Influence Of External Stress Research Articles

Hydrogen and vacancy concentrations in [formula omitted]-iron under high hydrogen gas pressure and external stress: A first-principles neural network simulation study

The metal-hydrogen-vacancy interaction in α-iron is crucial for understanding hydrogen embrittlement behavior and developing reliable materials for green gaseous hydrogen applications; however, it remains underexplored, particularly in contexts involving external stress and high hydrogen gas pressure. In this study, we performed quantitative analyses of metal-vacancy–hydrogen interactions in α-iron, measured by hydrogen solubility and the thermodynamics of vacancy–hydrogen complexes, under such challenging conditions using a reliable first-principles neural network potential. High hydrogen gas pressures reaching up to 2 GPa were investigated. As the atomic concentration surpasses approximately 0.01, hydrogen solubility is dominated by hydrogen-induced lattice distortion (primarily volumetric expansion) and the interactions between hydrogen atoms within the metal matrix, resulting in significant deviations from Sieverts’ law. Our results reveal a significant effect of shear stress on hydrogen solubility, deviating from previously used equations. Moreover, the influence of external stress on the thermodynamics of the vacancy–hydrogen complex, particularly vacancy formation free energy, is uniquely characterized by hydrogen solubility, regardless of the external stress magnitude. It thereby offers a rapid method to estimate the vacancy properties under external stress based on readily accessible external-stress-free data.

Morphology evolution of P-Ti3AlC carbides and their influence on creep properties in a crept Ti-45Al-5Nb-0.75C alloy

In this study, the influence of the Ti3AlC carbide morphology on the creep properties, the interaction between carbides and dislocations during creep deformation as well as the influence of external stress on carbide morphology evolution were investigated in a Ti-45Al-5Nb-0.75C alloy. The results show that the best creep properties are obtained after annealing at 800 °C for 336 h. This is probably due to the splitting of the carbides into conglomerates of sub-particles, which provides an increased number of interfacial area and interfaces to hinder dislocation glide. After prolonged annealing for 1054 h at 800 °C, although the carbide splitting still existed, the matrix grains coarsened and the lamellar structure was decomposed, which counteracted the positive effect of carbide splitting and led to a reduction in the creep resistance. By comparing the carbide morphology evolution after creep and after annealing alone, it can be concluded that the external stress does not significantly affect the morphology evolution. During creep at 800 °C the Ti3AlC carbides obviously interact with dislocations, and the majority of them were identified to be ½<110] ordinary dislocations. The glide of these dislocations was strongly hindered, and thus the creep properties of the alloy can be improved by carbide precipitation.

Analysis of fracture structure evolution of bituminous coal subjected to in situ steam pyrolysis combined with in situ micro-computed tomography technology

ABSTRACT Underground in situ pyrolysis mining of coal will be a new trend for utilizing coal resources in the future. Steam heating is a feasible and key technology used in this process. Investigating the evolution mechanism of microstructural parameters during coal in situ steam pyrolysis is essential. The influence of external stress on microstructural parameters of coal has not been considered in previous studies. Herein, the permeability and fracture structure parameters of bituminous coal subjected to in situ steam pyrolysis were studied using a high-temperature and high-pressure triaxial testing machine combined with in situ micro-computed tomography (micro-CT) technology. Moreover, the advantages of steam pyrolysis were revealed by comparing it with the natural pyrolysis process. Results showed that (1) the evolution law of fracture ratio and the proportion of large fractures (equivalent fracture diameter R >100 μm) with temperature is consistent. The proportion of large fractures has a considerable impact on the fracture ratio. (2) From 25°C to 600°C, the permeability and fracture structure parameters of bituminous coal exhibit an “increase – decrease–increase” trend with increasing temperature. The threshold temperature points for changing fracture structure parameters are 300°C and 400°C. The promoting effect of pyrolysis on fracture structure parameters competes with the inhibition effect of external stress on fracture development, determining the evolution law of fracture structure parameters with temperature. (3) The threshold temperature zone where the microstructural parameters change considerably is 400°C–600°C. The fracture ratio, proportion of large fractures, and permeability of coal increase considerably. (4) Unlike natural pyrolysis, steam pyrolysis promotes the advancement of threshold temperature point. After 450°C, steam pyrolysis promotes the development of large fractures (R >100 μm) and the fracture ratio is about twice that observed in case of natural pyrolysis. These findings provide theoretical support for the engineering practice of coal in situ underground pyrolysis mining and are of great importance to the development of micromechanics.

