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Author: Subject: Time for a upgrade i think
madteg

posted on 2/9/16 at 05:50 PM Reply With Quote
Time for a upgrade i think

I have just ripped one of the diff mount of chassis, That's another part i will have to make stronger. What will be next i wonder
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907

posted on 2/9/16 at 07:27 PM Reply With Quote
My first breakage was an engine mount.
Replaced 3mm with 4mm. 5mm next I dare say.


Paul G






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CosKev3

posted on 2/9/16 at 07:50 PM Reply With Quote
quote:
Originally posted by madteg
I have just ripped one of the diff mount of chassis, That's another part i will have to make stronger. What will be next i wonder


Is this on the stainless steel chassis mentioned in your avatar?

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madteg

posted on 2/9/16 at 07:59 PM Reply With Quote
Yes it is the stainless chassis but i would imagine it still would have happened with mild steel. it was the 3mm bracket holding the diff, i am now going up to 6mm and extending the bracket the whole length of box section.
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CosKev3

posted on 2/9/16 at 08:07 PM Reply With Quote
Pretty sure stainless is much weaker than mild,has been discussed on here before for chassis use?

It cracks/splits way easier,hence why a lot of rally cars don't use stainless steel exhausts,as a mild one will dent rather than splitting/cracking

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coyoteboy

posted on 2/9/16 at 08:53 PM Reply With Quote
Stainless both heat and work hardens to brittle form. Depends on the failure mode you've seen as to whether stainless is the issue or just pure strength.





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liam.mccaffrey

posted on 3/9/16 at 07:50 AM Reply With Quote
Stainless grades are also prone to stress corrosion cracking when exposed to salts/chlorides.

If you repair in stainless consider painting the area. You won't see the cracks as soon but it will probably last longer.





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907

posted on 3/9/16 at 01:56 PM Reply With Quote
@ Madteg

Well Madteg, what are we going to do now mate?


Best replace my PAG exhaust with a rusty mild steel one for a start.
Then there's the higher strength of mild steel to consider. That internet page that I found had it all wrong.
The 30 versus 45 ton a square inch tensile was the wrong way round. Bugger !
To think of all that money I spent on heavy duty tools to cut the stuff and I could have bought smaller ones all along.
Then there's heat makes it brittle. I won't need my toffee hammer any more.
And to cap it all, no more trips down the seaside. Must stay away from the salt air.

Best get the paint brush out then.

Still, Look on the bright side. At least according to LB you can weld it with a bit of mild steel filler wire.










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liam.mccaffrey

posted on 3/9/16 at 02:25 PM Reply With Quote
Boys, I was trying to be constructive not troll anyone.
Chloride stress corrosion cracking is a real problem in my industry (oil refining)

Good luck with repair.
Liam Mc





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CosKev3

posted on 3/9/16 at 04:27 PM Reply With Quote
quote:
Originally posted by 907
Well Madteg, what are we going to do now mate?


Best replace my PAG exhaust with a rusty mild steel one for a start.
Then there's the higher strength of mild steel to consider. That internet page that I found had it all wrong.
The 30 versus 45 ton a square inch tensile was the wrong way round. Bugger !
To think of all that money I spent on heavy duty tools to cut the stuff and I could have bought smaller ones all along.
Then there's heat makes it brittle. I won't need my toffee hammer any more.
And to cap it all, no more trips down the seaside. Must stay away from the salt air.

Best get the paint brush out then.

Still, Look on the bright side. At least according to LB you can weld it with a bit of mild steel filler wire.






Suppose you used stainless steel bolts to bolt on all your suspension too?

Always one...........

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907

posted on 3/9/16 at 09:09 PM Reply With Quote
Afraid so.






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spiderman

posted on 3/9/16 at 10:31 PM Reply With Quote
quote:
Originally posted by 907
Afraid so.


Ohh dear.





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Irony

posted on 3/9/16 at 11:02 PM Reply With Quote
quote:
Originally posted by 907
Well Madteg, what are we going to do now mate?


Best replace my PAG exhaust with a rusty mild steel one for a start.
Then there's the higher strength of mild steel to consider. That internet page that I found had it all wrong.
The 30 versus 45 ton a square inch tensile was the wrong way round. Bugger !
To think of all that money I spent on heavy duty tools to cut the stuff and I could have bought smaller ones all along.
Then there's heat makes it brittle. I won't need my toffee hammer any more.
And to cap it all, no more trips down the seaside. Must stay away from the salt air.

Best get the paint brush out then.

Still, Look on the bright side. At least according to LB you can weld it with a bit of mild steel filler wire.






