A rate-dependent shape memory polymer composite for self-folding 2D-to-3D structural transition with improved impact resistance

Mechanical impacts posed significant safety threats to individuals and equipment, driving the increasing demand for high-performance protective materials and structures. Here, by combining shear stiffening elastomer (SSE) with ethylene-vinyl acetate (EVA), a novel strain rate-dependent shape memory polymer composite (SEVA) was developed. The storage modulus of SEVA increased from 63.08 kPa to 0.30 MPa as the shear frequency rose from 0.1 Hz to 50 Hz. A phase-transition-viscoelastic combined constitutive model was proposed, which successfully described the shape memory and rate-dependent properties of SEVA. Furthermore, based on the UMAT subroutine, the shape memory deformation process of SEVA was accurately simulated via a commercial ABAQUS software. Based on the thermo-dependent deformation mechanism, a self-folding hinge was fabricated by assembling pre-stretch programmed SEVA with polyethylene terephthalate film tape. The maximum folding angles were influenced by heating temperatures, programmed strains and PET film tape spacing. Additionally, various 2D-to-3D self-folding structures, including W-shaped, hexagonal, spiral, and gripper configurations were further designed, which presented enhanced impact resistance against dynamic drop hammer loads. Particularly, the hexagonal structure demonstrated superior impact attenuation performance, achieving reductions of 69.2 % in the maximum impact force and 78.5 % in the maximum residual impact force. Finally, an optimal self-folding honeycomb multicell structure was developed, which effectively improved impact energy transmission and dissipation through structural deformation, offering a semi-active protection solution. This work expanded the application potential of protective materials and structures in impact resistance.