Cold weather and tensile strength

[JeffR]

OK, so I've had a bit of a morning.  Started swapping out the very leaky power steering box and sheared 3 out of 4 7/16 bolts (not a problem got new ones and a new box) so it got me thinking. Air temp round here is currently -5 C. thats a tad chilly, actually there's a queue of female sorceress' awaiting breast reconstructions, the bolts were put in during the summer and torqued up to 60ft lbs. 

also sheared the alternator belt tensioner on the family passat, but thats aluminium, so its not really metal.....

Anyone know how much the tensile strength is affected by a reduction in temp? I wonder what the change in tension is when a relatively hot bolt (mid 20 C) cools down.

Edited January 18 by JeffR

[Snagger]

It could be moisture or water in the threads or bolt hole frozen and expanded, wedging the bolts.  Lowered temperatures do increase brittleness, but I think you’d need much lower than -5oC to significantly affect bolt tensile strength (but open to correction on that).

[JeffR]

could well be, but the threads on the cattle trucked bits showed no galling (cross threading is natures loctite), moisture or corrosion. Bolt heads sheared with a clean clearly defined "crystalline" pattern at the junction between threaded section and unthreaded section. Of course it could just be the bolts were ancient and past their sell by date (like their owner).

To top it all I set fire to my beard again

[Maverik]

50 minutes ago, JeffR said:

 

To top it all I set fire to my beard again

It was the "again" bit that had me fall off my chair 🤣

[FridgeFreezer]

Wikipedia suggests it's got to get down to about -74 for steel to become brittle:

https://en.wikipedia.org/wiki/Embrittlement#Low_temperature_embrittlement

[Gazzar]

Ordinarily.

 

But this is Jeff we're talking about.

 

[miketomcat]

It is definitely easier to snap bolts off in this weather. In fact in my experience anything you touch at subzero temperatures is likely to break. I'm sure there's science to it and plastic is worse you only need look in it's general direction.

Mike

[ThreePointFive]

This is really interesting. If the science says the difference isn't in the materials, maybe it's in the interface between them. 

I.e. everything is contracted in colder weather, clearances become tighter and the torque to break free becomes higher. Add in any rust in the threads and a tight tolerance may become no tolerance. 

I dunno, I'm neither a scientist nor an engineer, as evidenced by my car. 

[FridgeFreezer]

10 minutes ago, ThreePointFive said:

This is really interesting. If the science says the difference isn't in the materials, maybe it's in the interface between them. 

I guess it's a line or curve down towards that -74 figure too, not a sudden change.

[elbekko]

13 minutes ago, ThreePointFive said:

I.e. everything is contracted in colder weather, clearances become tighter and the torque to break free becomes higher. Add in any rust in the threads and a tight tolerance may become no tolerance. 

That's what I was thinking too. But the things it's bolting down should shrink as well, so not sure how much any of that matters.

[toenden]

A couple of years ago, I was making "long postponed maintenance" in the depth of -15c (some time you get proud of yourself....) doing so, I dropped a 19mm spanner on the concrete paving and it snapped in two with a very high "pling"... the spanner was a reputable make. At the time the only reason I could come to was the temperature. Of course my dad pointed out, that I ought to use it faster next time, to get some heat buildup into it... 🙄

/mads

Edited January 19 by toenden
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[Escape]

What was the response to the warranty claim?

[bishbosh]

The answer to this is "it was your beard's fault"  . Standard bolts are good down to -50 so it was definitely your beard.

[smallfry]

The other day I had a G clamp frame snap. Have used it for years, and I never strain them by using any extension on the T bar.  I also put it down to the temperature. Not an expensive one, so was probably cast iron rather than steel. Who know ?

A few weeks ago I watched half of a program about ships disappearing in the late 19th, early 20th century in cold climates. They attributed this to failure of the steel plates or rivets. Not high tensile obviously, but interesting none the less.

[Snagger]

Different materials have different expansion and contraction rates with temperature.  Aluminium expands more with threat than steel for example, so also contracts more.  That means a steel bolt into aluminium will be much tighter in the threads when the cold sets in.  The same will apply to a lesser extent with different grades of steel.