That was a nice first test, but now you have your confidence I really think you should be going a bit faster and braking a bit harder.

Image is a bit small dude, doesn’t do it justice.

Just out of interest you don’t work for Boeing do you?

7 layers eh? what made you think of 7?

What was that about composites having to have a balanced and symmetrical layup?

Anyway, It looks woven, are all the layers woven? are all of the layers in the same orientation? Any idea what the weight of the reinforcement is ? g/m2 ?

“Galvanic effect? Given the epoxy and anodising and the fact that it’s effectively sealed, is that likely?”

I wouldn’t worry about that if I were you given the expected life span. Just cross it of the list of things to worry about, or list under trivial.

How much do you weigh out of interest and how many plies of fibre did you slap on there?

want a real bike?

take this:

http://www.bmc-racing.com/ch-en/bikes/2013/road/model/impec/impec/super_record_eps.html

Gulp ! 8O

Not the best I have seen, but full marks for the innovative approach. However, if you really intend to use this things there are somethings you should be aware of (maybe you already are).

Carbon composites, work best in tension, rather than compression and their strength or rather performance will be affected by a number of factors. The braking force is probably going to induce mostly tensile in your bracket, although there could be the possibility of a moment there that could put the lower part of the bracket into compression. If I were you I would be sure to have a fed wraps of continuous fibres which are wrapped around the bracket and the fork leg. How many? depends on the weight of the fabric you are useing (maybe its UD) it also depends on the resin type.

A couple of other things. The mechanical properties of the composite part will be affected by porosity content and resin content. You have tried to get rid of excess resin (i assume) with your tape. (which is not a bad idea) but just so you know, there is a product called shrink wrap. Wrap it around, heat with heat gun and it will shrink to give you a very good compression.

Resin type, what is the cure temperature and what temp do you intend to cure it at? if you dont reach the recommended temp for the right time you will not get the properties. Left in a cold garage to cure=not so good.

Galvanic corrosion, carbon in contact with AL is not so good. Probably ok for the time that this will last (:-) but longer term bonds will deteriorate.

Positioning on fork, well. You are attempting to modify a fork which has not been designed for this. In use you will be applying a significant and sometimes very aggressive and concentrated force, to a part of the fork which is probably highly loaded.

But I guess that anyway you are just doing it for fun and don’t really intend to use it??

Personally I would ditch the carbon XC bike. Carbon is great for road bikes, but less so for XC applications. Depends also a great deal on how hard you ride and also how often and hard you fall.

My wife’s face still looks ok :lol:

Nevertheless, your post has stimulated some discussion and also brought to light similar problems which others have had. Would be interesting to know just how many steerers are failing like this.

ahwiles has mentioned that that his star fangled nut was the culprit in his case. Sounds highly likely. Overtightening of these can put an indent into the inside of the steerer, this can serve as a crack initiation point and lead to this type of failure.

That’s real interesting.

Is your post a “just out of interest post”? or are you looking to determine the reason for failure for a warranty challenge?

I would be interested to know how old the forks are. If you have a good macro lens a close up of the fracture surfaces would be very useful to provide some clues as to the reason of the failure. when things like this happen, its always tempting to put the two pieces back together to see how they fit, however this can destroy some of the “evidence” which tells the tale of the failure.

Dude,

Some positive comments coming your way here. No one here is gonna knock someone who wants to ride. I would certainly recommend a riding buddy.

I was well over weight a while back and (i know people are gonna laugh) i tried an american style video training thing. It gave exercise you could do at home every day for no longer than an hour. I saw massive improvements very fast in terms of weight loss and fitness improvements.I combined this with biking and it was great.

Stick with it buddy

The huge mark ups on bicycle gear, be it bikes clothing or whatever. Then using marketing which implies that you are an idiot to justify the high prices.

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 think this is a valid question….

Plenty of crap coming from bike companies. Marketing budgets are huge in comparison with development.

Question for you Toys19

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.]

Maybe you could shed some light on how this works? I would not expect any metals to become more ductile with reduced temperature. This seems very odd, of course I would expect ductility to increase with temperature as they progress towards melting point.But certainly not the other way round. Would be interested to hear why?

Cheers

great feedback chaps. I am moving towards XT 2×10 chainring.

Now if the groupset does not include brakes…. that is gonna be my next question :-)

Great responses so far guys, very grateful. One more question that comes up.

I have just noticed that there seems to be a move towards having only 2 rings on the front rather than 3. Any comments here? I will be riding some serious up hills technical and all. Do you thing that I will get the range I need with a 2×10?

Cheers

Ch

I wouldn’t bother with any carbon rimed wheels. Stick with metal they are tried and tested. You may think the same about carbon rims, but you would be surprised how little bike designers know about these materials. I have seen several rims fail with terrible effects.

Its certainly worth protecting your head. My friends mother died a few years back after a relatively tame fall, however she smashed her head on a hidden rock.

That should have been enough to convince me but I still didn’t bother wearing one as I was more concerned about what type of hat I should wear. Then a couple of years ago I ended up being helicoptered off the mountain after a bit of a smash. I narrowly missed also smashing my head in, but the parts i did hit received enough damage to convince me to think about wearing one. Now I never go without one.

I would particularly recommend it for anyone who does a typical ski holiday type approach where you don’t ski for most of the year and then ski like crazy for a week. Athough great fun, people get tired and thats when accidents happen, also skiing when conditions are not so goo increases the risk. Ice can also be pretty hard and I have seen lots of people smash their heads in on ice and ruin their holidays. not fun at all.