Анализ воздействия ветровой нагрузки на каркас теплицы для выращивания сеянцев с закрытой корневой системой

Reforestation is one of the priorities of the state policy of the Russian Federation. Artificial recreation of forests, including a closed root system seedling cultivation technology, has shown its high efficiency in the conditions where natural recovery didn’t develop at the proper extent, especially in the areas affected by large-scale clearcuts and crown fires. Despite the high cost of the closed root system seedling cultivation technology, it is economically viable due to the high survival rate of the plants and the possibility to carry out the planting process over a long period of time. The industrial greenhouses are used for this technology and their construction engineering must consider the influence of external stress, including wind load that depends on the territorial location of the structure. The purpose of the study is to justify the construction characteristics of a greenhouse frame with a sufficient strength for the cultivation of seedlings with the closed root system. The object of the study is a rigid frame model of the greenhouse. The study was performed in the climate conditions of the Krasnoyarsk Krai. The stress and strain analyss are made on the greenhouse construction elements under the conditions of their own weight and wind load using the method for solid modelling. The principal and the peak loads, the dimensions of the most stained areas, the influence of the wind load in these regions are calculated by applying the finite element algorithm for stress analysis simulated in a CAD software. The recommendations for the optimization of the structure are given. For citation: Chernik D.V., Avdeeva E.V., Chernik K.N., Rovnykh N.L. Analysis of Wind Load Effect on Greenhouse Frame for Cultivation Seedlings with Closed Root System. Lesnoy Zhurnal = Russian Forestry Journal, 2023, no. 2, pp. 195–201. (In Russ.). https://doi.org/10.37482/0536-1036-2023-2-195-201

Influence of Mo Segregation at Grain Boundaries on the High Temperature Creep Behavior of Ni-Mo Alloys: An Atomistic Study.

Based on molecular dynamics simulations, the creep behaviors of nanocrystalline Ni before and after the segregation of Mo atoms at grain boundaries are comparatively investigated with the influences of external stress, grain size, temperature, and the concentration of Mo atoms taken into consideration. The results show that the creep strain rate of nanocrystalline Ni decreases significantly after the segregation of Mo atoms at grain boundaries due to the increase of the activation energy. The creep mechanisms corresponding to low, medium, and high stress states are respectively diffusion, grain boundary slip and dislocation activities based on the analysis of stress exponent and grain size exponent for both pure Ni and segregated Ni-Mo samples. Importantly, the influence of external stress and grain size on the creep strain rate of segregated Ni-Mo samples agrees well with the classical Bird-Dorn-Mukherjee model. The results also show that segregation has little effect on the creep process dominated by lattice diffusion. However, it can effectively reduce the strain rate of the creep deformation dominated by grain boundary behaviors and dislocation activities, where the creep rate decreases when increasing the concentration of Mo atoms at grain boundaries within a certain range.

Modeling Bainitic Transformations during Press Hardening.

We revisit recent findings on experimental and modeling investigations of bainitic transformations under the influence of external stresses and pre-strain during the press hardening process. Experimentally, the transformation kinetics in 22MnB5 under various tensile stresses are studied both on the macroscopic and microstructural level. In the bainitic microstructure, the variant selection effect is analyzed with an optimized prior-austenite grain reconstruction technique. The resulting observations are expressed phenomenologically using a autocatalytic transformation model, which serves for further scale bridging descriptions of the underlying thermo-chemo-mechanical coupling processes during the bainitic transformation. Using analyses of orientation relationships, thermodynamically consistent and nondiagonal phase field models are developed, which are supported by ab initio generated mechanical parameters. Applications are related to the microstructure evolution on the sheaf, subunit, precipitate and grain boundary level.

Discussion: Influence of external stress and initial density on the volumetric behavior of an expansive clay during wetting [Environ Earth Sci (2020) 79(10), 211

Discussion: Influence of external stress and initial density on the volumetric behavior of an expansive clay during wetting [Environ Earth Sci (2020) 79(10), 211

Single and bundled carbon nanofibers as ultralightweight and flexible piezoresistive sensors

This work demonstrates the application of electrospun single and bundled carbon nanofibers (CNFs) as piezoresistive sensing elements in flexible and ultralightweight sensors. Material, electrical, and nanomechanical characterizations were conducted on the CNFs to understand the effect of the critical synthesis parameter—the pyrolyzation temperature on the morphological, structural, and electrical properties. The mechanism of conductive path change under the influence of external stress was hypothesized to explain the piezoresistive behavior observed in the CNF bundles. Quasi-static tensile strain characterization of the CNF bundle-based flexible strain sensor showed a linear response with an average gauge factor of 11.14 (for tensile strains up to 50%). Furthermore, conductive graphitic domain discontinuity model was invoked to explain the piezoresistivity originating in a single isolated electrospun CNF. Finally, a single piezoresistive CNF was utilized as a sensing element in an NEMS flow sensor to demonstrate air flow sensing in the range of 5–35 m/s.

