What caused Simon Faithfull's chair to fall appart?

Question

There is an art/science video clip on youtube, by Simon Faithful, called Escape Vehicle no.6 (chair in space). It shows a simple steel office chair, tied to a weather balloon, ascending into the upper reaches of the atmosphere. Apparently it reaches about 30km above sea level. It's quite a beautiful clip.

At the start, the chair rises quite violently, as it is buffetted by surface turbulence, as would be expected. After a while (2:07-2:33, I suppose once it gets above the planetary boundary layer), the ascent becomes fairly smooth - there is still a lot of movement, but it's not so violent. Then at 2:45, when the chair is near the top of it's ascent (~30km), suddenly things start getting really violent again, and the chair looses a leg, then half the back is torn off, and then the chair is apparently torn from the rope, and disappears.

What forces would cause such a violent disintegration of what is a reasonably strong object, in such a thin atmosphere?

Answer 1

The flight actually took 25 minutes, the video you linked to is edited down, and the later stages of it look pretty turbulent. I'd guess it was the shaking that eventually broke off the chair leg, possibly due to metal fatigue. Note that the leg broke off after the balloon had burst and while the chair was falling back to Earth.

As Anna says, the low temperature may well have been a factor. The ductile-brittle transition for mild steel is around -50C so at -60C it would be a lot more brittle than at room temperature. From the way the leg broke off I'd guess it was the weld that failed rather than the steel itself.