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Author: Subject: What is a Cranfield stress analysis
Irony

posted on 21/2/13 at 11:00 PM Reply With Quote
What is a Cranfield stress analysis

There is a fella on eBay selling Viento chassis number 4. He claims to have a CRANFIELD UNIVERSITY’S  STRESS ANALYSIS FOR THE CHASSIS. What is that then?
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blakep82

posted on 21/2/13 at 11:19 PM Reply With Quote
I suspect its a stress test, done by cranfield university? If there is a cranfield university...
I guess it could only really be answered by someone that did the test personally





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plentywahalla

posted on 21/2/13 at 11:58 PM Reply With Quote
Cranfield University is probably the UK's premier uni for post grad Msc in Automotive Engineering.





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eddie99

posted on 22/2/13 at 12:04 AM Reply With Quote
I suspect either it's a physical test been done on that chassis such as torsional, how much force to move it x amount of mm

Or they have taken measurements, created a cad file and run it through FEA

Probably then just a printout of where the stresses are on the chassis and displacement

Having the fea results is one thing, it's only of any real value if they have used it properly and made the chassis any better.

[Edited on 22/2/13 by eddie99]





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fesycresy

posted on 22/2/13 at 08:13 AM Reply With Quote
Wasn't this part of the original sales blurb from the Luego factory?





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designer

posted on 22/2/13 at 08:56 AM Reply With Quote
Maybe he thinks it will make the chassis worth more!
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matt_gsxr

posted on 22/2/13 at 09:44 AM Reply With Quote
The most trivial amount of googling indicates that it was an MSc project

http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&ved=0CEUQFjAC&url=http%3A%2F%2Flocost7.info%2 Ffiles%2Fchassis%2FFinal_Thesis_A.doc&ei=Aj0nUau3HKHU0QXc0oCoBQ&usg=AFQjCNHPqbd6uh8X2lxgIn7IdYmLsyinVQ&sig2=ippflsYKnhFFRRyWx-CJOg&bvm =bv.42768644,d.d2k

All theoretical FEA and applied to all Luego.

I can't find out whether he passed the MSc or not, so it might all be wrong!

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matt_gsxr

posted on 22/2/13 at 09:45 AM Reply With Quote
locost7.info/files/chassis/Final_Thesis_A.doc

better link

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britishtrident

posted on 22/2/13 at 11:04 AM Reply With Quote
NB ANALYSIS not test

All it means is somebody has run a finite element analysis on a CAD model of the chassis --- which actually means nothing unless it was done by an experience FEM practitioner using a computer model that was valid and representative with the right restraints and loads.





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phelpsa

posted on 22/2/13 at 06:19 PM Reply With Quote
quote:
Originally posted by britishtrident
NB ANALYSIS not test

All it means is somebody has run a finite element analysis on a CAD model of the chassis --- which actually means nothing unless it was done by an experience FEM practitioner using a computer model that was valid and representative with the right restraints and loads.


This is from Cranfield University, i'm sure they wouldn't put their name to it unless it showed a reasonable level of validity.

These are the people who make quite a lot of money doing F1 crash testing...

EDIT: Having said that, 1300Nm/Deg sounds quite high!

[Edited on 22-2-13 by phelpsa]

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britishtrident

posted on 22/2/13 at 07:09 PM Reply With Quote
quote:
Originally posted by phelpsa
quote:
Originally posted by britishtrident
NB ANALYSIS not test

All it means is somebody has run a finite element analysis on a CAD model of the chassis --- which actually means nothing unless it was done by an experience FEM practitioner using a computer model that was valid and representative with the right restraints and loads.


This is from Cranfield University, i'm sure they wouldn't put their name to it unless it showed a reasonable level of validity.

These are the people who make quite a lot of money doing F1 crash testing...

EDIT: Having said that, 1300Nm/Deg sounds quite high!

[Edited on 22-2-13 by phelpsa]



The way I look at it is a project that was part of some bods Msc which isn't quite the same thing





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NeilP

posted on 23/2/13 at 10:55 AM Reply With Quote
From very dim and distant memory I recall Grant from the original Luego saying that a chassis had torsional measurements done on it. He still on here occasionally trading as OBP (Original Balance Parts or something similar) - Bet a google would get you a phone number then you'd know if it was just a virtual test (in which case it's also a feature of my chassis ) or a physical on number 4 (in which case it's been played with a bit by undergrads )...

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Sam_68

posted on 23/2/13 at 12:59 PM Reply With Quote
quote:
Originally posted by NeilPFrom very dim and distant memory I recall Grant from the original Luego saying that a chassis had torsional measurements done on it.


The link given by Matt above is only half of the document.

You need Part B as well, which gives details of the physical testing and FEA validation:

http://locost7.info/files/chassis/Final_Thesis_A.doc
http://locost7.info/files/chassis/Final_Thesis_B.doc

It's a very interesting and useful document, but sadly its terms of reference fell short of including the final part of the jigsaw, which would have been an analysis of predicted chassis deflections compared to the deflection of tyres, road springs and bushes... I did a few fag-packet calculations of these myself, once upon a time, but unfortunately I've lost them.

Received wisdom says that you need a torsional stiffness for the chassis of at least 10 times the roll resistance on the road springs/ARB's, but I think this was just someone's arbitrary rule-of-thumb. From memory, and contrary to popular belief, my sums suggested that the effects of torsional chassis deflection on suspension geometry were actually quite trivial - the fact that the chassis acts as an undamped spring and the effect that this has on instantaneous loads at the tyre contact patches is possibly more significant.

quote:
phelpsaHaving said that, 1300Nm/Deg sounds quite high!


I still think in lb.ft/degree, I'm afraid, and that's only about 980 lb.ft/degree, which is distinctly unexceptional?

That was for a largely unpanelled Luego chassis, though - I'd expect the fully panelled chassis to be lower-end ballpark for where you'd expect a 'typical' Seven-style spaceframe to be, in the region of 1,250-1,800 lb.ft/degree. The 'best' spaceframe 'Seven' chassis I'm aware of test figures for (the Caterham) achieved 2,000-2,500 lb.ft/degree (and they might have improved this further with recent development).

The predicted 'optimised' stiffness of over 6,000Nm/degree (4,425 lb.ft/degree) takes a bit of swallowing, though!

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