## 1 Introduction  
Metamaterials are artificial new materials with a periodic lattice arrangement, and their material properties can be artificially interfered with and adjusted through microstructural design to obtain supernatural properties that cannot be obtained in nature, such as negative stiffness [1; 2; 3; 4; 5; 6], negative thermal expansion [7; 8; 9] and a zero Poisson or negative Poisson ratio [10; 11; 12; 13; 14; 15; 16]. Due to the above excellent properties, metamaterials have been highly used in the domains of mechanics [17; 18; 19; 20], acoustics [21; 22; 23; 24], electromagnetism [25; 26; 27; 28], etc. The mechanical properties directly affect the service life and application range of the metamaterials, and many scholars have studied the mechanical properties of metamaterials. [PERSON] et al. [28] explored the elastic properties of a metamaterial composed of returnable hexagonal cells in two orthogonal directions. [PERSON] et al. [29] adopted the finite element method (FEM) to study the elastic properties of chiral, antichiral and hierarchical honeycomb metamaterials. [PERSON] et al. [30] proposed an innovative hierarchical antitetrahiral metamaterial which exhibited great tunability in the elastic modulus and Poisson's ratio. [PERSON] et al. [31] designed a novel returnable honeycomb metamaterial based on the idea of \"replacing straight with curved\", and used a multi-island genetic algorithm to optimize the parameters of the metamaterial and improve its mechanical properties. With the wide application of metamaterials in various fields, some complex projects have put forward the requirements of multifunctions that cannot be met by common metamaterials. These requirements led to the research on metamaterials with composite configurations by many scholars. In the work by [PERSON] et al. [32], a composite metamaterial with an expanded cellular structure and silicon material was presented, and its mechanical properties were investigated under quasistatic and quasidynamic compression conditions. The findings revealed that the presented composite metamaterial exhibited better performance in stiffness and energy absorption than that of the metamaterial made of a single material. [PERSON] et al. [33] designed and prepared a composite metamaterial made of a continuous fiber-reinforced thermoplastic composite (CFRTPC) and pure polylactic acid (PLA), and evaluated its mechanical properties using experimental and simulation methods. It was found that the stiffness of the designed composite metamaterial increased compared with that of the pure PLA metamaterial. [PERSON] et al. [34] proposed a honeycomb metamaterial, adding negative stiffness elements on the inclusions. The range of the negative stiffness of the metamaterial was widened by adding negative stiffness elements appropriately, and the mechanical properties and vibration-suppression properties were improved. These works indicate that the metamaterials with a composite configuration and multimaterial provide a useful design method to meet the multifunction requirements. Vibration properties are one of the most important characteristics of metamaterials, and the bandgap characteristics of metamaterials have an evident impact on the vibration-reduction effect, and have been a hot topic in recent years [35; 36; 37]. There are two main mechanisms of bandgap formation in metamaterials: Bragg scattering and local resonance [38]. Among them, the local resonance effect can promote the generation of a low-frequency bandgap, which can be explained by the mass-spring physics principle. In this principle, the metamaterial structure is equivalent to a \"mass-spring\" system, in which the natural frequencies of each order and the upper and lower bounds of the bandgap are determined by the equivalent mass and equivalent stiffness [39]. [PERSON] et al. [40] designed a new honeycomb lattice metamaterial by combining the traditional and additive material lattices, and its bandgap performed better than the traditional honeycomb metamaterial in the low-frequency region.