Method for producing a closed-section portion of an aircraft provided with deformation sensors

A method for producing a closed-section portion of an aircraft provided with deformation sensors comprising the steps of:

• a) inserting inside a mould (2) equipped with a first part (2a) and a second part (2b):
• at least a first sheet (3) of composite material,
• at least a second sheet (4) of composite material facing the first sheet and spaced apart therefrom;
• and
• interconnection elements (5) in a composite sheet material that extend between the first and the second sheets (3 and 4) of composite material to delimit an elongated cavity (7);
• b) inserting a tool (10) (plug) inside the elongated cavity (7), said tool (10) comprising a rigid elongated body delimited by a number of flat faces (11) and having a cross-section corresponding to that of the cavity (7)—the entire length of said rigid body being covered by and enveloped in a tubular sack (12) made of a deformable material;
• c) creating a vacuum in an autoclave inside which the mould is arranged to allow expansion of the sack (12), which presses against the walls of the cavity during a first heating cycle in which the sheets of composite material fuse with each other;
• d) extracting the tool from the cavity (7) at the end of the first heating cycle after having re-established the original pressure—at the end of the first heating cycle said cavity is delimitated by rigid walls,
• and characterized in that it further comprises the steps of:
• e) preparing a flat tape (15) having dimensions (l1 by l2) that allow it to be deposited on a face (11a) of the tool (10) covered by a tubular sack (12) made of a deformable material;
• f) permanently fastening a strain gauge (17) on said flat tape (15);
• g) arranging said tape (15) on the tool with its first face (15a) carrying the strain gauge (17) facing the tool and the sack, and a second face (15b) facing the outside;
• h) depositing an adhesive layer (23) on the second face (15b) of said tape (15);
• i) inserting said tool (10) supporting said tape (15) in said cavity (7);
• j) creating a vacuum and performing a second heating cycle to obtain the expansion of said vacuum sack (12), which performs the pressure gluing of said tape onto a wall of said cavity;
• k) extracting said tool (10) from said cavity—at the end of said second heating cycle, said tape being integrally fixed on a wall of said cavity such that any deformations applied to said wall are transmitted to said strain gauge.