The Effect of Hydrogen on the Master Failure Curve of APL 5L Gas Pipe Steels (original) (raw)
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Twelfth European Conference on Fracture (ECF 12)
Materials Science, 1998
which are the main structural units of the ESIS. Each Technical Committee had reviewed and selected the submitted presentations and, on this basis, formed the topics of the conference program. Every block of topics contained one or two invited lectures, and numerous oral and poster presentations.
The effect of hydrogen concentration on fracture of pipeline steels in presence of a notch
Engineering Fracture Mechanics, 2011
The comparative assessment of local fracture initiation at notches in API grade pipeline steels: X52, X70 and X100 have been done for conditions of electrochemical hydrogenating. The factor of hydrogen concentration in metal was taken into account. The relationship between hydrogen concentration in metal and work for initiation of the local fracture emanating from the notch has been derived. The existence of some critical hydrogen concentration, which causes the significant loss of local fracture resistance of material, was also shown and discussed.
International Journal of Fracture 100: 55--83, 1999
The mechanisms of fatigue-crack propagation are examined with particular emphasis on the similarities and differences between cyclic crack growth in ductile materials, such as metals, and corresponding behavior in brittle materials, such as intermetallics and ceramics. This is achieved by considering the process of fatiguecrack growth as a mutual competition between intrinsic mechanisms of crack advance ahead of the crack tip (e.g., alternating crack-tip blunting and resharpening), which promote crack growth, and extrinsic mechanisms of crack-tip shielding behind the tip (e.g., crack closure and bridging), which impede it. The widely differing nature of these mechanisms in ductile and brittle materials and their specific dependence upon the alternating and maximum driving forces (e.g., K and K max ) provide a useful distinction of the process of fatigue-crack propagation in different classes of materials; moreover, it provides a rationalization for the effect of such factors as load ratio and crack size. Finally, the differing susceptibility of ductile and brittle materials to cyclic degradation has broad implications for their potential structural application; this is briefly discussed with reference to lifetime prediction.
A fracture criterion for the notch strength of high strength steels in the presence of hydrogen
Journal of the Mechanics and Physics of Solids, 2014
High strength steels can suffer from a loss of ductility when exposed to hydrogen, and this may lead to sudden failure. The hydrogen is either accommodated in the lattice or is trapped at defects, such as dislocations, grain boundaries and carbides. The challenge is to identify the effect of hydrogen located at different sites upon the drop in tensile strength of a high strength steel. For this purpose, literature data on the failure stress of notched and un-notched steel bars are re-analysed; the bars were tested over a wide range of strain rates and hydrogen concentrations. The local stress state at failure has been determined by the finite element (FE) method, and the concentration of both lattice and trapped hydrogen is predicted using Oriani's theory along with the stress-driven diffusion equation. The experimental data are rationalised in terms of a postulated failure locus of peak maximum principal stress versus lattice hydrogen concentration. This failure locus is treated as a unique material property for the given steel and heat treatment condition. We conclude that the presence of lattice hydrogen increases the susceptibility to hydrogen embrittlement whereas trapped hydrogen has only a negligible effect. It is also found that the observed failure strength of hydrogen charged un-notched bars is less than the peak local stress within the notched geometries. Weakest link statistics are used to account for this stressed volume effect.
International Journal of Fracture.pdf
This paper discusses the relationship between striation spacing, i.e., the microscopic crack propagation rate, as measured in postmortem fractographic inspection of fatigue fractured surfaces, and the macroscopic crack propagation rate, i.e., da/dN, as monitored during fatigue crack growth tests. Compact tensile specimens C(T) in prevalent plane-strain conditions were extracted in LT orientation from the center of a 2-in. thick rolled plate of a SAE-AMS 7475-T7351 Al alloy. Testpieces were fatigue tested according to ASTM-E647 standard, at room temperature in a servo-hydraulic closed-loop MTS testing machine operating with the unloading elastic compliance technique. da/dN-K data points were collected in the Paris' law validity region, with crack growth rates typically ranging from 0.18 to 2.02 µm/cycle. Topographical survey was conducted on the test specimen fracture surfaces in a scanning electronic microscope in order to determine striation spacing created during the fatigue test. Macro-and microcrack growth rates were compared and good correlation have been obtained for the data within the range of K assessed in the study. Results of crack growth rates have been quantitatively evaluated in terms of fatigue life estimation.
Journal of the Mechanics and Physics of Solids, 2010
such degradation in mechanical behavior have remained an issue of contention for many years, but can be broadly classified into three primary mechanisms , namely (i) decohesion mechanisms, where hydrogen at internal interfaces lowers the cohesive strength there (''hydrogen embrittlement''), (ii) hydrogen-enhanced localized plasticity (HELP), where hydrogen affects the local instabilities associated with plastic flow, and in certain material systems, (iii) hydride formation, where the presence of highly brittle hydride precipitates results in a ''low energy'' fracture path. In addition, there are other hydrogen-related degradation mechanisms involving internal gaseous species; these include blistering, where high hydrogen concentrations, e.g., associated with electrochemical hydrogen charging, result in the reformation of internal gaseous hydrogen at internal interfaces, leading to high internal pressures and the formation of blistering, and hydrogen attack, where at high temperatures and pressures, such internal hydrogen can react with the carbides in steel to form internal methane gas with an associated loss in strength due to decarburization. Although the dominant view is that several of these mechanisms, specifically the decohesion and HELP mechanisms, have been considered to be mutually exclusive, it has been recognized that this may not be the case . Indeed, the present work presents a compelling argument that the two mechanisms may in fact be acting in concert.
Effect of hydrogen on the fracture behavior of high strength steel during slow strain rate test
Corrosion Science, 2007
The effect of hydrogen on the fracture behavior of the quenched and tempered AISI 4135 steel at 1450 MPa has been investigated by means of slow strain rate tests on smooth and circumferentiallynotched round-bar specimens. Hydrogen was introduced into specimens by electrochemical charging and its content was measured by thermal desorption spectrometry (TDS) analysis. Results showed that the steel had high hydrogen embrittlement susceptibility. For both smooth and notched specimens, the fracture mode was changed from microvoid coalescence (MVC) to brittle intergranular (IG) fracture after the introduction of a small amount of diffusible hydrogen. Fracture initiated in the vicinity of the notch root for notched specimens, while it started from around the center in smooth specimens. The fracture stress decreased with increasing diffusible hydrogen content, and the decreasing trend was more prominent for specimens with a higher stress concentration factor. Taking into account the stress-driven hydrogen diffusion and accumulation in the vicinity of the notch root, the local diffusible hydrogen concentration and local fracture stress in notched specimens have been calculated. According to numerical results, the relationship between the local fracture stress and local diffusible hydrogen concentration was independent of stress concentration factor, which could account for the effect of hydrogen on the fracture stress of the steel.