Friction, Fatigue and Failure: a Multiscale Approach Linking Physics, Fabrication and Geophysical Phenomena

该奖项支持跨学科的理论研究和教育，以促进对物理学的基本理解，这些物理学是本质上异质的，内部结构化的，在压力下，远离平衡的材料。研究的重点领域包括基础理论和动力学之间的相互作用和非均匀性的摩擦，疲劳和非晶固体和颗粒材料的故障，在微物理和摩擦补偿和控制的应用程序的多分辨率研究。该项目开始在最小的尺度，剪切颗粒材料的连续数值模拟计划。建立在PI的最近的工作，使用接触动力学探测的范围内的有效性的本构关系推导出的稀释（动力学理论）和密集（剪切转换区）的限制，计划包括调查的流动料斗和其他几何形状，以及详细的研究出现的力的相关性和堵塞在密集的制度。结果将与实验室摩擦研究以及速率和状态本构律进行比较。模拟也将扩大到调查更复杂的颗粒形状和更广泛的尺寸分布，老化和磨损的颗粒，详细的局部摩擦模型，以及流体动力学耗散与fluids.At中等规模的影响，调查集中在推导和验证描述颗粒系统，无定形固体，凝胶和润滑界面的本构关系。一个统一的，多尺度的方法，本构关系之间的中间微观动力学，并最终影响较大的尺度（粘滑不稳定性，瞬态过冲，剪切带的形成，可控性）描述。该方法扩展了非平衡统计物理的基础理论，使用计算机科学和工程系统理论的方法。该项目还侧重于与最近的实验室实验的定量联系，这些实验直接探测接触、老化、闪热和流体的微观时空动力学。在宏观尺度上，该提案描述了持续的地球物理应用以及摩擦补偿和控制技术应用方面的新工作。地球物理应用方面的工作包括动态裂纹前沿和材料不均匀性之间的相互作用，以及在存在空间材料梯度（其可能是由于温度或压力变化、老化或磨损）的情况下的破裂动力学。摩擦控制的研究是PI的一个新领域，她利用团队在物理摩擦模型和控制理论方面的综合专业知识，开发和测试用于器件制造的控制器。智力优势：研究致密非晶材料的变形、耗散、老化、磨损和断裂，包括开发和实施跨越广泛尺度的新理论和模拟工具。这既扩展了对远离平衡的物理系统的基本理解，又为描述其他复杂的、相互关联的系统提供了新的方法，这些系统表现出老化和级联故障现象。更广泛的影响：理解摩擦、疲劳和故障是目前开发新技术和预测自然灾害的主要限制因素。这里提出的工作将导致设备应用的控制器，和地震危险性估计模型。相关的实践演示将为公众和K-12教育和推广活动开发，旨在提高公众意识和安全性，并增加妇女和少数民族在物理科学中的代表性。非技术摘要：该奖项支持跨学科的理论研究和教育，以促进对固体和颗粒材料中摩擦，疲劳和断裂的基本理解。对这些现象的预测能力的基本理解仍然是难以捉摸和具有挑战性的，并且会发现从许多环境中的材料失效到地球物理灾害的广泛应用。 在更深的层次上，摩擦、疲劳和断裂广泛地作为某些类别的复杂系统的原型例子，为这些复杂系统寻找控制其行为的基本原理。这样的普遍原理将适用于许多复杂的系统，而不仅仅是发现它们的那个系统。他们的发现将推进统计物理学领域，该领域专注于远离平衡的系统。PI的方法将跨越这些现象的许多长度尺度。它本质上是多学科的;它将计算科学，工程，物理学，物理学和材料科学的元素引入到表征良好的系统中，以促进基础层面的理解。了解摩擦、疲劳和失效是目前开发新技术和预测自然灾害的主要限制因素。这里提出的工作将导致设备应用的控制器，和地震危险性估计模型。将为公众和K-12教育和外联活动开发相关的演示实践，旨在提高公众意识和安全，并增加妇女和少数民族在物理科学中的代表性。

TECHNICAL SUMMARY:This award supports interdisciplinary theoretical research and education to advance the basic understanding of the physics which underlies materials which are intrinsically heterogeneous, internally structured, under stress, and far from equilibrium. Focus areas of the research include basic theory and multiresolution studies of the interplay between dynamics and heterogeneity in friction, fatigue, and failure of amorphous solids and granular materials, with applications in geophysics and friction compensation and control.The project begins at the smallest scales, with plans for continuing numerical simulations of sheared granular materials. Building on the PI's recent work using contact dynamics to probe the range of validity of constitutive laws derived in the dilute (kinetic theory) and dense (shear transformation zones) limits, plans include investigation of flows in hoppers and other geometries, as well as detailed studies of the emergence of force correlations and jamming in the dense regime. Results will be compared to laboratory friction studies, as well as rate and state constitutive laws. The simulations will also be expanded to investigate effects of more complex particle shapes and broader size distributions, aging and wear of particles, detailed local friction models, as well as hydrodynamic dissipation associated with fluids.At intermediate scales, investigations focus on derivation and verification of constitutive laws describing granular systems, amorphous solids, gels, and lubricated interfaces. A unified, multiscale approach to constitutive laws as an intermediate between microscopic dynamics, and the ultimate implications for larger scales (stick-slip instabilities, transient overshoots, shear band formation, and controllability) is described.The approach expands basic theory for nonequilibrium statistical physics using methods from computer science and engineering