The ability of solids to withstand mechanical forces is one of their fundamental properties. When a solid is loaded externally, there reaches a point where its global energy can be reduced by breaking into pieces, i.e by creating new free surfaces instead of continuing to store mechanical energy. The major vehicle for these failure processes are cracks, which are non-equilibrium propagating dissipative structures. Cracks are "natural laboratories" for probing material behavior under extreme conditions as their tips concentrate stresses and strains that approach a mathematical singularity. Moreover, crack propagation involves many interacting time and length scales ranging from the linear elastic forcing on large scales to the strong non-linearities and dissipation on the small scales near the crack's tip.
The physics of frictional interfaces is central to a wide range of physical, biological, engineering and geophysical systems, ranging from crawling cells to earthquake faults. Yet, a basic understanding of the interfacial friction constitutive law and the spatiotemporal dynamics that emerge when two deformable macroscopic objects move one relative to the other is currently missing. In addition, novel laboratory and geophysical observations revealed new frictional phenomena, such as slow rupture, which are not yet well-understood. At a more fundamental level, frictional interfaces raise basic questions about strongly out-of-equilibrium physics and the roles played by lower dimensional objects in the macroscopic response of physical systems.
The ability of solids to deform irreversibly, i.e. plastically, is of enormous importance to human kind. Yet, we have a rather limited fundamental understanding of the physics of plastic deformation in amorphous and heavily dislocated solids. The ultimate theoretical challenge in these fields is to develop dynamic equations of motion - the analog of the Navier Stokes equations - for amorphous and heavily dislocated solids. Building on advances in understanding amorphous materials, through detailed experiments and computer simulations, we have recently extended the original Shear-Transformation-Zones (STZ) theory to conform with the internal-variable, effective-temperature non-equilibrium thermodynamics discussed above. Furthermore, we have recently explored the implications of this thermodynamic framework to strain hardening theory of heavily dislocated polycrystalline solids
Cells throughout our body constantly interact with their microenvironment. While biochemical communication has been extensively studied for a long time, the importance of mechanical interactions (i.e. cells' ability to apply, sense and respond to forces) has been recognized only recently. Precise mechanical conditions, from the subcellular level and up to the organ scale, are critical for tissue development, function, remodeling and healing. Nevertheless, understanding the precise nature of the mechanisms and processes underlying the response of living cells to mechanical cues - cellular mechanosensitivity - remains largely a basic open problem.