Papers by Keyword: Hydrogen Embrittlement

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Authors: Giovambattista Bilotta, Clara Moriconi, Gilbert Hénaff, Mandana Arzaghi, Damien Halm
Abstract: In this study we focus on the effect of hydrogen gas on the cracking resistance of metals. The main objective is to predict the fatigue crack propagation rates in the presence of hydrogen. For this purpose, a Cohesive Zone Model (CZM) dedicated to cracking under monotonic as well as cyclic loadings has been implemented in the ABAQUS finite element code. A specific traction-separation law, adapted to describe the gradual degradation of the cohesive stresses under cyclic loading, and sensitive to the presence of hydrogen is formulated. The coupling between mechanical behaviour and diffusion of hydrogen can be modelled using a coupled temperature - displacement calculation available in ABAQUS. The simulations are compared with fatigue crack propagation tests performed on a 15-5PH martensitic stainless steel. They show that while the proposed model is able to predict a lower resistance to cracking in presence of hydrogen, at this stage it cannot fully account for the detrimental effect induced by high pressure of gaseous hydrogen.
Authors: Laura Vergani, Giorgia Gobbi, Chiara Colombo
Abstract: Pipeline working environment is characterised by corrosive conditions, able to develop hydrogen formation. The presence of atomic hydrogen localized in correspondence of crack tip, where the plastic strain reaches the maximum value, is responsible for life reduction. For this reason, it is important to estimate and predict the mechanical properties decay, in terms of toughness and crack propagation, when steel is in contact with hydrogen. Aim of this study is to develop FE models of two carbon, low-alloyed steels used in pipelines applications: X65 and F22. A complex model including three simulations steps is presented. It considers the combined effect of plastic strain and hydrogen concentration on the material toughness. The results of the model are validated by a comparison with experimental tests carried out on the two low-alloyed steel.
Authors: Rainer Falkenberg
Abstract: The fracture mechanics assessment of materials exposed to harmful environments requires the understanding of the interaction between the soluted species and the affected mechanical behaviour. With the introduction of a mass transport mechanism the entire problem is subjected to a time frame that dictates the time-dependent action of soluted species on mechanical properties. A numerical framework within the phase field approach is presented with an embrittlement-based coupling mechanism showing the influence on crack patterns and fracture toughness. Within the phase field approach the modeling of sharp crack discontinuities is replaced by a diffusive crack model facilitating crack initiation and complex crack topologies such as curvilinear crack patterns, without the requirement of a predefined crack path. The isotropic hardening of the elasto-plastic deformation model and the local fracture criterion are affected by the species concentration. This allows for embrittlement and leads to accelerated crack propagation. An extended mass transport equation for hydrogen embrittlement, accounting for mechanical stresses and deformations, is implemented. For stabilisation purposes a staggered scheme is applied to solve the system of partial differential equations. The simulation of showcases demonstrates crack initiation and crack propagation aiming for the determination of stress-intensity factors and crack-resistance curves.
Authors: Seong Jong Kim, Seok Ki Jang
Abstract: Recently, there has been increased interest in using aluminum alloys in ship construction instead of fiber-reinforced plastic (FRP). This is because aluminum alloy ships are faster, have a greater load capacity, and are easier to recycle than FRP ships. In this study, we investigated the mechanical and electrochemical properties of aluminum alloys using the slow strain rate and potentiostatic tests under various potential conditions. The optimum protection potential range with regards to hydrogen embrittlement and stress corrosion cracking was determined to lie between -1.5 and -0.7 V (SSCE). These results can be used as reference data for ship design.
Authors: Loïc Oger, Eric Andrieu, Grégory Odemer, Lionel Peguet, Christine Blanc
Abstract: The effects of hydrogen during stress corrosion cracking mechanisms (SCC) have been highlighted for many years but hydrogen trapping mechanisms are not yet well understood for 7xxx aluminium alloys. The 7046-T4 Al-Zn-Mg alloy has been chosen for this study because its low corrosion susceptibility allows hydrogen embrittlement (HE) to be more easily distinguished during SCC tests. Tensile stress tests have been carried out at a strain rate of 10-3 s-1 on tensile samples after an exposure at their corrosion potential in a 0.6M chloride solution for 165 hours under an imposed loading of 80%Rp0.2. The results were compared to those obtained for samples pre-corroded without mechanical loading applied and healthy specimens. A loss of mechanical properties was observed for the pre-corroded samples and presumably attributed to the absorption, the diffusion and the trapping of hydrogen which affects a volume under the surface of the alloy and modifies its mechanical properties. Scanning electron microscope (SEM) observations highlighted a strong effect of hydrogen on fracture modes. The ductile-intergranular initial fracture mode observed on the healthy samples was partially replaced for the pre-corroded samples by a combination of two main fracture modes, i.e. brittle intergranular and cleavage, in relation with the nature of the hydrogen trapping sites and local stress state.
