General Mechanical

General Mechanical

Nitinol : how to input material properties, austenite v. martensite

    • tehadmiral

      Hi there!

      How do I associate the temperatures with their related Superelastic sigmas? My table of temperatures and sigmas is incorrect

      My first "working" model does not have ANY temperatures associated with the sigmas :

      Does this Nitinol model make sense?

      ...yet when I simulate a small segment of wire I am able to get deformation :

      NiTi wire elongation

      ...and subsequent return to original length :
      Superelastic or SMA behavior?

      Big Q: Is my "working" model returning to original length because of the SMA / superelastic properties i.e. I entered the material properties correctly? OR is it returning to original length regardless of my incorrect inputs? 

      2nd big Q: If my inputs are "correct", then how come my "working" model is not going from austenitic to stress-induced martensitic transformation? I have been running the simulation with a greater and greater force to cause elongation and deformation, but I have not yet seen the wire retain an elongated length. What am I missing? Is there a way to set the initial condition such that my sample begins in austenitic form?

      3rd big Q: Ansys and all other documents seem to emphasize the same thing: the stress-strain curve must be input with values into material properties in order for Ansys to simulate the SMA/superelastic effects. However, neither of my models has a temperature associated with each sigma. I think this is incorrect on my part; how do I input the stress-strain curve PROPERLY? 

      I THINK this is the part I need to fix in order to have a proper stress-strain curve...

      Any help is greatly appreciated!! A tutorial would be awesome *hint*hint* ;D

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