Materials Research Express

The development of lightweight, impact-resistant and high energy dissipation materials is of great significance to reduce the hazards of explosions and impacts. Metal rubber (MR) has the characteristics of low density, high damping performance and high elasticity, which shows great potential in the field of protection. However, there are few studies on the dynamic mechanical response of MR under high-speed impact. A series of experiments were carried out to study the mechanical properties of MR. It is found that the deformation mechanism of the metal wire inside the MR determines the mechanical properties. Under quasi-static conditions, the stress-strain of MR includes an elastic stage, a softening stage and a hardening stage, and the stress-strain under high-speed impact includes an elastic stage, a softening stage and a failure stage. In addition, the smaller the wire diameter, the higher the load-bearing capacity of the MR. The damage characteristics of MR under high-speed impact are divided into expansion failure and compaction failure, which will affect mechanical performance in the failure stage. The calculated energy absorption and ideal energy absorption efficiency show that MR is a material with excellent energy absorption properties. The dynamic elastic modulus and dynamic peak stress of MR have strain rate effect and density effect. A constitutive model based on Sherwood-frost equation was established, which can precisely forecast the dynamic mechanical properties.

We construct new quasi-three-dimensional fractal acoustic metamaterials based on adoption of the Menger structure, which offers extraordinary parameters such as double-negative properties and a near-zero density. The resulting metamaterials can thus achieve negative refraction, acoustic focusing and sound tunneling. Using the finite element method and the S-parameter retrieval method, the band structures and the effective parameters of these acoustic metamaterials are researched, respectively. The negative refraction property is numerically simulated using a Gaussian beam passing through a double negative prism. A plate lens with a refractive index of n = −1 is constructed to achieve acoustic focusing and the sound tunnelling ability is verified using the near-zero-density metamaterial. The results show that the Menger fractal structures have excellent acoustic properties and are promising for acoustic applications.

In this work, BaTiO₃, Ba(Mg_0.01Ti_0.99)O₃, Ba(Mg_0.015Ti_0.985)O₃, Ba(Mg_0.02Ti_0.98)O₃ and Ba(Mg_0.01Zr_0.15Ti_0.84)O₃ ceramics have been prepared through conventional solid-state route to investigate the effects of Mg²⁺ and Zr⁴⁺ dopants as mono-substitution (only Mg²⁺) and co-substitution (Mg²⁺ and Zr⁴⁺) of B-site on the structural, electrical and optical properties of BaTiO₃ ceramics. Exhibiting perovskite structure, Ba(Mg _x Ti_1−x)O₃ ceramics revealed a decrement pattern of tetragonality with the increment of the concentration of MgO which was confirmed through Rietveld analysis. Morphological analysis of the sintered samples by scanning electron microscope showed a grain growth retardation phenomenon with Mg²⁺ addition. Releasing from this retardation process, Ba(Mg_0.01Zr_0.15Ti_0.84)O₃ showed a maximum dielectric constant of ∼1269.94 due to the enhanced domain wall motion and the confinement within the solubility limit of Mg²⁺. The ferroelectric characteristic of Ba(Mg _x Ti_1−x)O₃ was sluggish due to the effects of grain size and its boundary. The optical band gap for BaTiO₃ was found to be decreased from 3.55 eV to 3.06 eV with the addition Mg²⁺ content but for Ba(Mg_0.01Zr_0.15Ti_0.84)O₃, the value increased due to the Burstein-Moss effect. Again the FTIR analysis proved that no impurity phases were formed during the doping phenomenon, but in Ba(Mg _x Ti_1-x)O₃ ceramics, a significant reduction of Ti-O bond strength was observed. However, BaTiO₃, Ba(Mg_0.01Ti_0.99)O₃, Ba(Mg_0.015Ti_0.985)O₃ and Ba(Mg_0.02Ti_0.98)O₃ ceramics had manifested P-E loop having lower remanent polarization and coercive field compared to Ba(Mg_0.01Zr_0.15Ti_0.84)O₃ ceramics with moderate electrical and optical properties. So, co-doping with Mg²⁺ and Zr⁴⁺ evidenced a favorable accession for the increment of the properties of BaTiO₃ ceramics.