systems theory. The project also focuses on quantitative connections with recent laboratory experiments, which directly probe the microscopic spatio-temporal dynamics of contacts, aging, flash heating, and fluids.At macroscopic scales, the proposal describes continuing geophysical applications as well as new work on technological applications in friction compensation and control.Work on geophysical applications includes interactions between dynamic crack fronts and material inhomogeneities, as well as rupture dynamics in the presence of spatial material gradients (which may be due to temperature or pressure variations, aging, or wear). Work on control of friction represents a new area for the PI, and leverages her group's combined expertise in physical friction models and control theory to develop and test controllers for device fabrication.Intellectual Merit: The research on deformation, dissipation, aging, wear, and fracture in dense, amorphous materials, involves development and implementation of new theory and simulation tools spanning a broad range of scales. This both expands basic understanding of physical systems far from equilibrium, and provides new methodologies for describing of other complex, interconnected systems which exhibit aging and cascading breakdown phenomena.Broader Impact: Understanding friction, fatigue, and failure is currently a primary limiting factor both in developing new technologies and forecasting natural hazards. The work proposed here will lead to controllers for device applications, and models for seismic hazard estimation. Related hands on demonstrations will be developed for public and K-12 education and outreach activities, aimed at public awareness and safety, and increasing representation of women and minorities in the physical sciences.NON-TECHNICAL SUMMARY:This award supports interdisciplinary theoretical research and education to advance the fundamental understanding of friction, fatigue, and fracture in solids and granular materials. A fundamental understanding with predictive power of these phenomena remains elusive and challenging, and would find widespread applications from materials failure in many settings to geophysical hazards. At a deeper level, friction, fatigue, and fracture serve broadly as prototypical examples for some classes of complex systems for which fundamental principles governing their behavior are sought. Such universal principles would be applicable to many complex systems, not just the one in which they were discovered. Their discovery would advance the area of statistical physics that focuses on systems that are far from equilibrium. The PI's approach will span the many length scales characteristic of these phenomena. It is inherently multidisciplinary; it brings to bear elements of computational science, engineering, geophysics, physics, and materials science on well characterized systems to advance understanding at a fundamental level. Understanding friction, fatigue, and failure is currently a primary limiting factor both in developing new technologies and forecasting natural hazards. The work proposed here will lead to controllers for device applications, and models for seismic hazard estimation. Related hands on demonstrations will be developed for public and K-12 education and outreach activities, aimed at public awareness and safety, and increasing representation of women and minorities in the physical sciences.