Based on comments and articles that I have read elsewhere early this week since the Sao Paulo Grand Prix, I thought I might put a follow up Tech Draft together to explain in a little more depth, a recently topical issue in Formula 1, composite failures and repairs.
If we are to take at face value the public comments that Mercedes have made about the DRS-Gate, there was some sort of failure in the rear wing assembly that resulted in the non-conformance.
Unless there is something a lot more complicated going on, and I accept that there more than likely is, I can think of a couple of failure modes that may be the root cause.
What could have gone wrong?
Firstly, there is the possibility of a failure at the wing element pivot point. However, let’s not assume that it would be something as silly as a drilled hole in a composite panel that has flogged out and elongated. That is far too agricultural for Formula 1.
Generally, a joint like this in a composite assembly would be either a plastic or metallic bush bonded to the composite. Usually the bond is achieved using a two part epoxy paste, filled to some extent with micro glass spheres or balloons to increase the bond line thickness and achieve desirable strength. The bushes are bonded in the parts at ambient temperature after they have been autoclaved, hot pressed, or whatever the lay-up method used. If the bond line of the bush and the composite panel is compromised or fractured, it’s likely that misalignment of the pivot joint would occur.
Secondly, there is the possibility that an internal spar or rib joint failed. F1 aero-foil sections are not hollow. The skins are very thin, obviously to minimize weight, and so if an F1 wing section was hollow, it would simply collapse and fail, even under a fairly insignificant downforce load.
Consequently, as per an aircraft wing section, there are a series of reinforcing ribs or spars to increase the cross sectional rigidity and mitigate collapse. In the days of aluminum wings, ribs were fastened to the skins with countersunk rivets. In the composite era the ribs are bonded internally, once again using the micro-ballooned epoxy paste. If the bond line of a rib was compromised, it may be possible that the very thin composite skin may flex locally under load.
What Red Bull did for their wings
The other discussion to be had with respect to wings and composites is the issue(s) Red Bull seem to have been encountering ever since Austin. I need to make an important point at this juncture. Regardless of what people thought they may have seen or heard, teams just don’t fix structural composite components with tape.
However, what I saw televised on two separate occasions was Red Bull technicians hurriedly repairing what was admitted to be cracking at the loaded joint of the rear wing main plan element and the end plate. What appeared to be tape was instead highly likely rolls of pre-preg glass scrim. This scrim is a very fine unidirectional weave of continuous filament glass fiber that is pre-impregnated with resin.
The give-away was the color of the scrim, and the technicians waving hairdryers around to cure the resin. This method is only used for minor hairline cracking and any form of more significant cracking would have involved a more in-depth composite repair using carbon cloth and vacuum bagging.
Composite parts serve an important role in F1, but it is important to acknowledge that they can be quite fragile, reliant on multiple bond joints, and can be brittle under loading in certain directions.