Mechanical properties of 3D printed architected polymer foams under large deformation

We report a new type of three-dimensional architected polymer foams composed of perforated spherical shells and flat strut connectors, which can be precisely produced by 3D printing techniques. We investigate the effects of foam architectures, manufacturing process, and constitutive material on the deformation patterns and failure modes of the proposed architected foams. We demonstrate that flat strut connectors offer unprecedented design flexibility for controlling the mechanical performance. By tuning the geometric parameter of flat strut connectors, the stiffness of architected foams can increase about one order of magnitude while the relative density increases only by 5%. Furthermore, the failure modes can be engineered from a catastrophic one to a progressive one by using weak flat strut connectors. Our experiments elucidate the salient roles of the layer-by-layer manufacturing process and constitutive polymer on the mechanical behavior of the proposed architected foams

Stiffness, Energy Dissipation, and Hyperelasticity in Hierarchical Multilayer Composite Nanocoated Open‐Cell Polyurethane Foams

The paper describes the manufacturing, testing and modelling of a class of open cell polyurethane foams doped with multi-walled carbon nanotubes and nano polyurethane dispersions and subjected to quasi-static cycling compressive loading at large deformations. The doped nano-ink foams are produced using a multiple steps dip coating technique that makes possible the development of nano- based porous materials by post-processing existing off-the-shelf open cell foams. Tests are carried out up to 18.5% of compressive strain to identify loading/unloading moduli and energy absorbed after 5 cycles of stabilization. Hyperelastic Ogden models also considering the Mullins effect for cyclic loading are used to identify the constitutive parameters for these foams. The results show that the use of the multi-walled carbon nanotube layers provide an effective increase of the stiffness and energy absorbed compared to pristine and nano polyurethane dispersions-treated foams. The volume average energy absorbed after the stabilization cycles is increased by 200% compared to the pristine foam when the multi-walled carbon nanotube layers are used. The parameters of the constitutive models extracted from the tests show that these nano-ink foams can be modelled following state-of-the-art hyperelastic representation