A Modular Nitinol Model with Lode Angle-Based Asymmetry and Improved Representation of the Superelastic Loops for Medical Device Applications

We describe a phenomenological constitutive model for representing Nitinol in medical device applications. The intent is to capture some of the response features important to medical device applications that are neglected in prevalent state of the art models. These features include better representation of the response under compression which is needed to assess bending, and asymmetric plastic yield. We will refer to this implementation as the Thornton Tomasetti (TT) model to distinguish it from other existing implementations that have evolved from the baseline underlying theory. We implement the model in a modular form suitable for use in commercial finite element software and describe initialization from laboratory test data.