Self-stiffened casing consisting of a composite material with an organic matrix

1. A gas turbine casing made of composite material comprising reinforcement densified by a matrix, said casing being in the form of a body of revolution and wherein said casing comprises a first external flange at its upstream end and a second external flange at its downstream end, a retention zone provided between the first external flange and the second external flange, an air inlet passage, and at least one stiffener portion made of said composite material, the at least one stiffener portion having an annular plateau having an outer radius at a center of an outer surface thereof extending at a radius greater than an outer radius at a center of an outer surface of the retention zone and a radius of upstream and downstream portions of the casing that are adjacent to said at least one stiffener portion so as to form an annular recess in an inside surface of the casing, the casing comprising the retention zone presenting thickness that is greater than a remainder of the casing, said at least one stiffener portion being situated outside of and downstream from the retention zone and adjacent to the downstream end of the casing, the air inlet passage extending between the first external flange and the at least one stiffener portion, wherein the annular plateau has a rectilinear shape that is offset radially towards an outside of the casing relative to the inside surface of the casing, the annular plateau being connected to the upstream and downstream portions via respective annular risers, wherein an angle is formed between each of the annular risers and the upstream and downstream portions, and wherein each angle is greater than 90 degrees and less than 180 degrees, and wherein an entire inside surface of the retention zone that is made of the composite material defines in part the air inlet passage.

2. The casing according to claim 1 , wherein the at least one stiffener portion presents, in axial section, an omega-type shape.

3. The casing according to claim 1 , wherein the annular recess formed by the at least one stiffener portion is filled in with a filler material or structure so as to provide continuity of the inside surface of the casing between the upstream and downstream portions of the casing that are adjacent to the at least one stiffener portion.

4. The casing according to claim 1 , wherein the annular recess formed by the at least one stiffener portion is filled in with an acoustic attenuation material or structure.

5. The casing according to claim 1 , wherein an axial section of the annular plateau and annular risers is rectilinear.

6. A gas turbine aeroengine having a fan retention casing according to claim 1 .

7. An aircraft including one or more engines according to claim 6 .

8. A method of fabricating a gas turbine casing out of composite material, the method comprising: weaving a fiber texture in the form of a single-piece strip by three-dimensional or multilayer weaving; shaping said fiber texture by winding it on a support tooling to form a fiber reinforcement; and densifying the fiber reinforcement with a matrix to obtain the casing,

wherein said casing comprises a first external flange at its upstream end and a second external flange at its downstream end, a retention zone provided between the first external flange and the second external flange, an air inlet passage, and at least one stiffener portion made of said composite material, the at least one stiffener portion having an annular plateau having an outer radius at a center of an outer surface thereof extending at a radius greater than an outer radius at a center of an outer surface of the retention zone and a radius of upstream and downstream portions of the casing that are adjacent to said at least one stiffener portion so as to form, an annular recess in an inside surface of the casing the casing comprising the retention zone presenting thickness that is greater than a remainder of the casing, said at least one stiffener portion being situated outside of and downstream from the retention zone and adjacent to the downstream end of the casing, the air inlet passage extending between the first external flange and the at least one stiffener portion, wherein the annular plateau has a rectilinear shape that is offset radially towards an outside of the casing relative to the inside surface of the casing, the annular plateau being connected to the upstream and downstream portions via respective annular risers, wherein an angle is formed between each of the annular risers and the upstream and downstream portions, and wherein each angle is greater than 90 degrees and less than 180 degrees, and wherein an entire inside surface of the retention zone that is made of the composite material defines in part the air inlet passage.

9. The method according to claim 8 , wherein the at least one stiffener portion presents, in axial section, an omega-type shape.

10. The method according to claim 8 , wherein the annular recess formed by the at least one stiffener portion is filled in with a filler material or structure so as to provide continuity of the inside surface of the casing between the upstream and downstream portions of the casing that are adjacent to the at least one stiffener portion.

11. The method according to claim 8 , wherein the annular recess formed by the at least one stiffener portion is filled in with an acoustic attenuation material or structure.