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

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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.