Search

In order to study the effects of notched parameters on the hydrogen embrittlement (HE) behaviors of pipeline steel in hydrogen-blended natural gas environments, the mechanical properties of notched X80 steel specimens with various depth (δ), angle (ω) and curvature radius (ρ) were studied using slow strain rate tensile (SSRT) tests combined with scanning electron microscope (SEM) and finite element analysis (FEA). The tests indicate that the presence of notches greatly reduces the fracture strain, and increases the sensitivity of the specimen to HE. The geometric shape of the notch greatly affects the HE sensitivity of the notch specimen. The sharper the geometric shape of the notch, the higher the hydrostatic stress at the notch root, and the higher the diffusion hydrogen concentration, thereby increasing the hydrogen embrittlement sensitivity of the specimen. In addition, specimen with shallow notches also exhibits high hydrogen embrittlement sensitivity due to its shorter hydrogen atom diffusion distance. • The sharper the notch geometry, the higher the hydrogen embrittlement sensitivity. • The shallower the notch, the easier hydrogen atoms accumulate at the notch root. • The hydrostatic stress distribution affects hydrogen concentration distribution. • The lower stress concentration, the lower hydrogen embrittlement sensitivity. [ABSTRACT FROM AUTHOR]

Intracrystalline diffusion is an invaluable tool for estimating timescales of geological events. Diffusion is typically modeled using gradients in chemical potential caused by variations in composition. However, chemical potential is derived for uniform pressure and temperature conditions and therefore cannot be used to model diffusion when there are gradients in stress. Internal stress variations in minerals will create gradients in strain energy which, in addition to gradients in composition, will drive diffusion. Consequently, it is necessary to have a method that incorporates stress variations into diffusion models. To address this issue, we have derived a flux expression that allows diffusion to be modeled in ionic, crystalline solids under arbitrary stress states. Our approach is consistent with standard petrological methods but instead utilizes gradients in a thermodynamic potential called "relative chemical potential." Relative chemical potential accounts for the lattice constraint in crystalline solids by quantifying changes in free energy due to the exchanges of constituents on lattice sites under arbitrary stress conditions. Consequently, gradients in relative chemical potential can be used to model diffusion when pressure is not uniform (i.e., under conditions of non-hydrostatic stress). We apply our derivation to the common quaternary garnet solid solution almandine–pyrope–grossular–spessartine. The rates and directions of divalent cation diffusion in response to stress are determined by endmember molar volumes or lattice parameters, elastic moduli, and non-ideal activity interaction parameters. Our results predict that internal stress variations of one hundred MPa or more are required to shift garnet compositions by at least a few hundredths of a mole fraction. Mineral inclusions in garnet present a potential environment to test and apply our stress-driven diffusion approach, as stress variations ranging from hundreds of MPa to GPa-level are observed or predicted around such inclusions. The ability to model stress-induced diffusion may provide new information about the magnitudes of both intracrystalline stresses and the timescales during which they occurred, imparting a better understanding of large-scale tectono-metamorphic processes. [ABSTRACT FROM AUTHOR]

In this work, small-scale, low-cycle fatigue experiments on hydrogen charged nickel specimens are performed that highlight particular grain boundaries (GBs) and triple junctions as potential intergranular crack initiation sites. To understand the micromechanics and underlying physics, a dislocation density-based crystal plasticity model coupled with slip-rate based hydrogen transport model is developed. A fatigue indicator parameter (FIP) is also developed that models the crack initiation process by considering the contributions of accumulated plastic slip, GB normal stress, and local hydrogen concentration. Depending on the diffusivity, hydrogen binding energy, and misorientation, GBs are categorized as 'special' or 'random', and their role on hydrogen distribution is analysed using a model microstructure. Special GBs are ones with low diffusivity and high hydrogen binding energy whereas the random GBs have high diffusivity but low hydrogen binding energy. Complying with the experimental observations, the evolution of FIP with load cycles suggests certain triple junction configurations in the microstructure involving in the crack initiation process. For the case of uniform initial hydrogen concentration, special GBs are found to retain more hydrogen with load cycles primarily due to their low hydrogen diffusivity whereas the random GBs diffuse hydrogen out quickly to the bulk. The high hydrogen concentration and favourable stress state in the form of high hydrostatic stress spots generally found at triple junction of special/random GBs fulfil the necessary condition leading to an intergranular crack initiation. • Fatigue experiments on H charged samples performed to understand crack initiation. • Role of grain boundaries and triple junctions on intergranular cracking is analysed. • A coupled crystal plasticity and hydrogen transport model is developed. • A fatigue indicator parameter (FIP) considers HELP, HEDE, and HELP + HEDE mechanisms. • Regions of high hydrogen & hydrostatic stress are potential crack initiation sites. [ABSTRACT FROM AUTHOR]

Electromigration (EM) has become one of the most significant challenges considering longterm reliability in integrated circuit design. The problem is caused by the large current density in circuit interconnections. However, in most cases, we are interested in the EM stress at specific points of the interconnect, such as vias, junctions and boundaries. As a result, Model Order Reduction (MOR) techniques can provide attractive methodologies to reduce the complexity of the original systems. System-theoretic techniques like Balanced Truncation (BT) offer very reliable bounds for the approximation error, compared to moment-matching methods. In this paper, we apply a computationally efficient Low-Rank BT procedure based on the extended Krylov subspace method, that can handle large-scale models and significantly accelerate the EM stress analysis for any general interconnect or power grid structure. For the experimental evaluation, we first consider a general structure interconnect tree to demonstrate the generalizability of the proposed method and then we employ our method on the industrial IBM power grid benchmarks where the its scalability is shown. For the latter, we demonstrate that our method can achieve a speedup up to 238 × over a standard transient analysis method and a speedup up to 15 × over COMSOL, while exhibiting negligible error. • Practical numerical approach that can be applied on general multi-segment structures. • Accurate results within a predefined error bound by using Balanced Truncation. • Efficient reduction by using low-rank EKS method for solving the Lyapunov equations. • Reusable reduced models for different electromigration stress scenaria. [ABSTRACT FROM AUTHOR]

Slow strain rate tensile tests under hydrogen cathodic charging are conducted on 17-4 PH steel with two surface conditions: mirror polished and ball-burnished. In both cases, significant subcritical cracking initiating at the surface is observed leading to considerable reduction in elongation to fracture. However, ball-burnished specimens show better elongation and much less secondary cracking than the polished ones. Ball-burnishing introduces high compressive residual stresses in the specimen sub-surface. However, EBSD showed a very limited impact of ball-burnishing on the microstructure, so little effect on hydrogen trapping is expected. The beneficial effect of ball-burnishing on the resistance of the hydrogen assisted cracking is mainly explained by the high compressive longitudinal stress at the specimen surface, which makes crack initiation more difficult and hence delays specimen failure. In addition, it is estimated that the amount of hydrogen introduced at the specimen surface is decreased by approximately 30% due to the high compressive hydrostatic stress. [Display omitted] • Ball-burnished specimens are mechanically tested in hydrogen-rich environment. • Ball-burnishing results in high compressive residual stress and limited roughness. • A better resistance to HE is observed when specimens are ball-burnished. • The introduction of CRS at the surface delays the specimen failure. [ABSTRACT FROM AUTHOR]

• Effect of the hydride eigenstrain and dislocations on hydride growth is modeled. • Stress functions are derived using the strain nucleus model and elastic complex potential method. • The hydrogen transport governed by stress-assisted diffusion is analytically solved. • The autocatalysis and new-nucleation-locus effects raised by the in-situ observations are analytically explained. The formation of hydrides can significantly decrease the mechanical reliability of Zr servicing in the nuclear reactor. This study investigates the effect of the local stress field resulting from the hydride eigenstrain and dislocations on hydrogen transport and explores the hydride growth regulation. The stress functions, which can be extended and further applied to the realistic crystal structure and servicing status, are derived using the dislocation-based strain nucleus model and elastic complex potential method. The nonhomogeneous equation of hydrogen transport governed by diffusion and hydrostatic stress gradient is analytically solved. The results show that: (1) In the absence of dislocations, the hydride grows toward 11 2 ¯ 0 direction under the hydrostatic stress gradient resulting from the hydride eigenstrain. (2) The lower the temperature is, the higher the hydrogen concentration gradient in the adjacent area of the hydride is. The higher hydrogen fraction can also accelerate the growth rate. (3) Dislocation defects are capable of inducing triangle-shaped and asymmetric growth tendencies and providing new nucleation loci for hydrides. Based on the significant hydrostatic stress gradient led by dislocation singularity, this study analytically explains the autocatalysis and new-nucleation-locus effects raised by the in-situ observations. [ABSTRACT FROM AUTHOR]

