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Mechanisms for acoustic emissions generation during granular shearing

机译：颗粒剪切过程中产生声发射的机制

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摘要

Shear deformation of granular media leads to continual restructuring of particle contact network and mechanical interactions. These changes to the mechanical state include jamming of grains, collisions, and frictional slip of particles-all of which present abrupt perturbations of internal forces and release of strain energy. Such energy release events typically result in the generation of elastic waves in the kHz frequency range, termed acoustic emissions (AE). The close association between grain-scale mechanics and AE generation motivated the use of AE as surrogate observations to assess the mechanical state of complex materials and granular flows. The study characterizes AE generation mechanisms stemming from grain-scale mechanical interactions. Basic mechanisms are considered, including frictional slip between particles, and mechanical excitation of particle configurations during force network restructuring events. The intrinsic frequencies and energy content of generated AEs bear the signature of source mechanisms and of structural features of the grain network. Acoustic measurements in simple shear experiments of glass beads reveal distinct characteristics of AE associated with different source mechanisms. These findings offer new capabilities for non-invasive interrogation of micromechancial interactions and linkage to a stochastic model of shear zone mechanics. Certain statistical features of restructuring events and associated energy release during shearing were predicted with a conceptual fiber-bundle model (FBM). In the FBM the collective behavior of a large number of basic mechanical elements (representing e.g. grain contacts), termed fibers, reproduces the reaction of disordered materials to progressive loading. The failure of fibers at an individual threshold force corre- sponds to slipping of a particle contact or a single rearrangement event of the granular network. The energy release from model fiber breakage is the equivalent to elastic energy from abrupt grain rearrangement events and provides an estimate of the energy available for elastic wave generation. The coupled FBM-AE model was in reasonable agreement with direct shear experiments that were performed on large granular assemblies. The results underline the potential of using AE as a diagnostic tool to study micro-mechanical interactions, shear failure and mobilization in granular material.
机译：颗粒介质的剪切变形会导致颗粒接触网络和机械相互作用的不断重组。机械状态的这些变化包括颗粒的堵塞，碰撞和颗粒的摩擦滑移，所有这些都呈现出内力的突然扰动和应变能的释放。这种能量释放事件通常会导致在kHz频率范围内产生弹性波，称为声发射（AE）。晶粒尺度力学与AE产生之间的紧密联系促使使用AE作为替代观察来评估复杂材料和颗粒流的机械状态。该研究表征了源自晶粒尺度机械相互作用的AE产生机理。考虑了基本机制，包括粒子之间的摩擦滑移，以及在力网络重组过程中粒子构型的机械激发。产生的AE的固有频率和能量含量具有源机制和晶粒网络结构特征的特征。在玻璃珠的简单剪切实验中，声学测量显示出与不同来源机制相关的AE的独特特征。这些发现为微机械相互作用的非侵入式询问以及与剪切带力学随机模型的链接提供了新的功能。用概念性纤维束模型（FBM）预测了剪切过程中重组事件和相关能量释放的某些统计特征。在FBM中，称为纤维的大量基本机械元件（代表例如谷物接触）的集体行为再现了无序材料对渐进载荷的反应。纤维在单个阈值作用力下的失效与颗粒接触的打滑或颗粒网络的单个重排事件相对应。模型纤维断裂产生的能量释放等效于突然的晶粒重排事件产生的弹性能量，并提供了可用于产生弹性波的能量的估计值。耦合的FBM-AE模型与在大型颗粒组件上进行的直接剪切实验完全吻合。结果强调了使用AE作为诊断工具来研究颗粒材料中的微机械相互作用，剪切破坏和动员的潜力。

著录项

  • 来源
    《Granular matter》 |2014年第5期|627-640|共14页
  • 作者

    Gernot Michlmayr; Dani Or;

  • 作者单位

    Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland;

    Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    Acoustic emissions; Shear zone formation; Granular mechanics;

    机译：声发射;剪切带形成;颗粒力学;

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