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Author: Subject: Any opinions on what may have caused this?
gaz_gaz

posted on 26/5/14 at 07:44 PM Reply With Quote
Any opinions on what may have caused this?

Anglesey today.

Lap 8... Jump on the brakes at 100ish mph and BANG

As they say, A picture speaks a thousand words.. So here are 2 pictures.



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DIY Si

posted on 26/5/14 at 07:49 PM Reply With Quote
Is the metal on the chassis all clean and shiny, or rusty in places?





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Ben_Copeland

posted on 26/5/14 at 07:51 PM Reply With Quote
Holy shit. Looks like the weld has weakened the tube which looks very thin!





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joneh

posted on 26/5/14 at 07:52 PM Reply With Quote
Don't know if it's the photo but that tube doesn't look much thicker than the paint!
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Wadders

posted on 26/5/14 at 07:55 PM Reply With Quote
Looks like a stress fracture, possibly aided by hydrogen embrittlement of the weld. At the end of the day it's only 16g tube, are you running slicks ?

Think I would be tempted to replace the whole tube on both sides of the car and braze the brackets on rather than weld.

Hard to tell from the pics, but if it's a flat bracket welded to round tube, then it's a poor design as well, the bracket needs to wrap round the tube or have some gussets.


Al.

[Edited on 26/5/14 by Wadders]

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AdrianH

posted on 26/5/14 at 07:59 PM Reply With Quote
I wonder how much turning torque or force there is when you slam the brakes on, Probably a ton or more trying to rotate the wishbones before the tyres brake loose. Couple of tonnes for an instant trying to rip the brackets from the metal.

Any slight pin holes or flaws in the weld area leading to stress fractures and over time that, I would suggest that is what you get. Brown trouser moment, hope you are OK and no one else taken out.

If all new fracture would be clean all around, if some of the fracture has been there for a while then possible signs or corrosion on parts of the fracture or at least a discolouration as pointed to by DIY Si.

Adrian





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Alfa145

posted on 26/5/14 at 08:07 PM Reply With Quote
Seized rose joint?
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gaz_gaz

posted on 26/5/14 at 08:08 PM Reply With Quote
There is certainly some discoloration around the break. It's not clean and fresh by any means..
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big_wasa

posted on 26/5/14 at 08:09 PM Reply With Quote
Is it even 16swg ? looks more like 1.2mm ???

[Edited on 26/5/14 by big_wasa]

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austin man

posted on 26/5/14 at 08:13 PM Reply With Quote
What car is it off I would agree that the material looks a little thin for using where excessive force is going to be applied through either braking or suspension movement. This joint will have been receiving stresses in at leat 2 planes due to braking and the movement of the suspension.

Other with the same car may need to check theirs especially when you state this has discolouration this would indicate a prolonged problem





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mookaloid

posted on 26/5/14 at 08:18 PM Reply With Quote
Gotta ask - is it a home built chassis or from a manufacturer? If it's a manufacturer other owners need to know so they can check theirs





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britishtrident

posted on 26/5/14 at 08:23 PM Reply With Quote
Yupp. Looks like a brittle fracture in the heat affected zone of the parent metal, The tube looks like it could be 18 swg tube which is 1.2 mm thick thinners than 1.5/1.6 mm thick.
The joint design is less than ideal, forming the bracket as a strap bent around the tube would be better.
I would also go for bronze welding (brazing)that type of joint in that material.

[Edited on 26/5/14 by britishtrident]

[Edited on 28/5/14 by britishtrident]





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nick205

posted on 26/5/14 at 08:26 PM Reply With Quote
To me, the chassis tube looks too thin walled for the location and the flat bracket to round tube design looks wrong.

What car/chassis is it?






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chris mason

posted on 26/5/14 at 08:44 PM Reply With Quote
Looks like an MNR

Is the lock nut loose, it looks it from the picture, although I'm not saying that's the reason for the failure.

The steel looks extremely thin, I often wonder if some manufacturers use inappropriate steel all in the name of weight reduction.

I was advised by a large company that supplies specialist steel too Motorsport teams, not too use T45 unless you have the correct facilities too weld it, as the welds would make the steel brittle if not done correctly. You shouldn't weld it with just the usual mig set although I can't remember the exact reasons I was told.

Might be worth a word with the manufacturer and see if the chassis can be strengthened for your future use.

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iank

posted on 26/5/14 at 10:17 PM Reply With Quote
quote:
Originally posted by chris mason
Looks like an MNR
...
I was advised by a large company that supplies specialist steel too Motorsport teams, not too use T45 unless you have the correct facilities too weld it, as the welds would make the steel brittle if not done correctly. You shouldn't weld it with just the usual mig set although I can't remember the exact reasons I was told.

...



