VISOELASTIC MODELING

- November 23, 2020 at 12:03 pm
  
  b.x. Yang
  Subscriber
  
  Hello,nI am modeling 3D chip stacking structure, which contains underfill (belongs to viscoelastic material). To some reasons I can not simplify this material as elasticity, so I want to ask if I want to simulate viscoelasticity, what material data I have to input . As far as I know, 'Viscoelastic test data', 'Prony series pairs', and 'Shift function' are related to defining viscoelasticity in workbench. I should input all three kind of data ? Or Prony series pairs + Shift function(I have to consider the effect of temperature, so Shift function is necessary).nIf you could help me about this, it is nice! Besides , if you are also in this region (electronic packaging), welcome discussing!nBest wishes!n
- December 1, 2020 at 5:07 pm
  
  John Doyle
  Ansys Employee
  
  If you have stress relaxation data (i.e. stress vs time), you can use this as input in curve fitter to calculate alpha and tau prony properties.nYou can use a shift function if material exhibits Thermal-Rheologically Simple (TRS) behavior, but you do not have to do this.nYou could also just generate separate Prony Coefficients for each temperature and use them directly. The shift function is more convenient when it applies (TRS behavior).nSee Section 4.7.2 of the MAPDL Material Reference for more details. You should also consult with Articles and/or text books about shift functions in general to get a better understanding of when and how to use. It is more of a material science question, not just an FEA question.n
- December 5, 2020 at 2:29 am
  
  b.x. Yang
  Subscriber
  
  Dear nThanks for replying.nBest wishes!n

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