General Mechanical

General Mechanical

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Why the Equivalent (von-Mises) stress is excessivly high for non-linear Nitinol?

    • f.yasmin
      Subscriber

      Hi there,

      I am currently performing stress analysis on a Nitinol self-expanding stent, following the guidelines provided in the course found at https://learninghub.ansys.com/learn/courses/574/self-expanding-stents. I successfully replicated the entire model (see Fig. 1). 

      However, when modeling my own different geometries using only the crimping analysis module, I am encountering an issue where the von Mises stress reaches a value of 2451 MPa, which is unexpectedly high 👇.

      Despite this, both the equivalent plastic strain and elastic strain are within the acceptable range of 5-7%. Could you please advise if this might be an issue related to my geometry or a potential contact-related problem or any other else?

      I would greatly appreciate your insight on this matter.

      Kind regards,
      Farhana Yasmin

    • Kaushal Vadnere
      Ansys Employee

      Hello,
      What is the location of highest magnitude of Eq. VMS in your model? is it over a larger area or on a single node/element? can you attach a screeshot?

      The reason I am asking is, this seems like a case of artificially high stress or stress singularity. Artificially high stresses arise in structural FEA model due to variety of reasons such as sharp corners in contact, over-oconstraint, etc. Also, you are using a hyperelastic material model which makes the analysis highly non-linear. You can refer to 'lesson 3 - understanding and dealing with artificially high stress' in this free Ansys Innovation course: Numerically Accurate Results - Innovation Space (ansys.com) to understand how to deal with stress singularities.

      Thanks

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