Composite analysis using 3D elements for Honeycomb core

Staedtlerp
Staedtlerp Altair Community Member
edited October 2020 in Community Q&A

Hi everybody,

 

I want to perform a non-linear structural analysis of a sandwich panel. As stated by the title of this topic, I modelled the sandwich panel by using 2D shell elements for upper and lower skin, and 3D solid elements for honeycomb core (I have created the 3D solid elements by using solidmap/linear solid command and matching elements of upper and lower skin).

The panel has been loaded with a centrifugal force using RFORCE, trying to simulate the centrifugal force of a rotor (the panel I modelled is located at the tip of that rotor). Being the panel subjected to inertial force, I decided to use the Inertia Relief (activating it on PARAM with value -1) and adding Support1 constraints.

The question (the issue) is the sequent:

Upper and lower skin plies have been modelled using 2D elements, MAT8 as material, and PCOMPP property. To model the core, I decided to use 3D elements, MAT9ORT as material card and PSOLID as property.

Looking at the online help, MAT9ORT 'Defines the material properties for linear, temperature-independent, and orthotropic materials for solid elements in terms of engineering constants', so I decided it was suitable for my aim.
To fill in engineering constants, I have used values coming from HEXCEL datasheet (Aramid Fibre/Phenolic Honeycomb), considering 1 directions as the Y direction of the AxysSystem, 2 direction as the X direction of the AxysSystem and 3 as the Z direction. Following the used properties:

 

  • E1=E2=0.01 (very small according to HEXCEL guidance material)
  • E3=138 MPa (HEXCEL material properties)
  • mu12=mu13=mu23=0.01 (very small according to HEXCEL guidance material)
  • G12=0.01 (very small according to HEXCEL guidance material)
  • G13=45MPa HEXCEL material properties)
  • G23=23MPa HEXCEL material properties)

 

As long as I start the analysis, I get the following message:

 

 A fatal error has been detected during input processing:

  *** ERROR # 1551 ***
  for material id = 2 referenced from property id = 4.
  Material coefficients Gij on MAT9 card produce material matrix with negative
  eigenvalues. This violates material stability conditions.
  Eigenvalues of G: 1.010049e-002 9.900507e-003 -3.630604e+002
                    1.000000e-002 2.300000e+001 4.500000e+001

 *** Run terminated because of error(s) in the input data.

 

I don't know exactly what It means....:unsure:/emoticons/default_unsure.png' title=':unsure:' /> I suppose is something related to the material card...

But the stranger thing is that changing the E3 value from 138 MPa to 0.138 MPa it works...:unsure:/emoticons/default_unsure.png' title=':unsure:' /> I'm completely confused

 

Does anyone know the reason why It behaves that way??

 

Is correct to use MAT9ORT to simulate 3D honeycomb?

Thanks in advance

 

Attached you can find the model. Thank you

Unable to find an attachment - read this blog

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Answers

  • Koushik Chandrashekhar_21806
    Koushik Chandrashekhar_21806
    Altair Employee
    edited July 2020

    Hi,

    - To avoid the material check, you can activate the parameter MATCHECK NO. To do so, please go to Setup -> Control Cards -> Param within HyperMesh.
    - It might be an alternative to check the interdependancy between your entered MAT9ORT values using the comments in the OptiStruct Solver help and adapt your values to be aligned with the composite material law.

  • Staedtlerp
    Staedtlerp Altair Community Member
    edited July 2020

    Hi @Koushik Chandrashekhar,

     

    thank you very much for your prompt reply. I've looked for the MATCHECK parameter in the PARAM control cards but I haven't found it. I tried even by search command (CTRL+F) but It doesn't appear in the search result list. Maybe it is the version of the software I work with (I have got the 2017.2 version).

    I have found in the PARAM control card the parameter CHECKMAT..Is it the same??

     

    Thank you

     

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