Panel design


Usual panel design consists of aluminium plate made of material 2024, which is reinforced by L shape stringer made of the same material. The design is illustrated in Figure 13 below.


Figure 13: Schematic drawing of the construction of the riveted panel

Because of the use of the different technology for joint creation between stringers and the panel plate, changes of the design should be considered. Applying design that would utilize FSW technology benefits fully can improve mechanical properties of the panel, while reducing its weight. Further in this thesis, three options (Variants A, B and C) for the design changes were considered and their benefits were assessed.

6.1.1     Variant A – Based on original construction

In this variant (Figure 14) the all the design would be kept and only the technology of welding would differ. That would bring following benefits:

-          No need for change of part documentation

-          Easy fitting panel with improved design into the current construction

-          Keeping tested and reliable construction

It would also take disadvantages:

-          Not using potential of FSW technology fully

-          Design not suitable for FSW technology

-          Complicated gripping equipment needed


Figure 14: Scheme of Variant A joint design


6.1.2     Variant B – Substitution of original stringers with T profiles

In this variant original L-profile stringers would be substituted with T-profile stringers connected to the other parts by butt welds creating together panel surface as shown in Figure 15.


Figure 15: Scheme of Variant B joint design

This variant would have several benefits

-          Reducing weight while keeping mechanical properties

-          Easy work piece gripping and welding

-          FSW butt joint connection well investigated and tested

 

and some disadvantages as well

-          Two welds needed for welding of one stringer

-          Lower productivity and more expensive

-          More residual stress introduced

-          Higher chance of crack growth

6.1.3     Variant C – Incorporating stringers into panel design

In this variant simple plate shape stringers would be welded onto the base panel plate as shown in Figure 16.


Figure 16: Scheme of Variant C joint design

 

This variant would posses following advantages

-          Low weight and good mechanical properties

-          Productive use of FSW technology

and disadvantages

-          Gripping and welding tool positioning demanding higher accuracy

 

The variant C provides good mechanical properties, lowest weight and at the same time requires low number of welds. All the variants provide the joint with impermeability that would be needed in case of need of fuselage pressurisation or using the panel as a part of an integrated tank. At the same time, we can presume lower manufacturing costs and higher production speed in all cases when FSW is substituting riveting. This point is discussed later to determine the economy of production related benefits.

All the FS welded variants are likely to suffer from post-welding residual stresses and eventual deformation of the panel caused by them, which are an inherent feature of FSW. The residual stresses introduced by FSW are much lower than the ones caused by traditional welding methods, so we do not expect significant deformation to occur. The real influence of the residual stresses has to be assessed after the welding of the first panel and measures have to be taken to limit their influence on the part.

Due to the aforementioned benefits, only the Variant C was taken into account in further calculations and was compared to the basic design of the panel with stringers connected to the panel by riveting.



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