Forces For stiffness Test

[Sarah800]

Hi,

I Have a nylon part that is made by laser sintering, the core of the part is a lattice structure, and i will do a stiffness test on it by applying a force and measuring the deflection.
How can i determine the range of forces i can apply to the part without destroying it?

Thanks

 

[drawoh]

Sarah800,

Do structural analysis.

What does the part look like?

If your part is rigid, you could have have problems measuring deflection. A springy configuration allows for large, measurable deflections.

--
JHG

 

[Sarah800]

drawoh,

I can't do it computationally, it is a very complex shape and i only have it in .stl format.
The part was manufactured using selective laser sintering machine, the core of the part is complex too (Lattice structure).
I will do a physical stiffness experiment but i want to find the calculations or way to know what is the range of forces i can apply on the part.

Thanks

 

[drawoh]

Sarah800,

Can you feed the model into an FEA program?

If the part is 3D and complex, it is probably rigid.

Can you mount the thing into a rigid fixture and use a dial indicator to record deflections under low forces?

--
JHG

 

[dhengr]

Sarah800:
This is an engineering forum. Reread your two posts and tell us if there is anything in either of them, other than the word sintering, which would indicate that you have any engineering experience or knowledge. Where did you get your engineering degree, and in what field? If you can’t define your own problem any better than you have; if you know nothing about the material properties of the part; if you can’t show some sketches of what you are trying to do; you will probably destroy some parts before you even start to hone in on what you are trying to do. We can’t see it from here, and have no idea what you have or are really trying to do, so it is unlikely that you will get any meaningful answers here. Maybe try the “Answers Is Us” store, they sell bulk answers by the gram, pound, ton, you pick the units.

Even reading drawoh’s post (I mean really reading, and trying to understand what he was getting at) and answering his questions would have been a step in the right direction, shown some technical initiative and moxy. What is it about engineers these days? They don’t really read for meaning, think every post is just another Twitter, with no more meaning either, and if a computer program can’t do it, they are just lost. Go talk to your superior and get their help and guidance.

 

[Sarah800]

drawoh,

No, i cant feed the model into an FEA software duo to the file format (.stl).
And yes, I will mount the physical manufactured part on a testing rig and apply a force and measure the displacement.
My question is how can i determine the value of acceptable froces that can be applied into the part without destroying it (plastically deforming it).

Thanks.

 

[btrueblood]

"My question is how can i determine the value of acceptable froces that can be applied into the part without destroying it (plastically deforming it)."

To answer that will require the destruction (plastic deformation) of at least one test sample. That would have been true even if you had a method of calculating the force required, just to verify the model. Without a reliable mathematical model, you are forced to perform mulitple trials on sample parts.

 

[Sarah800]

dhengr,

Excuse me but, I have explained my case, and i dont have deep information in this area, otherwise i won't ask for advice.
If you couldn't understand and you dont want to help that is fine, you are not obligated to. Just as much as i am not obligated to justify that i am an engineer to you and answer to your childish questions.

Thanks

 

[Sarah800]

btrueblood,

I only have 2 samples manufactured and it is very hard to produce more, duo to financial reasons. That's why i wanted to get the most information from them as possible without destroying them. That is why i wanted to know if there is a way to even find an estimation of the acceptable forces that wont destroy them.

Thanks.

 

[drawoh]

Sarah800,

Either you are doing some form of structural analysis, or you are destroying at least one of them.

--
JHG

 

[Tmoose]

Hi Sarah,

I'm guessing the STL model may have started as a solid model. I'd ask who created the STL model.

I believe some (maybe most?) programs can import STL format files and create models suitable for some level of FEA, although like most models some trimming or simplification is desirable or even necessary.

https://forum.solidworks.com/message/340803

 

[MintJulep]

You do an analysis, or you do a test.

You've said that you can't do an analysis and won't do a test.

What other advice do you imagine is possible for anyone to give you?

 

[Sarah800]

drawoh,

Thank you for your advice.

__

Tmoose,

I recieved the actual file in (.igs) format, and then i had to export it to (.stl) and added some features to it before sending the file to the SLS machine. And i tried changing the file fromat back to (.igs) or any other suitable format but it didnt work.
So i guess the best solution for me is to work more on finding a way to change the file format and do a structural analysis on it.

Thanks alot for your advice.

 

[SnTMan]

Sarah800, to echo MintJulep, you do an analysis, or you do a test. You might kind of scope your test load by pulling, pressing or so forth on the object, and note in a qualitative way the forces and deflections involved. This will get you in the range of "a few pounds, neglegible deflection, a lot of pounds, a lot of delfection".

Now design your test set up such that you can gradually increase the applied load while measuring the deflection at each load. You will have to decide the degree of precision required and design your test accordingly. You can get simple, low precision devices such as a spring scale, or more elaborate and higher precision devices such as air cylinders and linear transducers.

You can send the whole thing, object and test program, to a testing lab.

You must be prepared for the possiblility of destroying the object in the process.

Regards,

Mike

 

[MikeHalloran]

Someone, somewhere, must know the intended service load.
Apply that.
If the part breaks, it wasn't strong enough anyway, and the stiffness doesn't matter.

Better, apply the intended service load incrementally, e.g. P/10, 2*P/10, etc., which will show you how/if the part behaves nonlinearly.
... and if you are present, may allow you to stop the test before the part actually fails, assuming that an intact but still unsatisfactory part has some value to you.






Mike Halloran
Pembroke Pines, FL, USA

 

[KENAT]

Unless you changed a lot to go from the iges to the stl originally why not do an analysis of the original iges file and make some kind of allowance for the changes you made?

Else, do your test in such a way that you can start with 0 load and gradually increase it recording deflection as you go.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[chicopee]

It seems that the part is a composite of Nylon and of some other material such as metal or ceramics. Before doing any of the test mentioned above, you should be familiar with the properties of each component in the part. Knowing the properties will make you more aware of the limitations that maybe importan to your test.