Fracture dynamics—a photoelastic investigation

Bradley, W.B.; Kobayashi, A. S.

doi:10.1016/0013-7944(71)90041-5

Cited by 68 publications

(15 citation statements)

References 19 publications

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“…Now proceed to analyse in detail the solution to the equation of motion, (5). To make progress, we need some information for the form of the local velocity response to the stress, v(r).…”

Section: The Equation Of Motion: Analysis and Fracture Kineticsmentioning

confidence: 99%

“…The reason for the factor of two discrepancy between predictions and measurements is not explained within the paradigm of energy balance considerations. Another poorly understood issue concerns the physical mechanisms for crack initiation and arrest and the reason for the stress hysteresis between the two [4,5]. Lattice trapping [6] on atomic length-scales is related to this issue and an initial understanding of this phenomenon in the microscale starts to emerge [7].…”

Section: Introductionmentioning

confidence: 99%

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Dynamics of fracture propagation in the mesoscale: Theory

Blumenfeld¹

1998

Theoretical and Applied Fracture Mechanics

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A recent theoretical model (Blumenfeld, Phys. Rev. Lett. 76 (1996) 3703) is described for modes I and III crack propagation dynamics in noncrystalline materials on mesoscopic lengthscales. Fracture has been one of the longest standing problems in physics and materials science, and despite much eort, several fundamental issues have stubbornly resisted resolution:(i) Running cracks reach a steady-state velocity of roughly half the shear wave speed, while theoretical predictions based on energetics are twice as high. The discrepancy originates from dynamics, but a consistent dynamical model has been slow to emerge.(ii) There is little understanding of the mechanisms for crack initiation and arrest and the hysteresis between them. Lattice trapping, although relevant on the atomic scale, cannot explain this phenomenon on mesoscopic and macroscopic scales.(iii) Another intriguing phenomenon is appearance of velocity periodic oscillations in some materials and the relation between this and material properties.(iv) As a result of the above issues, there is currently no consensus on the form of the equations of motion that govern mesoscale fracture dynamics.Whether explicitly or implicitly, most traditional models use quasi-static and near-equilibrium concepts to analyse the dynamics of propagation. It is argued here that such approaches are bound to fail. Two reasons are responsible for this and consequently for the dire understanding of this problem: First, most fast fracture processes are usually restricted to post-mortem measurements of the already fractured system, while the process itself is too fast to capture. Only recently there emerged experiments where the dynamic process is continuously monitored. Second, it is strongly contended here that the fracture phenomenon is governed by dierent mechanisms on dierent length-scales, a crucial aspect that has not received sucient attention. In ideally brittle propagation, the crack is atomically sharp and therefore atomic potentials are important (5±10 # A). Anharmonicity plays a signi®cant role on this scale due to large local strains at the crack tip, which gives rise to a strong nonlinear behaviour. On large scales (>lm), continuum linear elasticity describes quite well the stress ®eld and the far-away elastic energetics. This is exactly because cracks propagate slower than the bulk speed of sound, which allows the bulk stress to relax to its static value in the frame of the moving crack. Ultimately, this is the reason why contour integral calculations of energy in¯ux into the crack tip are valid as long as the contours are taken well away from the tip. Between the atomic and the continuous scales there are at least two more relevant length-scales: One is that of the cohesive zone, which is the region where the continuous stress ®eld description breaks down due to the discreteness of the lattice. It is of the order of several lattice constants and about one order of magnitude above the atomic scale ($10±50 # A). The fourth length-scale, and the one we focus o...

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“…Now proceed to analyse in detail the solution to the equation of motion, (5). To make progress, we need some information for the form of the local velocity response to the stress, v(r).…”

Section: The Equation Of Motion: Analysis and Fracture Kineticsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dynamics of fracture propagation in the mesoscale: Theory

Blumenfeld¹

1998

Theoretical and Applied Fracture Mechanics

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“…The validity of the above two dynamic crack curving criteria were assessed through re-evaluated dynamic photoelasticity results of I Homalite-100 fracture specimens [14][15][16][17][18]. ro for the minimum S criterion was equated to rc which was found to be about 1.3 mm for the Homalite-100 data used in evaluating the maximum circumferential stress criterion.…”

Section: Homalite-lo0 Fracture Specimensmentioning

confidence: 99%

Further Studies on Dynamic Crack Curving

Sun¹,

Kobayashi²,

Kang³

1981

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“…instantaneous dynamic stress intensity factor, during crack propagation the dynamic stress intensity fact(.-, which is extracted from transient dynamic isochromatics surrounding the propagating crack tip, is used to measure the dynamic fracture toughness. A commonly used data reduction procedure for this purpose is to fit a theoretical, near-field, static isochromatics to the recorded experimental dynamic isochromatics and to then equate the resultant static stress intensity factor of the former to the unknown dynamic stress intensity factor of the latter [2][3][4][5]. Error estimates for using a static near-field stress to extract the dynamic stress intensity factor have been made by several investigators [6][7][8] and in particular, exhaustively by Rossmanith and Irwin [8].…”

Section: Introductionmentioning

confidence: 99%

Dynamic stress-intensity factors for unsymmetric dynamic isochromatics

Kobayashi

1981

Experimental Mechanics

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The mixed mode, near-field state of stresses surrounding a crack propagating at constant velocity is used to derive a relation between the dynamic stress intensity factors K i , KII, the remote stress component oox and the dynamic isochromatics. This relation together with an overdeterministic least-square method form the basis of a data reduction procedure for extracting dynamic K i , KII and ox from the recorded dynamic photoelastic pattern surrounding a running crack. The overdeterministic least-square method is also used to fit static isochromatics to the numerically generated dynamic isochromatics. The resultant static K I , KII, and aox are compared with the corresponding dynamic values and estimates of errors involved in using static analysis to process dynamic isochromatic data are obtained. The data reduction procedure is then used to evaluate the branching stress intensity factor associated with crack branching and the mixed mode stress intensity factors associated with crack curving.

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Fracture dynamics—a photoelastic investigation

Cited by 68 publications

References 19 publications

Dynamics of fracture propagation in the mesoscale: Theory

Dynamics of fracture propagation in the mesoscale: Theory

Further Studies on Dynamic Crack Curving

Dynamic stress-intensity factors for unsymmetric dynamic isochromatics

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