Frame failures – At which low temperature do you not risk riding your mtb?

Nice description! (especially the ruck in the carpet bit)

Back to brazing – Sifbronze no.1 is 60% copper, 39% ish zinc and a few other bits (Si and Sn I think). From a brief google FCC / BCC in brass seems to depend on more than just the zinc / copper ratio. If you find anything I’d be interested to know (not that I think it is a major problem in the UK).

Might have a chat with the metallurgist that sits opposite at work (but brazing isn’t commonly used in most industries so probably need to dust off some books).

Tbh I know very litte about brazing metallurgy other than what I have forgotten since uni, and that wasn’t much..

Orbital loading of the ISS is tiny, not even a remotely comparable application! Add to that the fact that alloys massively change properties with heat treatments and are very customisable, that’s a generalisation you really can’t make,

all irrelevant because Al doesnt undergo a DBTT. Not a function of which alloying elements you add to it (which form precipitates, rather than changing the basic structure).

The electron microsopes I used to study Al alloys were themselves made largely of Al alloy, and cooled by liquid nitrogen (so below 77K, ~195C). None of them snapped…

so if you are a metallurgist too, please do not shoot me down, I’m sensitive..)

I’m sure theres a joke there (sensitive, ductile, brittle)… Not been one for a few years now but sounds good to me.

notch sensitivity…

The thing that impressed me most was the ability of the engines to work in those temperatures.

Intake air temperature is raised by 500C just through compression alone – before any fuel is added to the mix. by the the time the air reaches the turbine we are talking about 1500C – well beyond the melting point of even the most expensive Nickel Alloys used in turbine construction. Bleed air from the compressor is used to cool the blades to acceptable levels by way of some incredibly sophisticated plumbing. Despite all this the maximum allowable temperature within the turbine is the major limiting factor of engine performance in terms of both thrust and efficiency – so engines are run as hot as physically possible.

….so you dont have to worry about air temperature the next time you go on holiday – in fact lower temperature is probably better since a greater temperature increase is possible and therefor better performance – but you would probably need to have designed the engine around these conditions to gain any significant advantage.

Do people really consider this when going out for a ride? 😯

No I consider getting salt all over the bike from the minging roads and then not being able to remove it when I get back as the hosepipe is frozen – result = rotting bike

Hi Toys19,

Thanks for taking the time to generate a nice long reply. Now i’m gonna be annoying 🙂 I just really find this interesting.

There me be some difference in the nomenclature regarding ductility that we are both using I will explain what I understand it to be. There is stiffness and also ductility. These are not the same for me. Stiffness can be described as what happens in the elastic region. Ductility on the other hand is what happens when you get into the plastic zone (dislocation movement as you rightly describe).

Back to the original question: You mentioned: “In fact some aluminium alloys actually get more ductile at low temps. (6061 T6 for example) I can explain that if anyone wants to know about slip planes and arrhenius equations”

Being a geek, I questioned this to myself as it does not seem to correspond with the physics that I have studied (a long time ago). Even with your lengthy reply I still cannot see this. So I have to conclude that we may be talking about different things here. I looked through some of the literature you cited and this seems also to be in opposition to what you have mentioned. (S.W. Van Sciver, Helium Cryogenics, International Cryogenics Monograph Series)

6063-t6 is at its stiffest (highest E) at 0 degrees kelvin dropping with temperature increase.

I believe that the original question was related operating temperature. In general for materials as temperature reduces, stiffness increases, and as stiffness is increases flexibility is reduced. This essentially makes them more brittle.

With composites, as temp reduces polymer chain mobility is reduce also making the matrix material more brittle. There was an earlier reference to aircraft and composites which implied that bike composites must also be ok. Well not necessarily, you cant make that assumption. There are many different types of matrix materials each with their own optimum operating temps. Aircraft materials are carefully selected after years of testing (they are also hugely expensive) bikes on the other hand are a different kettle of fish. Designers skills related to these materials (in the cycle industry) are still in their infancy. Many mistakes are still made and many failures still occur. but that’s another discussion.

Back to the original discussion. Could it be that you are thinking of heat treatments and cooling of cast materials and the effects that you would see described in a phase diagram? You also mention interstitials and describe them differently to what I understated them to be. Interstitial element sizes are usually smaller than those of the base material, thus they can fit in between the lattice framework. As i understand it these are normally added intentionally to inhibit dislocation movement (Alloying elements).

I believe that the original question was related operating temperature. In general for materials as temperature reduces, stiffness increases, and as stiffness is increases flexibility is reduced. This essentially makes them more brittle.

Ah unfortunately this is just incorrect. Increased stiffness does not neccesarily make things more brittle, I guess I did not explain it very well.

The major contributor to brittle failure is a lack of ductility.

The more I consider this the more dissapointed I am, you have completly misunderstood my explanation, and that can really only be my fault for not making it clear enough. bugger.

Chief900, did you have any luck understanding what I was trying to explain or shall I go a bit deeper/shallower?

4130 should be good down to -100 °C, safe limit would be -70 °C.

may not survive a martian winter.

HTH 😉

experianced two sdg ibeam posts fail in cold weather 1 whilst riding on a canal path (under 1 month old) + witnessed two others fail around the same time there was a defect with the bonded joint IMO as design defect (I like the clamp mechanism / interface) however I would not risk my life with them especially after experiancing SDG’s importers arrogant responses (…..never seen one of our posts fail….. blah blah blah…. doesn’t happen blah blah blah….

maybe the products improved??? I hope so…I for one do not trust them

I had my free hub go at -13 and had to push my bike the rest of the way to work 🙁

Seriously?

Orbital loading in the ISS is not high, but loading due to the differential pressure between the interior if the capsules and the vacuum of space is very very high, as are the thermal stresses imparted when the craft moves from the sunny side of the Earth to the dark side where the temp goes from minus hundreds of degrees to plus hundreds of degrees, not to mention the temp difference between the structure that faces the sun compared with the parts of the structure that are facing away from the sun.

The stresses on a bike frame are tiny with high factors of safety in comparison whether they be steel, alloy or CF frames. Cracks in frames are more likely to be due to abuse, damage or quality defects rather than overstressing or fatigue.

Yes, you can manipulate the mechanical properties of al alloys, but there are limits.

I’m not getting you wobbliscott, what is it you are agreeing or disagreeing with?

I am more worried about mr Winkie turning into a foo-foo
I tie a bit of string to mine before I go out in the cold.

That way if it does turn inwards I can yank it back out again with the string.

Sir, That’s a Belter.