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#1
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![]() http://www.ndtint.com/amigo.htm wrote in message ps.com... The cracks shown in that link are exactly like the ones I found in my 20 yr old rigging. The cracks in mine were very difficult to find until I used fine sandpaper. They were all on the lower swaged end. Most of the cracks were under small brown stains that were the result of the stainless in the crack becoming non-stainless and rusting. They required a 10X magnifier to find. At work, I ground the fittings away to see how deep they went and they went through the entire fitting. I even used dye penetrant with no luck. I replaced all the rigging and lifelines last year. NOW, although thefittings and wire and rod are stainless, stainless can be slightly ferromagnetic and can be tested via flux leakage methods (I used to do magnetic NDT research). Furthermore, the area around a fatigue crack is less stainless and more ferromagnetic than the bulk material. This may allow testing via mag particle inspection (so-called magnafluxing). It is entirely that nobody has done this because they simply assumed that teh stainless material wouldnt allow this to work. Unfortunately, I threw the old rigging away so I cannot try this. |
#2
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Bob:
Yes, that is eddy current testing. I have not yet considered it. I'd prefer to use mag particles (iron filings) as this does not require runing a probe along all possible surfaces. |
#3
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How about sending an acoustic pulse along the rod rigging the same as a time
domain reflectometer works. The pulse speed is a property of material and tension and the reflectance a function of acoustic impedance. Cracks would raise the impedance. The cracks could be located along the length of the rod by simply applying the pulse signal at one point. http://www.tscm.com/riprcop.html wrote in message oups.com... Bob: Yes, that is eddy current testing. I have not yet considered it. I'd prefer to use mag particles (iron filings) as this does not require runing a probe along all possible surfaces. |
#4
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Cracks would
raise the impedance. The cracks could be located along the length of the rod by simply applying the pulse signal at one point. Seems to me that for this to work well you'd need to remove the rod from the boat and tension it is some sort of way, equally. Then you might read cracks, but be unable to actually locate them, meaning a small non-dangerous imperfection in the rod might give a false reading. Seems like a tool that would get abused to sell a lot of uneeded rigging.. Just about every rig failure I've ever heard of was wire. While I'm sure rod has failed....I've never heard of it. Anyone know of a rod rigging failure they can point to online? I'm too sleepy to google today. RB 35s5 NY |
#5
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Rob:
You don't have to remove the rigging at all. On the TDR pulse you can easily see the where the spreader touches to rod, you can run your hand up and down the rod and see its location on the TDR. Since sound waves don't propagate through cracks, the sound energy would be reflected back at the source and the location of the crack could easily be identified. All you need is a good piezo transducer that transmits and receives, a pulse generator (a simple circuit) and some display like an oscilloscope. You can even make a display on a laptop. With some signal processing you could really do some great analysis of the rigging. Think of a sonar with metal instead of water as the medium. One could even spot cracks and corrosion in the end fittings. Also think of a musical instrument. If the fret or neck on a guitar is damaged, it is easy to hear. These same principals apply to the TDR. Amen! "Capt. Rob" wrote in message oups.com... Cracks would raise the impedance. The cracks could be located along the length of the rod by simply applying the pulse signal at one point. Seems to me that for this to work well you'd need to remove the rod from the boat and tension it is some sort of way, equally. Then you might read cracks, but be unable to actually locate them, meaning a small non-dangerous imperfection in the rod might give a false reading. Seems like a tool that would get abused to sell a lot of uneeded rigging.. Just about every rig failure I've ever heard of was wire. While I'm sure rod has failed....I've never heard of it. Anyone know of a rod rigging failure they can point to online? I'm too sleepy to google today. RB 35s5 NY |
#6
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Bob Crantz wrote:
How about sending an acoustic pulse along the rod rigging the same as a time domain reflectometer works. The pulse speed is a property of material and tension and the reflectance a function of acoustic impedance. Cracks would raise the impedance. The cracks could be located along the length of the rod by simply applying the pulse signal at one point. Sounds good to me, I don't belive tension (or compression) has anything to with the speed of transmission in a solid. Cheers Marty |
#7
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Sounds good to me, I don't belive tension (or compression) has anything
to with the speed of transmission in a solid. But to get the expected measurements in a solid structure that is being read for resonent feedback variances, wouldn't said feedback be effected if the the solid had a wide range of motion? Seems like it would require isolation for relaible readings. Out of my depth on this one, folks....just guessing based on what I've read from Bob C. RB 35s5 NY |
#8
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![]() "Martin Baxter" wrote in message ... Sounds good to me, I don't belive tension (or compression) has anything to with the speed of transmission in a solid. Assume a completely rigid guitar neck. Adjusting the tension of the string adjusts its resonant frequency. If the length does not change, but the resonant frequency does, then the velocity in the string must change. C = tension/linear density http://www.faqs.org/docs/sp/sp-172.html |
#9
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Bob Cranz is correct, this would work for cracks in the rod, even when
it was attached at both ends. When rod fails, where does it fail, I'd bet at the ends where TDR would be harder. Given identical types of ends and repeatedly stressed, any engineer would expect that solid rod would fail before cable type. A crack in a single strand of wire cannot propogate anywhere except in that strand. A crack in solid can go all the way through and probably will because the crack itself becomes a stress concentrator. |
#10
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Given identical types of ends and repeatedly stressed, any engineer
would expect that solid rod would fail before cable type. This guy is a funny troll. Even the makers of standing rigging admit that rod is more durable. It's also a supperior system due to lower weight. Just take care of it. Surveyors who have no market interest in selling either also say rod is longer lived. This guy is some engineer. RB 35s5 NY |
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