Authors: Hong Chang
Abstract: Acoustic emission signals were continuously monitored during corrosion fatigue crack propagation for X52 steel in 3.5% NaCl and AZ31 magnesium alloy in 0.1%NaCl solution. There are different microstructure and corrosion fatigue crack propagation mechanism for X52 steel and AZ31B magnesium alloy. Combined with the existing research results of LY12CZ and 7075-T6 aluminum alloys, the acoustic emission waveform parameter, the frequency centroid ratio, was tried to use as a criterion to distinguish the corrosion fatigue crack propagation mechanism for anodic dissolution and hydrogen embrittlement. The results also show that the nature of the acoustic emission source determines the main characteristics of the signal parameters and waveforms, and little to do with the experimental material.
Authors: Xin Pang, Fateh Fazeli, Michael Attard, Chao Shi
Abstract: This study aims to develop novel experimental procedure that quantifies response of AHSSs with different microstructures, deformation status, and strength levels to hydrogen. The capacity for trapped hydrogen, kinetics of hydrogen absorption and loss, and hydrogen mobility are measured and analyzed by permeation tests. The experimental findings are discussed in terms of microstructural features for an interstitial free (IF) and a dual phase (DP) steels. Further, the density of trap sites and its effect on effective diffusivity of hydrogen in the steel are analyzed by means of a diffusion model.
Authors: Tomohiro Tsutsumi, Takahito Watakabe, Goroh Itoh
Abstract: Investigation on the behavior of hydrogen is needed to spread the use of hydrogen fuel cell vehicles. Hydrogen microprint technique (HMPT) has been known as an effective method to investigate the hydrogen behavior by visualizing the microscopic location of hydrogen in relation to the microstructure. In the present study, the behavior of electrolitically charged hydrogen in 6061 and 7075 aluminum alloys with T6-temper has been investigated by means of HMPT. Both in the two alloys, hydrogen was detected on constituent particles and in the matrix. Total amount of detected hydrogen was markedly larger in 7075 than in 6061, although the distribution in depth direction far narrower and the fraction of hydrogen detected in the matrix with respect to that on the constituent was larger. These fact was presumed to be caused by the difference in the fine precipitates between the two alloy formed during final aging treatment.
Authors: Lucie Páleníková, Lenka Klakurková, Pavel Gejdoš, Michaela Remešová, Martin Juliš, Ladislav Čelko
Abstract: In this article, the causes of damage of a cover were investigated by metallographic and fractographic analysis. The component part was made from non-alloy quality steel for cold forming DC04. The failure occurred during high temperature pulsation (90 °C, 7b, 1 Hz) after 180,000 cycles. This component part was fabricated by deep drawing. After this process’s step, outlets were soldered at 1100 °C/5 min. to this part and then whole component part was coated using method without any specification. The coating layer was formed of Zn-Ni. The last step in this process was hemming where all component parts were assembled together. This case study was solved using light and scanning electron microscopy. The chemical composition was detected by energy dispersive X-ray analysis.
Abstract: A high strength bolt with hot dip galvanizing treatment failed shortly after being installed for two days on a padeye of mooring dolphin. The bolt was installed with increasing stress on the second day in which the value was nearly twice. Investigation results showed the bolt fractured with the nut head separated from the pin. Corroded fracture surface with brittle characteristic and no plastic deformation observed dominating the failed area. Characterization of hardness and chemical composition followed with microstructure and fractography observation on the fracture surface then conducted in order to analyze the reason for this brittle fracture occurrence. Results indicate that, while the bolt conforms to the material specification in term of chemical composition, the hardness value was high. The microstructure observation reveals a transgranular crack propagation and cleavage failure occurred. The cleavage failure was clearly observed under fractography observation using scanning electron microscope. Failed galvanize layer due to mechanical failure becomes preferential site for hydrogen evolution in marine environment, which leads to hydrogen diffusion into the matrix, thus results in hardness increase. The increasing stress during installation become detrimental to the bolt and facilitate the hydrogen induce cracking. Detrimental effect of hot dip galvanize layer is pointed out in the application of high strength material in marine environment.
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