Quasistatic, Dynamic and Acoustic Characteristics of Microlattice Metamaterials*

The quasistatic, dynamic (strain rate~1000/s) and acoustic characteristics of ultrathin and highly porous microlattice metamaterials were investigated. The 3-D microlattice architectures were systematically varied in such a way that bending deformation increasingly dominated, so that the Poisson’s ratio of the microlattices transitioned from positive to negative. Under quasistatic testing, this auxetic behaviour was found to improve the energy absorption properties of the microlattices, but played a much lesser role during dynamic compression tests, due to the onset of a secondary buckling mode which nullified the auxetic behaviour. In addition, it was also found that auxetic microlattices were able to significantly reduce the transmission of ultrasonic waves over an extended frequency range when compared to non-auxetic designs. Numerical computations suggest that the bending deformation of the auxetic microlattices introduced different mode shapes for the propagation of elastoacoustic waves. The insights derived from these studies are expected to contribute to the design of microlattice metamaterials with novel properties, such as ultrahigh impact/ acoustic energy absorption efficiency.