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R. Paul Young - One of the best experts on this subject based on the ideXlab platform.
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Kibble-Zurek Mechanism in Microscopic Acoustic Cracking Noises
Bulletin of the American Physical Society, 2015Co-Authors: Hamed O. Ghaffari, Philip Benson, Kaiwen Xia, R. Paul YoungAbstract:The fast evolution of microstructure is key to understanding "crackling'' phenomena. It has been proposed that formation of a nonLinear Zone around a moving crack tip controls the crack tip velocity. Progress in understanding the physics of this critical region has been limited by our lack of hard data describing the detailed physical processes that occur within. For the first time, we show that the signature of the non-Linear elastic Zone around a microscopic dynamic crack maps directly to generic phases of acoustic noises, supporting the formation of a strongly weak Zone near the moving crack tips. We additionally show that the rate of traversing to non-Linear Zone controls the rate of weakening, i.e. speed of global rupture propagation. We measure the power-law dependence of nonLinear Zone size on the traversing rate, and show that our observations are in agreement with the Kibble-Zurek mechanism (KZM). In addition, we illustrate that cracks exhibiting global rupture fronts with velocity faster than Rayleigh waves (i.e., super-shear rupture fronts) display a complex configuration of non-Linear Zone prior to the fast weakening phase.
Hamed O. Ghaffari - One of the best experts on this subject based on the ideXlab platform.
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Kibble-Zurek Mechanism in Microscopic Acoustic Cracking Noises
Bulletin of the American Physical Society, 2015Co-Authors: Hamed O. Ghaffari, Philip Benson, Kaiwen Xia, R. Paul YoungAbstract:The fast evolution of microstructure is key to understanding "crackling'' phenomena. It has been proposed that formation of a nonLinear Zone around a moving crack tip controls the crack tip velocity. Progress in understanding the physics of this critical region has been limited by our lack of hard data describing the detailed physical processes that occur within. For the first time, we show that the signature of the non-Linear elastic Zone around a microscopic dynamic crack maps directly to generic phases of acoustic noises, supporting the formation of a strongly weak Zone near the moving crack tips. We additionally show that the rate of traversing to non-Linear Zone controls the rate of weakening, i.e. speed of global rupture propagation. We measure the power-law dependence of nonLinear Zone size on the traversing rate, and show that our observations are in agreement with the Kibble-Zurek mechanism (KZM). In addition, we illustrate that cracks exhibiting global rupture fronts with velocity faster than Rayleigh waves (i.e., super-shear rupture fronts) display a complex configuration of non-Linear Zone prior to the fast weakening phase.
Kaiwen Xia - One of the best experts on this subject based on the ideXlab platform.
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Kibble-Zurek Mechanism in Microscopic Acoustic Cracking Noises
Bulletin of the American Physical Society, 2015Co-Authors: Hamed O. Ghaffari, Philip Benson, Kaiwen Xia, R. Paul YoungAbstract:The fast evolution of microstructure is key to understanding "crackling'' phenomena. It has been proposed that formation of a nonLinear Zone around a moving crack tip controls the crack tip velocity. Progress in understanding the physics of this critical region has been limited by our lack of hard data describing the detailed physical processes that occur within. For the first time, we show that the signature of the non-Linear elastic Zone around a microscopic dynamic crack maps directly to generic phases of acoustic noises, supporting the formation of a strongly weak Zone near the moving crack tips. We additionally show that the rate of traversing to non-Linear Zone controls the rate of weakening, i.e. speed of global rupture propagation. We measure the power-law dependence of nonLinear Zone size on the traversing rate, and show that our observations are in agreement with the Kibble-Zurek mechanism (KZM). In addition, we illustrate that cracks exhibiting global rupture fronts with velocity faster than Rayleigh waves (i.e., super-shear rupture fronts) display a complex configuration of non-Linear Zone prior to the fast weakening phase.
Philip Benson - One of the best experts on this subject based on the ideXlab platform.