• HE of an AISI 4340 steel was evaluated using two different methodologies: nSSRT and CLT. • Threshold stress in CLT can be assumed to be 90 % of the minimum stress found in the nSSRT. • The hydrostatic stress peak is comparable to the intergranular fracture region, suggesting a higher hydrogen concentration. • A correlation between the fracture surface appearance and HEI σ_SSRT was done. The assessment of hydrogen embrittlement (HE) susceptibility in high-strength steels, intended for use in subsea components that are exposed to cathodic protection for corrosion control, is of great importance. Therefore, the present study investigates the behavior of AISI 4340 steel with hardness of 32, 36 and 40 HRC. The investigation involves employing slow strain rate test (nSSRT) and constant load test (CLT) on notched specimens with three different notch root radii. These tests were carried out under two different levels of cathodic protection (−1100 and −950 mV Ag|AgCl) in a 3.5 % wt NaCl aqueous solution. The outcomes from the tests on notched specimens were compared with the hydrostatic stress profile obtained through finite element analysis (FEA). Additionally, the post-test fracture surfaces were analyzed using scanning electron microscopy (SEM). The test results revealed a higher hydrogen embrittlement index (HEI) with increasing material hardness and the applied cathodic potential. Moreover, a smaller notch radius was associated with a higher HEI. A clear correlation was observed between HEI and the extent of intergranular fracture in the test samples. Furthermore, the results from the nSSRT tests were correlated with the threshold stress (σ th) obtained from CLT. It was evident that a relationship of σ th = 90 %σ nSSRT_min could be employed for a faster determination of this parameter. [ABSTRACT FROM AUTHOR]

• Coupled hydrogen transport implemented in a novel explicit scheme. • Numerical limitations circumvented by the chemical potential formulation. • User-defined subroutines in ABAQUS Explicit general to all element. • Results validated against implicit frameworks. • Stress-dependent hydrogen uptake is naturally captured. Hydrogen embrittlement prediction demands a numerical framework coupling a damage model with local hydrogen concentration. The inherent nonlinearity in hydrogen-stress-damage interactions challenges convergence in implicit schemes. To address this limitation, we propose a novel chemical potential-based explicit formulation for simulating hydrogen transport in metals. Our approach exploits a heat transfer analogy, linking mechanical and hydrogen transport via inelastic energy as a heat source. By employing chemical potential rather than lattice concentration, our method eliminates the need for user-defined boundary conditions and hydrostatic stress gradient determination. We integrate a VUMATHT subroutine for diffusion modelling and a VUMAT subroutine for material behaviour, coupling stress and strain rates as a heat source for diffusion. Validating against a classical benchmark, we compare our explicit approach with hydrogen concentration-based methods in ABAQUS Standard and Comsol Multiphysics. Stability conditions are assessed for different mesh sizes and mass scaling densities and the capabilities of our approach are showcased for 3D simulations of notched tensile specimens. Our framework offers a novel and efficient pathway for integrating hydrogen transport with user-defined material behaviour, promising advancements in hydrogen-informed damage models. [Display omitted] [ABSTRACT FROM AUTHOR]

• Tubular specimens of AM 18NI300 maraging steel were subjected to multiaxial loading. • Fatigue life of AM 18Ni300 maraging steel is insensitive to axial-torsion phase shift. • Lifetime prediction model was built based on physics-constrained Gaussian process. • Inherent surface defects play a key role in fatigue of AM 18Ni300 maraging steel. The study aims to estimate the role of surface defects in the fatigue life of age-hardened and unmachined additively manufactured 18Ni300 maraging steel and to verify the effectiveness of stress-based life prediction models. Axial-torsional cyclic loading paths involving in-phase and out-of-phase cases are applied. Scanning electron microscopy and micro-computed tomography are performed to detect the fatigue crack initiation sites and paths. The effectiveness of the classic models and a physics-constrained Gaussian process for regression in fatigue life prediction is estimated. Results show that the intrinsic orientation of the surface defects affects the fatigue mechanism by increasing the material sensitivity to axial stress. Additionally, the steel is insensitive to the phase shift between the axial and torsional loading components. The hydrostatic stress and the integrated shear stress amplitudes over the critical plane are pointed as the most effective load-related quantities for life prediction. [ABSTRACT FROM AUTHOR]

[Display omitted] • The α" plates induced by hydrostatic pressure form self-accommodation morphologies via {1 1 1} twinning. • A peculiar hierarchical microstructure was induced in the Ti-30Zr-10Nb alloy by hydrostatic pressure. • The hierarchical microstructure effectively coordinates both isotropic macroscopic strains and local shear stresses. • The hydrostatic pressure facilitates the β to ω transformation but hinders the β to α" transformation. Hydrostatic pressure is a crucial tool to regulate the structure and properties of materials. However, the influence of hydrostatic pressure on the microstructure of metastable β-Ti alloys remains unclear. In this work, the microstructure and microhardness evolution of a metastable β-type Ti-30Zr-10Nb alloy under hydrostatic pressure (≤10 GPa) were investigated and compared with those under uniaxial pressure (≤1106 MPa). The results revealed that under hydrostatic pressure, Ti-30Zr-10Nb alloy formed a peculiar hierarchical microstructure composed of submicron-scaled α" plates with self-accommodating morphologies, nanoscale ω particles, and microscale shear bands containing nanoscale α" domains. The formation of a hierarchical microstructure effectively coordinates not only the isotropic macroscopic strains but also the local shear stresses under hydrostatic pressure. Compared to uniaxial pressure, the hydrostatic pressure facilitates the β to ω transformation, but hinders the β to α" transformation. The microhardness of the Ti3010 alloy reaches approximately 319 HV at a hydrostatic pressure of 10 GPa, which is 28 % higher than the highest microhardness obtained under uniaxial pressure. The current results highlight the promising potential of hydrostatic pressure in optimizing the mechanical properties of metastable β-Ti alloys. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) crystal is a third-generation semiconductor material, which is widely used in the fields of radio frequency components, aerospace, new energy vehicles, etc. The anisotropy of 4H–SiC leads to differences in material removal characteristics of different crystal surfaces, which influences the design of process parameters for SiC crystal polishing. A model of single abrasive scratching 4H–SiC crystal was established using molecular dynamics. The effect of scratching speed and depth on the material removal characteristics and the wafer surface morphology was investigated when a single abrasive scratches the C surface and Si surface. Scratching experiments were conducted to verify the model by measuring scratch cross-sectional area, scratch profile, and surface roughness. The simulation results reveal that compared to the Si surface, the distribution range of high hydrostatic stress of the C surface is less, resulting in fewer amorphous atoms and easier dislocation, which means the C surface is more favorable for getting plastic removal and obtaining better surface quality. The experiment data suggested that the C surface has a smaller surface roughness and a friction coefficient, and the cross-sectional area of the scratch is larger than that of the Si surface. Under low-speed conditions, the influence of anisotropy is more pronounced. Consistent with the simulation result, the material removal characteristics of the C surface are better than those of the Si surface when single abrasive scratching 4H–SiC crystal. [ABSTRACT FROM AUTHOR]

Hydride induced embrittlement is one of the main causes for the stress corrosion crack of titanium alloys. The formation process of the hydride at atomic level remains controversial as it is not accessible directly by experiments. In the present work, the formation of titanium hydride is investigated by using a first principles method. By calculating the formation energies of TiH m with various types of H occupation state in HCP and FCC Ti matrix, we show that there exists phase equilibrium between α-Ti-H solid solution and δ/ε hydrides with χ and γ hydrides appearing as metastable phases. The energy barrier for the HCP → FCC structure transformation for the formation of the hydrides decreases with increasing H:Ti ratio m. The structure transformation is accompanied with spontaneous shift of half amounts of the H atoms from the octahedral to the tetrahedral interstices. The energy barrier for the migration of the remaining half of the H atoms from the octahedral to the tetrahedral interstices reduces with increasing m and approaches to a constant value. The hydrostatic compressive stress acting on TiH m , resulted from the H-induced lattice dilation tendency and the constraint of the surrounding matrix, does not facilitate the HCP → FCC transformation and the migration of the H atoms. The present work sheds light on the hydride formation process at atomic level. [Display omitted] [ABSTRACT FROM AUTHOR]

