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Effect of hydrogen on the mechanical response and fracture locus of commercial TWIP steel was investigated comprehensively by tensile testing TWIP steel samples at room temperature and quasi-static regime. 5 different sample geometries were utilized to ensure different specific stress states and a digital image correlation (DIC) system was used during tensile tests. Electrochemical charging method was utilized for hydrogen charging and microstructural characterizations were carried out by scanning electron microscope. Stress triaxiality factors were calculated throughout the plastic deformation via finite element analysis (FEA) based simulations and average values were calculated at the most critical node. A specific Python script was developed to determine the equivalent fracture strain. Based on the experimental and numerical results, the relation between the equivalent fracture strain and stress triaxiality was determined and the effect of hydrogen on the corresponding fracture locus was quantified. The deterioration in the mechanical response due to hydrogen was observed regardless of the sample geometry and hydrogen changed the fracture mode from ductile to brittle. Moreover, hydrogen affected the fracture locus of TWIP steel by lowering the equivalent failure strains at given stress triaxiality levels. In this study, a modified Johnson-Cook failure mode was proposed and effect of hydrogen on damage constants were quantified. • Hydrogen degraded the mechanical properties regardless of the sample geometry. • Hydrogen enhances the microstructural activities. • Hydrogen affects fracture locus of TWIP steel significantly. • Hydrogen reduces equivalent fracture strains at given stress triaxiality levels. [ABSTRACT FROM AUTHOR]

Effects of hydrogen and temperature on impact response and corresponding microstructure of aluminum (Al) 7075 alloy were investigated under medium strain rate impact loading. The specimens were subjected to impact energy of 12 J and 25 J, corresponding to impact velocities of 2.13 m/s and 3.08 m/s, respectively. These energy levels were decided after a couple of impact tests with different impact energy values, such as 6 J, 10 J, 12 J, 25 J. The experiments were conducted at five different temperatures. Electrochemical charging method was used for hydrogen charging. Microstructural observations of hydrogen uncharged and hydrogen charged specimens were carried out by scanning electron microscope. Hydrogen changed the crack propagation behavior of Al 7075 alloy depending on the temperature. Coexistence of several hydrogen embrittlement mechanisms, such as hydrogen enhanced decohesion (HEDE) and hydrogen enhanced localized plasticity (HELP) were observed under impact loading. The impact response of Al 7075 was significantly deteriorated by the hydrogen charging and changing temperature affected the absorbed energy of hydrogen-charged specimens. In addition, molecular dynamics simulations were conducted to uncover the atomistic origin of hydrogen embrittlement mechanisms under impact loading. In particular, hydrogen decreased the cohesive energy and enhanced the average dislocation mobility. Therefore, the experimental results presented herein constitute an efficient guideline for the usage of Al alloys that are subject to impact loading in service in a wide range of temperatures. • Hydrogen embrittlement is observed under impact loading. • Impact toughness and ductility are degraded by hydrogen charging. • Coexistence of several hydrogen embrittlement mechanisms is observed. • Atomistic simulations are performed to better understand embrittlement mechanisms. • Hydrogen increases the avarage dislocation mobility and reduces the cohesive energy. [ABSTRACT FROM AUTHOR]

The Hydrogen Enhanced Localized Plasticity (HELP) mechanism is one of the most important theories explaining Hydrogen Embrittlement in metallic materials. While much research has focused on hydrogen's impact on dislocation core structure and dislocation mobility, its effect on local dislocation density and plasticity remains less explored. This study examines both aspects using two distinct atomistic simulations: one for a single edge dislocation under shear and another for a bulk model under cyclic loading, both across varying hydrogen concentrations. We find that hydrogen stabilizes the edge dislocation and exhibits a dual impact on dislocation mobility. Specifically, mobility increases below a shear load of 900 MPa but progressively decreases above this threshold. Furthermore, dislocation accumulation is notably suppressed at around 1 % hydrogen concentration. These findings offer key insights for future research on Hydrogen Embrittlement, particularly in fatigue scenarios. [Display omitted] • Hydrogen increasingly stabilizes the 1/2 <111>{-1-12} edge dislocation core in BCC Fe. • Hydrogen boosts dislocation velocity at low shear levels and diminishes it at high shear levels. • Hydrogen presence reinforces the Fe matrix, leading to suppressed dislocation nucleation in hydrogen-rich areas. [ABSTRACT FROM AUTHOR]

