The flexibility of planar triboelectric nanogenerators (TENGs) enables them to be embedded into structures with complex geometries and to conform with any deformation of these structures. In return, the embedded TENGs function as either strain‐sensitive active sensors or energy harvesters while negligibly affecting the structure's original mechanical properties. This advantage inspires a new class of multifunctional materials where compliant TENGs are distributed into local operational units of mechanical metamaterial, dubbed TENG‐embedded mechanical metamaterials. This new class of metamaterial inherits the advantages of a traditional mechanical metamaterial, in that the deformation of the internal topology of material enables unusual mechanical properties. The concept is illustrated with experimental investigations and finite element simulations of prototypes based on two exemplar metamaterial geometries where functions of self‐powered sensing, energy harvesting, as well as the designated mechanical behavior are investigated. This work provides a new framework in producing multifunctional triboelectric devices.

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This article evaluates the amount of energy that can be extracted from a gust using an aeroelastic energy harvester composed of a flexible wing with attached piezoelectric elements. The harvester operates in a subcritical flow region. It is modeled as a linear Euler-Bernoulli beam sandwiched between two piezoceramics. The extended Hamilton's principle is used to derive the harvester's equations of motion and an eigenfunction expansion is used to form a three-degree-offreedom reduced-order model. The degrees of freedom retained in the model are two flexural degrees for the in-plane and out-of-plane displacements, and a torsional degree for the rotational displacement. Wagner and Küssner functions are used to represent the unsteady aerodynamic and gust loading, respectively. The amount of energy extracted from the system is then compared for two different deterministic gust profiles, 1-COSINE and two sharp-edged gusts forming a square gust, for various magnitudes and durations. The results show that the harvester is able to extract more energy from the square gust profile, although for both profiles the harvester extracts more power after the gust has subsided.

Cushion curves enable packaging designers to optimize a design solution for a given product fragility and expected distribution environment drop height. The industry accepted techniques for developing these curves are time intensive and devoid of a physical understanding of the materials and the physics involve in energy absorption. This paper delves into a qualitative understanding of the dynamics of a platen impacting an open cell foam cushion material. An hyperelastic material model is used to describe the foam's nonlinear stress-strain relationship, while its damping and hysteretic behaviour are represented with linear viscoelasticity. Using a simple nonlinear, discontinuous model of a drop test along with numerical simulations, the study examines the physics of the impact. The numerical studies show that the model is able to provide predictions of the shock pulse's shape, duration and amplitude at various static stresses and drop heights. The dynamic cushion curves generated by the model retain the characteristic concave upward 'trough' shape of the experimental curves. Furthermore, the model shows that the optimal amplitude of shock absorbed for a given set of drop conditions depends on the foam's thickness and cross-sectional area. Lastly, the model is validated using the comparison of a predicted curve and experimental data captured using a cushion tester.

The demand to lower costs and reduce the amount of packaging materials utilized in a packaged product system has placed increased importance on the development of tools to model the behaviour of packaging systems. This manuscript examines the accuracy and convergence of a reduced-order model (ROM). The ROM is derived from an idealized packaging system consisting of a rod of polymer foam with an attached end mass. The work begins with an introduction to the complex cyclic softening and the viscoelastic and nonlinear stress-strain behaviour exhibited by expanded polymer foam. The partial differential equations and associated boundary conditions governing the motion of the system are obtained. The equations are reduced to an ROM using the assumed modes method. Approximate eigenvalues are compared with both exact and experimental eigenvalues reported in literature. Finally, the ROM is compared with the frequency response functions of the exact solution and those obtained experimentally. Both results are used to determine the number of modal equations needed for the ROM to accurately capture the steady-state dynamic behaviour of the packaging system.