Any Engineers here?

Duff-Man said:
You can't even begin to compare a simple analytical formula like "Euler's rule" with a proper finite element analysis. Analytical formulae are only ever, at best, an idealised approximation to the solution of simple problems.
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Sure I can. Both are an attempt to work out the stress distribution in the beam. Euler's rule will give you the "wrong" answer sure, but it won't be orders of magnitude off. A badly run FEA can easily provide far worse answers. Stress which increases in magnitude with mesh density is fairly common and clearly incorrect.

I agree that FEA is a far superior approach - but it is certainly not immune to user error. Or for that matter, solidworks automation getting it wrong.

Duff-Man said:
(for what it's worth, numerical methods is what I do for a living. I've written a number of FE / FV / BE codes, though the main focus of my research is meshless methods).
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Good man. Give me a decade and I'll be doing the same.

-westy- said:
Yep, can only do it on single bodies, but Inventor allows you to do it on assemblies. I've set the mesh resolution to "fine", but it seems to have made no difference :/
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Can you post a screenshot of the mesh near the holes? Automated meshing tools are not flawless.
 
JonJ678 said:
Sure I can. Both are an attempt to work out the stress distribution in the beam. Euler's rule will give you the "wrong" answer sure, but it won't be orders of magnitude off. A badly run FEA can easily provide far worse answers. Stress which increases in magnitude with mesh density is fairly common and clearly incorrect.
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I agree there is no accounting for thickness of engineers.
 
[FnG]magnolia;24143620 said:
This might be the only time in GD history where the use of the word 'Engineer' hasn't resulted in a **** storm of indignation and name calling.

Which is a shame because I was kinda hoping that would happen :(
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Duff-Man said:
You can't even begin to compare a simple analytical formula like "Euler's rule" with a proper finite element analysis. Analytical formulae are only ever, at best, an idealised approximation to the solution of simple problems.

FEA takes into account the geometry of the object, the appropriate traction boundary conditions, and the spatial distribution of loads. If the problem has been set up properly, the question boils down to one of resolution. With a simple convergence analysis ("mesh independence testing") you can quantify the error in your solutions, and then reduce it as low as you like.


...In short - trust the finite element analysis - assuming that you have set it up correctly and used a sufficiently well refined mesh. The plot posted in post #5 looks reasonable to me, but be careful that you are properly representing the effect of any 'pin' that might pass through the holes.


(for what it's worth, numerical methods is what I do for a living. I've written a number of FE / FV / BE codes, though the main focus of my research is meshless methods).
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Mag - this is because this is the proper use of the term engineer and some one with a proper engineers problem

As for the other - I dealt with CAD on models for CFD and I also had loads of issues when building it if the mesh was not the right size or in occasions not properly aligned (how it managed to do that I've no idea)..


Rock on the engineers.... ;)
 
UncleRuckus said:
This is nonsense! Since when has Math or design had anything to do with "engineering"?!? ;D
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I could say since when has FEA got anything to do with a simple box strut. But I would probably be shot down by all the brains on here.

The strut design would be based on the force in the connection (obv). So a pin in double shear would give a size which would give a bearing diameter and thickness. The bearing OD would provide a wall thickness of the box. A look up in the available section tables will provide a range of suitable sizes.

Using Eurocode 3 or previous BS5950 calculation will determine slenderness ratios and a suitable area, section modulus and radius of gyration for a grade of steel for a given length.

Choose your section, job done.
 
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From a quick read over the relevant section, it doesn't seem to cover loading through pin joints or reference stress concentration points?
 
Look at the section for compression, this gives you a factor to use for KL/r your K factor is dependent if you are using pin-pin/fixed-fixed etc.

The design of the pin connection is simple bearing calc, shear pull out and pin shear/bending calculation.

Your FEA package will not give you this as you are probably not running a non-linear analysis.

KaHn
 
Voltar said:
Why did I attempt to read and understand this thread :confused:


/abort
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me too, and I am an engineer (sound) :eek:

Zrb0x3j.gif
 
-westy- said:
KaHn, that's fantastic, cheers. The only part I don't understand is where the value of 235N.mm^-2 came from?
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Nominal values of yield strength, fy based on standard and steel grade also thickness. see table 3.1 EN 1993-1-1: 2005 and national annex.
 
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