[Closed] Carbon frame Non Destructive Testing

I went to see a chap the other day and he basically said go here http://www.lavender-ndt.co.uk/location-uk.htm

NDT is usually costly and in this case it is not worth the expense. Why?

Well, you are looking for defects or damage. The point is you don't know what defects or damage were there right from the start. You don't know what is acceptable in terms of defects or damage either, so of you find something you will not know if it is something to worry about or not. If you had your bike NDT'd at the start it could help.

my opinion is save your money and do a tap test yourself.

Thanks chief. Tap test was good but cracking around a joint so hard to tell if difference in sound is due to problem or bonding around thicker joint. Any thoughts? Cheers

I've been riding a carbon frame with three witness cracks in it for 5000 miles and despite blasting over numerous cattle grids and potholes, nothing has broken. Older carbon frames had extremely thick, hard brittle paint, which would crack anywhere there was flexion. This (and weight) is one reason why so many bikes now have thin, matt paint.

This witness crack is four years and around 5000 miles old and hasn't grown:

[img] [/img]

I've got more alarming cracks in the fork crown and BB shell but I'm still alive. Even the guys at Specialized admitted it was common on older frames. If nothing creaks or graunches when you apply force, stop worrying and carry on riding.

Cracks in composites are more likely to be between the plies (delamination) rather than through the thickness. Therefore, I think the crack you can see is most likely just in the paint.

I'd remove the paint and see what you can see. If the carbon looks good underneath and there's no sign of any distortion in the top ply, you're probably OK.

If the carbon shows any distortion, or a tap test sugests some delamination, ride carefully! The most likely failure mode to result in paint cracking is a compressive failure. Google Image it to get some idea of what you looking for signs of.

Also, contrary to common belief, carbon actually hangs together quite well in the case of failure. It's extremely unlikely that all of the fibres break in one go. This is differnet to an ally frame, where a crack can become critical and break all the way through in one go.

Also, contrary to common belief, carbon actually hangs together quite well in the case of failure. It's extremely unlikely that all of the fibres break in one go. This is differnet to an ally frame, where a crack can become critical and break all the way through in one go.

Really depends on the CF. UD carbon fibres goes with one hell of a bang as soon as it gets slightly compromised 😀

Op, Canyon provide a [url= http://www.canyon.com/_en/supportcenter/article.html?supportcenter_categories_id=20&supportcenter_articles_id=270&page=1 ]CF inspection service[/url] using a CT scanner to look at the internal structure and give you a definitive answer if it is ok to ride. It is open to non-Canyon bikes too. Pricey but may be worth it for an expensive frame

It may well go bang, but I bet there's still a load of intact fibres. It may not have a lot of strength but it will hold together.

Never seen carbon break but I'd imagine it goes more like a greenstick bone fracture than a catastrophic clean snap.

Loads of good info. Could I drop a carbon tube inside the integrated seat post to reinforce the seat tube/top tube joint from inside in a belt and braces approach?

Ps thanks for all help....I'm neurotic geek at the best of times so always like to ask the questions and know the answers!!

Original thread:
http://singletrackmag.com/forum/topic/helpcarbon-frame-crackspaint-or-carbon

Original seller has been class and hadn't spotted the cracks so offered a refund if needed....I just need to decide how to proceed now!

Hello

I work for an aerospace NDT company so may be able to help if you still need advise.

First off, as others have said, carbon fiber really doesn't crack the same way metals do. When it does go, it shatters down through the layup in a pretty catastrophic way. For this to happen the part has to be way overloaded, or have lost its strength through delamination (as a result of an impact etc.) It doesn't suffer fatigue in the traditional sense and because it can be pretty flexible, that is compared to the paint or lacquer, what you see on the surface is unlikely to be a problem with the material itself.

If you really want to be sure, the first thing to do is get the paint off the area of interest. Then, if the indication is still there a tap test will tell you if there is any delamination.

There are further inspections we can do with ultrasonics, and in some cases we would X-ray an area to see what is going on beneath the surface. This can be pretty hard to interpret though.

Let me know if I can be of any further help.

[b]mmel[/b] - would appreciate picking your brains further if you could drop me an email?
Thanks
chrisj.ross@btinternet.com

If this is a recent second hand purchase I would take the seller's offer of a refund. It may be nothing but it'll cost to check and perhaps cost more on top to repair. I wouldn't be happy to find a potential crack on a used frame only at the point when it has landed on my doorstep. Who knows what other potential issues lie in the frame in the near future. I wouldn't risk it or want the hassle but I realise lots of people are less fussy.

Heres what failed carbon looks like