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Author: Subject: Is there any magic way to check a chassis for cracks and stress fatigue....
carpmart

posted on 31/12/09 at 06:00 PM Reply With Quote
Is there any magic way to check a chassis for cracks and stress fatigue....

...... other than getting it X-rayed?

I'm trying my best to check over my race chassis for cracks etc. Its painted black metallic which doesn't lend itself well to inspection! (wish it was grey!)

I'm using as much natural light and florescent etc but I'm still not convinced.

Does the collective have an easy (foolproof) way of inspecting a used chassis?

Thanks in advance!





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clairetoo

posted on 31/12/09 at 06:08 PM Reply With Quote
The foolproof way of testing for cracks is to pressurize the chassis - my drag bike frames were used as the air tank for the air shift , so any cracks meant no racing till it was fixed (not that I ever had such a failure , but you get the idea)
The downside to this is it has to be planned for at the build - all connecting tubes have to be drilled at the joint , and every joint has to be perfect.........





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907

posted on 31/12/09 at 06:46 PM Reply With Quote
Dye Penetrant would show up cracks.

It's a simple aerosol system.

Paul G

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britishtrident

posted on 31/12/09 at 06:51 PM Reply With Quote
Dye pentrant and visual inspection is the only viable way --- you have to wire brush the paint off at the joints.
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907

posted on 31/12/09 at 06:58 PM Reply With Quote
Magnetic particle works as well.

Paul G

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tommyab

posted on 31/12/09 at 07:18 PM Reply With Quote
As Paul said, MPI is probably easiest, but needs paint to be removed first. Would probably be easiest way on the welds.

Tom

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carpmart

posted on 31/12/09 at 07:24 PM Reply With Quote
Thanks for all the replies!

I'm not in a position to fully strip the chassis and then remove paint from welds so I guess its a good visual check this year, then full strip down next year.

Claire - love the frame pressurisation method!





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alistairolsen

posted on 31/12/09 at 07:33 PM Reply With Quote
pressurised frame is the same reason I dont mind banded steel wheels, 100% Non destructive testing cycle!





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britishtrident

posted on 31/12/09 at 08:11 PM Reply With Quote
quote:
Originally posted by carpmart
Thanks for all the replies!

I'm not in a position to fully strip the chassis and then remove paint from welds so I guess its a good visual check this year, then full strip down next year.

Claire - love the frame pressurisation method!


Porsche used in real racing time, the Le Mans cars ran with the chassis pressurised with argon and had a pressure gauge mounted on the roll hoops if the pressure went down you knew the chassis was broken.

The disadavantage is it will only show up a through thickness crack ie one that has already broken through both surfaces ie it is already a fracture.



[Edited on 31/12/09 by britishtrident]





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907

posted on 31/12/09 at 08:24 PM Reply With Quote
When I used to make coded stuff the lifting lugs were always MPI'd. (You can't Xray a fillet)

The inspector would spray the weld area with quick drying white paint and allow to dry, then spray with the particle liquid.

The iron power magnetic field lines were easier to see on the white paint.

What you need is a white chassis.

Happy New Year
Paul G

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liam.mccaffrey

posted on 31/12/09 at 09:03 PM Reply With Quote
MPI is the easiest.





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major

posted on 1/1/10 at 07:12 AM Reply With Quote
On bikes "chalk dust" was used.

Happy New Year

marcel.






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JB
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Building: Built: V8 Kitten, 2 litre Lada, Space frame Minor,

posted on 26/1/10 at 01:22 PM Reply With Quote
First learn to indentify where cracks are likely to occur. Carroll Smiths book Engineer To Win will help.

Then you will know where to look.

I would start where the big loads go in (engine, suspension and dampers) where ever there are welds and a change in section.

Sharp edges are also a common place for cracks to start as are holes. So no drilling lightening holes!

[Edited on 26/1/10 by JB]

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