving of warp yarns and weft yarns in the form of a Mock-Leno weave grid, said at least one fabric being present between two skins present at the surface of the first portion and being linked to the skins by warp yarns belonging to said skins that are locally deflected into said fabric.
2. A fiber structure according to claim 1 , wherein the Mock-Leno weave fiber fabric presents, in a direction perpendicular to the warp and weft directions, a thickness that decreases going towards the second portion.
3. A fiber structure according to claim 1 , wherein the first and second portions have the same number of warp yarns woven continuously between said first and second portions, and wherein the first portion includes in its core a number of warp yarn layers that is greater than the number of warp yarn layers present in the core of the second portion.
4. A fiber structure according to claim 3 , wherein the first portion includes in its core a number of warp yarn layers that is equal to twice the number of warp yarn layers present in the core of the second portion.
5. A fiber structure according to claim 1 , wherein the structure comprises carbon yarns or ceramic material yarns.
6. A composite material part comprising fiber reinforcement densified by a matrix, said fiber reinforcement being constituted by a fiber structure according to claim 1 .
7. A part according to claim 6 , said part corresponding to a turbine blade, the first portion of the fiber structure constituting the blade root portion of the fiber reinforcement.