Crack-microcrack interactions in dynamical fracture

Scripta Metallurgica et Materialia, 1994

Physical Review B, 1992

We report on experimental investigations of the propagation of cracks in the brittle plastic polymethyl methacrylate (PMMA). Velocity measurements with resolution an order of magnitude better than previous experiments reveal the existence of a critical velocity (330+30 m/s) at which the velocity of the crack tip begins to oscillate, the dynamics of the crack abruptly change, and a periodic pattern is formed on the crack surface. Beyond the critical point the amplitude of the oscillations depends linearly on the mean velocity of the crack. The existence of this instability may explain the failure of theoretical predictions of crack dynamics and provides a mechanism for the enhanced dissipation observed experimentally in the fracture of brittle materials.

Crack trajectories under different loading conditions and material microstructural features play an important role when the conditions of crack initiation and crack growth under fatigue loading have to be evaluated. Unavoidable inhomogeneities in the material microstructure tend to affect the crack propagation pattern, especially in the short crack regime. Several crack extension criteria have been proposed in the past decades to describe crack paths under mixed mode loading conditions. In the present paper, both the Sih criterion (maximum principal stress criterion) and the R-criterion (minimum extension of the core plastic zone) are adopted in order to predict the crack path at the microscopic scale level by taking into account microstress fluctuations due to material inhomogeneities. Even in the simple case of an elastic behaviour under uniaxial remote stress, microstress field is multiaxial and highly non-uniform. It is herein shown a strong dependence of the crack path on the material microstructure in the short crack regime, while the microstructure of the material does not influence the crack trajectory for relatively long cracks.

Philosophical Magazine B, 1998

The classical theory of fracture mechanics states that a crack propagating in an unbounded body should smoothly accelerate until it reaches the Rayleigh wave speed. We introduce here a general approach for solving the equation of motion of the crack tip. We show that the loading conditions and the geometry of the con® guration do not produce inertial e ects. The equation of motion of a propagating crack is always a ® rst-order di erential equation.

Physical Review E, 2013

We employ a recently developed model that allows the study of two-dimensional brittle crack propagation under fixed grip boundary conditions. The crack development highlights the importance of voids which appear ahead of the crack as observed in experiments on the nano-scale. The appearance of these voids is responsible for roughening the crack path on small scales, in agreement with theoretical expectations. With increasing speed of propagation one observes the branching instabilities that were reported in experiments. The simulations allow understanding the phenomena by analyzing the elastic stress field that accompanies the crack dynamics.

The European Physical Journal Special Topics, 2007

The properties of slow crack growth in brittle materials are analyzed both theoretically and experimentally. We propose a model based on a thermally activated rupture process. Considering a 2D spring network submitted to an external load and to thermal noise, we show that a preexisting crack in the network may slowly grow because of stress fluctuations. An analytical solution is found for the evolution of the crack length as a function of time, the time to rupture and the statistics of the crack jumps. These theoretical predictions are verified by studying experimentally the subcritical growth of a single crack in thin sheets of paper. A good agreement between the theoretical predictions and the experimental results is found. In particular, our model suggests that the statistical stress fluctuations trigger rupture events at a nanometric scale corresponding to the diameter of cellulose microfibrils.

Physical Review Letters, 2001

We address the role of material heterogeneities on the propagation of a slow rupture at laboratory scale. With a high speed camera, we follow an in-plane crack front during its propagation through a transparent heterogeneous Plexiglas block. We obtain two major results. First, the slip along the interface is strongly correlated over scales much larger than the asperity sizes. Second, the dynamics is scale dependent. Locally, mechanical instabilities are triggered during asperity depinning and propagate along the front. The intermittent behavior at the asperity scale is in contrast with the large scale smooth creeping evolution of the average crack position. The dynamics is described on the basis of a Family-Vicsek scaling.

Journal of Applied Physics, 2003

Evaluation of the relationship between the effective strain and the springback behavior during the deformation of metallic glass ribbons Appl. Phys. Lett. 105, 061906 (2014); 10.1063/1.4893159

Fracture analysis is one important role in a material characterization. Many theory and observation on the subject especially after the matter was broken or post cracked, but on the other hand, as far as author knowledge, only a few research are did in in situ observation on micro crack propagation, because of the propagation is in a micrometer scale and can't be observed using a naked eye and has difficulties to observed using standard optical microscope. In this study, different material are observed, the micro cracks propagation in Aluminum foil is observed in an in situ mode using an optical microscope during loaded in an axial tensile mode, the other is a Si thin plate was observed using TEM after compressed in axial compressed.

Journal of Engineering Materials and Technology, 2020

The dynamic fracture behavior of brittle materials that contain micro-level cracks should be examined when material subjected to impact loading. We investigated the effect of micro-cracks on the propagation of macro-cracks that initiate from notch tips in the Kalthoff–Winkler experiment, a classical impact problem. To define predefined micro-cracks in three-dimensional space, we proposed a two-dimensional micro-crack plane definition in the bond-based peridynamics (PD) that is a non-local form of classical continuum theory. Randomly distributed micro-cracks with different number densities in a constant area and number in expending area models were examined to monitor the toughening of the material. The velocities of macro-crack propagation and the time required for completing fractures were considered in several predefined micro-cracks cases. It has been observed that toughening mechanism is only initiated by exceeding a certain number of micro-cracks; therefore, there is a positive...

Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 1996

This paper describes a formalism designed to answer questions about Hamiltonian systems in contact with a heat bath. The formalism is applied to a simple model of fracture to find, first, the rate at which a crack creeps through a brittle body as a result of thermal fluctuations and, second, the rate at which the crack jumps from creeping to rapid motion. The dominant exponential behavior of these processes is calculated exactly, but the prefactors are only estimated. Some of the solutions cannot be viewed in the traditional manner as corresponding to passage over a saddle point. Viewed as an isolated Hamiltonian system, the crack shows that irreversible behavior can arise because, although the probability of traveling from past to present equals the probability of traveling backwards from present to past, the probabilty of traveling still further into the future is exponentially greater. ͓S1063-651X͑96͒06410-0͔

Physical Review Letters, 1999

Mendeleev Communications, 2003

The terminal velocity of a crack determines the reasonability of the application of classical or quantum approaches to the description of phenomena at the crack tip; an expression for the fractoemission intensity of crystals accounting the quantum character of energy transfer at the tip of a fast-moving crack was obtained.

2020

The main objective of this research is to determine the influence of micro-crack on the propagation of a semi-infinite crack. This study is mainly based on the determination of the strain energy during the interaction between the semi-infinite crack and the neighboring microcrack. The problem is formulated by a plane element, having a micro-crack varies around itself and around a semi-infinite crack. The cracked element is subjected to a uniform load according to mode I. The theoretical analysis of the strain energy is based on the stress found during the propagation of the semi-infinite crack. During the positioning of the micro-crack with respect to the semi-infinite crack, according to the strain energy results, the presence of the micro-crack can amplify, reduce and sometimes arrest the propagation of the semi-infinite crack.

2013

Nonlinear dynamics of crack propagation is investigated experimentally and theoretically with a goal to clarify the nature of limiting crack velocity, the transition from steady-state to branching regimes of crack dynamics, the dynamics of crack arrest. Theoretical explanation of limiting steady-state crack velocity and the transition to branching regime was proposed due to the study of collective behavior of microcrack ensemble at the crack tip area. Experimental study of crack dynamics was carried out in the preloaded plate PMMA specimen using the high speed camera coupled with the photo-elasticity method, the point stress recording with a laser system, the failure surface roughness measurement.