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Kibble-Zurek Mechanism in Microscopic Acoustic Cracking Noises
Bulletin of the American Physical Society, 2015Co-Authors: Hamed O. Ghaffari, Philip Benson, Kaiwen Xia, R. Paul YoungAbstract:The fast evolution of microstructure is key to understanding "crackling'' phenomena. It has been proposed that formation of a nonLinear Zone around a moving crack tip controls the crack tip velocity. Progress in understanding the physics of this critical region has been limited by our lack of hard data describing the detailed physical processes that occur within. For the first time, we show that the signature of the non-Linear elastic Zone around a microscopic dynamic crack maps directly to generic phases of acoustic noises, supporting the formation of a strongly weak Zone near the moving crack tips. We additionally show that the rate of traversing to non-Linear Zone controls the rate of weakening, i.e. speed of global rupture propagation. We measure the power-law dependence of nonLinear Zone size on the traversing rate, and show that our observations are in agreement with the Kibble-Zurek mechanism (KZM). In addition, we illustrate that cracks exhibiting global rupture fronts with velocity faster than Rayleigh waves (i.e., super-shear rupture fronts) display a complex configuration of non-Linear Zone prior to the fast weakening phase.
Eran Bouchbinder - One of the best experts on this subject based on the ideXlab platform.
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dynamic crack tip equation of motion high speed oscillatory instability
Physical Review Letters, 2009Co-Authors: Eran BouchbinderAbstract:A dynamic crack tip equation of motion is proposed based on the autonomy of the near-tip nonLinear Zone of scale 'nl, symmetry principles, causality, and scaling arguments. Causality implies that the asymptotic Linear-elastic fields at time t are determined by the crack path at a retarded time t � � d, where the delay timed scales with the ratio of 'nl and the typical wave speed cnl within the nonLinear Zone. The resulting equation is shown to agree with known results in the quasistatic regime. As a first application in the fully dynamic regime, an approximate analysis predicts a high-speed oscillatory instability whose characteristic scale is determined by 'nl. This prediction is corroborated by experimental results, demonstrating the emergence of crack tip inertialike effects. Introduction.—Fundamental puzzles in the dynamic fracture of brittle materials remain unresolved mainly due to the lack of a well-established equation of motion for a crack's tip. The study of dynamic fracture has focused on the central idea of Linear-elastic energy flowing into the crack tip nonLinear and dissipative Zone (1,2). While this approach is successful in determining the crack growth rate when its path is known a priori, it is fundamentally defi- cient in the general and most interesting case in which the crack's path is selected dynamically (e.g., instabilities (2,3)), without being supplemented with a path selection rule. This long-standing problem hampers the development of a predictive and complete theory of dynamic fracture. In this Letter we propose a dynamic crack tip equation of motion for isotropic materials under plane deformation, based on rather general physical considerations. A basic starting point is the concept of the autonomy of the crack tip nonLinear Zone in the canonical theory of fracture, Linear-elastic fracture mechanics (LEFM) (1). The idea is that the mechanical state within the small near-tip non- Linear Zone of scale 'nl (''inner problem''), where LEFM breaks down, is uniquely determined by the asymptotic Linear-elastic fields surrounding it (''outer problem''), but is otherwise independent of the applied loadings and the geometric configuration (e.g., crack path) in a given prob- lem. Therefore, the near-tip nonLinear Zone is coupled to the applied loadings and the geometric configuration through the asymptotic Linear-elastic fields and the crack tip itself evolves according to the dynamics within the near-tip nonLinear Zone. What role then plays the near- tip nonLinear Zone in determining the path selected by a crack tip? The main idea of this Letter is that in the presence of a finite nonLinear near-tip Zone, causality implies that the asymptotic Linear-elastic fields at a given time t, which control the crack tip motion at that time, are determined by the crack path at a retarded time t � � d, where the delay timed scales with the ratio of 'nl and the typical wave speed cnl within the nonLinear Zone. That is, we propose that the only essential properties of the near-tip nonLinear Zone are its size 'nl and its typical wave speed cnl, and that these appear in a macroscopic continuum theory mainly through their causal effect. This physical effect is missing in LEFM since its basic tenet is that the nonLinear near-tip Zone acts as an energy sink, but otherwise 'nl ! 0 can be assumed. The mathematical formulation of these ideas leads to a simple, continuum level, dynamic equation of motion for a crack's tip. This equation agrees with the well-known ''principle of local symmetry'' (4) in the quasistatic limit, but is shown to have novel implications in the fully dy- namic regime. As an example, we perform an approximate Linear stability analysis of rapid mode I cracks. It predicts the existence of a spontaneous symmetry breaking, high- speed oscillatory instability whose characteristic scale is determined by 'nl. Using the recently developed weakly nonLinear dynamic fracture theory (5-7) to estimate 'nl, this prediction is shown to agree well with recent experi- ments (3). These results explicitly demonstrate the impor- tance of the length scale 'nl at high propagation speeds, as well as the emergence of crack tip inertialike effects. Crack tip dynamics.—The mathematical formulation of the ideas described above follows in three steps. Consider a