Originally Posted by
Firemansam
When in Hamburg recently i was talking to my cousin who works for Lufthansa Technik. He was telling me wing root problem lies with the part that shows the cracks is to rigid and when the wing flexes eventually it may crack, so apparently the fix for them is currently in the works and it willl be a new part made from softer more flexible material.
Actually I've just been reading up more on the issues of the wing cracks located on the Airbus A380s. Came across this interesting article:
For a start, there are two different cracks being investigated:
1. Hairline cracks around fastener holes in the internal wing structure, and
2. Cracks at the edges of the vertical web of the feet.
The fastener holes are located in “rib feet” which are L-shaped brackets extending from the wing rib for attaching to the aircraft skin, using bolts through these holes. It is my understanding that it is the rib-feet attached to the lower skin which have this problem.
A number of wing ribs are distributed along the wing – more than 40 on each wing of the Airbus A380 – and these run from the front to the back of the wing’s internal structure.
These ribs help maintain the aerodynamic shape of the wing and transfer the aerodynamic and fuel loads to the spars – beam-like structures running along the length of the wing that are the main load-carrying structure of the wing.
The cracks found around these holes are being attributed to the manufacturing process used at Broughton, UK, where the wings are made.
This manufacturing process may be related to the combination of the use of “interference-fit” fasteners and the loads being applied when the wing skin is attached to the wing.
Interference-fit refers to the process whereby the fastener hole is made slightly smaller than the fastener diameter. When the fasteners are inserted, this has the effect of inducing stresses which offset the tensile stresses on the lower wing skin during flight, increasing fatigue life.
If the high loads being applied to the fasteners during assembly are not adequately accounted for, they will combine with the stresses arising from the interference fit, potentially leading to cracking. The particular type of aluminium alloy used will also affect this joint behaviour where a balance has to be achieved between stiffness, strength and fracture toughness.
The cracks at the edges of the vertical section of the L-shaped rib feet have been reported as more severe than those observed around the fastener holes (Type II, using Airbus terminology, as opposed to Type I for the fastener hole cracks).
These cracks are likely to be at the corners of the rib feet where stresses are higher. These are of greater concern and could be fatigue driven. The AD also states that this condition, if not detected or corrected, could potentially affect the structural integrity of the aircraft.
That said, the cracks observed so far have not been on the main load-bearing structure of the wing. It would take multiple simultaneous structural failures along a number of ribs to give rise to a structural integrity issue. It’s worth noting that there are around 4,000 rib-feet on each A380.
So what can be done about these cracks?
Well, once detected, these faults may be repaired by various means, depending on the extent of damage. For small surface cracks, metallic or carbon-fibre composite patches can be used and there is always the more-costly alternative of part replacement.
More here:
The Airbus A380 wing cracks: an engineer’s perspective