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Carbon Frame - Tap test. What do you think?

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Carbon Frame - Tap test. What do you think?

Old 10-13-09, 09:54 PM
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bobthib
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Carbon Frame - Tap test. What do you think?

Had a rather bad experience a week ago when, unbeknownst to me, a small rag fell out of my back jersey pocket and fell on my chain at a stop light. When I took off, the rag got sucked into the RD and snapped it off. The pulley housing came around and hit the seat stay. See it here: http://www.bikeforums.net/showthread.php?t=593808

Anyway, when I asked about assessing the damage, one of the posters suggested the "tap test." The idea behind it is sound (no pun intended.) Tapping a good carbon tube will yield a certain sound. If it is cracked, the sound will be "dead." Short of an Xray, it seems like a petty good test.

What do you think?

BTW, the mfgr has a "no-fault" replacement policy, but since this "failure" is not "manufacturing defect" related, it will not be a "no charge" replacement. There will be a discount off list. I figure I'll probably just ride the crap out of it and if it fails (and I survive) I'll consider the replacement then.
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Old 10-13-09, 09:56 PM
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Wha?

That's BS.
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Old 10-13-09, 10:06 PM
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Actually, the tap test would work as long as you had a control group to compare it to (ie another identical frame). Solid tubes make one kind of sound, a cracked/broken tube will make another. In a non cycling example, a solid bell will make a pure ringing tone, a cracked bell just clanks.
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Old 10-13-09, 10:09 PM
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Well your "control group" is a normal part of your frame in a similar area. Since your frame is still a frame and not a pile of rubble I'm assuming you have something to compare it to. And you probably don't want to ride it till it fails... not a good plan.
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Old 10-13-09, 10:12 PM
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I just don't think you are going to be able to discern enough of a difference. Especially given the damage to the OP's frame that I remember from another thread.
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Old 10-14-09, 09:19 AM
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Originally Posted by umd View Post
I just don't think you are going to be able to discern enough of a difference. Especially given the damage to the OP's frame that I remember from another thread.
And there is the 64 dollar question, it kind of depends on how much ring you get to begin with, with a metal frame I would think that the difference would be more obvious.
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Old 10-14-09, 09:33 AM
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your going to need to sand down and repaint the area anyway. So sand it down and check for a crack.
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Old 10-14-09, 09:47 AM
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All of this sounds bad. Buy a frame and move on.

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Old 10-14-09, 10:04 AM
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A tap test? Well and good, but do you have the ears to discern subtle differences and the knowledge which sound is which?
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Old 10-14-09, 10:17 AM
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Originally Posted by Barrettscv View Post
All of this sounds bad. Buy a frame and move on.

Michael
Touch it up and go. If Lance Armstrong can race a stage of the TDF with a broken stay, you'll be fine...
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Old 10-14-09, 10:29 AM
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I work with carbon structures quite a bit. As a first cut, this is actually a pretty decent way to determine if it's OK or not. It's more of a way to see if the carbon had delaminated from some sort of core (often foam or honeycomb), but could be used on tubes as well. The deal with tubes is that if you've hit it hard enough to mess it up, it will usually have a massive tear, dent or kink in the tube (and, yes, you can 'dent' a carbon structure, it is not always a catastrophic failure) that will be pretty much impossible to ignore.

So, if you take a screwdriver and tap it on a part of the frame that you know is good, it'll give you a certain sound which will be very sharp. Move around the entire bike. It will continue to sound the same way unless you get to a bad spot which will sound very flat. I don't know how else to describe it, but if you get to a bad spot, they really stand out.

Incidently, the is a reasonable way to do non-destructive testing on a lot of things. Steel parts will often 'ring' when hit with a screwdriver (assuming you aren't damping the vibrations by holding the piece in your hand). If the piece is cracked, it won't ring. Again, a little hard to describe, but very apparent once you come across it in real life.
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Old 10-14-09, 10:58 AM
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psst... Just get you some yellow fingernail polish or model paint and cover the marks. Ride it till it falls apart one day. Make sure your medical and dental insurance is adequate.
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Old 10-14-09, 01:38 PM
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Originally Posted by Fat Boy View Post
Incidently, the is a reasonable way to do non-destructive testing on a lot of things. Steel parts will often 'ring' when hit with a screwdriver (assuming you aren't damping the vibrations by holding the piece in your hand). If the piece is cracked, it won't ring. Again, a little hard to describe, but very apparent once you come across it in real life.
I think that the sounds are different in different spots of the bike, depending on the diameter of the tubing at that particular spot
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Old 10-14-09, 01:52 PM
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Originally Posted by grafik1979 View Post
I think that the sounds are different in different spots of the bike, depending on the diameter of the tubing at that particular spot
absolutely true, ergo the need for a control frame to compare the noises to.
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Old 10-14-09, 02:05 PM
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Originally Posted by grafik1979 View Post
I think that the sounds are different in different spots of the bike, depending on the diameter of the tubing at that particular spot
You're absolutely right. Each spot will have it's own particular sound based on tube size, wall thickness, etc. Having said that, they will all share the 'sharp' (I don't know how else to describe it) quality as long as it's in good shape.

