General Mechanical

General Mechanical

Viscoelastic sandwich plate analysis

    • adkh
      Subscriber
      I want to perform modal analysis of viscoelastic sandwich structure, i.e, viscoelastic material in between two steel plates, in Ansys.
      My question is that do i have to input only shear relaxation test data in ansys or i have to add additional data like uniaxial, planer, volumetric also for such type of analysis. Thanks
    • Sandeep Medikonda
      Ansys Employee
      Hi Modal analysis is a linear analysis and non-linear materials or contacts cannot be used.

      Regards Sandeep
    • peteroznewman
      Subscriber

       Sandeep, I think adkh means vibration analysis when he says modal analysis, given the answers we gave in his other discussion.


      Adkh, for your application, start with shear relaxation test data and fit a Prony series to your data.

    • Sandeep Medikonda
      Ansys Employee

      ok thanks peter.


      Yes, shear relaxation would do. You would only need bulk modulus if volumetric incompressibility is a factor. You might find this discussion helpful.


      Regards,
      Sandeep

    • Bhargava Sista
      Ansys Employee

      Hi Sandeep, Peter,


      Looking at this and the other discussion with adhk, I wanted to add something that might be relevant:


      you can perform a full harmonic analysis on viscoelastic materials by defining frequency dependent elastic modulus, Poisson's ratio and damping using TB,ELASTIC and TB,DAMP commands (WB does not support this in GUI, so you'll need to use command snippets). It still assumes linear response so large-deformation effects are not included.

    • adkh
      Subscriber

      Hi Sandeep, sorry i mean vibration analysis. Thanks peter for clarifying it.

    • adkh
      Subscriber

      Hi bsista, can you please add a little more detail of your previous answer because i didn't understand, you mean that shear relaxation test w.r.t time should not be used?. Thanks

    • Bhargava Sista
      Ansys Employee

      You can use the shear relaxation test to calculate the Prony series constants. These properties are in time-domain so you'll need to convert them into frequency-domain using the following equations, which is nothing but calculating the storage and the loss modulus. 



      You'll need to define a starting and the ending frequency to calculate these quantities. Once you do this conversion, you can input these properties into ANSYS Mechanical using command snippets.

    • adkh
      Subscriber
      Ok thank you so much, but what tool should i use to convert it from time domain to frequency domain, in case i have the data of relaxation test.
      Secondly, can you provide a reason why i can't use directly the time domain data.
    • Bhargava Sista
      Ansys Employee

      You can use ANSYS WB to perform curve fitting on shear relaxation data and calculate Prony series constants. Once you have them, you can use Matlab, Python, Excel or even APDL math (if you're familiar with it) to perform these conversions. 


      As Sandeep and Peter have mentioned earlier, viscoelasticity is a nonlinear material behavior while harmonic analysis is a linear analysis. So, we use Fourier transforms to linearize the property by converting the data from time-domain into the frequency domain. 

    • adkh
      Subscriber

      I understand now, thanks to Sandeep, Peter and Bsista.

    • seventanapply
      Subscriber

      You can read this paper 


      "Methods of interconversion between linear viscoelastic material functions Part I- a numerical method based on Prony series" by S W Park and R A Schapery.

    • seventanapply
      Subscriber

      Hi bsista,


       


      Is it possible to use transient structural module to see the phase lag angle delta?   tan delta is defined by loss modulus/storage modulus.


      Thanks.

    • JHPontes
      Subscriber
      Hi all,nI already have the data for storage and loss modulus vs frequency but not really sure how to insert it into ansys WB engineering data.nCould anyone help me?n
    • Laurentiomoto
      Subscriber
      Im looking for the same answer as JHPontes .n
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