Investigating the interaction between hydrogen and dislocations is essential for understanding the origin of hydrogen-related fractures, specifically hydrogen embrittlement (HE). This study investigates the effect of hydrogen on the mobility of ½<111>{110} and ½<111>{112} edge dislocations in body-centered cubic (BCC) iron (Fe). Specifically, molecular dynamics (MD) simulations are conducted at various stress levels and temperatures for hydrogen-free and hydrogen-containing lattices. The results show that hydrogen significantly reduces dislocation velocities due to the pinning effect. Based on the results of MD simulations, phenomenological mobility laws for both types of dislocations as a function of stress, temperature and hydrogen concentration are proposed. Current findings provide a comprehensive model for predicting dislocation behavior in hydrogen-containing BCC lattices, thus enhancing the understanding of HE. Additionally, the mobility laws can be utilized in dislocation dynamics simulations to investigate hydrogen-dislocation interactions on a larger scale, aiding in the design of HE-resilient materials for industrial applications. [Display omitted] • Effect of hydrogen and temperature on the mobility of edge dislocations is studied. • The effect of hydrogen on kink-pair formation and propagation is discussed. • Thermally activated mechanisms and viscous damping dynamics are discussed. • Hydrogen decreases the mobility of both dislocations via pinning effect. • Hydrogen-induced phenomenological mobility laws are proposed. [ABSTRACT FROM AUTHOR]

The atomistic mechanisms of dislocation mobility depending on the presence of hydrogen were investigated for two edge dislocation systems that are active in the plasticity of α-Fe, specifically ½<111>{110} and ½<111>{112}. In particular, the glide of the dislocation pile-ups through a single crystal, as well as transmission of the pile-ups across the grain boundary were evaluated in bcc iron crystals that contain hydrogen concentrations in different amounts. Additionally, the uniaxial tensile response under a constant strain rate was analyzed for the aforementioned structures. The results reveal that the presence of hydrogen decreases the velocity of the dislocations – in contrast to the commonly invoked HELP (Hydrogen-enhanced localized plasticity) mechanism -, although some localization was observed near the grain boundary where dislocations were pinned by elastic stress fields. In the presence of pre-exisiting dislocations, hydrogen-induced hardening was observed as a consequence of the restriction of the dislocation mobility under uniaxial tension. Furthermore, it was observed that hydrogen accumulation in the grain boundary suppresses the formation of new grains that leads to a hardening response in the stress-strain behaviour which can initiate brittle fracture points. • Atomistic origin of hydrogen embrittlement is studied by molecular dynamics simulations. • Hydrogen decreases edge dislocations mobility by influencing the kink-pair formation. • Pinning effect of hydrogen causes hardening during pre-existing dislocation activity. • Hydrogen decreases the critical stress for dislocations emission and facilitates softening. • Hydrogen inhibits the slip transmission across grain boundary. [ABSTRACT FROM AUTHOR]

Effects of strain rate and hydrogen on crack propagation from a notch were investigated using a Fe-33Mn-1.1C steel by tension tests conducted at a cross head displacement speeds of 10−2 and 10−4 mm/s. Decreasing cross head displacement speed reduced the elongation by promoting intergranular crack initiation at the notch tip, whereas the crack propagation path was unaffected by the strain rate. Intergranular cracking in the studied steel was mainly caused by plasticity-driven mechanism of dynamic strain aging (DSA) and plasticity-driven damage along grain boundaries. With the introduction of hydrogen, decrease in yield strength due to cracking at the notch tip before yielding as well as reduction in elongation were observed. Coexistence of several hydrogen embrittlement mechanisms, such as hydrogen enhanced decohesion (HEDE) and hydrogen enhanced localized plasticity (HELP) were observed at and further away from the notch tip resulting in hydrogen assisted intergranular fracture and cracking which was the key reason behind the ductility reduction. • Effects of strain rate and hydrogen on crack propagation from a notch are studied. • Yield strength and elongation are degraded by hydrogen charging. • Early crack initiation at the notch tip before apparent yielding is observed. • Coexistence of several hydrogen embrittlement mechanisms are observed. [ABSTRACT FROM AUTHOR]

Understanding the dislocation motion in hydrogen atmosphere is essential for revealing the hydrogen-related degradation in metallic materials. Atomic simulations were adopted to investigate the interaction between dislocations and hydrogen atoms, where the realistic hydrogen distribution in the vicinity of the dislocation core was emulated from the Grand Canonical Monte Carlo computations. The depinning of edge dislocations in α -Fe at different temperatures and hydrogen concentrations was then studied using Molecular Dynamics simulations. The results revealed that an increase in bulk hydrogen concentration increases the flow stress due to the pinning effect of solute hydrogen. The depinning stress was found to decrease due to the thermal activation of the edge dislocation at higher temperatures. In addition, prediction of the obtained results was performed by an elastic model that can correlate the bulk hydrogen concentration to depinning stress. [ABSTRACT FROM AUTHOR]