• Hydrogen diffusion model in X80 pipeline steel girth welded zone was established. • The distribution of hydrogen concentration coincides with the hydrostatic stress. • Residual stress has a greater impact than structural inhomogeneity in diffusion. Hydrogen embrittlement failure, caused by hydrogen permeation and diffusion in the girth weld zone of pipelines, is the main obstacle to large-scale hydrogen blending transportation. Accordingly, a three-dimensional model of the girth weld zone of X80 pipeline steel was established. Considering the influence of structural inhomogeneity in the weld zone, multi-field sequential coupling simulation technology was used to analyze the diffusion process of hydrogen under the combined action of the residual stress and hydrogen concentration fields. A synergistic mechanism between hydrogen enrichment, structural characteristics, and residual stress in the weld zone was revealed. The results indicated that the structural inhomogeneity in the girth weld zone and residual stress field significantly influenced the hydrogen concentration distribution. Moreover, for the hydrogen diffusion process at the grain boundaries, the impact of the residual stress was greater than that of the structural inhomogeneity. This study further clarifies the spatial distribution of hydrogen atoms induced by multi-field coupling in the weld zone and provides a reference for the safety assessment of girth weld layers from an engineering perspective. [ABSTRACT FROM AUTHOR]

In this paper, we present a first-order Stress-Hybrid Virtual Element Method (SH-VEM) on six-noded triangular meshes for linear plane elasticity. We adopt the Hellinger–Reissner variational principle to construct a weak equilibrium condition and a stress based projection operator. In each element, the stress projection operator is expressed in terms of the nodal displacements, which leads to a displacement based formulation. This stress-hybrid approach assumes a globally continuous displacement field while the stress field is discontinuous across each element. The stress field is initially represented by divergence-free tensor polynomials based on Airy stress functions, but we also present a formulation that uses a penalty term to enforce the element equilibrium conditions, referred to as the Penalty Stress-Hybrid Virtual Element Method (PSH-VEM). Numerical results are presented for PSH-VEM and SH-VEM, and we compare their convergence to the composite triangle FEM and B-bar VEM on benchmark problems in linear elasticity. The SH-VEM converges optimally in the L 2 norm of the displacement, energy seminorm, and the L 2 norm of hydrostatic stress. Furthermore, the results reveal that PSH-VEM converges in most cases at a faster rate than the expected optimal rate, but it requires the selection of a suitably chosen penalty parameter. [ABSTRACT FROM AUTHOR]

In order to observe type IV fracture occurring in the HAZ fine-grained zone of a modified 9Cr–1Mo steel at high resolution, the creep damage process of a single notched specimen was continuously observed in three dimensions. The initiation, growth and coalescence behaviour of individual creep voids were clearly observed. This was combined with an analysis of the local stress state using the finite element method. Furthermore, all creep voids that could be observed in the final loading stage were traced backward in time to determine the loading stages at which the creep voids were initiated together with the growth behaviour of the individual creep voids. Significant creep void formation was observed a little further in from the bottom of the notch, where the maximum principal and hydrostatic stresses were greatest, while the stress triaxiality was greatest a little closer to the centre of the specimen than the maximum principal and hydrostatic stresses, where significant creep void growth was observed. It was found that the creep voids nucleated at an early loading stage dominated the creep failure of the specimen. The growth behaviour could be well approximated by the model that combined the diffusion law and power creep law with the constraint effect from neighbouring grains. Engineering parameters that describe the progress of type IV damage were also investigated. [ABSTRACT FROM AUTHOR]

This paper describes a modification of Ehlers' model for the inelastic behavior of geomaterials. The newly developed modified model is intended to describe the inelastic behavior of highly porous media such as open-cell foams. The key feature is a subtle change of the yield potential, which allows the correct orientation of the triangularly-shaped yield surface cross sections that depend on the hydrostatic stress state. The model is incorporated into a general framework for isotropic plasticity. An elastic predictor/plastic corrector algorithm is employed to solve the constitutive equations. The necessary analytical derivatives for a Newton update are also given in detail. The model is calibrated using stress and strain data obtained from finite element simulations of a generic highly-porous, open-cell Weaire–Phelan foam. The modified model provides an almost perfect prediction of the yield potential of the generic foam structure. The suggested modeling approach therefore shows great promise for its applicability to a wide range of isotropic porous structures. [Display omitted] • Constitutive model, which accounts for a correct yield surface cross section. • Thermodynamical framework for foam structures with a general return algorithm. • Data-driven approach using generic RVEs of foam structures with realistic geometry. [ABSTRACT FROM AUTHOR]

Junctions are discontinuities in flat grain boundaries that arise in all polycrystalline materials and are thought to play important roles in the response of a grain boundary network to thermal and mechanical loads. A key open question concerns the mechanisms by which solute segregation to junctions impacts properties of the grain boundary. In this work, we investigate the influence of grain boundary facet junctions on solute embrittlement, and we present an analytical model that uses the hydrostatic stress field contributed by dislocations at multiple junctions to describe these effects. Specifically, we study junctions between {112} facets of various lengths in Au 〈 111 〉 Σ 3 tilt grain boundaries. Copper and silver solutes are employed to determine if the effect of junctions on solute segregation and embrittlement is dependent on size relative to the host. Combined, atomistic simulation data and the analytical model show that Cu and Ag have opposite segregation responses to junctions due to the sign of the hydrostatic stress field induced by junctions. However, a positive shift in the embrittling potency is computed near junctions regardless of solute type or the stress state of the segregation site. Hence, for the conditions studied, junctions consistently shift the energetic landscape towards embrittlement. [Display omitted] [ABSTRACT FROM AUTHOR]

An increase in hydrostatic stress improves the plasticity of metallic materials. However, for some special components, such as large thin-walled components with high ribs, excessive hydrostatic stress can cause several problems that make it impossible to prepare such components using plastic forming methods. In this study, the effect of hydrostatic stress on the deformation behavior of large thin-walled components with high ribs was investigated using a combination of numerical simulations and theoretical derivations. The results indicated that excessive hydrostatic stress leads to die failure, causing metal flow difficulties, uneven deformation, inconsistent mechanical properties, and reduced forming accuracy. Therefore, a low-hydrostatic-stress extrusion method was proposed by adjusting the contact friction, metal flow direction and displacement, and force boundary conditions to reduce the hydrostatic compressive stress. These principles are mainly reflected in the following three aspects: First, the size of the difficult deformation zone was reduced by changing the friction conditions from dry friction to fluid friction or boundary friction to reduce the frictional resistance. Second, the high-stress zone was eliminated by changing the metal flow direction, adjusting the strain state from unidirectional to multi-directional flow, shortening the metal flow path, and reducing the metal flow resistance. Third, the strong compressive stress state in the three directions was weakened by regulating the force boundary conditions and changing the loading method from one-way extrusion to multi-directional loading. Based on these principles, a series of new forming technologies have been developed, such as actively counteracting frictional resistance, slotting, and ditching on dies for long-lasting lubrication, multi-directional short-range metal flow, drawing-assisted extrusion, and multi-directional active loading. The adoption of these technologies realizes the labor-efficient formation of large thin-walled components with high ribs and provides the formed members with high precision and uniform mechanical properties. [Display omitted] • The influences of hydrostatic stress on metal flow, forming forces and strains were revealed. • The principle of low hydrostatic stress extrusion was developed, which can be employed to reduce the working stress. • The forming force was reduced, and the deformation uniformity and forming accuracy of thin-walled components were improved. [ABSTRACT FROM AUTHOR]

