Mechanisms of dislocation multiplication at crack tips

Bitzek, Erik; Gumbsch, Peter

doi:10.1016/j.actamat.2012.11.016

Cited by 64 publications

(49 citation statements)

References 61 publications

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“…Emphasis was given to new nanoscale measurement capabilities that are being applied to characterizing such cracks, especially with regard to determining the nonlinear size and structure of the distorted region at the crack tip. The experimental evidence for crack tip plasticity is overwhelming and detailed mechanisms have been reported, for example, proceeding from a simple calculation of dislocation nucleation in the plane of the crack [61] to a more general description of crack-assisted dislocation multiplication linked with the pre-existing dislocation density [62]. Antolovich & Armstrong [63] have reviewed the issue.…”

Section: Crack Size In Fracture Mechanicsmentioning

confidence: 99%

Material grain size and crack size influences on cleavage fracturing

Armstrong

2015

Phil. Trans. R. Soc. A.

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A review is given of the analogous dependence on reciprocal square root of grain size or crack size of fracture strength measurements reported for steel and other potentially brittle materials. The two dependencies have much in common. For onset of cleavage in steel, attention is focused on relationship of the essentially athermal fracture stress compared with a quite different viscoplastic yield stress behaviour. Both grain-size-dependent stresses are accounted for in terms of dislocation pile-up mechanics. Lowering of the cleavage stress occurs in steel because of carbide cracking. For crack size dependence, there is complication of localized crack tip plasticity in fracture mechanics measurements. Crack-size-dependent conventional and indentation fracture mechanics measurements are described also for results obtained on the diverse materials: polymethylmethacrylate, silicon crystals, alumina polycrystals and WC-Co (cermet) composites.

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Section: Crack Size In Fracture Mechanicsmentioning

confidence: 99%

Material grain size and crack size influences on cleavage fracturing

Armstrong

2015

Phil. Trans. R. Soc. A.

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“…For eight different iron potentials, they concluded that there was too much variation of unstable stacking fault energies and the resulting K IC variation for emitting dislocations of 40% was far too large. However, use of other material simulation techniques, [194][195][196][197] mostly theoretical and applied mechanics, have produced some success, but are not often compared to the atomistic fundamentals. To achieve a more complete understanding of DBTs over multiple modeling scales, detailed in situ experiments measuring plastic and fracture properties of multiple materials are needed.…”

Section: Future Nanomechanical Approaches To Brittleness Transitionsmentioning

confidence: 99%

“…These data are similar to the multiscale modeling of plastic deformation of molybdenum and tungsten. 195,215 Further consideration of high stresses in metals by Gr€ oger et al 215 and silicon by Rabier and Demenet,197,216 respectively, shows what happens to the dislocation core structure at high stresses. For example, Gr€ oger et al 215 demonstrated a very gradual change of V* at shear stresses of 400 to 800 MPa in Mo (close to the Peierl's stress) as V* $ 1 b 3 is approached.…”

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confidence: 99%

Review Article: Case studies in future trends of computational and experimental nanomechanics

Tadmor

Kysar

Zimmerman

et al. 2017

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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With rapidly increasing numbers of studies of new and exotic material uses for perovskites and quasicrystals, these demand newer instrumentation and simulation developments to resolve the revealed complexities. One such set of observational mechanics at the nanoscale is presented here for somewhat simpler material systems. The expectation is that these approaches will assist those materials scientists and physicists needing to verify atomistic potentials appropriate to the nanomechanical understanding of increasingly complex solids. The five following segments from nine University, National and Industrial Laboratories both review and forecast where some of the important approaches will allow a confirming of how in situ mechanics and nanometric visualization might unravel complex phenomena. These address two-dimensional structures, temporal models for the nanoscale, atomistic and multiscale friction fundamentals, nanoparticle surfaces and interfaces a) Electronic

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“…Fortunately, hundreds of nanometers are sometimes large enough to mimic a metallic nanostructure, which can be handled effectively by MD. Depending on specific problems, MD can recognize important deformation mechanisms even at high strain rates [13,[34][35][36][37][38]. In the case of Ni 3 Al, atomistic simulations have already shown novel deformation mechanisms when the sample size is reduced to the form of nanocubes [39], or nanopillars [40].…”

Section: Introductionmentioning

confidence: 99%

“…But the meaningful strength of a large-volume structural material with engineering relevance is usually governed by its fracture toughness instead of the ideal strength which is only associated with the uniform bond breaking strength [29,33]. Alternatively, classical MD with a reliable empirical interatomic potential could be an alternative method for understanding the microscopic deformation mechanisms, fracture modes, and the mechanical properties of nanostructures which are usually dominatingly governed by their extended defects [13,[34][35][36][37][38]. The reliability of MD is strongly related to the choice of empirical potentials.…”

Section: Introductionmentioning

confidence: 99%

Size-dependent plastic deformation and failure mechanisms of nanotwinned Ni3Al: Insights from an atomistic cracking model

Wang

Tsuchiya

Dai

2016

Materials Science and Engineering: A

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a b s t r a c tThe polycrystalline Ni 3 Al is brittle since the notorious intergranular fracture mode hinders its applications. Here we perform molecular dynamics to highlight the unique role of nanotwin boundary in the plastic deformation and failure mechanisms of Ni 3 Al via an atomistic cracking model. Surprisingly, the strength, ductility and fracture toughness of the nanotwinned Ni 3 Al are revealed to increase simultaneously with reducing twin size, possibly evading a traditional tradeoff between ductility/toughness and strength. A possible quasi-brittle fracture mode in single crystalline Ni 3 Al is recognized as nucleating twinning partials from crack tip. However, the pre-existing twin boundaries can suppress the emission and propagation of successive twinning dislocations. Instead, dislocation avalanches happen and serve as a crack blunting mechanism which leads to the ductile fracture pattern of the nanotwinned Ni 3 Al. A sizedependent transition of fracture mode from dislocation nucleation to shear localization is observed as twin becomes very small. A physical model combined with energetics analysis is provided to rationalize the transition. Our atomistic insights are in qualitative agreement with recent observations of improved strength and ductility of Ni 3 Al with disordered nanotwinned structure after severe plastic deformation.

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Mechanisms of dislocation multiplication at crack tips

Cited by 64 publications

References 61 publications

Material grain size and crack size influences on cleavage fracturing

Material grain size and crack size influences on cleavage fracturing

Review Article: Case studies in future trends of computational and experimental nanomechanics

Size-dependent plastic deformation and failure mechanisms of nanotwinned Ni3Al: Insights from an atomistic cracking model

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