Hopkins Extreme Materials Institute, Johns Hopkins University, Baltimore, MD 21218.
Atmospheric, Earth, & Energy Division, Lawrence Livermore National Laboratory, Livermore, CA 94550.
Proc Natl Acad Sci U S A. 2020 Jul 14;117(28):16234-16242. doi: 10.1073/pnas.2004356117. Epub 2020 Jun 29.
Ultrasound propagation through externally stressed, disordered granular materials was experimentally and numerically investigated. Experiments employed piezoelectric transducers to excite and detect longitudinal ultrasound waves of various frequencies traveling through randomly packed sapphire spheres subjected to uniaxial compression. The experiments featured in situ X-ray tomography and diffraction measurements of contact fabric, particle kinematics, average per-particle stress tensors, and interparticle forces. The experimentally measured packing configuration and inferred interparticle forces at different sample stresses were used to construct spring networks characterized by Hessian and damping matrices. The ultrasound responses of these network were simulated to investigate the origins of wave velocity, acoustic paths, dispersion, and attenuation. Results revealed that both packing structure and interparticle force heterogeneity played an important role in controlling wave velocity and dispersion, while packing structure alone quantitatively explained most of the observed wave attenuation. This research provides insight into time- and frequency-domain features of wave propagation in randomly packed granular materials, shedding light on the fundamental mechanisms controlling wave velocities, dispersion, and attenuation in such systems.
超声在受外部应力的无序颗粒材料中的传播特性进行了实验和数值研究。实验采用压电换能器激发和检测穿过单轴压缩随机堆积蓝宝石球体的不同频率的纵超声波。实验特点是原位 X 射线断层扫描和接触织物、颗粒运动学、平均颗粒内应力张量和颗粒间力的衍射测量。实验测量的堆积结构和在不同样品应力下推断的颗粒间力用于构建具有 Hessian 和阻尼矩阵的弹簧网络。模拟这些网络的超声响应以研究波速、声路径、色散和衰减的起源。结果表明，堆积结构和颗粒间力的非均匀性对控制波速和色散起着重要作用，而堆积结构单独定量解释了大部分观察到的波衰减。这项研究提供了对随机堆积颗粒材料中波传播的时域和频域特征的深入了解，揭示了控制此类系统中波速、色散和衰减的基本机制。