Utilizing ab-initio modeling, this study analyzes the possibility of replacing Lead with Francium halide perovskite for use in potential photovoltaic or optoelectronic device applications. Density functional theory is employed to estimate the structural, electronic, bonding, optical, anisotropic elastic, and mechanical characteristics of FrNBr 3 (N Ca, Sr) at various hydrostatic stresses scaling from 0 to 80 GPa. The calculation of the tolerance factor validates the structural stability. At 0 GPa pressure, the computed lattice constants for FrCaBr 3 and FrSrBr 3 are 5.78 Å (5.38 Å) and 6.03 Å (5.62 Å), respectively, using GGA (HSE03) approximation potential. FrNBr 3 (N Ca, Sr) perovskites show increased band gap values using the HSE03 method. Notably, these HSE03-derived values align with the trends observed in the GGA-PBE scheme, under both normal and hydrostatic pressure conditions. As pressure increases, both the lattice constant and unit cell volume decrease significantly. The estimated direct band gaps demonstrate the semiconducting nature of the compounds under ambient pressure. However, when pressure increases, the band gap narrows, increasing conductivity, and makes it as one of the great contenders of microelectronics as well as tandem photovoltaics due to its shift from ultraviolet to visible light energy region. Applying pressure enhances the optical properties, showcasing its utility in various semiconductor applications within the visible ranges and overcoming its limited usage in the ultraviolet domain. In the same vein, the application of hydrostatic pressure significantly impacts mechanical properties without compromising stability. The ductile and anisotropy character become more pronounced when pressure is exerted. [Display omitted] • This research investigates the physical characteristics of FrNBr 3 (N Ca, Sr) non-toxic halide perovskites under ambient and high-pressure (0−80 GPa). • The bandgaps narrowing with increased pressure enhancing conductivity for microelectronics and tandem photovoltaics. • Enhanced optical properties under pressure expand their utility in visible range semiconductor applications by overcoming limitations in the ultraviolet domain. • Hydrostatic pressure enhances ductility and anisotropy without compromising mechanical stability. [ABSTRACT FROM AUTHOR]

Continuous silicon carbide fiber-reinforced silicon carbide matrix (SiC f /SiC) composites, used as thermal structures for gas turbines, are prone to degrade under the gas stream (mainly composed of O 2 and H 2 O). Here, the degradation of the composites in wet oxygen environment was investigated by Raman spectroscopy. Results show that the composites exhibit significant residual stress as the oxidation proceeds. SiC matrix in the as-received condition exhibits average hydrostatic tensile stresses of approximately 1350 MPa, while SiC fiber exhibits compression stress of approximately 1450 MPa. Both the residual stresses in matrix and fiber decrease with the increasing oxidation temperature. Moreover, the residual stress evolution is found to be related to the formation of cristobalite and the volatilization of Si(OH) 4 , CO, H 2. This work can open new alternatives for understanding the degradation mechanism of SiC f /SiC composites in gas turbine environment, and for developing mathematical model to predict their service life. [ABSTRACT FROM AUTHOR]

• The stability of a circular tunnel is analyzed using a novel semi-analytical method. • The complex stress conditions and 3D rock mass strength are considered. • The systematic laws of characteristics and distribution of plastic zone are revealed. • Two indices are suggested for the rapid analysis of surrounding rock stability. • The notable linear correlation with the indices is found by numerous cases. The morphological characteristics and distribution range of the plastic zone around tunnels, influenced by the true three-dimensional high geostress environment in deep engineering, constitute fundamental reference data for both tunnel design and the control of surrounding rock stability. Based on the GZZ three-dimensional rock mass strength criteria and the complex variable method, a novel semi-analytical method for solving the plastic zone of a circular tunnel subjected to non-hydrostatic stress is presented. The conformal mapping is employed to intricately transform the complex boundaries of plastic zones characterized by diverse shapes onto the unit circle boundary within the image plane. This framework proves invaluable for the precise analytical process of the complex plastic zone morphology and the plastic influence range within the surrounding rock under complex stress conditions. In contrast to traditional analytical methods, the efficacy and versatility of our proposed approach are substantiated. Notably, it demonstrates unique advantages, particularly in the context of non-hydrostatic stress fields and varied rock mass parameters, with respect to predicting both surrounding rock stability and plastic zone morphology. Through the analysis of numerous cases, the study reveals the systematic patterns of influence that in-situ stress and surrounding rock characteristic parameters have on the shape and maximum depth of the plastic zone. The results indicate that (1) there are notable disparities in the morphology and extent of the plastic zone between the GZZ and GHB criteria; (2) the transition of the plastic zone in surrounding rock from U-shaped to V-shaped is significantly influenced by the geostress-to-strength ratio K σ ; (3) there is a notable linear correlation observed between the maximum plastic zone thickness r max and both K σ and the stress concentration factor K SCF , importantly, this correlation is independent of far-field stress and the brittleness characteristics of the surrounding rock. These findings provide a novel discriminative method for the rapid analysis of surrounding rock stability in deep circular tunnels. [ABSTRACT FROM AUTHOR]

In 1969, Rice and Tracey proposed that the rate of void growth during ductile failure is a strong function of the hydrostatic stress state. Numerous in-situ x-ray computed tomography (XCT) studies demonstrated that the average rate of void growth is well-predicted by modified versions of the Rice-Tracey equation. However, recent in-situ XCT studies of void growth demonstrated that individual voids grow in highly heterogeneous manners in a way that is not predicted by Rice-Tracey or similar models. Model-based studies using crystal plasticity finite element (CP-FE) suggest that local effects of grain orientation play a strong role during void growth, but we lack experimental data to test this hypothesis. The present study leverages recent advances in laboratory-based diffraction contrast tomography (Lab-DCT) and in-situ XCT to systematically examine the effects of grain orientation on void growth experimentally in an Al-2219 alloy. CP-FE modeling was used to assess the local stress states associated with voids and their influence on void growth rates. These data indicate that void growth is not simply controlled by the local hydrostatic stress or stress triaxiality. Additionally, no clear relationship between void growth rates and grain orientation were observed. Instead, void growth rates were highly stochastic in ways that could not be directly linked to the local stress or strain states. The combination of experimental and modeling data suggests that our current assumptions regarding the mechanisms of void growth are flawed and that additional factors, which may include the local dislocation density, affect the rate of void growth. [Display omitted] [ABSTRACT FROM AUTHOR]

The interaction of Zircaloy fuel cladding components with coolant water in a nuclear reactor leads to embrittlement and potentially delayed hydride cracking (DHC). We explore rate controlling mechanisms for the detrimental DHC process via Discrete Dislocation Plasticity (DDP) modelling of an intragranular δ -hydride, informed by Crystal Plasticity Finite Element (CPFE) analysis of a notched Zircaloy-4 (Zr-4) polycrystal. It is believed that nano-hydride plasticity occurs under a background (polycrystalline) stress state that depends on the grain-scale stress re-distribution associated with plastic deformation at a notch. We find that depending on grain size the background stresses can enhance plasticity during hydride growth (cooling), enhancing the residual hydrostatic stresses on hydride dissolution (heating), which encourages local hydrogen accumulation and re-precipitation. This 'memory effect' can be enhanced further by obstacles preventing dislocations from gliding backwards and annihilating during dissolution, highlighting that the discrete nature of plasticity can play important role in the DHC process. Our analysis provides a stepping-stone to modelling interacting nano-hydrides and irradiation effects for supporting the design of better nuclear materials. • We combine CPFE and DDP modelling to explore delayed hydride cracking in Zr alloys. • Nano-hydride plasticity is enhanced by grain-scale background stresses. • Grain-scale background stresses are limited by plasticity at the Zr cladding notch. • Small grains constraint the relaxation of hydride misfit stresses by dislocations. • Obstacles prevent misfit dislocations from annihilating upon hydride dissolution. [ABSTRACT FROM AUTHOR]

The hydrogen diffusion and damage characteristics within the microstructure at the crack tip are direct factors determining hydrogen embrittlement (HE) phenomena, yet research in this area from a mesoscale perspective is still insufficient. This study employs a non-local crystal plasticity constitutive model coupled with a hydrogen diffusion model that considers grain boundary (GB) characteristics and incorporates fracture initiation parameter accounting for the HELP + HEDE mechanisms. The research investigates hydrogen diffusion behavior at the crack tip in pure nickel and provide a detailed exploration of the mechanism underlying hydrogen-assisted crack propagation. The results indicate that the non-local model exhibits advantages in simulating the hydrogen diffusion process. Hydrogen induces intragranular cracks to propagate along slip planes with a high dislocation density. High-energy GBs and triple junctions are more susceptible to hydrogen accumulation, and under the influence of the HEDE mechanisms, they represent the primary sites for crack initiation. The entire fracture process involves the continuous coalescence of primary cracks with secondary cracks. Moreover, the HE resistance is better in equiaxed microstructures compared to rolled microstructures, particularly when the crack plane is parallel to the TD direction. • The hydrogen diffusion behavior in the microstructure at the crack tip was studied. • The interaction between hydrostatic stress and strain induces hydrogen-assisted cracking. • High-energy GBs serve as the primary enrichment sites for hydrogen atoms. • The HE resistance of the rolled microstructures is inferior to the equiaxed ones. [ABSTRACT FROM AUTHOR]

