1. Title of the invention

"Eliminating the delamination in Co-Cured assembly made of laminated Composite material".

2. Field of invention
Design of Co-Cured structure made of laminated Composite material.

3. Use of invention
This invention eliminates the delamination of carbon fiber plies occurring during curing and subsequent demoulding of Co-Cured Composite structure.

4. Prior art
In Co-curing of composite structures, the structural elements are cured simultaneously together to get a large integral structure. The type of structure of this invention is closed multi cell structure wherein the layup completely envelops the tool which are plural in numbers (except on one side for the extraction of tool block), thus posing delamination during cure due to the mal expansion mismatch and subsequent demoulding due to mechanical locking of the tool block by the cured component.

In existing process, the metallic tool blocks are not provided with chamfers at both ends. Also there was no reinforcement bridging the skin and flange of the stiffener making the interface prone to delamination.

5. Draw backs of prior art

The draw backs of the existing design are as follows:

a) Delamination of plies between Rib flange and Skin, thus opening up near the flange
end.

b) Being a closed shell type structure, Ultrasonic inspection is carried out by filling the cavity with water, this lead to seepage of water into the (delamination) gap between Rib flange and Skin, this makes the detection of delamination difficult and unreliable during the inspection.

c) The undetected the delaminations started growing in service the same were observed during subsequent inspection of aircraft.

6. Comparison between prior art and present invention

In the present invention, the two ends of a metallic tool block are chamfered to ensure smooth and gradual layup over a tapered surface. The presence of additional 0° UD Overlay ply (bridging ply) which connects the Rib flange inner face and skin provides substantial improvement on the resistance against peel and delamination. This invention ensures that the Carbon fiber plies are intact after extraction of tool blocks after curing. In the existing metallic tool blocks, both the ends are not chamfered causing delamination while demoulding.

Further the bridging layer ensures good reliability in detecting the delamination between the skin and the Rib flange.

7. Aim of the invention
Aim of the invention is to eliminate the present drawbacks and to improve the quality of the Co-Cured structure and reliable and easy detection of delamination and thereby decrease the rejection rate.

8. Summary of the present invention
The metallic tool blocks (1) & (2) which are required to produce Co-Cured assembly are provided with chamfers at both the ends to ensure smooth and gradual layup of plies over the tapered tool surface. An additional UD Overlay ply (4) with 0° orientation is laid as shown in Fig.4. The laminate is cured in an autoclave and tool blocks are extracted at room temperature. The presence of taper due to chamfer in metallic tool block ensures easy removal of the tool and elimination of delamination in component. The presence of 0° Overlay ply improves strength of Web-Skin joint and offers manifold resistance against peel and delamination.

9. Brief description of drawings

Fig. 1 shows the Co-Cured structure with tool blocks (1) & (2) for existing scheme.

Fig. 2 shows view of Co-Cured structure of an aircraft.

Fig. 3 showing tapered Rib (5) flanges, Skin (3) and additional 0° UD ply (4) of Co-Cured structure.

Fig. 4 shows the sectional view of the Co-Cured assembly with tapered Rib blocks (1), (2) upon which plies are laid.

Fig. 5 shows 0° Overlay ply (4) laid over the tool surface.

10. Statement of invention

In the present invention, the two ends of a metallic tool block are chamfered to ensure smooth and gradual layup over a tapered surface.

A 0° UD Overlay ply which connects the Rib flange inner face and skin.

11. Detailed description of invention
Refer Fig. 1

This figure represents the existing scheme. In this the metallic tool blocks (1), (2) are not chamfered and
is one of the reasons for delamination. The delamination zone is shown in this figure.

Refer Fig. 2
Shows the Co-Cured component of an aircraft with several Ribs (5) and Top & Bottom skins (3) produced by use of tapered metallic tool blocks (1) & (2).

Refer Fig. 3
Shows the 0° UD Overlay ply (4) which acts as locking ply. This ply prevents the entry of moisture between Rib-Skin interfaces.

Refer Fig. 4
The taper tools (1) & (2) having tapered ends positioned accurately held in fixtures. The hand layup is done over the tool face including taper area. Since tool ends are tapered, it facilitates easy removal of tools after the curing.

Refer Fig. 5
Shows another view of 0° UD Overlay ply (4).

Claims
We claim that

1. The improvement to the existing Co-Cured part has been done by HAL.
2. The delamination has been completely eliminated by adopting the improved technique.
3. The rejection / rework of Co-Cured assembly due to this method reduced to zero.