Its all down to choice, but I would certainly recommend it.

Trimix,

Perhaps that’s good advice. I have the tendency to make fast decisions. I should perhaps savour this one and try some things out eh…

Well, call me a traditionalist but I am not really considering the 29 option. I don’t muck like the look of them.

As for maintenance, I need simplicity and reliability, but would I expect to have to do a lot of maintenance on a FS?

Mr Nickhart, not really sure what your angle is there, but I need to climb as well as descend, like I say, Im not so interested in just getting in a lift and coming down without much pedalling.

Hey guys,

Thanks a lot of the input. I feel more educated now :-)

Cheers

There is also lots online about the thickness and the number of layers used on boat hulls. By the looks of things lots of companies use double layers of 6mm and use the outer as a of type sacrifical skin. Very similar to how galvanising was used in the olden days for sacrifical protection. Been a while since I did my materials module on my degree so maybe resins have changed and the pre-treatment process has changed for the better.

Hello Chaps, I can help a little the technical aspects.

Mr Dimmadan, Sorry but you are almost there. I recommend a refresher from your course notes. :D

Carbon fibre is on its own is not woven. But it can be, its not always used in a woven form. Getting it wet is nothing like getting water on cardboard and your bars will never bend rather than snap. Carbon fibres do not soak up water. Carbon composites are stiff, but also brittle. In the marine industry you do sometimes see outerskins of different materials, but this is not anything to do with galvanising (galvanising prevents corrosion on a surface, I think you meant galvanic corrosion and the use of a sacrificial anode) This is not related to our problem here.

So to the question: I guess it is whether the bars are still ok and usable?

My first question is how hard did you hit them ? I can see that you have a scratch, but did they experience some real impact ? If they did it is likely that you have caused some internal damage to the bars which will help them to fail later. You are unlikely to know this without the use of some non-destructive testing equipment (ultrasound is good!) If you don’t happen to have this at your disposal you could strip the bars off your bike and use something to tap the surface. Tap the around the good end and then the area of suspected damage, if there is a change in tone its likely that damage is significant. Although this still does not guarantee that your bars are fine. If you are doing very aggressive and demanding riding it could be a problem and the bars have some internal damage. They could just snap and probably leave a very jagged and sharp surface which might be a danger in itself.

The real worry might be that you have started a crack with your scratches any crack will propagate and cause the bars to fail. In short, if they have really had an impact I would probably not use them again. Although its hard to tell without seeing and touching them. If you want some more info and have more detail, drop me an email and we could discuss further if they are good or if you might want to repair them.

Cheers

Carbon fibre is basically weaved material with a resin on to make it rigid. If the carbon itself gets wet it starts to go bad bit like getting water on cardboard. But over time it will start to get very weak and then bend rather than snap. Most people put nail varnish over small cracks and knocks on frames to stop water getting in

[Well that’s not very eco is it bwaarp.]

Titanium is not very eco (steel 6-15 MJ/kg, Titanium 900-940MJ/kg

Although it would help if these frames lasted longer than 5 years!!!!!

:D

Cheers

Hello Mark and all,

I have been lurking around for some time with an interest in Titanium bikes and I came across this thread. It is something that I know a little about as I am a materials scientist so I thought I would add my 2 pence worth. The majority of my expertise lies within the composites area, however I also used to work for a F1 team in their materials laboratory where failure analysis of titanium components was my forte. So here are my comments:

Firstly, the warranty.
Specifying a 5 year life for a mountain bike is a complete nonsense and a ridiculous argument to base their decision on not honouring your warranty. As some members have already commented, fatigue could have a roll to play in this failure. However, fatigue is not sensitive to time (years of ownership). it is sensitive to cycles of a certain amplitude. This could be linked to the number hours of riding and type of riding and also probably your weight. Now Im rambling, but in short, there is no way that they can tell how many hours this bike has been used for therefore it is unreasonable to assume that it has reached the end of its useful life. After all you could have bought it used it twice and left it in the garage for the remaining years. So this is my first point. They have no way of estimating how much or little the bike has been ridden.

My second point is that realistically, unless these guys have cut up your bicycle, and examined it under a scanning electron microscope, it is unlikely (highly) that they will be able to know if materials or workmanship is at fault. You have a crack on the weld, this is probably a fatigue crack. To determine the cause they will need to cut away and section the weld to reveal the fracture surfaces. These surfaces will show markings which will indicate the origin of crack. There are numerous potential cause of crack initiation. These can include a simple scratch on the surface to inclusions and impurities in the materials that have occurred during welding or even during the production of the welding materials. So to summarise they don’t know.

In my opinion, you have had the bike a while, and you know how much you have used it, so you will know or feel whether you have had reasonable usage. If you do not, I think you have a scientific case to follow this up.

I once bought a litespeed stem which i never used. I had it for a year or so then decided to use it. I realised it was bent (you couldn’t see with out the handlebars in. Anyway, I had to really push them to change it so it doesn’t surprise me at all that you are in this position.

Personally I also thinks its a complete kick in the balls that they have the cheek to try and charge you 500 for a repair !! i mean what the hell is that ! I think we all know its not going to cost that much, they should do it for free for good will! Anyway, if anything you can be safe in the knowledge that your post has made up my mind to never buy a litespeed frame!

If you need any help with this drop me a mail.

Cheers