How to test carbon fiber components for damage - help



frenchyge said:
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.
It is possible to have an interlaminar fracture without any surface indication. Whether it's a likelyhood worth worrying about is another question.
 
frenchyge said:
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.
Good point. Of course, it depends on how long it takes and whether it uses up resources (e.g., film). If it only takes a few more seconds to scan the rest of the wheel, then it might make sense to do the whole wheel.
 
RapDaddyo said:
Good point. Of course, it depends on how long it takes and whether it uses up resources (e.g., film). If it only takes a few more seconds to scan the rest of the wheel, then it might make sense to do the whole wheel.
Or pass it to a skilled tech only in cases where the surface inspection reveals cause for alarm.
 
frenchyge said:
Or pass it to a skilled tech only in cases where the surface inspection reveals cause for alarm.
Good point. BTW, I wonder how CF wheels fail? Do they simply crack but stay intact, or do they crack and come apart?
 
My guess would be a failure similar to fiberglass. Once the resin cracks-through the strength is gone, but the fibers tend to hold the pieces together at the floppy, flex-y, joint. Problem with bike wheels is that the small clearances involved can cause problems if the wheel flexes a lot, even if it doesn't come completely apart.
 
frenchyge said:
My guess would be a failure similar to fiberglass. Once the resin cracks-through the strength is gone, but the fibers tend to hold the pieces together at the floppy, flex-y, joint. Problem with bike wheels is that the small clearances involved can cause problems if the wheel flexes a lot, even if it doesn't come completely apart.
So, I guess if one is going down a hill at 50+mph and hears a sort of shredding sound that's not a good thing.:eek:
 
RapDaddyo said:
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?

Depends on the test procedure and equipment available. For example, testing for flaws in a structure can be done by taking interferograms of the piece in question while vibrating the object at its resonant frequencies. While this method only images the vibrational modes on the surface, research has shown that it can find very small defects well below the surface. It's a very quick and easy test. However, it can't necessarily tell you the size or shape of the defect. In that case, a second step might be xray or ultrasound studies.

Someone earlier mentioned that cat scans focus xrays. This is not the case. You can vary the power of an xray source to get less or more penetration. Cat scans image a cross section of a person/animal, by essentially adding together the images of said cross section taken from different angular positions as measured from the cat scans axis of rotation.
 
RapDaddyo said:
So, I guess if one is going down a hill at 50+mph and hears a sort of shredding sound that's not a good thing.:eek:
I'd say you should *hope* it's just your shorts ripping. :D

Here's a thought: after each ride, take the wheels to the airport or some other government facility and have the guards pass them through the x-ray machine there.
 
I consulted with the engineers in my family over the weekend, and the collective opinion was that it depends on the size of the crack and where it is located. Xray may not be able to detect small cracks, and even larger cracks could be missed if the angle of the crack relative to the direction of the x-ray is not optimal.

Ultrasound is used in the aerospace industry to detect delaminations (separation of the layers), but ultrasound might not pick up a small crack within a layer. The size of the crack that could be detected depends on the frequency of the ultrasound.

Another method that would detect surface cracks is vapor deposition. This uses a heated inert fluid that is vaporized. This vapor is sprayed onto the surface and with the light at the proper angle, you can visualize the actual crack since the fluid film on the tested surface bends the light differently as the film goes into the cracks. This requires some patience and a trained eye, but it really doesn't take that long for someone to learn how to do it. Again, this method would only be of value for surface defects and not internal ones.

The most economical method to test for defects would be a guy with very good eyes, a magnifying glass, and a lot of time on his hands. :)
 
RickF said:
I consulted with the engineers in my family over the weekend, and the collective opinion was that it depends on the size of the crack and where it is located. Xray may not be able to detect small cracks, and even larger cracks could be missed if the angle of the crack relative to the direction of the x-ray is not optimal.

Ultrasound is used in the aerospace industry to detect delaminations (separation of the layers), but ultrasound might not pick up a small crack within a layer. The size of the crack that could be detected depends on the frequency of the ultrasound.

Another method that would detect surface cracks is vapor deposition. This uses a heated inert fluid that is vaporized. This vapor is sprayed onto the surface and with the light at the proper angle, you can visualize the actual crack since the fluid film on the tested surface bends the light differently as the film goes into the cracks. This requires some patience and a trained eye, but it really doesn't take that long for someone to learn how to do it. Again, this method would only be of value for surface defects and not internal ones.

The most economical method to test for defects would be a guy with very good eyes, a magnifying glass, and a lot of time on his hands. :)
Thanks for taking the time to consult with the engineers in your family. Sounds as though you could field your own basketball team. Do I understand correctly that ultrasound trumps x-ray for internal cracks?
 
RapDaddyo said:
Thanks for taking the time to consult with the engineers in your family. Sounds as though you could field your own basketball team. Do I understand correctly that ultrasound trumps x-ray for internal cracks?
Yes, ultrasound trumps x-ray. Both methods could miss small cracks within a single layer, but ultrasound will detect delamination (which as I was told, is a far more common form of failure than a crack within a layer). Cracks tend to be on the surface, propogate rapidly, and can be seen with a trained eye and good light. Hidden damage is more likely to be delamination, and ultrasound is the way to detect that.

