Crack formation?

tkr

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Uuuuuhhhhh......We've found these diagonal markings on the entire length of one of our shock hoops. Is this something to be worried about?

Matt Nelson
Team Kwik Racing
 

ACID_RAIN28

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It looks like a tube replacement is in order. Is it just like that the whole length of the tube? and do you have anymore pics? Depending on the whole big picture, if it does not matter that much to you mabey you could brace the tube half way from the two nearest intersecting points, but it all matters on the big picture, how long it is where it is what foreces are acting on it, coilover or not, etc. post more pics.

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FABRICATOR

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A good method on the car is a dye penetrant crack checking kit (available at most welding shops, Graingers, etc.). A cheaper way is to cover the area with carbon black from an over rich acetylene torch. Heat one side just enough to burn the black away and watch it as it approaches the suspected crack. If it's cracked the cleaning process will stop at the crack. If not it will keep cleaning right across it. This is a temperature much lower than that used to stress relieve, so it won't hurt anything. BTW, this temperature is also good for annealing aluminum sheet.

<font color=orange>The best ideas are the ones that look obvious to the casual observer.</font color=orange>
 

tkr

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I don't have any more pictures at the moment. Those marks are on various places the entire length of the hoop. This is one of the front front shock hoops on the race car to which both the coilover and bypass shock mount, so it definitely matters a lot. We haven't found anything like this anywhere else on the car, which concerns me. Sounds like we should look into one of those crack checking methods, Thanks for the advice guys!

Matt Nelson
Team Kwik Racing
 

Dave_G

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Matt,
It's hard to tell by the photo but there are several clues here that tell me that those cracks (if you want to call them that...) are from the manufacturing of the material. Possibly occlusions. Out of all the thousands of parts I have Mag inspected over the years cracks have a tendancy to be very sharp and defined. This photo shows too much zig zag formation and pitting to be a crack caused by stress or cycles. Having three of them side by side like this is also very uncommon. I'll bet they have been there all along and you have just now noticed them. Just to be safe I would replace the structure for the piece of mind. ;-)

Best,
Dave

"I know it all, but I can't remember most of it..."
 

tkr

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Thanks Dave. I appreciate the advice.


Matt Nelson
Team Kwik Racing
 

ACID_RAIN28

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I have seen steel shatter with a spiral pattern similar to that.

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Kritter

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Shatter? What was the hardness?

Kris
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orvacian

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Don't do crack, it will mess you up. Oh wait, I thought you said crack information, my bad.

<P ID="edit"><FONT SIZE=-1>Edited by orvacian on 11/19/02 09:32 AM (server time).</FONT></P>
 

singlehanded

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Oh, I was hoping for info on where to get some?LOL

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ACID_RAIN28

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It was a different application. it was about a 1.125" piece about 6" long, solid. I belive it was somewhere around the equivilant of tools steel. It was a drive shaft for a pump. The constant twisting action on it shattered it in a checkered spiral formation similar to that. Wierdest part about them was the they all broke the in the same fashion, they all shattered but none of the square shapes came off, it just splilt the surface about .75" in depth. The place I used to work for got them in all the time, and all the same.

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Kritter

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OK tool steel explains the "shattering". Very brittle.

Kris
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ACID_RAIN28

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I know that it is very brittle but I am not sure that is the grade used, I have never heard of it used for a hydro pump shaft, but that is what someone said it might be.

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ntsqd

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Those look a lot like the Cold Laps I'm dealing with in a forging at work. I'd replace the tube.

As to the pump shaft failures, Sounds like someone garunteed failure by specing a brittle material in a mildly reversing torsion application. Depending on the budget it should have been made from 1045, 300M, or some of the more exotic stuff Dave G gets to play with.

TS

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Dave_G

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Thom,
I suspect the shaft they are talking about here was probably case hardened to Rc-62 and probably not tool steel. A lot of OEM folks like to case harden splines for wear reasons. Unfortunately no one ever masks the shaft area that sees all the torsional twisting with No Carb before heat treat because it's a pain in the butt so the entire length of the shaft is case hardened. In the Mag machine you will usually see a fine spider web like pattern all over the shaft and cracks migrating out of the root of the splines if it has seen a lot of torsional loading but not yet completely failed.

Dave

"I know it all, but I can't remember most of it..."
 

tkr

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Thanks for all the advice guys. We tried the crack checking method that Fabricator was talking about using a torch. It cleaned right across the marks without any change. We're still debating whether or not to replace it anyway.
Anyway, thanks again.



Matt Nelson
Team Kwik Racing
 
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