The Influence of artificial gaps in locally resonant elastic metamaterial under impact loading

Locally resonant elastic metamaterials have garnered significant attention due to their unique capacity to attenuate stress waves without requiring large structures. However, the application of these elements is compromised by the narrowness and high frequency of their band gaps. Despite existing efforts to enhance the band gap performance, reducing its frequency to more favourable ranges for engineering applications is challenging. This study provides a new solution by introducing artificial gaps between the core and coating of locally resonant elements (LREs). Numerical analysis first revealed that introducing artificial gaps would shift the band gap location to lower frequencies. An experimental test was designed to validate this prediction. Specimens were numerically designed to ensure the experimental measurable band gap frequency range was fulfilled and that their core–coating combination would generate an effective band gap. A Split Hopkinson Pressure Bar system was used to propagate high-frequency stress waves through samples incorporating locally resonant elements with artificial gaps. The experimental tests successfully detected the band gap in the specimens, confirming the predicted shift to lower frequencies. A parametric analysis was then carried out using the numerical model. It revealed that artificial gaps not only shift the band gap to lower frequencies but also increase its width. The load amplitude, number of resonators, and artificial gap size all influence the performance of the LRE with artificial gaps. A design methodology was proposed that could account for the effects of artificial gaps on band gap location, width, and attenuation, enabling the optimal design of locally resonant elements with artificial gaps.