Dynamic failure of 3D printed negative-stiffness meta-sandwich structures under repeated impact loadings

Achieving superior reusable energy absorption and mitigation properties under repeated
impact loadings with high strain rates, yet maintaining the lightweight design feature, is still a
challenge for thin-walled structure design. In this work, combined with the concept of
mechanical metamaterial, several kinds of negative-stiffness meta-sandwich structures (NSMSs)
are developed and their dynamic responses under repeated high strain-rate impacts are
systematically investigated. The 3D printing technique of selective laser sintering (SLS) is
applied to fabricate the composite NSMSs with glass fiber reinforced (GFR) Nylon. The
bistability of the hyperbolic topology and the remarkable impact resistance to the repeated impact
loadings are theoretically, numerically, and experimentally analyzed. An analytical model based
on the Gibson-Ashby framework is presented to predict the mechanical behavior of NSMSs, and
a series of evaluation indicators are developed to quantitatively describe the energy absorption
performance. Compared with a conventional honeycomb structure, the unique layer-by-layer
failure mode for NSMSs, leading to a significant improvement in the capacity of multiple-impact
resistance, is unambiguously demonstrated. This new type of artificial structure paves a feasible
way to achieve superior energy absorption and impact resistance features under repeated impacts