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Journal ArticleDOI

Numerical analysis of hydrogen transport near a blunting crack tip

TL;DR: In this paper, Oriani's equilibrium theory is used to relate the hydrogen in traps (micro-structural defects) to concentration in normal interstitial lattice sites (NILS), and the resulting non-linear transient hydrogen diffusion equations are integrated using a modified backward Euler method.
Abstract: T he hydrogen transport problem is studied in conjunction with large deformation elastic—plastic behavior of a material. Oriani's equilibrium theory is used to relate the hydrogen in traps (micro-structural defects) to concentration in normal interstitial lattice sites (NILS). The resulting non-linear transient hydrogen diffusion equations are integrated using a modified backward Euler method. Coupled diffusion and plastic straining is analysed with this numerical procedure in the area around a blunting crack tip. A uniform NILS concentration as dictated by Sievert's law at the pressure and temperature of interest is used as initial condition throughout the body. The crack is initially blunted by plane strain mode I (tensile) loading. The finite element results show that hydrogen residing at NILS is generally very small in comparison with the population that develops in trapping sites near the crack surface. That is, lattice diffusion delivers the hydrogen but it is predominantly the trapping that determines its distribution at temperatures of interest. The predominance of trapped hydrogen over lattice concentration prevails even in the case when hydrogen migrates under steady state conditions. Hence, the hydrostatic stress effect is less important than traps created by plastic straining as far as the creation of high total hydrogen concentration is concerned. The trapping site locations and the temperature determine the amounts and locations of high hydrogen concentrations. Consequently, ahead of a blunting crack tip, the total hydrogen concentration and plastic strain diminish with distance from the crack tip whereas the hydrostatic stress rises. This would seem to have significant consequences for fractures induced by the presence of hydrogen.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the role of hydrogen in reducing ductile crack growth resistance is attributed to the increased creation of vacancies on straining, which is supported by a recent finding of amorphisation associated with crack growth.
Abstract: Recent studies of the characteristics and mechanism of hydrogen related failure in steels are overviewed. Based on an analysis of the states of hydrogen in steels, the role of hydrogen in reducing ductile crack growth resistance is attributed to the increased creation of vacancies on straining. Cases showing the involvement of strain induced vacancies in susceptibility to fracture are presented. The function of hydrogen is ascribed to an increase in the density of vacancies and their agglomeration, rather than hydrogen itself, through interactions between vacancies and hydrogen. The newly proposed mechanism of hydrogen related failure is supported by a recent finding of amorphisation associated with crack growth.

375 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present a comprehensive physical-based statistical micro-mechanical model of hydrogen embrittlement which they use to quantitatively predict the degradation in fracture strength of a high-strength steel with increasing hydrogen concentration, with the predictions verified by experiment.
Abstract: Intergranular cracking associated with hydrogen embrittlement represents a particularly severe degradation mechanism in metallic structures which can lead to sudden and unexpected catastrophic fractures. As a basis for a strategy for the prognosis of such failures, here we present a comprehensive physical-based statistical micro-mechanical model of such embrittlement which we use to quantitatively predict the degradation in fracture strength of a high-strength steel with increasing hydrogen concentration, with the predictions verified by experiment. The mechanistic role of dissolved hydrogen is identified by the transition to a locally stress-controlled fracture, which is modeled as being initiated by a dislocation pile-up against a grain-boundary carbide which in turn leads to interface decohesion and intergranular fracture. Akin to cleavage fracture in steel, the “strength” of these carbides is modeled using weakest-link statistics. We associate the dominant role of hydrogen with trapping at dislocations; this trapped hydrogen reduces the stress that impedes dislocation motion and also lowers the reversible work of decohesion at the tip of dislocation pile-up at the carbide/matrix interface. Mechanistically, the model advocates the synergistic action of both the hydrogen-enhanced local plasticity and decohesion mechanisms in dictating failure.

344 citations


Cites background or methods from "Numerical analysis of hydrogen tran..."

  • ...The coupling of the hydrogen transport problem with the material elastoplastic deformation followed the approach documented by Sofronis and McMeeking (1989) and Liang and Sofronis (2003)....

    [...]

  • ...The hydrogen transport equation 4 accounting for stress-driven diffusion and trapping at all three trapping sites is described by (Sofronis and McMeeking, 1989) D Deff @CL @t ¼ DCL;ii DVH 3RT CLskk;i ;i X j aðjÞyðjÞT @NðjÞT @ep 0 @ 1 A @ep @t ; ð6Þ where (),i ¼ @()/@xi, @/@t denotes partial…...

    [...]

Journal ArticleDOI
TL;DR: In this paper, the effect of hydrogen on the fracture behavior of quenched and tempered AISI 4135 steel at 1450 MPa was investigated by means of slow strain rate tests on smooth and circumferentially-notched round-bar specimens.

