stress analysis results

[matthewbrindley]

I have a problem with stress analysis.

The material override does not give me different results when I choose a material I have created.

For example a steel plate under load has a deformation of say 10mm.

I change this to aluminium and get for example 30mm deformation.

If I change the steel plate to Domex ( I created this based on steel style but with much higher yield and uts )

I get exactly the same results as mild steel.The program is ignoring the custom material specification.

Anyone know anything about this.

Thanks.

INVENTOR PROF 2011 (LATEST)

WIN7 64BIT

[Anonymous]

Did you change the Young's Modulus?

Deformation / displacement won't change unless the stress / strain ratio or section profile changes - thickens etc.

(Can't open this by ra way - on lowly 2010)

[Inv_kaos]

What did you enter for your elastic (Young's) modulus 'E' and your Poisson's ratio? Why would you think Yield and UTS would effect your results?

I worry what will go wrong with the continual integration of FEM and CAD..

There is heaps of information on the web, if you are going to use FEA, you should at least do some introductory reading. NAFEMS has a standard that recommends the minimum experience required (by engineers) to be competent to apply FEA. Rubbish in = rubbish out.

[matthewbrindley]

Thanks,

I am currently trying to find this out.

It is not readily available on the internet so I have contacted swedish steels direct.

Oh by the way your reply was quite friendly unlike some one else on here.

Thankyou very much.

[Inv_kaos]

My reply wasn't meant to be unfriendly but it is reality. I have seen very bad results from inexperienced or unqualified users. Best of luck with your study of FEM.

[Anonymous · Accepted solution]

Hi Matthew,

this behavior is correct. It's all because the displacements and therefore stresses are only dependent of the geometry and Young's Modulus, which is nearly the same for all steels. Thus it would be strange when the deformations of mild steel and Domex would be different...

Please note that this says nothing about Yield Strength and Ultimate Tensile Strength, which are indeed different for different kinds of steel! Since Inventor Simulation presumes the calculations are performed in linear-elastic area of the material, i.e. no permanent deformation, only the safety-factor should give a different outcome, since that is based on the Yield Strength.

[matthewbrindley]

Thankyou for your reply.

I read earlier that the youngs modulus was probably very similar for mild and high strength steel.

I am currently trying to compare a mild steel fabrication with a version in domex.

The mass being an issue.

Swedish steel say for example I can replace a 6mm thick mild steel plate for a 3mm thick domex 700mc plate.

If I use fea on such a plate according to what you have said the results will show the 3mm mild and 3mm domex giving the same deformations.

I see what you mean about the safety factor.

I must admit as a visual tool this can be counter intuative.

I am not as you may have guessed a stress engineer.

I have on the other hand had direct experience with the steels mentioned and when put under load

they do not behave as inventor shows.

Putting it simply 2 boxes where built one from 3mm mild one from 3mm domex

they where both loaded the same manner.

The domex box did not deform as much as the mild steel box.This is not what is reflected in inventor.( both within elastic limit)

I am slightly confused.

[Anonymous]

I understand. As far as theory is concerned there should be no difference, but in practice there is.

Some thoughts: the theory assumes the materials are isotropic. This means that the material properties are the same in every direction. But in practice this is not the case, for metal plates are produced in different ways. This causes non-isotrope material parameters, which basically influence the Young's Modulus. F.e., when your plate (see your .ipt) is cut in different orientations from the different base plates, of which one comes from a coil and the other does not, this will lead to different results in practice.

[matthewbrindley]

Thankyou for your reply.

I must admit I was starting to ramble on a bit there.

I understand that the 2 plates would basically deform the same amount but the container made from domex would

take a much higher load to push it past the elastic limit.

Therefore If I am looking to keep the sides flat then some bracing is required in either case to resist bending.

I will have to be careful when interpreting the results of these simulations.

I am happy to say I have found some very helpful and clever people here.