Background: Metaconcrete is a new concept of concrete, showing marked attenuation properties under impact and blast loading, where traditional aggregates are partially replaced by resonant bi-material inclusions. In a departure from conventional mechanical metamaterials, the inclusions are dispersed randomly as cast in the material. The behavior of metaconcrete at supersonic frequencies has been investigated theoretically and numerically and confirmed experimentally. Objective: The feasibility of metaconcrete to achieve wave attenuation at low frequencies demands further experimental validation. The present study is directed at characterizing dynamically, in the range of the low sonic frequencies, the—possibly synergistic—effect of combinations of different types of inclusions on the attenuation properties of metaconcrete. Methods: Dynamic tests are conducted on cylindrical metaconcrete specimens cast with two types of spherical inclusions, made of a steel core and a polymeric coating. The two inclusions differ in terms of size and coating material: type 1 inclusions are 22 mm diameter with 1.35 mm PDMS coating; type 2 inclusions are 24 mm diameter with 2 mm layer natural rubber coating. Linear frequency sweeps in the low sonic range (< 10 kHz), tuned to numerically estimated inclusion eigenfrequencies, are applied to the specimens through a mechanical actuator. The transmitted waves are recorded by transducers and Fast-Fourier transformed (FFT) to bring the attenuation spectrum of the material into full display. Results: Amplitude reductions of transmitted signals are markedly visible for any metaconcrete specimens in the range of the inclusion resonant frequencies, namely, 3,400-3,500 Hz for the PDMS coating inclusions and near 3,200 Hz for the natural rubber coating inclusions. Specimens with mixed inclusions provide a rather uniform attenuation in a limited range of frequencies, independently of the inclusion density, while specimens with a single inclusion type are effective over larger frequency ranges. With respect to conventional concrete, metaconcrete reduces up to 90% the amplitude of the transmitted signal within the attenuation bands. Conclusions: Relative to conventional concrete, metaconcrete strongly attenuates waves over frequency bands determined by the resonant frequencies of the inclusions. The present dynamical tests conducted in the sonic range of frequencies quantify the attenuation properties of the metaconcrete cast with two types inclusions, providing location, range and intensity of the attenuation bands, which are dependent on the physical-geometric features of the inclusions.

中文翻译：

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含有两种共振夹杂物的超强混凝土声波范围内衰减特性的实验验证

背景：超混凝土是混凝土的一个新概念，在冲击和爆炸载荷下显示出显着的衰减特性，其中传统骨料部分被共振双材料夹杂物取代。与传统的机械超材料不同，夹杂物在材料中铸造时随机分散。超音速下超混凝土的行为已经在理论上和数值上进行了研究，并通过实验得到了证实。目标：超混凝土在低频下实现波衰减的可行性需要进一步的实验验证。本研究旨在动态表征低声频范围内不同类型夹杂物组合对超混凝土衰减特性的可能协同效应。方法：动态测试是在圆柱形超混凝土试样上进行的，这些试样浇铸有两种类型的球形夹杂物，由钢芯和聚合物涂层制成。两种夹杂物在尺寸和涂层材料方面有所不同：1 类夹杂物直径为 22 毫米，PDMS 涂层为 1.35 毫米；2 类夹杂物直径为 24 毫米，天然橡胶涂层为 2 毫米。低声波范围 (< 10 kHz) 中的线性频率扫描，调谐到数值估计的夹杂物特征频率，通过机械致动器应用于样品。传输的波由换能器和快速傅立叶变换 (FFT) 记录，以充分显示材料的衰减频谱。结果：对于在包含共振频率范围内的任何超混凝土试样，传输信号的幅度减小是明显可见的，即 3,400-3,500 Hz 的 PDMS 涂层夹杂物和接近 3,200 Hz 的天然橡胶涂层夹杂物。具有混合夹杂物的试样在有限的频率范围内提供相当均匀的衰减，与夹杂物密度无关，而具有单一夹杂物类型的试样在更大的频率范围内有效。与传统混凝土相比，超强混凝土可将衰减带内传输信号的幅度降低多达 90%。结论：相对于传统混凝土，超混凝土在由夹杂物的共振频率确定的频带内强烈衰减波。目前在声波频率范围内进行的动态测试量化了具有两种类型夹杂物的超混凝土浇筑物的衰减特性，提供了位置、