Nonlinear Simulation Vs Linear Simulation

- February 7, 2019 at 9:45 pm
  
  harryzhou4498
  Subscriber
  
  I’m trying to compare ANSYS nonlinear simulation results vs ANSYS linear simulation results and I had a question about multilinear kinematic hardening.
  
  The way that I have my simulations set up currently is that my linear/nonlinear simulations are pulling the same material data from the same place – however, the linear model has the property “Multilinear Kinematic Hardening” with the accompanying stress/plastic strain curve data suppressed while the nonlinear model has that property active. However, I’m encountering an issue where if the same value at a low displacement is applied to both models, the resulting elastic strain results are not equal. My understanding of multilinear kinematic hardening is that this setting will only apply when plastic strain begins to occur, thus meaning that at low deformations and thus low elastic strain, the accompanying stress strain curve data with multilinear kinematic hardening shouldn’t come to play; hence why I’m having trouble understanding why I’m getting different strains using the same displacement. I'd appreciate insight here.
- February 7, 2019 at 10:38 pm
  
  peteroznewman
  Subscriber
  
  Please show the table used for the nonlinear material: stress vs plastic strain and show the stress result for the displacement.
- February 8, 2019 at 12:55 pm
  
  harryzhou4498
  Subscriber
  
  Table and stress result are shown below. The beam is fixed at one end and there is a displacement with a magnitude of .01 ft pulling at the other. The beam is 12 inches long and the area of the cross section is 2x2 inches.
- February 8, 2019 at 9:52 pm
  
  peteroznewman
  Subscriber
  
  Harry,
  
  The first entry in the stress column of the multilinear kinematic hardening table is the yield stress.
  
  You have entered a value of 1e-6 psi as the yield stress. That is why your model immediately begins yielding.
  
  Change the first value of stress in the table to the yield stress you want and rerun the model.
  
  If the stress stays below that value, the linear and nonlinear models will give the same answer.
- February 13, 2019 at 2:40 pm
  
  harryzhou4498
  Subscriber
  
  Peter,
  
  In that case then, if I don't have a data point for yield stress but I want to model a plastic or a polycarbonate nonlinearly and I have tensile data to accompany it, what model would be ideal for this? It seems like multilinear kinematic hardening would not be an option here.
- February 13, 2019 at 9:54 pm
  
  peteroznewman
  Subscriber
  
  Harry,
  
  Your original question was to compare a linear material with a nonlinear material at low loads and you wanted to know the reason why you didn't get the same result. I think that question has been answered. Please mark that post with Is Solution.
  
  Multilinear kinematic hardening is an option if you are done comparing. Did you convert the Engineering Stress-Strain to True Stress-True Strain? If you have another question, start a New Discussion in the Structural Mechanics section as this one will be marked as Solved.