Scattering of first and second sound waves by quantum vorticity in superfluid Helium

We study the scattering of first and second sound waves by quantum vorticity in superfluid Helium using two-fluid hydrodynamics. The vorticity of the superfluid component and the sound interact because of the nonlinear character of these equations. Explicit expressions for the scattered pressure and temperature are worked out in a first Born approximation, and care is exercised in delimiting the range of validity of the assumptions needed for this approximation to hold. An incident second sound wave will partly convert into first sound, and an incident first sound wave will partly convert into second sound. General considerations show that most incident first sound converts into second sound, but not the other way around. These considerations are validated using a vortex dipole as an explicitely worked out example.Comment: 24 pages, Latex, to appear in Journal of Low Temperature Physic

Roughness of Crack Interfaces in Two-Dimensional Beam Lattices

The roughness of crack interfaces is reported in quasistatic fracture, using an elastic network of beams with random breaking thresholds. For strong disorders we obtain 0.86(3) for the roughness exponent, a result which is very different from the minimum energy surface exponent, i.e., the value 2/3. A cross-over to lower values is observed as the disorder is reduced, the exponent in these cases being strongly dependent on the disorder.Comment: 9 pages, RevTeX, 3 figure

Crackling Noise

Crackling noise arises when a system responds to changing external conditions through discrete, impulsive events spanning a broad range of sizes. A wide variety of physical systems exhibiting crackling noise have been studied, from earthquakes on faults to paper crumpling. Because these systems exhibit regular behavior over many decades of sizes, their behavior is likely independent of microscopic and macroscopic details, and progress can be made by the use of very simple models. The fact that simple models and real systems can share the same behavior on a wide range of scales is called universality. We illustrate these ideas using results for our model of crackling noise in magnets, explaining the use of the renormalization group and scaling collapses. This field is still developing: we describe a number of continuing challenges

Tough glass, tough topology: the fractal dimension of fracture surfaces

The process of brittle fracture is strongly affected by propagating stress waves. In studying the tensile failure of a brittle carbon foam, we observe that by damping out the stress waves, the fracture toughness (resistance of the material to crack growth) increases. This change in a material property leaves behind an altered fracture surface landscape, which can be characterized by a fractal dimension

Tough glass, tough topology: the fractal dimension of fracture surfaces

The process of brittle fracture is strongly affected by propagating stress waves. In studying the tensile failure of a brittle carbon foam, we observe that by damping out the stress waves, the fracture toughness (resistance of the material to crack growth) increases. This change in a material property leaves behind an altered fracture surface landscape, which can be characterized by a fractal dimension

The Sound of Breaking Glass

Fracture is an old, but unsolved problem where physical processes on the microscopic scale affect the properties on the macroscopic scale. Two important properties affecting brittle fracture are the amount. of disorder in the material and the amplitude of stress waves. We are studying the tensile failure of a brittle glassy carbon foam. We observe that propagating stress waves are one cause of avalanches of bond breaking events just before the final rupture

The Sound of Breaking Glass

Fracture is an old, but unsolved problem where physical processes on the microscopic scale affect the properties on the macroscopic scale. Two important properties affecting brittle fracture are the amount. of disorder in the material and the amplitude of stress waves. We are studying the tensile failure of a brittle glassy carbon foam. We observe that propagating stress waves are one cause of avalanches of bond breaking events just before the final rupture

Pop, crackle and snap: the sound of broken glass.

The Physics of Fracture is the study of a driven, disordered system with many degrees of freedom. The many degrees of freedom manifests itself in that any sample of a material can respond to the driving force in a multitude of ways. Like many other similar systems (such as earthquakes, martinsitic structural phase transitions, and magnetic materials in a changing magnetic field), a brittle material can crackle when pulled apart by a tensile force. Crackling is the emission of energy in discrete avalanches of many different sizes. In studying the tensile failure of a brittle carbon foam, we observe that the process of fracture passes through stages of popping , crackling and finally snapping . Each of these stages are described by a complex statistical model which may by applied to crackling systems in general

Pop, crackle and snap: the sound of broken glass.

The Physics of Fracture is the study of a driven, disordered system with many degrees of freedom. The many degrees of freedom manifests itself in that any sample of a material can respond to the driving force in a multitude of ways. Like many other similar systems (such as earthquakes, martinsitic structural phase transitions, and magnetic materials in a changing magnetic field), a brittle material can crackle when pulled apart by a tensile force. Crackling is the emission of energy in discrete avalanches of many different sizes. In studying the tensile failure of a brittle carbon foam, we observe that the process of fracture passes through stages of popping , crackling and finally snapping . Each of these stages are described by a complex statistical model which may by applied to crackling systems in general