4D printed shape memory sandwich structures: experimental analysis and numerical modeling

Additive manufacturing has provided a unique opportunity to fabricate highly complex structures as well as sandwich structures with various out-of-plane cores. The application of intelligent materials, such as shape memory polymers, gives an additional dimension to the three-dimensional (3D) printing process, known as four-dimensional (4D) printing, so that the deformed structures can return to their initial shape by the influence of an external stimulus like temperature. In this study, 4D printing of smart sandwich structures with the potential of energy absorption is investigated. The samples were fabricated considering various process parameters (i.e. layer height, nozzle temperature, printing velocity, and wall thickness) and tested mechanically. The experimental work reveals that the deformed sandwiches can fully recover their initial form by applying simple heating. Besides, a reliable finite element model (FEM) was developed to predict the functional behavior of the horseshoe sandwich structures in compression analysis. The experimental and simulation results show that among process parameters, wall thickness, layer height, and nozzle temperature are the most significant parameters to increase the compressive load and, consequently, the energy absorption rate. The concept, results, and modeling provided in this study are expected to be used in the design and fabrication of 4D printed sandwich structures for energy absorption applications.