Multi-Scale Experimental Investigation of Sliding Friction

*9908218玻璃工程师一直依赖于依赖于速率和状态的本构模型(行为标准)。凝聚态物理学界的最新进展导致了对滑动摩擦阻力的假想理论机制。这些模型解释了从埃尺度到千米长地震位错的行为，并为理解圣安德烈亚斯断层上的物质蠕变和自愈滑动提供了理论框架。由于几乎没有直接的实验证据证明假定的基本物理机制确实在起作用，PI将利用它们的实验和解释能力来描绘微观机制。鉴于摩擦连接的基本运动学导致声子(振动，因此是声学能量)的产生，定量声发射和波形反转的组合是唯一能够成像这些运动学的方法。格拉泽已经开发出表面和可嵌入的传感器，NIST已经证明能够测量从10 kHz到1 MHz到3分贝以内的皮秒计位移。研究表明，这些传感器转换的动态记录与理论运动学波形匹配得非常好，允许对震源运动学进行全波形反演，而不是单点矩张量反演。该项目的成果将在多个层面上促进科学和工程的发展。对滑动和摩擦背后的物理机制的基本理解，导致对物理世界的基本理解的改进。这将有助于完善目前对摩擦的经验理解，并允许极大地改进从纳米机械到亚千米级结构的机械设计。此外，还将回答有关千米级震源机制的基本问题，特别是围绕自愈性滑移概念的问题，从而提高对地震错动机制的理解，并最终提高地震安全性。

***9908218GlaserEngineers have always relied on rate- and state-dependent constitutive models(behavioral criteria). Recent advances by the condensed-matter physicscommunity have resulted in hypothetical theoretical mechanisms responsible forfrictional resistance to sliding. These models explain behaviors from angstromscale to kilometers-long earthquake dislocations, and provide a theoreticalframework for understanding material creep as well as self-healing slip on theSan Andreas fault. Since there has been little direct experimental proof thatthe posited fundamental physical mechanisms indeed are at work, the PIs willleverage their experimental and interpretive ability to image thesemicro-mechanisms. Given that the fundamental kinematics of frictional junctionsresults in production of phonons (vibrational, hence acoustic, energy), thecombination of quantitative acoustic emission and waveform inversion isuniquely able to image these kinematics. Glaser has developed surface andembeddable sensors proven capable by NIST of measuring picometer displacementsfrom 10 kHz to 1 MHz to within 3 dB. Studies show that the dynamic recordtransduced by these sensors match the theoretical kinematic waveformsremarkably well, allowing whole-waveform inversion for source kinematics ratherthan single-point moment tensor inversion. The results of this project will further science and engineering on severallevels. Fundamental understanding of the physical mechanisms behind slidingfriction, leading to improvement of basic understanding of the physical world. This will help refine current empirical understanding of friction and allowgreat improvement in mechanical design from nanomachines to sub-kilometer-scalestructures. In addition, fundamental questions about kilometer-scaleearthquake source mechanisms will be answered, in particular the issuessurrounding the notion of self-healing slip, thereby leading to an improvedunderstanding of the earthquake dislocation mechanism, and ultimately improvedseismic safety.***