颗粒材料中的声传播与力链
Sound propagation and force chains in granular materials
摘要：
颗粒材料本质上是异质的，导致在制定准确的声音传播模型方面的挑战。为了量化空间和时间上的声学响应，我们在光弹性颗粒材料中进行实验，其中内部应力模式（以力链的形式）是可见的。我们利用两种互补的方法，高速成像和压电换能，提供粒子尺度的测量的振幅和速度的声波在近场制度。我们观察到，波的振幅平均最大的粒子内经历最大的力量，特别是在那些链辐射远离源，与力的依赖性，这种振幅在定性上与一个简单的赫兹粒子接触面积的模型。此外，我们能够直接观察到罕见的瞬态力链形成的打开和关闭的接触在传播过程中。脉冲前沿的速度与一维链的预测在数量上一致，而峰值响应的速度较慢表明它包含了即使在这个近场区域内也经过多条路径传播的波。这些效应突出了颗粒尺度行为在确定颗粒材料声学特性中的重要性。
英文摘要：
Granular materials are inherently heterogeneous, leading to challenges in formulating accurate models of sound propagation. In order to quantify acoustic responses in space and time, we perform experiments in a photoelastic granular material in which the internal stress pattern (in the form of force chains) is visible. We utilize two complementary methods, high-speed imaging and piezoelectric transduction, to provide particle-scale measurements of both the amplitude and speed of an acoustic wave in the near-field regime. We observe that the wave amplitude is on average largest within particles experiencing the largest forces, particularly in those chains radiating away from the source, with the force-dependence of this amplitude in qualitative agreement with a simple Hertzian-like model of particle contact area. In addition, we are able to directly observe rare transient force chains formed by the opening and closing of contacts during propagation. The speed of the leading edge of the pulse is in quantitative agreement with predictions for one-dimensional chains, while the slower speed of the peak response suggests that it contains waves which have travelled over multiple paths even within just this near-field region. These effects highlight the importance of particle-scale behaviors in determining the acoustical properties of granular materials.
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