Whereas Youngs Modulous is well known work considering the fatigue life of notched parts in aluminium and steel has only recently been studied. This work is normally carried out by the R&D departments of big material companies. So, sorry D4v1d, I know that this kind of study was published only just before the A2 was launched and in the way that automotive developemnt cycles go Audi engineers will have been working to a different knowledge. OK, cracks will get bigger, this crack is of the tear variety, it is not through corrosion, by the way do you understand the different corrosion that can happen with aluminium? If this part suffered from stress cracking, as the Americans describe inter granular corrosion then my first post on this subject would have been very different and panic stations would have been well in order. There will be none of this with the A2 as the alloys chosen are the least likely to suffer. The exposed part of the crack in my door is approx 2mm long, its caused by the fact that the door opens a little more than was planned and caused the sheet metal to tear over time through the use of the door. If the sheet metal was a bit thicker it wouldn't have happened, as the tears are so small after so long I am not worried and will take my car to the dealer later. The car itself is nearly 6 years since build. It has been driven 55K miles. I'll be dead before the door drops off, in fact my son will be dead before the door drops off and he is just a teenager. Indeed if the door drops off it will not be because of that crack.
The A2 was an experiment. No manufacturer had produced a high volume vehicle composed mainly of aluminium before to fit in with modern day motoring with all the demands for crash, economy, comfort and longevity legal and otherwise. The demands on materials in the automotive environment is harsh and car manufacturers take great care in material and process selection, sometimes errors are made, often because of the neeed to make compromises for technical reasons. The joining of aluminium is difficult and costly. Choose the wrong alloy and the wrong process and you get AlanB's cycles that fall in bits -2000 series and welding are a fatal mix and I personally warned one UK cycle importer to change from this. Today most mainstream ali cycles use 6000 series alloys and will last a very long time just as I know that my A2 and all of yours will last. Your lawnmower will have failed due to poor design and execution and with respect to you Audi have a bit more resources.
Emm am I grateful to Audi for doing this repair for free? Yes and no. Yes because legally on many vehicles the warranty is out, it's not a paint defect. No because Audi I expect to stand by their product, they have a reputation and I am sure that in the future more mainstream high volume cars will be built predominently from aluminium. Audi will use all of this experience to build better the next time. Part of doing better next time is to take on board every little issue that arises. If this problem needed a huge fix their attitude might be different, but I doubt it, just longer to reach the right decision as the costs are more. Audi are thinking of the future.
So in my humble opinion people should relax, get the fix and continue to enjoy one of the best little cars there is.