As far as basketball goes, we have connections with some top programs. Between my children and their spouses we have representatives from Kentucky, North Carolina, Duke, and Maryland. Not a bad start for a basketball team. (UNC does not have an engineering school, but they usually play basketball fairly well, this season notwithstanding).
 
RickF said:
Yes, ultrasound trumps x-ray. Both methods could miss small cracks within a single layer, but ultrasound will detect delamination (which as I was told, is a far more common form of failure than a crack within a layer). Cracks tend to be on the surface, propogate rapidly, and can be seen with a trained eye and good light. Hidden damage is more likely to be delamination, and ultrasound is the way to detect that.

As far as basketball goes, we have connections with some top programs. Between my children and their spouses we have representatives from Kentucky, North Carolina, Duke, and Maryland. Not a bad start for a basketball team. (UNC does not have an engineering school, but they usually play basketball fairly well, this season notwithstanding).
This is great. Thanks for the useful info. BTW, I guess we're entering prime time for your basketball fans.
 
RapDaddyo said:
This is great. Thanks for the useful info. BTW, I guess we're entering prime time for your basketball fans.
Yes. There are only two seasons in Kentucky - basketball and the Kentucky Derby (and the Derby only lasts two minutes). One sports bar in North Carolina had more than 50 Kentucky fans watching the South Carolina at Kentucky game on Saturday. I have to admit that the Atlantic Coast Conference plays basketball well, but their fan base cannot hold a candle to the Southeastern Conference fans. Kentucky, LSU, and Florida fans regularly fill the sports bars in North Carolina.
 
RickF said:
Yes. There are only two seasons in Kentucky - basketball and the Kentucky Derby (and the Derby only lasts two minutes). One sports bar in North Carolina had more than 50 Kentucky fans watching the South Carolina at Kentucky game on Saturday. I have to admit that the Atlantic Coast Conference plays basketball well, but their fan base cannot hold a candle to the Southeastern Conference fans. Kentucky, LSU, and Florida fans regularly fill the sports bars in North Carolina.
I hope frenchyge doesn't see this thread. He's from Kansas and they seem to think they play basketball out there reasonably well. Oh, well, his consolation is that he's increased his FT over the winter.
 
RapDaddyo said:
I hope frenchyge doesn't see this thread. He's from Kansas and they seem to think they play basketball out there reasonably well. Oh, well, his consolation is that he's increased his FT over the winter.
He has a valid point, at least from an historical perspective. Adolph Rupp and Dean Smith both played for Kansas and later became better coaches than they were players.

To bring this back to cycling - I spend hours with my bike on the trainer in front of the big screen TV spinning during basketball games.
 
RapDaddyo said:
I hope frenchyge doesn't see this thread. He's from Kansas and they seem to think they play basketball out there reasonably well. Oh, well, his consolation is that he's increased his FT over the winter.
He has a valid point, at least from an historical perspective. Adolph Rupp Hank Iba, and Dean Smith all played for Kansas and later became better coaches than they were players. Kansas is number 3 (behind Kentucky and UNC) in number of wins.

To bring this back to cycling - I spend hours with my bike on the trainer in front of the big screen TV spinning during basketball games. The more exciting the game, the faster and longer I can spin.
 
RickF said:
He has a valid point, at least from an historical perspective. Adolph Rupp Hank Iba, and Dean Smith all played for Kansas and later became better coaches than they were players. Kansas is number 3 (behind Kentucky and UNC) in number of wins.

To bring this back to cycling - I spend hours with my bike on the trainer in front of the big screen TV spinning during basketball games. The more exciting the game, the faster and longer I can spin.
Cool. A game is about the right length for a good workout, as long as they don't go into multiple OTs. In fact, periods are about the right length for a good L4 interval.
 
frenchyge said:
Here's a thought: after each ride, take the wheels to the airport or some other government facility and have the guards pass them through the x-ray machine there.

That kind of equipment is tailored to react to the densities, and sometimes the molecular structure of the items being scanned. It's very improbable that an airport scanner would pick up a flaw that wouldn't be immediately detectable by hand or eye, they really don't have the resolution for that.
 
RapDaddyo said:
Do I understand correctly that ultrasound trumps x-ray for internal cracks?

It's all down to the orientation of the crack. X-ray is basically an imaging technology based on differences in transparency. If the plane of the crack coincides with the x-ray viewing angle then the crack ideally should show up as a line on the image. But if the plane of the crack is perpendicular to the viewing angle it becomes more difficult, like trying to judge the number of cards in a deck of card seen straight on. Ultrasound on the other hand is transmitted through the material, and a shift in density will cause some of the transmitted energy to be reflected back at the source where it can be detected.
 
RapDaddyo said:
I hope frenchyge doesn't see this thread. He's from Kansas and they seem to think they play basketball out there reasonably well. Oh, well, his consolation is that he's increased his FT over the winter.
Yeah, they like their high school sports around here. ;)
I'm a transplant, so I don't get involved. Plus, my Alma Mater hasn't seen a good team since David Robinson graduated.
 

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