Kirigami, a modified form of origami which includes paper cutting, has been used to improve material stretchability and compliance. However, this technique is so far underexplored in patterning piezoelectric materials towards developing efficient and mechanically flexible thin-film energy generators. Motivated by existing kirigami-based applications, we introduce interdigitated cuts to polyvinylidene fluoride (PVDF) films to evaluate the effect on voltage generation and stretchability. Our results from theoretical analysis, numerical simulations, and experimental tests show that kirigami PVDF films exhibit an extended strain range while still maintaining significant voltage generation compared to films without cuts. Various cutting patterns were studied, and it was found that films with denser cuts have a larger voltage output. This kirigami design can enhance the properties of existing piezoelectric materials and help to integrate tunable PVDF generators into biomedical devices.

No abstract

No abstract

Helices are ubiquitous building blocks in natural and engineered systems. Previous studies showed that helical ribbon morphology can result from anisotropic driving forces and geometric misorientation between the principal axes of the driving forces and the geometric axes. However, helical ribbon shapes induced by elastic modulus anisotropy have not been systematically examined even though most natural and engineered structures are made of composite materials with anisotropic mechanical properties. We build on a previously developed model using continuum elasticity and stationarity principles to predict helical ribbon shapes induced by material anisotropy under both isotropic and anisotropic pre-stretching conditions. Results from finite element analysis and table-top experiments showed that the principal curvatures, chirality, and helix angles can be further tuned in anisotropic ribbons under both isotropic and anisotropic pre-stretching conditions. This work can promote programmable design and fabrication of curved structures and devices.

The programmable shape transition of a two-dimensional sheet to a three-dimensional (3D) structure in response to a variety of external stimuli has recently attracted increasing attention. Among the various shape changing materials, shape memory polymers (SMPs) can fix their temporary shape and/or their length and recover under proper thermal treatment. In this work, we create a bilayer composite by bonding one layer of elastomer with one layer of stretched SMPs, which can undergo a series of shape transitions via the storage and release of internal stresses. The programed shapes are achieved by adjusting the orientation and elongation of the SMPs. Meanwhile, the 3D structures exhibit tristability and can transit between hemihelical, left-handed helical, and right-handed helical shapes. Both theoretical analysis and finite element simulations were conducted to understand the mechanism of shape transformation and used to predict the deformed configuration by adjusting preprogramming parameters. Our work provides a new strategy and design space for fabricating smart reconfigurable structures and paves way for the design and development of bioinspired four-dimensional active matter for a broad range of applications in intelligent materials.