Problem with aluminium.

General cycling advice ( NOT technical ! )
Des49
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Re: Problem with aluminium.

Post by Des49 »

Peter W wrote:I posted a reasoned follow up earlier this evening on my experience with the apparent durability of carbon fibre composite v. aluminium alloy in other sports, (with some questions for Brucey) which I felt could reasonably be carried over into cycle construction and durability. It was added to the thread at the time, but has since disappeared, or been removed.

I'm at a loss to understand why?


I would be interested to read your follow up, if you can re-type it please. I too have lost the odd post and it can be a pain to re-type things. Like Brucey, it is wise to copy your text in case of mishap.

I generally don't like the idea of aluminium long term, due to corrosion and fatigue. However I do ride an old Alan Al frame as a winter fixed, must be 25 yrs old at least. Also we have a couple of old Cannondale Al mtb frames still in use. One I tarted up a couple of years ago and touched up corroded areas where the paint had blistered and treated the inside of the frame, all seems fine. The other needs a good strip down now as there are some pitted areas and it may be a concern.

Some of the very recent Al frames seem to be getting good reviews, but they seem to be lighter and also softer riding. This also leads me to think that long term life will be compromised.
colin54
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Re: Problem with aluminium.

Post by colin54 »

I saw this today by coincidence, I didn't notice if the steerer was aluminium or not,

it looks like aluminium corrosion in the third picture at the top of the stem to me.

It was on a well used Marin MTB.


P1090665 (411x640).jpg


P1090666 (537x640).jpg


P1090667 (640x480).jpg
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NATURAL ANKLING
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Re: Problem with aluminium.

Post by NATURAL ANKLING »

Hi,
I am not sure alu was ever used for steerer tube, but certainly looks like aluminium.

The plug in the pic of handlebars, is obviously to strengthen the tube, but alas in the wrong place right where it will break for sure..............
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Peter W
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Re: Problem with aluminium.

Post by Peter W »

I'll not repeat my deleted post. I asked, but received no explanation. (It definitely was posted when submitted at tea time, but on later checking had been deleted.)

The gist though, was that I retired the alloy bike after just 4 years use because i became paranoid about failure at what I assumed to be a highly stressed weld point. (The skinny curved seat stays were obviously meant to soften the harsh alloy feel to the ride by giving a little, but that in turn meant (in my understanding) transmitting the bending forces to the thicker stronger chain stays. Those forces would then be concentrated at the weld point at the very rigid and inflexible bottom bracket. The thought of that joint parting at high speed down some bumpy steep hill, and the back wheel taking over the steering filled me with horror. (As Brucey confirmed, there are 'nasties' connected with the areas arond tig welded joints.)

As for carbon composite experience, I won't detail it all again, except to say that experience with carbon masts (windsurfing) has shown that, in practical terms, they have no discernable fatigue life. (Hotly contested by many experts, no two of which are seemingly in agreement about long term durability.) They only break if the stress forces exceed the bearable load they can take.

Hence I feel that, a carbon bike protected (coating) against U.V. sunlight exposure, will be very long lasting if treated safely. (Certainly no welded joints, a big plus for composite structures.) My main question was, what do they mean when they say carbon? In windsurfing, carbon content is listed as a percentage. e.g. 60% ,70%, (the rest being epoxy) or even 100% (Not so durable.) So are carbon bikes similar? Or are they actually 100% carbon?
Peter W
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Re: Problem with aluminium.

Post by Peter W »

Incidentally, the tables are completely turned when dealing with mountain bikes.

Alloy makes perfect sense for frame structures for three reasons (in my estimation). 1) they have full suspension to absorb the shock loadings. 2) they are built strong enough to stand the 'big hits' of the radical young hero brigade. 3) Us less radical and more concerned riders (no broken bones thank you) don't stress the bikes anywhere near to their limit.

I have two good modern full suspension mountain bikes and it's not the frames that bother me. It's the confounded cost of for ever having to replace drive train and suspension bearings from riding them in grinding paste, soggy wet Merry England! But hey, we're lucky to be alive in such exciting two wheel times, and modern bikes, both road and off road, do really perform. (Quite a change from Sturmy Archer 3 speed hubs on old steel touring bikes of youthful times - but then, we didn't seem to have any less fun! (It's all in the mind, you know.)
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Si
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Re: Problem with aluminium.

Post by Si »

According to the forum logs, no post has been removed from this topic in the last couple of days, either by the forum staff or the author. Thus it would appear that the post in question never made it to the forum, or there has been some strange bug in the system. Not saying that this is the case, but one or two people have been caught out by pressing 'preview' rather than 'submit'....thus it looks like post is published but when you return it is not there.
Brucey
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Re: Problem with aluminium.

Post by Brucey »

CF varies quite a bit; it certainly isn't "all the same" any more than, say, all wood is the same. Under certain test conditions some grades of CF show what appears to be infinite fatigue life, but then so can steel; reality gets in the way and means that real applications generally don't show the same properties as can be seen in laboratory tests.

In many conventionally built structures, one is (often rightly) concerned with the joints as potential sites for a failure. On the plus side, using laid up CF in a complex structure means that one can free oneself of a lot of the geometric stress concentrations which occur at what would normally be joints.

On the minus side, the material itself is comprised entirely of 'joints' in that the material is comprised of fibres that are bonded within an adhesive matrix. Very many of the failure modes of CF involve degradation of the adhesive and/or the bonds to the CF at which point the fibres themselves can locally see conditions that lead to their failure.

