Multi-Head MEX 3D Printing of self-recoverable Joule-heating-based shape memory polymeric components

Shape-memory polymers (SMPs) are innovative smart materials able to return to their original shape after deformation, in response to specific external stimuli, such as heat, moisture or light. Their ability to recover their original configuration makes them versatile and promising in numerous applications. Some SMPs can be processed by additive manufacturing using material extrusion (MEX) technology. This work studies the use of multi-head MEX 3D printing to fabricate PLA-based shape memory multi-material objects. In particular, the obtained shape memory components are capable of being activated by electric current, thanks to the use of a conductive polymeric grid. This innovative approach avoids the use of external heat sources while still allowing the recovery temperature to be exceeded over the entire component, due to Joule effect. Therefore, the purpose of this work is to investigate multi-material structures able to recover their shape without the need to apply a direct heat source to the component. This study presented a finite element method simulation for the optimization of the grid geometry followed by an experimental plan for the optimization of the printing parameters, by varying the Line width and the layer thickness. The parameters significantly influenced the electrical and thermal conductivity by modifying the uniformity of the printed conductive grid ranging from 386 to 567 Ω. In addition, the scenarios obtained different mechanical performances and shape memory behavior, with a maximum shape recovery of 69% and an 81.3 MPa Ultimate Flexural Strength.