FEA analysis stress value not correct

[Anonymous]

Hi,

I have some issues with the stress analysis. I have attached two picture files. One is with support and another without support. All the setttings for stress analysis are made already. All the factors are same for both files. You can just simulate directly.

Practically stress must be less in the case which has supprot while here in the software its opposite. When I add support, stress increases which is not quite promising.

thanks,

Manish

[Anonymous]

I'm unable to attach .ipt files.

[JDMather]

What is the Material.

What is the Constraints?
What is the load?

What are the dimensions?

On what information are you stating the results are not correct?

[Anonymous]

I wish I could upload the file. I can mail you if you want.

Material: steel for inventor material library

               Yield strength: 207 MPa

All properties as default.

Attached are some pictures of dimensions.

[Anonymous]

it is constraint on the bottom side and

force = 100000 N applied in opposite direction.

[Anonymous]

all dimensions are in millimeters

[Anonymous]

all dimensions are in millimeters.

[mcgyvr]

Assuming INV 2014 64 bit.. Yes Autodesk broke it and it won't be fixed till January

BUT see page 3 for a workaround/registry hack..

http://autodesk.lithium.com/t5/Inventor-General/FEA-64-bit-problem/td-p/4625321

[JDMather]

Here are my results in SolidWorks (I didn't bother to set up the material properties to EXACTLY the same as Inventor or the mesh density.

The results are identical to your Inventor results (for all practical purposes).

I can run the analysis in Creo and Autodesk Simulation (Algor) if you want, but I know they will be the same.

Note: I should have set the images undeformed (or actual) like yours.  I can do that if needed and post back.

Here are Creo (Pro/E) results.

  again, I didn't run any convergence tests, but the results are essentially the same.

[JDMather]

---

@mcgyvr wrote:

.... Yes Autodesk broke it ...

---

I think that only applies to assembly FEA.

[Anonymous]

My question is for stress analysis problem

I think you are talking about uploading issue

[Anonymous]

But do you think this solution is right, I don't think this analysis is correct.

[mcgyvr]

---

@Anonymous wrote:

---

@mcgyvr wrote:

.... Yes Autodesk broke it ...

---

I think that only applies to assembly FEA.

---

Thats what I get for not looking at any of the attached images.. oops..

[JDMather]

---

@Manish wrote:

 I don't think this analysis is correct.

---

Why do you not think the analysis is correct (note that I edited my previous response to include Creo results).

[Anonymous]

It is not correct because it shows the stress value higher and in turn safety factor lower.

But in actual we can see from the results that after adding support, that block colour has changed from green to blue, meaning it is more safer.

Meaning there will be less deformation comparatively and stress must be less.

Also we have tested our one of the component in reality and it didn't break even after applying 2.5times the force. While the safety factor according to software was just 0.8.

How can we rely on the results then?

[JDMather]

---

manish wrote:

Also we have tested our one of the component in reality and it didn't break even after applying 2.5times the force. While the safety factor according to software was just 0.8.

How can we rely on the results then? 

---

Safety factor does not mean it "breaks".
This is a complex topic that usually requires extensive training to understand.

When you stretch a material it elongates a certain amount in what is referred to the Elastic Deformation.

If you release the load it will return to original form.

If you stretch the material beyond the Elastic Limit (Yield Strength) it enters what is referred to as Plastic Deformation.

If you release the load - the part will permanently deformed (compared to original condition).

For many material as you continue to stretch in the Plastic Deformation range - the material actually becomes stronger, that is, it takes more force to create same increment of deformation up to Ultimate Strength.  Then it will suddenly fracture (break) or might suddenly experience additional elongation with less force and then fracture.

The Safety Factor is the measure of Yield Stress/Calculated Stress and does not indicate the Ultimate Strength of the part.

I would say you cannot "rely on the results" until you have done enough study backed by physcial testing to understand the results.  Otherwise, all you are doing is creating "pretty pictures".

"It isn't what we don't know that causes the most problems, but rather, what we think we know that just isn't so," Dean Kamen.

[Anonymous]

My first reaction in looking at the model is that the analysis reflects what's happening in real life.

[pball]

I did this quick in inventor and got similar numbers to the person who posted results. So I also feel these results are good. I'll also try to explain why the one with the rib has higher stresses which I believe is what is confusing your from reading your posts.

If you notice the stress in the corner between the two, the one with the rib has less stress which should be expected. The reason it has higher over all stress is because the rib is subjected to a large stress. The rib stops the center of the part from deflecting as much and is under a lot of stress because it's lowering the deflection in the center of the part. The difference in safety factors is because of the high stress in the rib, the rib will break before the part without a rib would break, but that does not mean the whole ribbed part would fail just the rib.

[Anonymous]

ok that case was easy , simple and had less stress.

Lets move to a complex part.

The part what we tested in reality is attached below.

Check next message for dimensions

[Anonymous]

can you please check what stress you get with this part.

I have tried inventor, ansys, creo, multi physics,etc. Stress is more than yield stress and close to tensile stress.

In reality we have done destructive test but doesn't break even applying 2.5 times the force. actually didn't break at all. but Slight deformation of 2 mm.

But in inventor displacement is quite low, around 0.2 mm. Not matching with actual results.

all dimensions are in millimeters.