Plastic pipes made of high density polyethylene material with known geometric eccentricities and residual stresses were subjected to long term hydrostatic stress until rupture at different stresses and temperatures. Cooling and crystallisation rates of the pipe wall during the extrusion process were simulated along the production line. Crystallisation profile and circumferential orientation of polymer chains were measured at different angular locations and thicknesses around the circumference. It was shown that the plasticity-controlled rapture times of plastic pipes are significantly depended on geometric eccentricity as a result of re-distribution of residual stresses and circumferential orientation. • Eccentric pipes of OD 32 mm and OD 110 mm were produced using an industrial scale polymer extrusion system. • Heat transfer and cooling phenomena throughout the pipe wall thickness as a function of time/length were simulated. • Re-distribution of residual stresses were measured and linked with the process thermal history. • Crystallinity and molecular orientation were measured as a function of geometric eccentricity. • Creep rapture of concentric and eccentric pipes were measured at different temperatures and internal pressures. [ABSTRACT FROM AUTHOR]

Zirconium transforms from the α→ω phase under high hydrostatic pressures. The critical transformation pressure is expected to be affected by internal stresses associated with defects. This study focuses on the effects of dislocations and twins and their associated stress fields on the transformation. Samples are pre-loaded to seed dislocations or twins. In-situ high-hydrostatic-pressure X-ray synchrotron experiments are performed revealing that microstructures with pre-existing prismatic 〈a〉 dislocations and { 10 1 ¯ 2 } twins promote the transformation more effectively than pyramidal 〈 c + a 〉 dislocations or { 11 2 ¯ 2 } twins. Post-mortem electron backscatter diffraction further shows that pre-seeded defects stabilize the ω-phase at ambient conditions. In-situ stress-hold neutron diffraction experiments are also performed combining both hydrostatic and deviatoric stresses capturing the role of deviatoric stresses on phase transformation kinetics. These results support the findings of recent atomistic simulations indicating flow of prismatic 〈a〉 dislocations at an α-ω interface promotes the growth of the ω domain. Dependence of the α→ω transition under hydrostatic pressure on the prevalence of dislocations and twins within the initial microstructure, and time dependence of the transition when deviatoric stresses are also present. [Display omitted] [ABSTRACT FROM AUTHOR]

• Derived conditions for geomechanical stability of large-diameter deep disposal boreholes. • Numerical code validated with experiments on shale. • Effects of pre-existing cross-borehole fractures on borehole stability derived from 3D models. • Casing requirement for borehole stability derived from analytical solution. Large diameter boreholes drilled to a depth of 1000–2000 m are currently investigated in Australia as a potential solution for waste emplacement and long-term containment for long-lived intermediate-level radioactive waste (ILW). Different potentially suitable types of host rocks are considered, including granite, shale and salt. This study is aimed at assessing the risk of borehole instability for a large diameter deep borehole in shale. The investigation is conducted with numerical simulations using the CSIRO-developed modelling tools FRACOD and FRCAOD3D, and the commercial code Irazu. Previous laboratory experiments on boreholes in deep shale reported in literatures have been used as validation tests of the numerical models. Under hydrostatic stresses, the FRACOD model showed extensive shear-dominated "log-spiral" fractures around a borehole in shale which is similar to the laboratory testings reported in literatures. Subsequently, 2D and 3D numerical models representing a 0.7-m diameter vertical borehole drilled to the depths of 1000 m and 2000 m have been used. "Strong" and "weak" shales are simulated. The strong and weak shales represent the higher and lower ends of the shale strength reported in literature, respectively. Results showed that a "strong" shale exhibited only small borehole breakouts at the depth of 2000 m. The "weak" shale showed large breakouts (>1.5 m) at depths of 1000 m and 2000 m caused by extensive shear fracturing. In the scenario where a pre-existing 3D fracture crosscuts the borehole, the existing fracture may propagate deeper into the rock formation depending on its orientation and on the in situ stress magnitudes. Predictions based on analytical solutions indicate a 0.02-m and 0.04-m thick casing could prevent severe failure of rock mass at 1000 and 2000 m depths, respectively. Insights from model-based investigations of borehole breakouts are critical during the site selection of rocks with suitable geomechanical properties for waste disposal and for optimising the design of large-diameter boreholes for drilling, waste emplacement and long-term safety. [ABSTRACT FROM AUTHOR]

We use the Stroh sextic formalism to solve the generalized plane strain problem associated with a finite incompressible liquid slit lying between dissimilar anisotropic elastic half-planes subjected to a system of uniform remote stresses. The liquid slit admits an internal uniform hydrostatic stress field and is perfectly bonded to the surrounding media. By enforcing the interface conditions on the solid-solid and liquid-solid interfaces, a Riemann-Hilbert problem of vector form is obtained and is solved analytically using a decoupling procedure. An application of the residue theorem following the imposition of the incompressibility condition of the liquid slit leads to the determination of the internal uniform hydrostatic tension within the liquid slit. When the elastic bimaterial is orthotropic, the internal uniform hydrostatic tension is equal to the remote normal stress component perpendicular to the surfaces of the liquid slit. The presence of the liquid slit will inhibit crack growth along the anisotropic elastic bimaterial interface. • Incompressible liquid slit between dissimilar anisotropic elastic half-planes. • Internal uniform hydrostatic stress field and remains perfectly bonded. • Determination of the internal uniform hydrostatic tension within the slit. • Presence of liquid slit inhibits crack growth along bimaterial interface. [ABSTRACT FROM AUTHOR]

In recent years, a new class of super saturated binary and ternary alloys have demonstrated the ability for the self-healing of creep-induced voids formed at the grain boundaries. However, a clear understanding of the parameters affecting the self-healing mechanism is still not yet complete. One of the main challenges is understanding the effect of microstructure and micromechanical stresses on the redistribution of the healing-solute and vacancies. To this end, we address this issue using a CALPHAD-informed diffusion model coupled with crystal plasticity. In principle, the approach is general and can be used for any binary Fe–X alloy, but in this work Fe–Au binary system is used since it experimentally showed the best healing efficiency. First, we present a multicomponent diffusion model considering cross and stress-driven diffusion. The effect of stress was also considered on the equilibrium vacancy concentration. To investigate the effect of the micromechanical stresses, a representative volume element (RVE) was obtained using the phase-field method. The results showed that the maximum vacancy concentration is at the grain boundaries (GBs) with the highest hydrostatic tensile stresses. These were also the regions of the highest Au enrichment. A crucial factor to achieve this is the high diffusivity of Au compared to the Fe matrix. Increasing the stresses, lead to an increase both in vacancy and Au concentration. The accompanying increased stress triaxiality is suggested to be the reason for the reduced self-healing efficiency observed in previous experimental studies. [Display omitted] • A model linking binary diffusion with stresses is presented for Fe–Au system. • Vacancies have maximum concentration at regions with high tensile pressure. • Au gets depleted from less tensile regions towards more tensile ones. • Interaction of stresses, Va and Au on void growth and self-healing is presented. [ABSTRACT FROM AUTHOR]

