Negative stiffness mechanical metamaterial with controllably programmable bandgaps

Materials with wide bandgap distributions have significant potential in the development of novel vibration isolation and damping systems, especially for aerospace and automotive applications. Three mechanical metamaterials were proposed, consisting of negative stiffness elements, honeycomb structures, and resonators, with the negative stiffness elements fabricated from shape memory polymers. By integrating the tunability of smart materials and analyzing from the perspective of phononic crystals, the metamaterials exhibit programmable and highly tunable bandgap properties. The results show that the configuration of negative stiffness elements directly affects the equivalent stiffness of the metamaterial, thereby altering its dispersion relation and transmission properties. The impact of geometric parameters on the modulation of bandgap frequency and transmission properties is systematically verified. Furthermore, two reversible methods, shape memory shape programming and stiffness programming are proposed. The highly nonlinear and impedance mismatch characteristics of the programming structures enable bandgap adjustment under complex loading conditions, achieving full-band vibration isolation within the 1000Hz frequency range. Additionally, interfaces with different gradients can accurately control the transmission and blocking of excitation frequencies. Programmable coordination based on mechanical pixels ensures the integration of negative stiffness mechanical metamaterials in high precision devices.