Woven fibrous preform for manufacturing a fan blade made of composite material

A fibrous preform intended to form a fibrous reinforcement of a fan blade of an aircraft turbine engine, in composite material with the fibrous reinforcement densified with a matrix, the fibrous preform being in a single piece and being obtained by three-dimensional weaving of a plurality of longitudinal yarns or strands, extending in a direction corresponding to the longitudinal direction of the blade, with a plurality of transverse yarns or strands, the preform comprising a blade root part and a blade airfoil part extending between the blade root part and a free end of the fibrous preform,

• wherein the airfoil part of the preform has a first area comprising a first skin corresponding to a lower surface of the blade, a second skin corresponding to an upper surface of the blade, and a longitudinal stiffener portion extending between the first skin and the second skin, and in that, in a transverse plane of the first area;
• transverse yarns or strands of the first skin and of the second skin are woven in pairs in the first skin and in the second skin on either side of the longitudinal stiffener portion;
• the yarns or strands of at least one first pair of transverse yarns or strands of the first skin are separated into two unit yarns or strands at the longitudinal stiffener portion, said unit yarns or strands being woven separately with longitudinal yarns or strands in said portion;
• the yarns or strands of at least one second pair of transverse yarns or strands of the second skin are separated into two unit yarns or strands at the longitudinal stiffener portion, said unit yarns or strands being woven separately with longitudinal yarns or strands in said portion;
• and
• at least one yarn or strand of the first pair and at least one yarn or strand of the second pair cross over each other at least twice in the longitudinal stiffener portion.