Low-speed impact mitigation of recoverable DNA-inspired double helical metamaterials

Metamaterials have attracted heated attention for possible impact mitigation and protection due to the outstanding mitigation capability on mechanical waves. In this study, impact mitigation of a novel metamaterials with double helixes inspired by the DNA structure is explored. The DNA-inspired double helical metamaterials (DDHM) are fabricated with the raw material of commercialized Nylon PA 2200, using an additive manufacturing machine based on selective laser sintering technology. Experiments revealed that DDHM has excellent recoverability and mitigation capability. Impact velocity, as well as the number of unit cells in DDHM chain (DDHMc) have a significant influence over the mitigation capability of DDHM. For single unit of DNA-inspired double helical metamaterials (sDDHM), mitigation rate eta decreases by 21.9% from 0.251 to 0.196 within the impact velocity range from 0.35 m/s to 1.46 m/s. While for DDHMc with 5-unit cells, eta decreases by 64.1% from 0.145 to 0.052 as impact velocity varied from 0.31 m/s to 1.33 m/s. Furthermore, a spring-mass model considering the nonlinear behavior is established and bandgap caused by resonance of unit cells in DDHMc is the key factor for excellent mitigation of DDHM. Results shed lights on the fundamental understanding of impact mitigation mechanism and provide useful guidelines for engineering design of impact mitigation/protection system.