• Strength–ductility synergy is achieved by lithiation in sulfur cathodes. • Brittle-to-ductile transition in amorphous lithiated sulfur is governed by cavitation nucleation mechanism. • Atomic chain bridging behind the crack tip enhances crack resistance at lower lithium concentrations. As an eminent candidate for next-generation cathode materials, sulfur undergoes severe volume changes during electrochemical cycling, resulting in material fractures and performance degradation. Although the electrochemical characteristics of lithiated sulfur have been rigorously studied, their mechanical properties, particularly fracture mechanisms, remain insufficiently understood. To address this gap, we conducted comprehensive atomistic simulations to investigate the fracture behavior of amorphous lithiated sulfur (a-Li x S). Our findings reveal that as lithium concentration increases, the fracture mechanism transits from brittle governed by nanoscale cavitation instability to ductile dominated by plastic shear bands launched at the crack tip. This transition is contingent upon local hydrostatic stress exceeding the cavitation strength, elucidated through atomic-level bonding dynamics including rupture, reformation and rotation. At low lithium concentrations, atomic chain bridging posterior to the crack tip is simultaneously identified to enhance crack resistance. The lithiation-induced fracture toughness enhancement is further quantified via domain J -integral analysis. Notably, a unique strength–ductility synergy is identified for a-Li x S, attributed to cooperation between lithiation induced heterogeneous bonding environments and atomic chain bridging. This study provides valuable atomic-scale insights into the fracture mechanisms of sulfur cathodes, thereby informing the design of high-energy and durable electrode materials for future applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Interstitial dislocation loops are typically formed in post-irradiated materials, such as Ferritic-Martensitic Fe–Cr alloys. These loops demonstrate solute segregation along their perimeters, effectively pinning the dislocation climb and resulting in high-density, small-sized loops that cause embrittlement. Phase-field simulations were conducted to investigate the behavior of Cr segregation in the stress field of a<100> type and various a/2<111> type interstitial dislocation loops in post-irradiated Fe–10Cr alloy. The study considers the long-range elastic interaction of solute Cr within the stress field of dislocation loops in a cubic elastic anisotropic material. The findings reveal a nonuniform stress distribution along the loop's perimeter depending on the included angle of habit plane normal n and Burgers vector b ; the nonuniformity becomes more pronounced as the Burgers vector deviates from the normal direction. Furthermore, this nonuniform stress induces Cr segregation within regions experiencing tensile stress and Cr depletion in compression stress regions. Furthermore, a comprehensive analytical solution has been developed to characterize the diverse stress fields and solute segregation induced by interstitial dislocation loops with varying habit planes and Burgers vectors. The proposed analytical model effectively depicts the stress distribution of various dislocation loops, resulting in a Cr segregation profile that closely approximates those obtained through phase-field simulations. A thorough analysis of solute segregation mechanisms also elucidates the dispersed fine-scale nature and high density observed in experimental investigations of dislocation loops. • The phase field model of a/2<111> interstitial dislocation loop is established for the first time. • The analytical model of hydrostatic stress field of interstitial dislocation loop is derived. • The phase field model is used to analyze the inhibition effect of Cr segregation on interstitial dislocation loop growth. [ABSTRACT FROM AUTHOR]

The structural reliability of sintered products depends on large defects introduced during powder processing, which cannot be removed by pressureless sintering. Here, we present a model how a large single ellipsoidal void is deformed, and finally disappears by pressure-assisted sintering. Taya-Seidel's model is applied to predict the shrinkage of a large void in a compressible linear viscous material by using bulk viscosity, shear viscosity, and sintering stress that are determined experimentally for sintering of alumina powder at low stress levels. The application of mechanical stress promotes the densification rate. Its effect is maximum for hot isostatic pressing (HIP) and minimum for sinter forging. The effect is intermediate for hot pressing (HP) and spark plasma sintering (SPS), because the hydrostatic component of stress varies with densification. While a crack-like defect can be removed during densification, a spherical void must be eliminated by shear deformation in the final stage during dwell time. [ABSTRACT FROM AUTHOR]

While hydrogen pipelines have attracted increased attention, safety of the pipelines has been a concern in terms of hydrogen embrittlement (HE) occurring upon hydrogen atom (H) generation and permeation in the steels. In this work, thermodynamic analyses regarding H generation and adsorption on pipeline steels by two potential mechanisms, i.e., spontaneous dissociation and dissociative adsorption, were conducted through theoretical calculations based on Gibbs free energy change of the H generation reactions. Moreover, H adsorption free energy and configurations were determined based on density functional theory (DFT) calculations. Effects of H adsorption site, H coverage and hydrostatic stress on H adsorption and absorption were discussed. Spontaneous dissociation of hydrogen gas molecules to generate hydrogen atoms is thermodynamically impossible. Dissociative adsorption is thermodynamically feasible at wide temperature and pressure ranges. Particularly, an increased hydrogen gas partial pressure and elevated temperature favor the dissociative adsorption of hydrogen. Hydrogen atoms generated by dissociative adsorption mechanism can adsorb stably at On-Top (OT) and 2-fold (2F) Cross-Bridge sites of Fe (100), while hydrogen adsorption at 2F site is more stable due to a higher electron density and a stronger electronic hybridization between Fe and H. The influence of H atom coverage on dissociative adsorption occurs at low coverages only, i.e., 0.25–1.00 ML as determined in this work. External stresses make dissociative adsorption more difficult to occur compared with a fully relaxed steel. Both tetrahedral sites (TS) and octahedral sites (OS) can potentially host absorbed H atoms at subsurface of the steel. Absorbed H atoms will be predominantly trapped at TS due to a low energy path and exothermic feature. Diffusion of H atoms from steel surface to the subsurface is more difficult compared with the dissociative adsorption. • Determined the thermodynamic infeasibility of spontaneous dissociation of hydrogen gas molecules in pipelines. • Demonstrated the thermodynamic possibility of dissociative adsorption of hydrogen gas on pipelines. • Determined the charge transfer pattern and formation of hybridization in hydrogen adsorption and absorption processes. [ABSTRACT FROM AUTHOR]

• Subject-specific pediatric femur and growth plate models were developed based on MRI data of one 6-year old child. • Bone growth was simulated for different physical activities (walking, hip flexion, hip fast flexion-extension, hip fast adduction-abduction, stairs up-down, jumping jack, cycling, heel-to-knee running, and heel-to bottom-running). • Growth was simulated in the principal stress growth direction. • Most physical activities evaluated induce the expected femur growth tendencies in an able-bodied child. Longitudinal bone growth is regulated by mechanical forces arising from physical activity, whose directions and magnitudes depend on activity kinematics and intensity. This study aims to investigate the influence of common physical activities on proximal femoral morphological tendency due to growth at the femoral head growth plate. A subject-specific femur model based on magnetic resonance images of one able-bodied 6-year old child was developed, and the directions of hip contact force were described as load samples at a constant magnitude. Finite element analysis was performed to predict growth rate and growth direction, and expected changes in neck-shaft angle and femoral anteversion were computed corresponding to circa 4 months of growth. For most loading conditions, neck-shaft angle and femoral anteversion decreased during growth, corresponding to the femur's natural course during normal growth. The largest reduction in neck-shaft angle and femoral anteversion was approximately 0.25° and 0.15°. Our results suggest that most common physical activities induce the expected morphological changes in normal growth in able-bodied children. Understanding the influence of contact forces during less common activities on proximal femoral development might provide improved guidelines and treatment planning for children who have or are at risk of developing a femoral deformity. [ABSTRACT FROM AUTHOR]

The results of existing constitutive models describing the behaviour of metal powder during compaction processes are very different. This reveals the high sensitivity of the mechanical behaviour of porous materials to the shape, arrangement and distribution of particles and pores. In order to clarify these discrepancies, the compaction behaviour under hydrostatic loads and high temperatures for a Nickel-based superalloy has been characterized. For this characterization, a numerical optimization procedure has been defined. In parallel, finite element models at a mesoscopic level have been built with the aim of estimating the parameters that define the mechanical behaviour of metallic powder under hydrostatic loads. Then a homogenization procedure has been used to compute the macroscopic behaviour of the powder. The results of both the experimental characterization and the mesoscopic models emphasize the limits of the analysed literature constitutive models to reproduce the compaction behaviour of the considered Astroloy powder. Unlabelled Image • High sensitivity of porous materials to shape and arrangement of pores. • Spherical pores show the greatest stability under external hydrostatic stresses. • Voids left by spherical particles are less stable, more prone to densification. • Simple cubic particle configuration fits best the experimental observations. • At high densities, the responses of both FCC and simple cubic are similar. [ABSTRACT FROM AUTHOR]

