In order to develop a smart and minimal invasive system for vertebral correction based on the control of growth of the vertebrae for children with progressive scoliosis and whose osseous growth is not completed. This therapeutic tool for the correction of the immature vertebrae will exploit the unique properties of SMA staple. Our hypothesis is that the forces generated by this system will induce a modulation and a progressive correction of the bone, according to the direction of the loads.
For SMA device the optimal design has been difficult due to lack of appropriate design tool. In this study we developed a SMA staple model using unified thermodynamic constitutive law. An elastic predictor-transformation corrector return mapping algorithm has been adopted. This algorithm is divided on:
1. A thermo elastic predictor step to preview the direction of a strain and a stress variation
2. A transformation corrector step to compute transformation strain, correcting stress value and deduce tangent stiffness tensor for each load and temperature increment.
The model was implemented and tested successfully in UMAT in the commercial FEA software.