Fact or fiction?

I was climbing over the weekend and whipped on a small brass nut. My partner went to clean it and it was burried. The route had entered the sun after I placed the nut. He was unable to resurrect the nut and claimed that the sun causes the brass and rock to expand, thus welding the nut even further. Fact or fiction?

I've heard people booty welded cams and nuts by waiting for shade.

Thermal expansion of rock in the sun is not a myth. It happens, and I've experienced it -- welded nuts fall out on their own after a cool night.

I got my fist stuck in Double Cross at JTree after it came into the sun. Had to wait til sundown before I could wiggle out. Hella embarrassing.

There is a finger crack that I can't get into in the sun but when its been in the shade all afternoon, I can lock just fine

Thermal expansion is a thing.

Whipping on a nut can, also, make it nigh-unextractable.

Hard to know which was the case here.

If thermal expansion was a problem in rock every expansion bolts would fail after a few day/night cycles. Chock-stones would be pulverized weekly.

If the crack was formed by a large flake with dirt behind it, then a cold night could heave the moist dirt and expand the crack.

Fact.

Last year my partner couldn't clean three small stoppers in a row while following the crux pitch of Spook Book. I had linked pitches and during the time I was leading the route moved into the sun. Annoyed that I'd have to rap 180 feet down to get them out - I rolled my eyes and got on with it...

...Sure enough, all three were irretrievably wedged. None had been subjected to body weight nor were any set with more than a gentle tug. It's not too hard to believe that the movement of a massive, 3-pitch long crack system/flake only a fraction of a millimeter would be enough to pinch a small stopper.

rocknice2, being that a crack or flake is a natural stress line in the rock - probably created by expansion and contraction to begin with, I speculate this is pretty different than a small bolt hole, which is surrounded by one piece of rock on all sides, changing size.

Years ago my partner got a #1 really stuck on lead. He tried to clean it on the way down. I tried to clean it on the way up. He went back up and tried again....no luck. He came down and grabbed some ice on the ground left by a storm the day before, went back up and packed it around the cam lobes, waited a couple minutes and it came right out.

More than once I've come across fixed gear that seemed hopeless, only to come back on a cold morning and was able to pull it out. All anecdotal, of course, but I believe.

Fact. When heated, both the nut and the rock would expand. Both sides of the rock would expand towards the nut and the nut would expand forcing it into the crack.

An example: 77F in the shade, in the sun its 95F. Assume your brassie is 2mm thick.

Your brassie will expand by 374 nano meters, which is .374 micrometers. Which is smaller than a bacterium by an order of magnitude. engineeringtoolbox.com/line…

If I was a betting man, I would say it was the whip, not the sun.

Matt Carroll wrote:The route had entered the sun after I placed the nut. He was unable to resurrect the nut and claimed that the sun causes the brass and rock to expand, thus welding the nut even further. Fact or fiction?

I don't know, it might depend on a lot of factors. If the entire rock mass warmed up uniformly, then heating the rock would expand the crack, not contract it. (Seems counter-intuitive, but consider the 2-D simulation in which you draw a crack on a sheet of paper, and then enlarge the image.)

But in the case of a straight-in crack, there are temperature gradients into the rock, so it seems plausible that the warmest part of the crack on the outside could contract in this case. Perhaps this accounts for the various observations mentioned above. I imagine some engineers have studied things like this for man-made structures.

Great replies! Pretty interesting idea. Thanks for the info all around.

Such a timely thread. Yes, some cracks (notably large "onion skin flakes" on exfoliating granite domes) can exhibit significant thermal motion. Don Mellor mentioned a crushed hex lying at the base of the Poko slab years ago. I've had pieces get tight over the course of an hour when the sun hit a slab.

Anyway... here's a BD 11 Stopper I found lying in the bottom of crack just a few hours ago at the Gunks (an area not known for thermal effects). I imagine this is the result of a full seasonal cycle of thermal expansion.

I wonder if I should send it to BD and ask them if it can be repaired.

Oh, and OP likely welded the nut by falling on it!

^^^^^^^^^^^^^

Insert comment " I would whip on that!" Or "send that to me for inspection"

I say insert because no way I would

Jon Nelson wrote: I don't know, it might depend on a lot of factors. If the entire rock mass warmed up uniformly, then heating the rock would expand the crack, not contract it. (Seems counter-intuitive, but consider the 2-D simulation in which you draw a crack on a sheet of paper, and then enlarge the image.) But in the case of a straight-in crack, there are temperature gradients into the rock, so it seems plausible that the warmest part of the crack on the outside could contract in this case. Perhaps this accounts for the various observations mentioned above. I imagine some engineers have studied things like this for man-made structures.

climbing friend,

How may I for possible consider this? Are you thinking of the funny stuff? I am not taking the LSD and the entire universe it expands as the 2D sheet of paper. Only the rock it expands due to heat, not the entire universe myah?

These two articles are about cracks expanding causing rock fall. Once a piece is placed, the difference in expansion might be harder to judge but it seems fair to say this can have an impact on stuck pieces, too.

nps.gov/yose/blogs/What-Cau…

techtimes.com/articles/1451…

Aleks Zebastian wrote: climbing friend, How may I for possible consider this? Are you thinking of the funny stuff? I am not taking the LSD and the entire universe it expands as the 2D sheet of paper. Only the rock it expands due to heat, not the entire universe myah?

A funny way to look at it, thanks.

Anyway, my only point is that it just isn't obvious that any crack will contract from heat. For example, in the workshop, when I've had a something like a nut stuck on a bolt (of the same metal) or a pin in a hole, sometimes I've loosened it by heating both up. In this case, the crack (the gap between nut and bolt, pin and hole) expands with heat. The cliff has gradients, so, as I said in my first post, it seems quite possible that the opposite can happen.

DaveBaker wrote:These two articles are about cracks expanding causing rock fall. Once a piece is placed, the difference in expansion might be harder to judge but it seems fair to say this can have an impact on stuck pieces, too. nps.gov/yose/blogs/What-Cau… techtimes.com/articles/1451…

These two articles are about a flake expanding with heat, and so the crack between the flake and the wall also expanded.

So, here it is the opposite as to what the OP suggested. So, like I said, what happens may depend on many factors.

David Gibbs wrote:Thermal expansion is a thing. Whipping on a nut can, also, make it nigh-unextractable. Hard to know which was the case here.

I would say it's definitely the whip. Very rapid thermal expansion of the metal would require a flame or other strong heat source to change the nut's volume quickly. It is unlikely that the amount of sunlight on the piece changes fast enough unless you are hanging there for a long, long, LONG time.

There is a physics demo on this topic, where a ball on a stick, and typically made of brass, is passed one way through a ring but cannot be passed the other way out once the ball is heated or the ring is cooled.

Thermal expansion is definitely a thing, but unless it took your partner an hour or two to get to the stuck piece I think we can safely say it was welded by the fall.

rocknice2 wrote:If thermal expansion was a problem in rock every expansion bolts would fail after a few day/night cycles. Chock-stones would be pulverized weekly. If the crack was formed by a large flake with dirt behind it, then a cold night could heave the moist dirt and expand the crack.

We´ve seen problems with glue-in bolts which move very slightly (we call them "clickies"). Really anoying when you check them on a hot afternoon and they move slightly but when you go back in the morning to replace them they are bomb solid.