This study investigates the fracture behavior of plastically deformed quenching and partitioning (Q&P) steel under hydrogen conditions. The experimental results from slow strain rate tensile (SSRT) tests reveal a considerable decrease in elongation with increase of hydrogen traps induced by pre-strains. The effect of pre-strain on hydrogen susceptibility is analyzed through fractography and microstructure measurements. The relative reduction of area decreased from 0.389 at 0 % pre-strain to 0.181 at 12 % pre-strain with hydrogen. For hydrogen-free case, fracture surfaces show typical ductile fracture with shallow dimples by micro-void coalescence induced by phase transformation. For hydrogen-charged specimens, the fractography indicates quasi-cleavage and transgranular fracture at specimen center and brittle-like fracture can be analyzed by the hydrogen-enhanced decohesion. Additionally, the brittle fracture area is enlarged with pre-strain. The mixed fracture between the edge and center of cross-section can be explained using finite element modeling, which calculates the distributions of dislocation density and flux, hydrostatic stress during SSRT at different pre-strains. As an effect of pre-strain in the hydrogen-charged Q&P steel, micro-cracks initiate at transformed martensite with low level of pre-strain, whereas their propagation is blunted at ferrite interface. For specimens with pre-strains exceeding 8 %, the cracks initiate predominantly at the martensite, which propagate through deformed ferrite matrix with high dislocations and trapped hydrogens. Our findings shed light on a new metallurgical design for improving the resistance to hydrogen embrittlement in Q&P steel when pre-strain, hydrogen transport, and phase transformation are properly controlled. The mechanism of the fracture behaviors in respect of a crac initiation and propagation under presence of hydrogen on the plastically deformed Q&P steels. [Display omitted] [ABSTRACT FROM AUTHOR]

Shape effect of nanofillers (NFs) on the properties of nanocomposites has attracted considerable attention in recent research. The present study aims to examine how NF shapes influence the confinement effect of polymer-NF interface on the physical properties of nearby polymer (the interphase). Herein molecular dynamics simulations are performed to capture the shift of interphase properties when NFs change from nanosphere to nanocylinder and nanofilm geometry. A stress analysis is then carried out in the interphase to identify a key parameter for characterizing the stress-property coupling and revealing the pathway of the NF shapes to impact the interphase properties. It is shown that the peak hydrostatic stress σ hyd quantifies the effect of internal stresses on the properties of the interphase. Specifically, the shape transition considered can substantially enhance the peak σ hyd by flattening the stress space in the interphase without largely affecting the polymer-NF interaction. Increased peak σ hyd in turn upshifts the interphase properties and thus, leads to the coupling between the NF shapes and interface confinement effect. [ABSTRACT FROM AUTHOR]

• Increasing the relative vacancy concentration, temperature, and hydrostatic stress decreases the activation free energy barrier and critical radius of the nucleated voids. • Synergistic effects of multiple dislocation pile-ups at dislocation boundary facilitate vacancy condensation to form voids. • The simulation results predicted a size of ∼35 nm for the incipient voids, which is consistent with the experimental value of ∼50 nm. Void nucleation is of great significance in understanding ductile fracture. Recent experiments have shown that voids are nucleated via vacancy condensation and dislocation boundaries are the main nucleation sites. However, it is unclear what role is played exactly by dislocation boundaries in promoting void nucleation. Here we propose a new mechanism for dislocation boundary-induced void nucleation and develop a corresponding model based on the classical nucleation theory and vacancy diffusion theory. The model suggests that void nucleation is mainly influenced by hydrostatic stress, temperature, and relative vacancy concentration, whose contributions are systematically studied. It is also suggested that the vacancy formation energy and the interaction energy of hydrostatic stress and vacancy, which are absent in the previous models and introduced in ours, exhibit a clear tendency to lower the activation free energy barrier. Analysis of the nucleation kinetic suggests that the growth rate of void depends on the vacancy diffusion coefficient and vacancy concentration; the higher the values of these parameters, the faster the growth rate of the void. The kinetic feasibility of the newly proposed mechanism is examined using three-dimensional discrete dislocation dynamics simulations. The results predict that the size of incipient voids nucleated at the dislocation boundary is ∼35 nm, which is consistent with the experimental characterization value of ∼50 nm. Finally, when the relaxation of the dislocation boundary is considered, the synergistic effect is weakened. [ABSTRACT FROM AUTHOR]

In this work, a three-dimensional finite element-based mechanics-diffusion coupling model is developed to determine the stress/strain distribution and hydrogen (H) atom concentration at an unconstrained dent on an X52 steel pipe which is to be used for transport of high-pressure hydrogen gas. Both von Mises stress and equivalent plastic strain concentrations and a high hydrostatic stress gradient exist at the dent. The distribution of H atom concentration coincides with that of the hydrostatic stress. The maximum H atom concentration in the steel lattice locates at the dent bottom, while the distribution of the H atom concentration at metallurgical traps is consistent with that of the equivalent plastic strain. A competitive effect exists between the hydrostatic stress and the plastic strain on the H atom distribution. At low initial H atom concentrations (e.g., 0.001 mol/m3), the equivalent plastic strain dominates the distribution of H atoms. At high initial H atom concentrations (e.g., 0.1 and 1 mol/m3), the hydrostatic stress is more important to determine the distribution of H atom concentration. As the dent depth increases, both the von Mises stress and plastic strain at the dent increases, while the total H atom concentration decreases due to decreased hydrostatic stress. When the internal pressure increases from 5 MPa to 15 MPa, there are slightly increases in von Mises stress, equivalent plastic strain and the total H atom concentration. • A novel numerical model to determine the hydrogen atom distribution at a dent on pipelines. • The effect of internal pressure and dent depth on hydrogen atom accumulation at the dent. • The quantitative evaluation and location of hydrogen atom distribution at the dent. [ABSTRACT FROM AUTHOR]

This study presents a solution for stress redistribution induced by dynamic excavation of a rock tunnel in hydrostatic and non-hydrostatic stress states. Considering rock as an elastic medium, the analytical solution of dynamic excavation unloading was derived in the Laplace transform space utilizing the wave function expansion method and mode decomposition, and transformed into the time domain using the approximate numerical inversion method. The effects of the unloading path (linear, cosine, and exponential), unloading rate, and initial stress state on stress redistribution were analyzed. The analytical results indicated that a high unloading rate led to a high stress concentration and oscillations around the tunnel, and instantaneous dynamic unloading caused 20–30% stress concentration. When dynamic unloading is complete, the stress state around the tunnel converges to the Kirsch solution. The 3D numerical results indicated that deformation of the tunnel boring face increased as the initial stress increased. Moreover, the accumulation and release of strain energy and stress state change paths were analyzed and discussed. The results of this study provide a theoretical basis for understanding the stress adjustment and failure of surrounding rock induced by excavation of deep-buried openings in hydrostatic and non-hydrostatic stress states. [ABSTRACT FROM AUTHOR]

Due to the nanoscale inverse Hall-Petch (H-P) effect, the grain size exerts a significant influence on the mechanical behaviour of the material. The impact of supersonic fine particle bombardment (SFPB) on the mechanical response of γ-TiAl alloy with varying grain sizes was investigated using molecular dynamics simulations. The dislocation density and stress state of the material surface were analyzed before and after SFPB treatment. The results indicate that the degree of grain refinement in the matrix varies depending on the grain size following SFPB treatment. In contrast, the critical average grain size for observing the H-P effect is determined to be 9.96 nm. The hardness of the material increases as the average grain size decreases, but it decreases below the critical average grain size. Moreover, monocrystalline samples exhibit the highest hardness and demonstrate greater sensitivity to elastic recovery in both depth and width directions compared to polycrystalline samples. The variation in grain size following SFPB impact influences the distribution of von Mises stress and hydrostatic stress. The present study investigates the grain refinement and mechanical behaviour of polycrystalline γ-TiAl alloys at the atomic scale, thereby offering valuable insights into the SFPB process. • Molecular dynamics is employed to investigate SFPB-induced plastic deformation. • The grain refinement is found in different grain size models after SFPB. • The mechanical properties of different average grain sizes are compared. • The critical average grain size of the inverse Hall-petch effect is 9.96 nm. • Demonstrate the plastic deformation mechanism with different mean grain sizes. [ABSTRACT FROM AUTHOR]

A canonical form of the hydrostatic stress equations for electromigration is proposed to determine the minimum number of parameters to calibrate the model. An efficient probabilistic lifetime checker is developed to determine the wire sizing of interconnect segments. Large networks can be checked on a segment-by-segment basis. To enable efficient evaluation of lifetime, multivariate models are constructed by precomputing the results for all possible interconnect segment geometries, model parameters, and current densities. • The electromigration hydrostatic stress model is calibrated to experimental data. • Machine learning is employed to make a design rule checker for electromigration. • The experimental setup for data collection on electromigration is optimized. [ABSTRACT FROM AUTHOR]

