How to test carbon fiber components for damage - help

[RapDaddyo]

Hey, all you engineers on the forum. What equipment would one use to test a carbon fiber component for structural damage (e.g., crack). I am specifically interested in testing used wheels for possible damage not visible to the naked eye. What sort of testing instrument would you use and who would have such equipment? Thanks.

 

[artmichalek]

Typically either x-ray or ultrasound. There are probably a few firms in your area that do aircraft inspection that might be willing to do it.

 

[RapDaddyo]

Typically either x-ray or ultrasound. There are probably a few firms in your area that do aircraft inspection that might be willing to do it.

Thanks. Is there a preferred methodology for a part the size and thickness of a wheel -- x-ray or ultrasound?

 

[frenchyge]

Typically either x-ray or ultrasound.

X-ray? Really? I'd think that'd go right through without much effect.

Liquid dye penetrant would be another possibility for detecting and highlighting *surface* defects. It's a very simple technique involving a brightly colored dye which is applied and flows into any cracks to make them more readily visible.

Surely Trek and other carbon frame makers have equipment which detects internal voids and defects.

 

[artmichalek]

X-ray? Really? I'd think that'd go right through without much effect.

Liquid dye penetrant would be another possibility for detecting and highlighting *surface* defects. It's a very simple technique involving a brightly colored dye which is applied and flows into any cracks to make them more readily visible.

Surely Trek and other carbon frame makers have equipment which detects internal voids and defects.

Cracks result in voids. Since x-rays show relative density, they're highlighted very clearly. I'm not sure exactly what procedure they use, but I would assume that companies like Trek x-ray a random sample of their frames for quality control.

 

[Jaguar27]

Cracks result in voids. Since x-rays show relative density, they're highlighted very clearly. I'm not sure exactly what procedure they use, but I would assume that companies like Trek x-ray a random sample of their frames for quality control.

Or maybe a Cat Scan?

 

[K50]

Typically either x-ray or ultrasound. There are probably a few firms in your area that do aircraft inspection that might be willing to do it.

And what would the cost be for something like that? Sounds big to me! Besides, carbon wheels aren't that much better than aluminum nowadays anyways! Well for XC bikes anyways...

 

[dhk]

Or maybe a Cat Scan?

Cat Scan isn't far off. Many years ago I saw a water-jet type slow-scan machine used on larger aerospace parts. It had a transducer that moved along with the waterjet, on the back side of the panel, and produced a raster-scan based on ultrasonic transmission thru the material. Delaminations or voids inside panels with 30 or more layers could be easily detected and recorded. Don't know if these are still in use today; maybe something newer and quicker has come along.

Would be interesting to know if Trek does x-ray or ultrasound sampling of frames. Since the frames aren't all that expensive to make, maybe they just do destructive sample testing, ie, loading up a frame until it breaks, or destructive inspection (cutting a frame open). They've been making CF frames and forks a long time, probably have process down and probably don't need to do a lot of test samples anymore.

 

[dabac]

And what would the cost be for something like that? Sounds big to me!

That really hard to say, pretty much down to their good will. If you want to have a wet-film X-ray done, then someone has to cover the cost of the film and the development.
An ultrasound scan really doesn't consume anything else than time and can be a rather speedy process at that. That's the type of thing you might get done for the price of a box of donuts if they're feeling helpful and aren't too busy at the moment. There are also x-ray machines that uses a sensor pickup instead of a film, so there's another chance to sneak something in for "free".

 

[RapDaddyo]

That really hard to say, pretty much down to their good will. If you want to have a wet-film X-ray done, then someone has to cover the cost of the film and the development.
An ultrasound scan really doesn't consume anything else than time and can be a rather speedy process at that. That's the type of thing you might get done for the price of a box of donuts if they're feeling helpful and aren't too busy at the moment. There are also x-ray machines that uses a sensor pickup instead of a film, so there's another chance to sneak something in for "free".

Would an ultrasound scan reveal the same defects as an x-ray scan? Does it take an expert to "read" these scans or are the defects obvious to a layman? Are there computer programs that "read" the scans and identify defects or is it always an "eyes-on" process? I have a few reasons to ask such detailed questions, but one is safety. I am finalizing my decision on a couple of sets of race wheels and the top candidates are CF -- seems to be the trend for the fastest wheels. Hence, following any sort of impact that might have caused damage (even a rock), the desire to have more confidence in the integrity of the wheel than just a visual inspection of the wheel.

 

[artmichalek]

Would an ultrasound scan reveal the same defects as an x-ray scan? Does it take an expert to "read" these scans or are the defects obvious to a layman? Are there computer programs that "read" the scans and identify defects or is it always an "eyes-on" process? I have a few reasons to ask such detailed questions, but one is safety. I am finalizing my decision on a couple of sets of race wheels and the top candidates are CF -- seems to be the trend for the fastest wheels. Hence, following any sort of impact that might have caused damage (even a rock), the desire to have more confidence in the integrity of the wheel than just a visual inspection of the wheel.