I have plenty of practical experience with using CF in certain applications and it can be the unintended service loads that catch you out. For example a certain part might only be meant to see bending loads and if laid up in CF to accommodate these loads there can be a massive weight saving vs steel. However the same part may occasionally see (largely unintended) loads of another kind, eg torsional loading. If the lay-up is altered to suit these loads then much of the weight (and/or cost) saving is lost. If the part is not designed to accommodate the occasional torsion loadings, it will (sooner or later) start to crack and this will cause a failure. Thus CF works best (and most simply) under simple loading conditions. By and large bike frames see complex (and highly variable) loadings. I would certainly not take it for granted that the lay-up in a frameset is optimised even if I thought the material itself was inherently durable under the service conditions.

cheers
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Tangled Metal
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Re: Problem with aluminium.

Post by Tangled Metal »

Basically, all bike materials have their strengths and weaknesses (positives and negatives).
A designer just needs to know how to get the best out of them for the application.
A good aluminium frame could be better than a bad steel frame for example. It's not just about the material but about good design. You can't override material properties and manufacturing methods but you can make the most of them.

Is that something you'd agree with?
pwa
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Re: Problem with aluminium.

Post by pwa »

Peter W wrote:Incidentally, the tables are completely turned when dealing with mountain bikes.

Alloy makes perfect sense for frame structures for three reasons (in my estimation). 1) they have full suspension to absorb the shock loadings. 2) they are built strong enough to stand the 'big hits' of the radical young hero brigade. 3) Us less radical and more concerned riders (no broken bones thank you) don't stress the bikes anywhere near to their limit.

I have two good modern full suspension mountain bikes and it's not the frames that bother me. It's the confounded cost of for ever having to replace drive train and suspension bearings from riding them in grinding paste, soggy wet Merry England! But hey, we're lucky to be alive in such exciting two wheel times, and modern bikes, both road and off road, do really perform. (Quite a change from Sturmy Archer 3 speed hubs on old steel touring bikes of youthful times - but then, we didn't seem to have any less fun! (It's all in the mind, you know.)

It has always been my understanding that ally makes sense for MTBs because the "suspension" comes from fat tyres and suspension mechanisms, while the frame itself is rigid and not subjected to flex. But as the OP asks, what happens when ally is used in a situation in which it is intended to flex as part of its design brief? According to everything I know (not much) that means a limited life.
Brucey
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Re: Problem with aluminium.

Post by Brucey »

Tangled Metal wrote:So basically all bike materials have their strengths and weaknesses (positives and negatives). A designer just needs to know how to get the best out of them for the application. A good aluminium frame could be better than a bad steel frame for example. It's not just about the material but about good design. You can't override material properties and manufacturing methods but you can make the most of them.

Is that something you'd agree with?


yes but each material has its limitations too. These limitations can be either fundamental or practical. For example that aluminium alloys appear not to show a fatigue limit is presumably fundamental. Whereas that you can't make a metal frame without there being some quite nasty stress concentrations in it is a practical limitation.

There's no such thing as perfection; just different sets of compromises that suit some folk better than others.

cheers
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Peter W
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Re: Problem with aluminium.

Post by Peter W »

Yes indeed. Thank you both.

I certainly want to keep and enjoy my year old C.F. Roubaix. It is by far the nicest bike I've been lucky enough to be able to own. Also, thank you to the admin staff. It must have been my error the post didn't stick. (put it down to senility - I've long since been retired and free of all those working cares.) :lol:
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mjr
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Re: Problem with aluminium.

Post by mjr »

I'm just going to add my old joke here:
Q. How can you tell whether aluminium has oxidised?
A. It's not on fire.

(Imagine https://www.youtube.com/watch?v=NauUM5ySWYQ but with more than a scratch on the aluminium... there's no video of it, but I have seen a similar reaction catch fire.)
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Mr Evil
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Re: Problem with aluminium.

Post by Mr Evil »

Peter W wrote:...In windsurfing, carbon content is listed as a percentage. e.g. 60% ,70%, (the rest being epoxy) or even 100% (Not so durable.) So are carbon bikes similar? Or are they actually 100% carbon?

I think those percentages actually refer to the ratio of carbon to glass fibres. Bicycle frames will usually be almost entirely carbon fibre, with glass and sometimes kevlar only used in small amounts in a few specific places. The better manufacturers do a pretty good job of squeezing out excess epoxy, so there's not a lot of that in there either.
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NATURAL ANKLING
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Re: Problem with aluminium.

Post by NATURAL ANKLING »

Hi,
On posts- I have been caught out many times, you submit and you are presented with what looks like your post-OK.

But If another has posted since you started constructing your post it will appear above yours, a chance to read this first and maybe alter yours.

But others posts since you started yours may well be up off the screen, and you don't notice.

When you look again and you have moved away from the post its not there because in this case you have to re submit.

That's when pressing submit does not work first time, miss that and its gone.

Time consuming posts that you are constructing should be saved in drafts or pasted to a text file...............as said.
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NATURAL ANKLING
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Re: Problem with aluminium.

Post by NATURAL ANKLING »

Hi,
Composite material....................on their own the individual parts may well be totally useless.

It's not rocket science that if its not chemically changed into to one compound it may well become two parts later.
NA Thinks Just End 2 End Return + Bivvy - Some day Soon I hope
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Please forgive the poor Grammar I blame it on my mobile and phat thinkers.
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