T45 is a Carbon/Manganese alloy which if MIG'ed should really be heat treated to stress relieve. As I understand it the HAZ is significantly more critical compared to regular tube and can be brittle.

If that chassis is T45 (or Chrome Moly) - which looks likely from the wall thickness chosen - then if it was MIG'ed (not completely clear from the chassis weld, it could be TIG or very nicely MIG'ed) it should have been stress relieved.

Have to agree the bracket design doesn't look ideal, but to be fair to the manufacturer that clearly hasn't failed and was stronger than the tube.





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mark chandler

posted on 26/5/14 at 11:08 PM Reply With Quote
That's a long way to go for 8 laps

The metal looks dirty on the right hand side so a stress fracture, best check the rest of them as well.

I would look at cutting some tube so it can "clip" around at least the front half to reinforce the area and do the other brackets as well, I guess running rose joints rather than rubber bushes has increased the shock load.

When I looked at my mud guard stays they had started fracturing like this.

If you cannot weld bring it around to mine with a bottle of red wine

Regards Mark

[Edited on 26/5/14 by mark chandler]

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designer

posted on 27/5/14 at 09:22 AM Reply With Quote
The tube is to thin to take suspension loads.

Suspension load should always be on intersections, where tubes meet, unless the section is thick enough.

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MK chippy

posted on 27/5/14 at 11:08 AM Reply With Quote
Any news on wether this is an mnr, mk or alike?

Bit worrying

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coyoteboy

posted on 27/5/14 at 11:54 AM Reply With Quote
Looks like a combination of dodgy design and poorly welded (or not properly treated) welds. A) you shouldn't be loading a beam in the centre like that and b) it's clearly a brittle fracture of the HAZ. If the tube had been thicker it might not have failed or might not have failed so soon. If the weld had been properly treated to not be brittle the tube thickness may well have been perfectly acceptable.

Incidentally all failures are stress fractures...

Also, looking at the bracket shape, it looks like the bracket has been crushed (i.e. spacers/top hats too narrow for the gap) - could be a camera angle but that loading on top of everything else may not help.

[Edited on 27/5/14 by coyoteboy]





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motorcycle_mayhem

posted on 27/5/14 at 12:00 PM Reply With Quote
It's enticing to take large amounts of kerb at Anglesey at speeds that are frighteningly fast, perhaps you were?, perhaps that was the last straw for what is not an ideal bracket on a round tube.
Fatigue break.

It it was mine I'd be looking at the other side, then the other end, very carefully. Actually, if I had that sitting in my garage right now, a piece of 1" square 16g tube would be going in.

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emwmarine

posted on 27/5/14 at 04:38 PM Reply With Quote
I've never actually measured it other than look at it after i've drilled a hole in it but I would guess that the square tube in my Dax Rush mush be around 2mm or maybe just under in terms of thickness. The engine mounts I made are 4mm thick. That tube does look too thin for heavy loads too me.





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PAUL FISHER

posted on 27/5/14 at 05:00 PM Reply With Quote
quote:
Originally posted by MK chippy
Any news on wether this is an mnr, mk or alike?

Bit worrying


Its a MNR

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gaz_gaz

posted on 27/5/14 at 05:06 PM Reply With Quote
The chassis is an inboard MNR

2000 miles, 2 trackdays. MNR have been helpful to a point.

There was no kerbs. I had never been to Anglesey and was feeling my way round.

I'm abit narked by this as it's my second MNR and both have had problems.
The last one had a habit of breaking rear wishbone mounts where the bracket had been welded to a round tube!

[Edited on 27/5/14 by gaz_gaz]

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designer

posted on 27/5/14 at 05:17 PM Reply With Quote
quote:

The last one had a habit of breaking rear wishbone mounts where the bracket had been welded to a round tube!



There would seem to be a design problem!

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Wadders

posted on 27/5/14 at 05:31 PM Reply With Quote
Slightly OT, but its a common misconception that T45 needs post weld heat treatment, provided the correct filler rod is used
and the material is under 3mm thick then no heat treatment is required.

Ideally TIG would be used to weld thin gauge T45 with A15 or A18 filler rod. You could of course bronze weld with either an oxy acetylene flame or TIG as the heat source, many bicycle frames are made this way, as were the old Caterham chassis made by Arch.

I don't think either of the above processes would be cost effective for a small locost manufacturer of Se7en chassis though, they tend to use MIG for speed and ease, although i don't know many that use T45 either, again on cost grounds.

Years ago my pal bought a Streetfighter frame for his FJ1200, it was made from chrome moly tube and fully mig welded
it lasted 50,000 plus hard miles before one of the down tubes cracked round an engine mounting bracket, he brazed it up and
AFAIK it never cracked again.

Al

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