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PostPosted: Thu Feb 15, 2007 11:02 pm 
Old School Grand Master
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Yeah paperclips are steel? 8)


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PostPosted: Thu Feb 15, 2007 11:04 pm 
Retro Guru
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russell to the rescue


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PostPosted: Thu Feb 15, 2007 11:12 pm 
Gold Trader
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I think the key phrase missing from all of these posts is CYCLES.

Every designed (ie. non organic) item that moves has a number of cycles that it is expected to undergo during it's life time. Your car door handle, the switch on your kettle and, yes indeed, the frame of your bicycle. All these are expected to last a certain number of 'moves' before they enter unknown teritory and probably break.

The designed life of a frame is say 1,000,000 cycles. (aluminum degrades an infintessimaly small amount each time)

Say my Pace RC-200 was NOS. It had a design life of 1,000,000 cycles BUT it has been on LBS wall for 16 years. This was never factored in in the design process and therefore cannot be allowed for. A prudent approach would be to HALVE the number of cycles that that frame can undertake safely before replacing it. (if it was an aeroplane wing spar this is what would happen).

So aluminum does degrade over time. But only so much. I think that too much 'worry' is generated over aluminium, I would be as concerned about the internal corrosion that may or may not have occured inside my Orange frame, or the condition of the epxoy bonding on my Dyna Tech as be concerned about my well used Pace RC-200.

The US airforce are cannabalising B-52 Stratofortress's (mainly B-52D's) that are mothballed in the desert to keep the last 458 B-52H and B-52G's flying. Some interesting facts:
The LAST Boeing B-52 built was an H model in 1967.
The B-52 has new replacement wing spars and skins at 350,000 Cycles (this is measured by stress guages in the wing) but many of the aircraft's stuctural members are original.

EVERY B-52D saw action in Vietnam and none were built later than 1962. These aircraft have useable parts on them today.

Yes aluminium degrades over time, but seriously what is the worst that can happen? Gravel rash? The USAF haven't lost a B-52 since the '70's for ANY REASON!

*The reason I chose the B-52 to illustrate my point is:
It is made almost entirely of aluminium and built with '50's technology. They are all very very old and they have had a serious amount of research done into their future viability by folks far smarter than I! What the USAF do with the B-52 amazes me, just think, every one is older than it's pilot now!

**The US Dept. of Defense (which just retired the F-14 Tomcat) wants to keep the B-52 flying until 2047 :shock: as the cost to design and build a replacement is unthinkable now.

:oops: Sorry this got a bit long-winded, I'll go and lie down now :wink:


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PostPosted: Thu Feb 15, 2007 11:28 pm 
Old School Grand Master
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Location: No brakes? Way to commit soldier.
Excellent point, well illustrated Pete :)


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PostPosted: Fri Feb 16, 2007 1:21 am 
BoTM Winner
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The ironic point to this thread is that Jez still has not revealed why he wants to know :?

As for the rest of the technical drivel...really folks, who gives a shit? If it's a bike, ride it til it breaks with a big ol' grin on your face :D

cheers,

rody


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PostPosted: Fri Feb 16, 2007 7:26 am 
Retro Guru
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Location: Hobart, Tasmania, Australia
rody wrote:
The ironic point to this thread is that Jez still has not revealed why he wants to know :?


Not strictly true ;)

jez-2-many-bikes wrote:
Not a great fan of aluminium frames Im afraid... no Im not buying one of these


As he's ditched the Mustang idea (sensible boy), I'd say he's looking at some sort of alloy bodied (or chassised) sports car ;)


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PostPosted: Fri Feb 16, 2007 9:59 am 
Old School Grand Master
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yeah but....

oh never mind ;)


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PostPosted: Fri Feb 16, 2007 11:15 am 
Retro Guru
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Russell wrote:
Paperclips are steel aren't they? They're magnetic.


That was just a simple example of fatigue. A paperclip made of aluminium would break almost immediately if you tried to bend it the same amount as a steel paperclip.

Sticklegs: What you're saying is true but aircraft don't just have fatigue life but 'X' amount of flying hours as well.


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PostPosted: Fri Feb 16, 2007 4:37 pm 
Dirt Disciple

Joined: Sat Jan 13, 2007 2:43 pm
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if hes talking about sports cars then thats different

am i an expert and do i talk crap before i became a composites guy i had lots to do with aluminium most of it capable of being pushed along by afterburners

in my day job im an expert

down the local pub i talk crap if its to get in a birds nickers i definitely talk crap

i believe the question original question was regarding aluminium degrading then white powder(not columbian) appearance on the surface was mentioned before lots of people mentioned fatigue

aeroplanes are mothballed in that desert because its dry and not humid meaning parts will remain relatively free of any atmospheric degradation however remember most parts used in aircraft are given various anodic and galvanic resistive treatments, these parts can then be brought back in the case of b52

and most of the f111 fleet which are sent to our good freinds down under for their ageing aircraft which are undergoing the same kind of refurbishment

we in the bicycle world neither need or have cost allowance to under go such treatments and so its either polished anodized or painted

the anodizing on frames is sometimes hard or soft hard anodizing used on frames isnt really full depth anodizing as its not good for fatigue resistance and alloys which readilyaccept hard anodizing cannot really be welded into bicycle frames due to the fact that they stress corrosion crack

The white powder which appears on aluminium is also a precursor of stress corrosion cracking which is not really the sameas a crack caused by fatigue though does share certain mechanical causes

even in space where there is no air aluminium degrades by other mechanisms including the fact that its in the abscence of the harsh realities of the earths atmosphere

so if the structure is just sat unpolished or protected for 10 years then yes there is a risk of the aluminium being more succeptible to cracking based on chemical processes alone but this depends on a vast range of variables the main being what type of aluminium it is


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PostPosted: Fri Feb 16, 2007 4:43 pm 
Dirt Disciple

Joined: Sat Jan 13, 2007 2:43 pm
Posts: 67
ps all you pace owners out there

be afraid

be very afraid


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