Wow, constructive comments! Why don't nip over to the Morgan factory and help them out with the wooden chassis parts while your at it

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Grimsdale

posted on 6/9/16 at 09:08 AM Reply With Quote
To dispel a few myths in this thread:

Heat only makes 304 austenitic stainless steel (used in exhausts) brittle due to chromium carbide precipitation above 500C, so not applicable to chassis.
See as an approx example: http://www.ssina.com/images/corrosion/IGAFig3.jpg

Chloride stress corrosion cracking only really affects similar steels above 60C, not really a big issue in winter when there is salt on the roads.

Work hardening is a process where plastic deformation of metals causes an increase in hardness / strength. Austenitic steels have much higher work hardening due to the different crystal structure. This is of note to anyone forming the chassis, but does not affect in service use unless you're in the process of crashing. It certainly does not make it brittle - a limit will be reached eventually, and if overloaded will still fail in a ductile manner.

Austenitic stainless steels do not thermally harden (other than the precipitation noted above).

A2/A4 - 80 bolts are pretty close to 8.8 grade bolts in terms of yield strength, from which you calculate fatigue strength. A2/A4 - 70 bolts are soft as cheese, very common, and shouldn't be used for suspension.

I think what it boils down to is design. If you want to use stainless, go ahead, but design for it. Know your material, know its strengths and weaknesses. Substituting stainless directly for mild may well give issues. In this case it has cracked, but as have many other stainless and mild steel chassis. Bearing in mind Mr Teg's car is exceptionally powerful, i don't think pointing the finger directly at stainless is really applicable.




This post is not meant to be authoritative, or directed at any individuals. APR 1456%.

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907

posted on 6/9/16 at 11:02 AM Reply With Quote
quote:
Originally posted by Grimsdale
To dispel a few myths in this thread:

Heat only makes 304 austenitic stainless steel (used in exhausts) brittle due to chromium carbide precipitation above 500C, so not applicable to chassis.
See as an approx example: http://www.ssina.com/images/corrosion/IGAFig3.jpg

Chloride stress corrosion cracking only really affects similar steels above 60C, not really a big issue in winter when there is salt on the roads.

Work hardening is a process where plastic deformation of metals causes an increase in hardness / strength. Austenitic steels have much higher work hardening due to the different crystal structure. This is of note to anyone forming the chassis, but does not affect in service use unless you're in the process of crashing. It certainly does not make it brittle - a limit will be reached eventually, and if overloaded will still fail in a ductile manner.

Austenitic stainless steels do not thermally harden (other than the precipitation noted above).

A2/A4 - 80 bolts are pretty close to 8.8 grade bolts in terms of yield strength, from which you calculate fatigue strength. A2/A4 - 70 bolts are soft as cheese, very common, and shouldn't be used for suspension.

I think what it boils down to is design. If you want to use stainless, go ahead, but design for it. Know your material, know its strengths and weaknesses. Substituting stainless directly for mild may well give issues. In this case it has cracked, but as have many other stainless and mild steel chassis. Bearing in mind Mr Teg's car is exceptionally powerful, i don't think pointing the finger directly at stainless is really applicable.




This post is not meant to be authoritative, or directed at any individuals. APR 1456%.






Well put sir. I wish I could write like that.

There are times when this forum needs a "like" button.
This is the best I can do with my limited computer skills.

We need a
We need a "like" button







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britishtrident

posted on 6/9/16 at 11:34 AM Reply With Quote
Without seeing the mode of failure it really strikes me as a design issue, increasing the thickness by such a massive amount might not be the way to go.
I am always very wary of welding material of very different thicknesses.
When welding anything other than plain vanilla mild steel it pays to be 100 percent sure of the weld metallurgy before welding.





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Slimy38

posted on 6/9/16 at 03:38 PM Reply With Quote
quote:
Originally posted by madteg
Yes it is the stainless chassis but i would imagine it still would have happened with mild steel. it was the 3mm bracket holding the diff, i am now going up to 6mm and extending the bracket the whole length of box section.


Which bit actually broke? Was it the bracket, the box section or the weld between them?

My limited understanding of metal (IE next to zero) is along similar lines to what BT says, is just increasing the thickness of the bracket the right thing to do or will it simply move the failure elsewhere?

I only ask because I've had to be creative with my diff mounting, and whilst I probably won't be running huge torque I'd like to see if I've gone for the wrong mounting choice.

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liam.mccaffrey

posted on 6/9/16 at 07:40 PM Reply With Quote
What is the stainless grade? Any pictures(.......thousand words and all that)

Good post Grimsdale





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