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When a soft mechanical metamaterial, consisting of a regular array of representative volume elements (RVEs), is stressed up to a large strain, the delicately tailored behavior of the RVE does not prevail in the metamaterial due to the boundary effect and manufacturing imperfections. A metamaterial sheet comprising RVEs designed for snapping-back behavior exhibits random snapping-through instability when uniaxially stretched. We conceptualize that loss of representativeness of RVE can be avoided by introducing fiber reinforcement to regulate boundary conditions. Through a combination of experiments and numerical simulation, we demonstrate that fiber reinforcements tune behavior of a metamaterial sheet from random snapping-through to sequential and even selective snapping-back instability by introducing small structural variations. Ideal snapping-back instability, characterized by sharp variations of forces in both loading and unloading processes, is captured, while the latter is typically hard to observe in real experiments. Enhanced energy dissipation rate from 25.3% for the case without fiber to 46.4% for the case with fiber-reinforcement is recorded in experiments, when the metamaterial sheet is stretched up to 200% and then released to restore its original length. [ABSTRACT FROM AUTHOR]

There are lots of sphere–plane air gaps in valve halls in extra-high-voltage and ultra-high-voltage converter stations. Accurate prediction for discharge characteristics of sphere–plane gaps is of great significance for the selection of shielding structure and determining the dielectric strength of the valve hall. In this paper, based on the physical process of corona inception and continuous leader inception, a computational model for calculating the discharge voltage of a sphere–plane air gap under positive switching impulse voltage is proposed, and the leader characteristics and discharge voltage are analyzed. Then, the switching impulse discharge test of the sphere–plane gap with 0.15, 2, and 0.3 m radius spherical electrodes is carried out to verify the correctness of the model. The results show that the discharge voltage calculated by the proposed method is consistent with the test results, and the error is within 7.3%. The leader inception voltage and inception time increase with the increasing spherical electrode radius at the same gap distance, and an identical spherical electrode require higher leader inception voltage and faster leader inception time with the increasing gap distance. [ABSTRACT FROM AUTHOR]

We combine experiment and finite element simulation and come up with a design for a mechanical metamaterial which demonstrates snap-back induced hysteresis and energy dissipation. The resultant is an elastic system that can be used reversibly for many times. The underlying mechanism of the existence of hysteresis and the physics of snap-back induced elastic instability is unveiled. Our results open an avenue for the design and implementation of recoverable energy dissipation devices by harnessing mechanical instability. [ABSTRACT FROM AUTHOR]