Hydrogen in steel—the stability of micro-cracks

Bilby, B. A.; Hewitt, Jon

doi:10.1016/0001-6160(62)90048-2

Cited by 57 publications

(7 citation statements)

References 16 publications

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“…Previous analyses were based on energetic considerations. mutually repulsive forces between neighboring dislocations are The most thorough treatement was by Bilby and Hewitt [1962]. counteracted by the externally applied shear stress (Figure 1).…”

Section: Nucleation and Propagation Of A Wedge Crack Stability Of A Wmentioning

confidence: 99%

A note on the propagation behavior of a crack nucleated by a dislocation pileup

Wong¹

1990

J. Geophys. Res.

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When an operating slip band encounters a microstructural obstacle, nucleation of tensile microcracking can occur by several mechanisms. Linear elastic fracture mechanics is used to analyze one such semibrittle cracking mechanism involving a dislocation pile-up. After crack nucleation, the dislocations move in and coalesce at one end of the wedge crack. Under overall compressire loading, the wedge crack propagation is stable and arrest occurs at an equilibrium length. Analytic estimates of the equilibrium length and crack orientation are obtained, and are compared with experimental observations of a peridotite and a quartzite. The critical driving shear stress (i.e. the resolved shear stress minus the lattice •friction " for wedge crack nucleation is relatively small in comparison with the macroscopic yield stress, implying that a significant portion of the applied deviatoric stress is used to overcome the shear resistance due to the lattice "riction • or Peierls stress. The equilibrium wedge crack length depends sensitively on the confining stress, and also depends on the differential stress and the Peierls stress.Kronenberg 1984]. A general conclusion of these studies is that 1976; Rovetta et al., 1986; Hirth and Tullis, 1986; Walniuk and the interaction of dislocation glide, mechanical twinning, Wenk, 1985] appealed to dislocation pile-ups for the nucleation microcracking, and diffusional mass transfer processes plays an of microcracks which grow intragranularly. important role in controlling the semibrittle deformation. The Francois and Wilshaw's [1968] stability analysis based on interaction may result in crack tip blunting. Dislocation pile-ups energetic consideration was developed for a two-dimensional and mechanical twins may also enhance microcracking by loading configuration with one compressive and one tensileproviding crack nucleation mechanisms. Such processes have principal stress. Although it has been widely quoted, this analysis been analyzed in the materials science literature; however, these does not provide any quantitative information on crack growth theoretical analyses are unlikely to be applicable directly to the behavior in cases where both princpal stresses are compressive.In this note, I obtain some analytic results for the all compressive loading case using linear elastic fracture mechanics. The approach is analogous to that of recent analyses of the "sliding crack" model for brittle rock deformation [e.g., Horii and Nemat-Nasser, 1986; Ashby and Hallam, 1986]. The Copyright 1990 by the American Geophysical Union. stabilization effect of pressure and the extent of semibrittle crack growth are analyzed, and the quantitative prediction of crack geometry are compared with experimental observations for a peridotite and a quartzite.

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Section: Nucleation and Propagation Of A Wedge Crack Stability Of A Wmentioning

confidence: 99%

A note on the propagation behavior of a crack nucleated by a dislocation pileup

Wong¹

1990

J. Geophys. Res.

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“…In the sixties, they have given a critical argument against the pressure-expansion hypothesis for hydrogen embrittlement of which the essence was the precipitation of gaseous hydrogen in pre-existing microvoids and their growth under increased internal hydrogen pressure (see, e.g. [30,31]. However, as was shown in [32], despite on the absence of cracks, the gaseous hydrogen of 1 bar pressure caused a greater embrittlement of high strength steels in comparison with electrolytic charging.…”

Section: Discussionmentioning

confidence: 99%

Hydrogen Grain Boundary Segregation and Migration in the Alpha-Iron

Gavriljuk¹,

Teus²

2017

Metallofiz. Noveishie Tekhnol.