This is really a case where you need to be able to have the ability to 'show and tell'. It's tough to describe it like this. It's probably not a good way of testing for a rank amateur.
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Old 10-14-09, 02:45 PM
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Originally Posted by grafik1979 View Post
Well your "control group" is a normal part of your frame in a similar area. .
such as the other seat stay.
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Old 10-14-09, 02:52 PM
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i've done this. friend endoed on his Felt F1SL. The bike suffered little cosmetic damage but the friend thought his top tube might be cracked, based on how the bike landed. Everything looked fine, but we did the "tap test" with a quarter and there was a noticeable difference in sound at one spot on the top tube. Whereas surrounding areas rapped sharply, this one spot thudded lifelessly.

Frame got sent to Felt and, sure enough, there was a crack in that spot.
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Old 10-14-09, 04:09 PM
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Indeed, I used the other seat stay as a control. There was no difference in the sound of the two. Several people in this forum and others have suggested this is a very good method.

Microscopic examination with a magnifying glass is also a good way, looking for damage to the carbon layer. This too appears fine. The damage appears limited to the paint and primer layers.

The plan now is to cover the "wounds" with a clear coat, apply bondo and sand down smooth. I'll then either mask and spray with black paint, or better yet, find an appropriate decal(s) to cover the spot and the corresponding area on the other seat stay.
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Old 10-14-09, 04:09 PM
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Originally Posted by umd View Post
Wha?

That's BS.
What's BS?
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Old 10-14-09, 06:21 PM
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Originally Posted by umd View Post
Wha?

That's BS.
http://rgl.faa.gov/Regulatory_and_Gu...LE/ac145-6.pdf

a. Damage Assessment and Teardown....
Due to the tendency of composites to rebound and mask any impact damage, and the strong likelihood of non-visible microcracking, a visual inspection or coin tap test for determination of the extent
of any composite damage should be supplemented with additional NDI techniques ( i.e.,

ultrasonic or other approved NDI methods)

Last edited by vettefrc2000; 10-14-09 at 06:25 PM.
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Old 10-14-09, 06:33 PM
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Originally Posted by vettefrc2000 View Post
http://rgl.faa.gov/Regulatory_and_Gu...LE/ac145-6.pdf

a. Damage Assessment and Teardown....
Due to the tendency of composites to rebound and mask any impact damage, and the strong likelihood of non-visible microcracking, a visual inspection or coin tap test for determination of the extent
of any composite damage should be supplemented with additional NDI techniques ( i.e.,

ultrasonic or other approved NDI methods)

Oh Dear Lord,

That's SOP from the FAA? Do I have to watch out for guys walking around under the plane with a quarter on my next flight? Fantastic.
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Old 10-14-09, 06:57 PM
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tap test works
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Old 10-14-09, 07:24 PM
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I have Level II NDI cert and yes, the tap test is valid. We use it on aircraft, a simple quarter and the human ear is decidedly one of the best ways to find delaminated areas or voids in composities. The difference in sound is easy to pick up. Of course we use other methods to delineate the damage for repair.

With a coin, tap the tube starting above the damaged area and continuie across the damage, if there is a change in tone that area is higly suspect.
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Old 10-14-09, 07:40 PM
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Originally Posted by Loose Chain View Post
I have Level II NDI cert and yes, the tap test is valid. We use it on aircraft, a simple quarter and the human ear is decidedly one of the best ways to find delaminated areas or voids in composities. The difference in sound is easy to pick up. Of course we use other methods to delineate the damage for repair.

With a coin, tap the tube starting above the damaged area and continuie across the damage, if there is a change in tone that area is higly suspect.
Just a note of clarification - "Change in tone in (the damaged area) ....

Due to the shape of the seat stay, there is a change in tone across the entire seat stay, the thicker top being low pitched, and thinner bottom being higher pitched. The important point here is to note that the same tones were heard across the same span of the "control" undamaged seat stay.
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Old 10-14-09, 07:46 PM
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Sorry dude.
It sounds to me like your wallet will be "tapped' bigtime.
Wear the dew rag around your head in the future.
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