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.

通过实验和数值研究了超声波通过外部应力、无序颗粒材料的传播。实验采用压电换能器来激发和检测穿过随机排列的受到单轴压缩的蓝宝石球体的各种频率的纵向超声波。实验的特点是原位 X 射线断层扫描和接触织物的衍射测量、颗粒运动学、平均每颗粒应力张量和颗粒间力。实验测量的堆积结构和推断的不同样品应力下的颗粒间力用于构造以 Hessian 矩阵和阻尼矩阵为特征的弹簧网络。模拟这些网络的超声响应，以研究波速、声波路径、色散和衰减的起源。结果表明，堆积结构和颗粒间力的不均匀性在控制波速和色散方面发挥着重要作用，而堆积结构单独定量地解释了大部分观测到的波衰减。这项研究深入了解了随机堆积颗粒材料中波传播的时域和频域特征，揭示了控制此类系统中波速、色散和衰减的基本机制。