Shape memory response of cellular lattice structures: Unit cell finite element prediction

NiTi, known as Nitinol, is the most common shape memory alloy which offers relatively low modulus of elasticity, shape memory properties, superelastic behavior, biocompatibility and low corrosion rate. In some applications, such as actuators and biomedical implants, it is common to use cellular lattice structure (CLS) to decrease the weight as well as equivalent modulus of elasticity (i.e., stiffness). The focus of this research is to model, at macro scale, the behavior of NiTi CLS (e.g., BCC and BCC-Z) processed through selective laser melting (SLM) additive manufacturing (AM) process. First, BCC and BCC-Z structures were fabricated and subjected to thermomechanical experiment to investigate their shape memory properties. Next, finite element analysis (FEA) was performed using a unit cell model with appropriate boundary conditions. The model is based on a three-dimensional constitutive model derived from the Souza theory. Finally, the stress-strain curves obtained from finite element simulations were compared with those generated from mechanical tests. The comparison showed good agreement between the model predictions and experimental results for BCC (R > 0.98, RMSE = 1.79 MPa, p < 0.05) and BCC-Z (R > 0.97, RMSE = 6.28 MPa, p < 0.05) structures. It was also revealed that the developed model was computationally more efficient than other multi-cell models.