• 1D regenerator model with hysteresis is used to assess caloric cooler's performance. • Modeling of six hypothetical materials with different caloric properties. • Effect of hysteresis is greater on coefficient of performance than on cooling power. • Materials with low isothermal entropy change are very sensitive to hysteresis. • Materials with low specific heat can tolerate high hysteresis values. Caloric cooling relies on reversible temperature changes in solids driven by an externally applied field, such as a magnetic field, electric field, uniaxial stress or hydrostatic pressure. Materials exhibiting such a solid-state caloric effect may provide the basis for an alternative to conventional vapor compression technologies. First-order phase transition materials are promising caloric materials, as they yield large reported adiabatic temperature changes compared to second-order phase transition materials, but exhibit hysteresis behavior that leads to possible degradation in the cooling performance. This work quantifies numerically the impact of hysteresis on the performance of a cooling cycle using different modeled caloric materials and a regenerator with a fixed geometry. A previously developed 1D active regenerator model has been used with an additional hysteresis term to predict how modeled materials with a range of realistic hysteresis values affect the cooling performance. The performance is quantified in terms of cooling power, coefficient of performance (COP), and second-law efficiency for a range of operating conditions. The model shows that hysteresis reduces efficiency, with COP falling by up to 50% as the hysteresis entropy generation (q hys) increases from 0.5% to 1%. At higher working frequencies, the cooling performance decreases further due to increased internal heating of the material. Regenerator beds using materials with lower specific heat and higher isothermal entropy change are less affected by hysteresis. Low specific heat materials show positive COP and cooling power up to 2% of q hys whereas high specific heat materials cannot tolerate more than 0.04% of q hys. [ABSTRACT FROM AUTHOR]

We establish the existence of an internal uniform hydrostatic state of stress inside a coated non-parabolic open elastic inhomogeneity when the surrounding matrix is subjected to a concentrated couple and uniform remote in-plane stresses. The proof of existence is accomplished through analytic continuation and the introduction of a specialized form of the conformal mapping function containing an infinite number of first-order poles. The complex constants appearing in the mapping function can be uniquely determined from a resulting set of non-linear recurrence relations for given material, geometric and loading parameters. The convergence criterion for the series in the mapping function is rigorously established. A simple condition on the remote loading in the matrix is found for given elastic constants of the inhomogeneity and the matrix in order to ensure that the internal stresses inside the non-parabolic inhomogeneity are uniform and hydrostatic. The analysis indicates that the internal uniform hydrostatic stress field, the constant mean stress in the coating and the constant hoop stress along the inhomogeneity-coating interface on the coating side are all independent of the specific open shapes of the two interfaces and are also independent of the existence of the nearby concentrated couple. However, the non-parabolic open shapes of the two interfaces are significantly influenced by the concentrated couple. We also accomplish the design of an uncoated non-parabolic harmonic elastic inhomogeneity in the presence of an arbitrary number of concentrated couples applied in the matrix. [ABSTRACT FROM AUTHOR]

Supersaturated solid solutions subjected to severe plastic deformation often exhibit decomposition of the solid solution, leading to a peculiar grain boundary phenomenon, the formation of few nanometer thin layer enriched in solute atoms along grain boundaries. Based on localized grain boundary sliding, this phenomenon can be explained by the formation of hydrostatic stress field, which induces up-hill diffusion in the solute atmosphere, resulting in solute atom accumulation along the stressed grain boundaries. Image, graphical abstract [ABSTRACT FROM AUTHOR]

To theoretically analyze the effects of voids and inner pressure on the nonlinear deformation behavior of porous metallic materials, a yield criterion related to the von Mises stress and hydrostatic stress has been developed based on variational approach. Under different stress triaxial loading conditions, the proposed criterion is applied to analyze the yield surface of porous single crystal with various porosities and inner pressures. It is revealed that the existence of voids and inner pressure significantly reduces the size of yield surface for porous single crystal under high stress triaxial loading, whereas this effect is insignificant in the case of low stress triaxiality. Furthermore, by considering the effect of inner pressure on the effective shear stress of dislocation movement, a modified crystal plastic theory is adopted to evaluate the plastic deformation behavior of porous single crystal with inner pressure. Combining the self-consistent theory, the influence of voids and inner pressure on the yield strength and flow stress of polycrystalline materials have been obtained. Numerical results of proposed criterion can match well with corresponding results of the finite element simulation and experiment, indicating the good accuracy and rationality of the proposed criterion. [ABSTRACT FROM AUTHOR]

• A modified version of the homogeneous anisotropic hardening (HAH) model is proposed. • The yield condition and state variable evolution equations are improved. • The influence of the hydrostatic stress is incorporated in the formulation. • The model is applied to the hardening description of a dual-phase DP780 steel sheet. • The model results successfully capture the physical experiments. An improved distortional plasticity framework that describes the anisotropic hardening occurring during strain path changes, such as the Bauschinger and cross-loading effects, is developed. This approach is a modified version of the homogeneous anisotropic hardening (HAH) framework proposed almost a decade ago. In the present formulation, the yield condition includes an alternative description of the distortion suggested by crystal plasticity simulation results. In addition, it incorporates the influence of the hydrostatic pressure, which manifests itself by a higher flow stress in uniaxial compression than in tension. The state variable evolutions are modified compared with the previous HAH version to improve the material response when the strain path changes occur near a pure cross-loading condition. The model is calibrated on a DP780 dual-phase steel sheet sample using the data of a tension-compression test with three full cycles, as well as a sequence of two uniaxial tension segments in different directions. After calibration, predicted and experimental stress-strain curves obtained for independent loading sequences are compared and shown to be good agreement. Finally, theoretical predictions of two-step tension tests using the constitutive coefficients of DP780 are discussed to highlight the improvement offered by this enhanced framework. [ABSTRACT FROM AUTHOR]

To further understand the internal residual stress that is microscopically generated via martensitic transformation in steels, the origin of internal strain attributed to Bain correspondence between face-centered cubic (fcc) and body-centered cubic (bcc) was evaluated from macro- and micro-viewpoints and its effect on hardness was investigated in an interstitial free Fe-16%Ni martensite. Neutron diffractometry and electron backscatter diffraction analysis showed that body-centered cubic (bcc) crystal structure of as-quenched martensite contained elastic distortions leading to small tetragonality, even in martensitic steels without solute carbon, and that the extended [001] bcc of martensite tended to be parallel to <001> fcc of prior fcc austenite. In addition, the combination of micro-scale focused ion beam (FIB) and high-precision digital image correlation techniques revealed that a micropillar fabricated by FIB processing within a martensite block was anisotropically deformed by the release of the residual strain distributed in as-quenched martensite in correspondence with the tetragonal distortions of the bcc crystal structure. These results prove that a small part of the Bain strain remained as an internal elastic residual strain and was microscopically distributed among Bain groups in lath martensite after martensitic transformation. Furthermore, the residual strain generated a hydrostatic internal stress, and therefore, the nanohardness decreased considerably by the micropillar fabrication accompanied by the release of the internal stress. This means that the internal residual stress in martensite among Bain groups influences the mechanical properties of martensitic steel. Image, graphical abstract [ABSTRACT FROM AUTHOR]

This study investigated the effects of hydrostatic compressive stress in retained austenite (RA) on mechanical properties and hydrogen embrittlement (HE) of the martensitic steels. It was found that a high hydrostatic compressive stress in RA, which was produced by the martensitic transformation, lead to an improvement of ductility for the steels without hydrogen. However, the mechanical properties were different after hydrogen charging. The low hydrostatic compressive stress in RA had little effect on HE resistance, but the high hydrostatic compressive stress (231 MPa) induced the twinning of RA and resulted in the aggravation of the HE sensitivity. Moreover, the detwinning of RA via tempering improved the HE resistance. • The nanotwins retained austenite formed via sub-zero treatment. • High hydrostatic stress leads to an excellent ductility without hydrogen. • The nanotwins retained austenite steel had low hydrogen embrittlement resistance. [ABSTRACT FROM AUTHOR]