306 citations

Journal ArticleDOI
TL;DR: In this paper, a modified hydrogen transport model was used to simulate the effect of the hydrostatic stress and trapping on the hydrogen distribution in a plastically deforming steel, where hydrogen atoms diffuse through lattice sites and trap sites are filled by lattice diffusion.
Abstract: The hydrogen transport model of Sofronis and McMeeking was used in order to simulate the effect of the hydrostatic stress and trapping on the hydrogen distribution in a plastically deforming steel. In this model it is assumed that hydrogen atoms diffuse through lattice sites and that trap sites are filled by lattice diffusion. These trap sites are formed due to plastic deformations. Coupled diffusion elastic–plastic finite element analyses were carried out in order to investigate the hydrogen concentration in lattice and trap sites near a blunting crack tip under small-scale yielding conditions. The numerical results of Sofronis and McMeeking were reproduced and it was found that in their model hydrogen is created. The hydrogen balance is satisfied by including a strain rate factor in the hydrogen transport equation. As a consequence no differences were found at steady state, i.e. at low strain rates. The strain rate factor decreases the hydrogen concentration in lattice sites due to the filling of trap sites. When the strain rate is sufficiently high, the lattice sites can be almost depleted of hydrogen while trap sites remain saturated. The modified hydrogen transport model predicts strong dependence of the hydrogen concentration in lattice sites on the strain rate, while the hydrogen concentration in trap sites is not affected significantly. The modified hydrogen transport model provides greater insight into the strain rate dependence of hydrogen embrittlement as observed in tensile tests.

267 citations

Journal ArticleDOI
TL;DR: In this paper, the authors examined the susceptibility to hydrogen embrittlement of martensitic steels by means of a delayed-fracture test and hydrogen thermal desorption analysis.
Abstract: The susceptibility to hydrogen embrittlement (HE) of martensitic steels has been examined by means of a delayed-fracture test and hydrogen thermal desorption analysis. The intensity of a desorptionrate peak around 50 °C to 200 °C increased when the specimen was preloaded and more remarkably so when it was loaded under the presence of hydrogen. The increment appeared initially at the low-temperature region in the original peak. As hydrogen entry proceeded, the increment then appeared at the high-temperature region, while that in the low-temperature region was reduced. The alteration occurred earlier in steels tempered at lower temperatures, with a higher embrittlement susceptibility. A defect acting as the trap of the desorption in the high-temperature region was assigned to large vacancy clusters that have higher binding energies with hydrogen. Deformation-induced generation of vacancies and their clustering have been considered to be promoted by hydrogen and to play a primary role on the HE susceptibility of high-strength steel.

256 citations

References
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Book
01 Jan 1989
TL;DR: In this article, the methodes are numeriques and the fonction de forme reference record created on 2005-11-18, modified on 2016-08-08.
Abstract: Keywords: methodes : numeriques ; fonction de forme Reference Record created on 2005-11-18, modified on 2016-08-08

17,327 citations

Journal ArticleDOI
James R. Rice1
TL;DR: In this paper, an integral is exhibited which has the same value for all paths surrounding a class of notches in two-dimensional deformation fields of linear or non-linear elastic materials.
Abstract: : An integral is exhibited which has the same value for all paths surrounding a class of notches in two-dimensional deformation fields of linear or non-linear elastic materials. The integral may be evaluated almost by inspection for a few notch configurations. Also, for materials of the elastic- plastic type (treated through a deformation rather than incremental formulation) , with a linear response to small stresses followed by non-linear yielding, the integral may be evaluated in terms of Irwin's stress intensity factor when yielding occurs on a scale small in comparison to notch size. On the other hand, the integral may be expressed in terms of the concentrated deformation field in the vicinity of the notch tip. This implies that some information on strain concentrations is obtainable without recourse to detailed non-linear analyses. Such an approach is exploited here. Applications are made to: Approximate estimates of strain concentrations at smooth ended notch tips in elastic and elastic-plastic materials, A general solution for crack tip separation in the Barenblatt-Dugdale crack model, leading to a proof of the identity of the Griffith theory and Barenblatt cohesive theory for elastic brittle fracture and to the inclusion of strain hardening behavior in the Dugdale model for plane stress yielding, and An approximate perfectly plastic plane strain analysis, based on the slip line theory, of contained plastic deformation at a crack tip and of crack blunting.

7,468 citations

Journal ArticleDOI
TL;DR: In this paper, the effects of hydrogen on the physical and mechanical properties of iron and steel are reviewed and a new mechanism for the cold work peak for hydrogen in iron is considered.
Abstract: The effects of hydrogen on the physical and mechanical properties of iron and steel are reviewed. A new mechanism for the cold work peak for hydrogen in iron is considered. Together, internal friction and mechanical properties indicate that hydrogen softens iron by enhancing screw dislocation mobility at room temperature but hardens iron by core interactions at low temperatures. No single mechanism exists for the degradation of the properties of steel by hydrogen. Instead a complex process involving many of the proposed mechanisms as contributing factors is shown to account for most degradation phenomena.

1,596 citations

Journal ArticleDOI
R.A. Oriani1
TL;DR: In this paper, the mobility of dissolved hydrogen in an iron lattice having a population of extraordinary, or trapping, sites for hydrogen is analyzed under the assumption of local equilibrium between the mobile and the trapped populations.

1,323 citations

Book
01 Jan 1948

1,253 citations