Material properties for plywood

Grasshopper Karamba3D
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1

Hello everyone,

I’m new to Karamba and I’m trying to manually enter the material properties for plywood (Sperrholz), but I keep getting an error in the Poisson’s ratio. Since I don’t have a specific material data sheet, I am using the information given in technical tables (Schneider Bautabellen) for plywood, which does not include the Poisson’s ratio, and unfortunately I have not been able to find any values for the Poisson’s ratio on the Internet.

Am I using the wrong values? Has anyone successfully implemented plywood in Karamba?

And also another question, which strength hypothesis should I use?

Screenshot 2024-05-20 163912
Screenshot 2024-05-20 1639121243×643 63.6 KB

Screenshot 2024-05-20 164118
Screenshot 2024-05-20 164118835×591 62.5 KB

Thanks in advance.
Best regards,
Daniel

2

Two observations:

  1. It says S235, so Karamba is assuming steel, not wood
  2. Poisson’s ratio is realted by the Elastizitätsmodul and Schubmoul, something like E = 2G( 1 + nue ). Not sure about your specific use case though.
3

Thanks for your reply :slight_smile:

  1. I think S235 is just the default name given, so it does not mean that steel is selected. It should also not affect anything since the material properties are defined from zero.

  2. If I recall correctly, the Poisson’s ratio formula you wrote is only valid for isotrophic materials. In the Karamba website it is given that the Poisson’s ratio for an orthotropic material is calculated taking into account the different Young’s modulus for each direction. (3.5.1: Material Properties | English 英文 | Karamba3D 2.2.0)

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4

Ran into the same problem years ago, see chapter Defining orthotropic elasticity by specifying the engineering constants:

https://classes.engineering.wustl.edu/2009/spring/mase5513/abaqus/docs/v6.6/books/usb/default.htm?startat=pt05ch17s02abm02.html

5

Thanks again for your reply!

I read the section on the website you attached, but I still don’t understand how to solve the error, since the equation used by Grasshopper to calculate nue1,2 using E1, E2, and G12 (the one from my previous post) will not fulfill the condition that nue1,2 must be smaller than sqrt(E1/E2) (the result is above 4). So I wonder if the values I used are the right ones or if I misunderstood the values in the table…

6

not sure how you come up with 320 and 240 from the attached screenshot.

7

Sorry, I should have mentioned in the first post that I used the E05 values instead of the mean values (E,05 = E,mean * 0.8 according to the table). Then I converted the values from N/mm2 to kN/cm2 as that is the unit used by Karamba.

8

Dear @Daniel48,
sorry for the inconvenience. I have to check the component and see whether the error can be turned into a warning.
– Clemens

9

In the next release of Karamba3D there will be warnings instead of errors when material properties do not correspond to the usual values.
– Clemens