Defining Plastic materials

[lucmartzz]

Hello,

I have been working hard for understand and determine a clear path of how to create a new plastic material in Nastan In-CAD based on the datasheet of the material manufacturer.

It has been a little bit frustrating the lack of documentation for make this on a secure and affordable way. 

I would like to know for example what are the minimum properties that are required for perform a non-linear analysis because it is hard to find all the material properties.

I'm attaching a datasheet of a plastic material as example of the information that I have.

Best Regards.

Esteban M.

P.S. by the way, please check my video tutorial about AnyCAD functionality

https://www.youtube.com/watch?v=DiFOnwA1wO8&t=7s

[Anonymous]

Hi Esteban,

your datasheet does not contain information that is suitable for creating a non linear model of your material.

You have some options:

- having your plastic specimen tested by a lab

- subscribing to a material database

  You can have a look at campus plastics:

  http://www.campusplastics.com

Please when using data in Nastran in-CAD be aware of the type of data that Nastran in-CAD requires as input. Here is the help page giving some details about it:

http://help.autodesk.com/view/NINCAD/2018/ENU/?guid=GUID-08427B19-885A-44A2-AAAA-577AEE5E7CA9

[John_Holtz]

Hi Esteban (@lucmartzz)

You asked "I would like to know for example what are the minimum properties that are required for perform a non-linear analysis".

The minimum properties are: modulus of elasticity (E) and [modulus of rigidity (G) or Poissons ratio]

The datasheet gives the tensile modulus and flexural modulus. Either of those would be suitable for the modulus of elasticity. But I do not see either of the other material properties that are required for the minimum input. I do not even see the mass density which is a common (and easy to measure) property, so those data sheets are rather useless for your purpose!

Of course, if you want to include nonlinear material properties, then you need additional data for the stress-strain behavior after yielding. Can it be approximated using a bi-linear stress-strain curve? Does it require a more detailed stress-strain curve by entering points along the curve?

I suggest you contact DuPont to see if the information that you need is available.

[shigeaki.k]

Hello @lucmartzz,

did the reply from @Anonymous or @John_Holtz answer your enquiry? If so, could you select the "accept as solution" button so that others may also easily find the answer.

Thanks & Regards,

Shigeaki K.

[lucmartzz]

Hello @Anonymous

Thank you so much for your post, I took a look to the Campus page unfortunately they have almost the same information of the datasheet.

Would be nice to have a database like MatWeb for Nastran where you can download the material file and just upload it to the materials list.

I will check how hard would be to have some testing on a Lab.

Thanks!!

[lucmartzz]

Hello @John_Holtz

Thank you so much for your answer.

So modulus of elasticity, Poissons ratio and density are the minimum inputs for linear analysis, for non-linear in addition I need the stress-strain curve after the Yield point.

The good news is that Dupont provides the stress-strain curve, the bad news, it only reach the Yield point (See attached).

Now, I have no problem by using an approximated bi-linear stress-strain curve. Looking on internet for how to determine the bi-linear stress-strain curve I found that is required the tangent modulus and this takes to the Ramberg-Osgood relationship but I don't want to over-complicate. Is there another way to get the bi-linear stress-strain curve?

Best.

[John_Holtz]

Hi @lucmartzz

The question is how much strain will your model experience.

• If the model only experiences a few percent strain, then you can use a linear analysis. The modulus of elasticity can be calculated from the slope of the stress strain curve.
• If the strain is more than a few percent and less than the yield, you would have to use the nonlinear-elastic option in InCAD and enter data points for the stress-strain curve using the graph from DuPont.
• If the model is stressed beyond the yield point, you cannot calculate BOTH the nonlinear elastic behavior AND the plastic behavior beyond yielding with InCAD. The options for yielding in InCAD all assume a linear elastic region, not the nonlinear elastic region that this material exhibits. (The yielding material models are based on metals which typically have a straight line, linear region in the elastic range, yield, and then go through plastic deformation.)

[Anonymous · Accepted solution]

Hi Esteban,

by looking at your SS plot and reading John's comments, you could give a chanche using non-linear elastic material model.

You can use a plot digitizer to capture a Stress-Strain curve from the picture supplied by Dupont.

If you're interested in what happens after yielding you'll have to test a specimen.

Good luck.

[John_Holtz]

Hi @lucmartzz

I wanted to check if you had any other questions or ideas for this post. What did you decide to do?

[lucmartzz]

@Anonymous @John_Holtz

Thanks for the follow up.

I inserted the SS plot into AutoCAD and copied one of the lines (at 23 Celsius degrees) in order to extract the points and create the SS plot in nastran.

I'm exploring and comparing linear and non-linear applying low forces.

Best Regards.

[Anonymous]

Thanks

---

@Anonymous wrote:

Hi Esteban,

your datasheet does not contain information that is suitable for creating a non linear model of your material.

You have some options:

- having your plastic specimen tested by a lab

- subscribing to a material database

  You can have a look at campus plastics:

  http://www.campusplastics.com

Please when using data in Nastran in-CAD be aware of the type of data that Nastran in-CAD requires as input. Here is the help page giving some details about it:

http://help.autodesk.com/view/NINCAD/2018/ENU/?guid=GUID-08427B19-885A-44A2-AAAA-577AEE5E7CA9

---

Thanks a lot for this piece of info. It's helpful for me as well. I had similar issues too

[lucmartzz]

@Anonymous 

Thanks for your answer, indeed I got better information from Campus Plastics 🙂

Best Regards

E.M.

[sakkie.coetzee]

@lucmartzz 

I'm new to NASTRAN, so I might be totally wrong here.

Question around the strain values in your table.  Those values do not look like true strain.  It looks like actual deformation or stretch.  To get to true strain, in excel     =LN((sample test length + stretch amount)/sample test length)

eg.  True strain at 1mm deviation on a 50mm sample test length  =LN((50+1)/50)) = 0.0198 true strain

For a sample to have a true strain value of 4, the sample will have to stretch something like 50x the test sample starting length. 

[sakkie.coetzee]

Default Setting in "Parameters" for true stress is "OFF", but strain only give LOG or GREEN.  Don't know what "GREEN" means.