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Based on the difference in diffusion mechanisms of substitutional and interstitial atoms and using molecular dynamics simulation of hydrogen migration, it is shown that accelerated hydrogen flux in the polycrystalline iron observed during cathodic charging cannot originate from the enhanced hydrogen grain-boundary diffusion. A possible role of grain-boundary cracking is supposed.Key words: hydrogen diffusion, grain boundaries, molecular dynamics simulation.Ґрунтуючись на відмінностях механізмів дифузії атомів заміщення та втілення і використовуючи молекулярно-динамічні розрахунки міґрації атомів Гідроґену, показано, що прискорений потік водню в полікристалі-чному залізі, який спостерігається в процесі катодного наводнення, не може бути наслідком прискореної зерномежової дифузії водню. Розгляда-ється можлива роль зерномежового розтріскування.Ключові слова: дифузія водню, межі зерен, молекулярна динаміка.Основываясь на отличиях механизмов диффузии атомов замещения и внедрения и используя моделирование методом молекулярной динамики миграции водорода, показано, что ускоренный поток водорода в поликри-сталлическом железе, который наблюдается в процессе катодного наводо-раживания, не может быть следствием ускоренной зернограничной диф-фузии водорода. Рассмотрена возможная роль зернограничного растрес-кивания.

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“…Although the phenomena of hydrogen embrittlement [- [16][17][18][19][20][21] and metal dissolution [-22, 23, 24] have been investigated extensively, the nature of either mechanism is controversial.…”

Section: Survey Of Possible Mechanisms Of Subcritical Crack Growth Inmentioning

confidence: 99%

Mechanisms of corrosion fatigue below K Iscc

Barsom¹

1971

Int J Fract

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Information on corrosion-fatigue crack growth in engineering structures is necessary for the prediction of service lives of structures subjected to both fatxgue loading and an aggressive environment. The rate of crack growth m corrosion fatigue is governed by the interaction between the chemical mechamsms and the mechanical mechanisms occurring at the crack tip. Thus, as part of a long-range program aimed at establishing the necessary relations for predicting the corrosion-fatigue behavior of structural steels, the crack-tip mechanisms in corrosion fatigue were studied by using controlled-potential techniques, pH measurements at the crack tip, and fractographic analysis of the crack surface.The tests were conducted on 12Ni-5Cr-3Mo maraging steel at a cyclic-stress frequency equal to 6 cycles per minute in a room-temperature pH 7, 3 percent solution of sodium chloride.The results showed that the controlled-potential techmque is inadequate for isolating the crack-tip mechamsms in thick specimens subjected to fatigue loading and an aggressive environment. At the crack tip the pH was 3. In addition, localized neighboring regions of basic and acldac solutions were observed in the proximity of the central portion of the crack tip. Hence, it is concluded that the effectiveness of cathodic protectmn decreases as the crack front moves away from the flee surface. The fractographac tests showed that hydrogen embrittlement is the primary mechanism responsible for acceleration of fatigue cracks in 12Ni-5Cr-3Mo steel in 3 percent sodium chloride solutmn.Finally, by using the corrosion-fatigue crack-propagation lawwhere da/dN is crack-growth rate per cycle, b is the crack-opening displacement, ay is the yield strength, and D(t) is a time-or frequency-dependent functmn, it is shown that, for the environment-material system investigated, hydrogen embrittlement accelerates corrosion-fatigue crack propagation by changing the ductility of the material (or 6). Introd~'tionSubcritical crack growth in corrosion fatigue may be divided into two components: one caused by cyclic stresses and the other caused by the environment. The cyclic-stress component has been thoroughly investigated, and it is generally accepted that it is caused by the mechanisms of plastic deformation at the crack tip [14]. However, the chemical mechanisms at the crack tip that increase crack growth in corrosion fatigue are yet to be investigated in detail. Most investigations on the influence of the environment on subcritical crack growth in highstrength steels have been designed to determine the existence of environmental effects in a given environment-material system [5][6][7][8][9][10][11][12][13]. Furthermore, in these investigations, the effect of the environment on crack growth was studied in terms of either time to failure or in terms of the change in crack-growth rates.In a recent investigation on the corrosion-fatigue behavior below K1~c of 12Ni-5Cr-3Mo maraging steel in a room-temperature 3 percent solution of sodium chloride, Barsom [14,15] showed (Figur...

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Hydrogen in steel—the stability of micro-cracks

Cited by 57 publications

References 16 publications

A note on the propagation behavior of a crack nucleated by a dislocation pileup

A note on the propagation behavior of a crack nucleated by a dislocation pileup

Hydrogen Grain Boundary Segregation and Migration in the Alpha-Iron

Mechanisms of corrosion fatigue below K Iscc

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