| CPC D03D 25/005 (2013.01) [B29B 11/16 (2013.01); B29C 70/24 (2013.01); B29D 99/0025 (2013.01); F01D 5/282 (2013.01); F01D 5/284 (2013.01); B29L 2031/087 (2013.01); F05D 2230/31 (2013.01); F05D 2300/20 (2013.01); F05D 2300/6034 (2013.01)] | 8 Claims |

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1. A fibrous preform intended for forming a fibrous reinforcement of a composite material part with fibrous reinforcement densified by a matrix, the fibrous preform being made as a single piece and obtained by three-dimensional weaving of a first plurality of threads or strands extending in a first direction of the composite material part with a second plurality of threads or strands extending in a second direction of the composite material part perpendicular to the first direction, the fibrous preform comprising a first skin, a second skin and a stiffening portion connecting the first skin to the second skin, the stiffening portion being intended to form a stiffening element of the composite material part in the first or second direction, wherein the fibrous preform has an intermediate portion extending at least in the first direction or second direction between two end portions, wherein the stiffening portion comprises, in the intermediate portion, a plurality of non-woven threads or strands extending in at least the first direction or the second direction and which are held together by a plurality of first threads or strands coming from the first skin and a plurality of second threads or strands coming from the second skin, and wherein, in the two end portions, the threads or strands of the stiffening portion are woven with threads or strands of the first or second plurality of threads or strands.
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