Preform and one-piece vane for turbomachine

1. A fiber preform for a turbine engine blade, the preform comprising a main fiber structure obtained by a single piece of three-dimensional weaving, said main first structure comprising:

a first longitudinal segment suitable for forming a blade root;

a second longitudinal segment extending the first longitudinal segment and suitable for forming an airfoil portion; and

at least one transverse segment extending transversely from a junction between the first and second longitudinal segments and suitable for forming a tongue for a platform;

wherein the at least one transverse segment extends axially over a length that is less than 30% of a length of the junction between the first and second longitudinal segments.

2. A preform according to claim 1 , wherein the at least one transverse segment includes a plurality of transverse segments extending transversely in a same direction from the junction between the first and second longitudinal segments and suitable for forming tongues for a common platform;

wherein said longitudinal segments are spaced apart from one another.

3. A preform according to claim 1 , wherein the main fiber structure further includes at least one additional transverse segment extending transversely from the junction between the first and second longitudinal segments, in a direction opposite to the at least one transverse segment, and suitable for forming a tongue for a second platform.

4. A preform according to claim 1 , wherein the at least one transverse segment extends axially from a front end of the junction between the first and second longitudinal segments.

5. A preform according to claim 1 , wherein the at least one transverse segment extends axially from a rear end of the junction between the first and second longitudinal segments.

6. A preform according to claim 1 , wherein the at least one transverse segment is formed by at least a portion of a free flap said free flap and said second longitudinal segment being woven jointly in a non-interlinked manner, said non-interlinking starting at the junction between the first and second longitudinal segments.

7. A preform according to claim 1 , further comprising at least one fiber strip, that is woven independently of the main fiber structure, and that is of a width substantially equal to the length of the junction between the first and second longitudinal segments, and that is suitable for forming a platform.

8. A preform according to claim 7 , wherein the fiber strip is fitted to the at least one transverse segment or at least one additional transverse segment of the main fiber structure by being put against a bottom surface of said at least one transverse segment or the at least one additional transverse segment.

9. A preform according to claim 7 , wherein a top surface of the fiber strip is flush with a top surface of the at least one transverse segment or the at least one additional transverse segment.

10. A preform according to claim 1 , wherein the at least one transverse segment extends axially over a length that is less than 15% of the length of the junction between the first and second longitudinal segments.

11. A turbine engine blade comprising:

a blade root;

an airfoil portion; and

a platform extending transversely to the airfoil portion at a level of a junction between the blade root and the airfoil portion;

said blade being characterized in that it is made as a single piece of composite material by means of a fiber preform according to claim 1 , said preform being shaped in a mold and embedded in a matrix.

12. A turbine engine fan, characterized in that it comprises a plurality of blades according to claim 11 .

13. A turbine engine, characterized in that it includes at least one blade according to claim 11 .