Micromorphic effects in an octet truss lattice

TL;DR

This study investigates elastic wave dispersion in an octet truss lattice, revealing how resonance effects induce dispersion and cut-off frequencies, interpreted through micromorphic continuum theory.

Contribution

It provides experimental evidence of dispersion and resonance effects in octet truss lattices and interprets these phenomena using micromorphic continuum models.

Findings

Wave speed varies with frequency, showing dispersion at certain wavelengths.

Resonance of ribs causes cut-off frequencies where signals cease to propagate.

Cellular solid behavior is characterized by elastic constants related to unit cell flexibility.

Abstract

Elastic wave dispersion is studied in an octet truss lattice and compared with a designed rib lattice known to exhibit strong Cosserat elastic effects. Dispersion entails variation of wave speed with frequency. The phenomenon is experimentally investigated by exciting standing waves in specimens of different length at discrete frequencies. At lower frequencies corresponding to long wavelengths, wave propagation is classically non-dispersive. As wavelength approaches a small multiple of the rib length, dispersion is observed. The material exhibited cut-off frequencies above which no signals were propagated. The physical origin of the dispersion and cut-off is resonance of the ribs. Interpreted as micromorphic continua, cellular solid behavior reveals elastic constants associated with flexibility of the unit cell in comparison with that of the overall material.