Either method will reveal the same defects, with varying degrees of resolution. I'm sure there are digital image processing routines being used for this, but they're probably highly specialized. For something like a bike wheel you would really need to know what you're looking for. How much are you saving by getting these wheels used rather than new?

 

[Trek5500]

Check out


http://www.bikeforums.net/archive/index.php/t-47704.html, which suggests use of a multimeter to detect defects.

Also-http://www.aer.bris.ac.uk/comptest2004/proceedings/posters/comptest_106.pdf

 

[el Ingles]

Cracks result in voids. Since x-rays show relative density, they're highlighted very clearly. I'm not sure exactly what procedure they use, but I would assume that companies like Trek x-ray a random sample of their frames for quality control.

knowing the trouble the medical profession has finding cracks in bones with x-rays I can´t imagine that they would help unless you had an x-ray of when the wheel was new and unused as a comparason - and I think the same might well apply to ultrasound .

 

[RapDaddyo]

How much are you saving by getting these wheels used rather than new?

Even if I buy a new wheel, what do I do after hitting something that might have caused damage -- throw away the wheel?

 

[artmichalek]

knowing the trouble the medical profession has finding cracks in bones with x-rays I can´t imagine that they would help unless you had an x-ray of when the wheel was new and unused as a comparason - and I think the same might well apply to ultrasound .

Regardless of what you happen to think, x-rays and ultrasound are the industry standards for non destructive testing of composite structures. Corporations wouldn't be investing so heavily in these methods if they weren't getting results.

 

[RickF]

knowing the trouble the medical profession has finding cracks in bones with x-rays I can´t imagine that they would help unless you had an x-ray of when the wheel was new and unused as a comparason - and I think the same might well apply to ultrasound .

The big difference between using x-ray or ultrasound to find a crack in a bone versus finding a crack in the wheel is that you can take the wheel off the bike and not try to guess whether what you are seeing is actually a crack in the wheel versus a difference in the density of the overlying blood vescles, muscles, fat, skin, etc. If it was possible to remove the bone in question, lay it on the table, and x-ray it without having to look through the rest of the body, x-ray would find the crack every time.

Or maybe a Cat Scan?

The CAT scan is a special subtype of x-ray that can be focused at different depths. What happens is that the x-ray source and detector move during exposure (think of points on opposite sides of a wheel with no spokes). The patient (or component) is placed so that the pivot point of the motion (think of the place where the hub should be) is at the place that is to be examined. Because everything above and below the pivot point is moving faster relative to the pivot point, everything except what is at the pivot is blurred out. Definitely overkill for examining a wheel, but if it was ever necessary to determine the condition of the interior of the bottom bracket without removing the bottom bracket from the bike, it would be an option - an expensive option compared to disassembling the bike, but an option, nonetheless.

 

[RapDaddyo]

The big difference between using x-ray or ultrasound to find a crack in a bone versus finding a crack in the wheel is that you can take the wheel off the bike and not try to guess whether what you are seeing is actually a crack in the wheel versus a difference in the density of the overlying blood vescles, muscles, fat, skin, etc. If it was possible to remove the bone in question, lay it on the table, and x-ray it without having to look through the rest of the body, x-ray would find the crack every time.

Would there be an advantage to using x-ray vs. ultrasound or vice versa? Also, would the scan images be equally easy (or difficult) to interpret? IOW, if one had a choice, which technology would be the technology of choice?

 

[RickF]

Would there be an advantage to using x-ray vs. ultrasound or vice versa? Also, would the scan images be equally easy (or difficult) to interpret? IOW, if one had a choice, which technology would be the technology of choice?

I would have to ask my son-in-law who routeinly tests aircraft parts for failure, but my guess would be that x-ray would be easier to do and easier to interpret. (And no, I cannot get my son-in-law to examine bicycle components for us. Although he is an avid cyclist, I am sure his employer would not allow it).

 

[frenchyge]

Another question is whether it's possible to damage a wheel internally without causing visible damage to the outside. IOW, do we really need to look *through* the wheel if the surface is clean? Internal inspection would only be necessary to determine the severity of a surface defect, right? If so, you can localize your scan to a very small area of the wheel and save the time of trying to ultrasound the entire wheel after every ride.

 

[artmichalek]

Would there be an advantage to using x-ray vs. ultrasound or vice versa? Also, would the scan images be equally easy (or difficult) to interpret? IOW, if one had a choice, which technology would be the technology of choice?

I can't really say for sure. X-rays give higher resolution, but a crack that's big enough to worry about might be detectable via ultrasound as well. Interpretation is about the same.