The onset of the frictional motion of dissimilar materials
The onset of the frictional motion of dissimilar materials
复制标题
不同材料摩擦运动的开始
DOI：
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发表时间：
2020
影响因子：
11.1
通讯作者：
J. Fineberg
中科院分区：
文献类型：
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作者：
H. Shlomai;David S. Kammer;M. Adda;J. Fineberg
意义我们考虑最普遍的摩擦运动类型：具有不同弹性性质或几何形状的不同物体(“双材料”)的摩擦滑动。通过实验、理论和数值计算的耦合，我们表明，在形核时，类似于剪切裂纹的破裂锋面引发了形成摩擦界面的接触的破裂。然而，这些破裂迅速加速并转变为高度局部化的“滑移脉冲”：双材料界面特有的奇异前沿，其中摩擦滑移在空间上限制在靠近其前沿的小区域内。这些结果为所有对摩擦过程感兴趣的社区提供了重要的基础性理解。特别是，它们涉及到地震在与不同材料接壤的自然断层内产生的定向损害和近场辐射模式的问题。接触体之间的摩擦运动是由传播的破裂前沿控制的，这些破裂前沿本质上是地震。这些前缘打破了构成界面的接触，将物体分开，使它们能够相对运动。最常见的摩擦运动发生在两个物体不同的时候。在这些所谓的双材料界面内，摩擦运动的开始通常由高度局部化的破裂前沿(称为滑移脉冲)来调节。在这里，我们展示了这种独特的破裂模式是如何发展、演变和改变界面行为的特征的。双材料的滑移脉冲以“亚剪切”裂纹(比剪切波慢)的形式开始，过渡到发展的滑移脉冲，在这种情况下，法向应力在前沿几乎消失。观测到的滑移脉冲只在一个狭窄的“跨音速”速度范围内传播，范围在较软材料的剪切波速度和极限速度之间。我们得到了亚剪切裂纹和滑移脉冲前沿的解析解。这些解决方案都很好地描述了我们的实验测量结果，并定量地解释了滑移脉冲的极限速度。我们进一步发现，局部法向应力变化与摩擦阻力之间的摩擦耦合实际上促进了界面分离，而界面分离是滑移脉冲局部化的关键。这些结果提供了滑移脉冲形成和结构的全貌，这对于我们对地震运动和最一般类型的摩擦过程的基本理解都很重要。
Significance We consider the most general type of frictional motion: frictional sliding of nonidentical bodies (“bimaterials”) with either different elastic properties or geometrical shapes. By coupling experiments, theory, and numerics, we show that, upon nucleation, rupture fronts akin to shear cracks initiate the rupture of the contacts forming a frictional interface. These ruptures, however, rapidly accelerate and transition to highly localized “slip pulses”: singular fronts unique to bimaterial interfaces, in which frictional slip is spatially confined to a small region near their leading edge. These results provide important fundamental understanding to all communities interested in frictional processes. In particular, they relate to questions of directed damage and near-field radiation patterns generated by earthquakes within natural faults bordered by different materials. Frictional motion between contacting bodies is governed by propagating rupture fronts that are essentially earthquakes. These fronts break the contacts composing the interface separating the bodies to enable their relative motion. The most general type of frictional motion takes place when the two bodies are not identical. Within these so-called bimaterial interfaces, the onset of frictional motion is often mediated by highly localized rupture fronts, called slip pulses. Here, we show how this unique rupture mode develops, evolves, and changes the character of the interface’s behavior. Bimaterial slip pulses initiate as “subshear” cracks (slower than shear waves) that transition to developed slip pulses where normal stresses almost vanish at their leading edge. The observed slip pulses propagate solely within a narrow range of “transonic” velocities, bounded between the shear wave velocity of the softer material and a limiting velocity. We derive analytic solutions for both subshear cracks and the leading edge of slip pulses. These solutions both provide an excellent description of our experimental measurements and quantitatively explain slip pulses’ limiting velocities. We furthermore find that frictional coupling between local normal stress variations and frictional resistance actually promotes the interface separation that is critical for slip-pulse localization. These results provide a full picture of slip-pulse formation and structure that is important for our fundamental understanding of both earthquake motion and the most general types of frictional processes.