Coupling between phase transitions and glassy magnetic behaviour in Heusler alloy Ni50Mn34In8Ga8

The transition sequence in the Heusler alloy Ni50Mn34In8Ga8 has been determined from measurements of elasticity, heat flow and magnetism to be paramagnetic austenite → paramagnetic martensite → ferromagnetic martensite at ∼335 and ∼260 K, respectively, during cooling. The overall pattern of elastic stiffening/softening and acoustic loss is typical of a system with bilinear coupling between symmetry breaking strain and the driving structural/electronic order parameter, and a temperature interval below the transition point in which ferroelastic twin walls remain mobile under the influence of external stress. Divergence between zero-field-cooling and field-cooling determinations of DC magnetisation below ∼220 K indicates that a frustrated magnetic glass develops in the ferromagnetic martensite. An AC magnetic anomaly which shows Vogel–Fulcher dynamics in the vicinity of ∼160 K is evidence of a further glassy freezing process. This coincides with an acoustic loss peak and slight elastic stiffening that is typical of the outcome of freezing of ferroelastic twin walls. The results suggest that local strain variations associated with the ferroelastic twin walls couple with local moments to induce glassy magnetic behaviour.

Influence of external stress and initial density on the volumetric behavior of an expansive clay during wetting

The swelling behavior of expansive clays is widely investigated in the literature, while fewer studies were focused on their collapse behavior under high-stress level during wetting. This paper investigates the development of one-dimensional volumetric strain (e) (1) with time during soaking and (2) with gravimetric water content (w) during wetting over a wide range of initial densities (ρd) and vertical stress (σv) levels, for an expansive clay collected from Nanyang, China. It was found that (1) specimens with high ρd tend to swell during wetting or soaking under low σv. Swelling gradually transfers to collapse with increasing σv and decreasing ρd. The amount of swelling or collapse is sensitive to the σv and ρd; (2) collapse and swelling e–log(t) relationships during soaking are similar and have three distinct stages. They are well described by a unique model; (3) the speed of the volumetric change during soaking is only sensitive to the σv and ρd when the ρd is higher than a threshold value (1.5 Mg/m3 for the investigated clay); (4) during soaking, relationships between the final e, ρd, and log(σv) are linear and continuous from swelling to collapse and are described using a linear equation; and (5) the collapse and swelling e–w relationships during wetting have similar nonlinear characteristics. A simple model was proposed to predict all measured swelling and collapse e–w relationships under various σv and ρd levels using only one set of parameters. Experimental data and models presented in this study contribute to better understanding and predicting the volumetric behavior of expansive clays for the long-term stability and serviceability evaluation of geotechnical structures.

Stresses in Circular Plates with Rigid Elements

Calculations of residual stress fields are carried out by numerical and static methods, using the flat cross-section hypothesis. The failure of metal when exposed to residual stresses is, in most cases, brittle. The presence in the engineering structures of rigid elements often leads to the crack initiation and structure failure. This is due to the fact that rigid elements under the influence of external stresses are stress concentrators. In addition, if these elements are fixed by welding, the residual welding stresses can lead to an increase in stress concentration and, ultimately, to failure. The development of design schemes for such structures is a very urgent task for complex technical systems. To determine the stresses in a circular plate with a welded circular rigid insert under the influence of an external load, one can use the solution of the plane stress problem for annular plates in polar coordinates. The polar coordinates of the points are the polar radius and the polar angle, and the stress state is determined by normal radial stresses, tangential and shearing stresses. The use of the above mentioned design schemes, formulas, will allow more accurate determination of residual stresses in annular welded structures. This will help to establish the most likely directions of failure and take measures at the stages of designing, manufacturing and repairing engineering structures to prevent these failures. However, it must be taken into account that the external load, the presence of insulation can lead to a change in the residual stress field.

Processing, basic characterization and standard dielectric measurements on PLZT x/65/35 (2≤x≤13) ceramics

ABSTRACTThe influence of external stress (0-800bar) on the dielectric properties of PLZT x/65/35 (2≤x≤13) ceramics was investigated. Applying uniaxial pressure leads to a change in the peak intensity of the electric permittivity (ϵ), of its frequency dispersion as well as in the dielectric hysteresis. The peak intensity of ϵ becomes broader and shifts to lower temperatures for PLZT x/65/35 with x = 2, 4, 6, 7, 9.75, 10, 11 and 13, with increasing pressure, on heating. It was concluded that applying uniaxial pressure induces an increase of Tm, and thus has similar effects as the increase of the Ti ion concentration in the PZT system. Results based on nanoregion switching processes under combined electromechanical loading were interpreted. Surveys clearly demonstrated that applied stress has a significant influence on the dielectric properties of PLZT ceramics.

Processing, basic characterization and standard dielectric measurements on PLZT x/65/35 (4 ≤ x ≤ 11) ceramics

The influence of external stress (0–800 bar) on the dielectric properties of lead lanthanum zirconium titanate (PLZT) x/65/35 (4 ≤ x ≤ 11) ceramics was investigated. Applying uniaxial pressure leads to a change in the peak intensity of the electric permittivity (ϵ), in its frequency dispersion as well as in the dielectric hysteresis. The peak intensity of ϵ becomes broader and shifts to lower temperatures for PLZT x/65/35 with x = 4, 7, 9.75 and 11, with increasing pressure, on heating. It was concluded that applying uniaxial pressure induces an increase of Tm, and thus has a similar effect as the increase of the Ti ion concentration in the lead zirconium titanate (PZT) system. Results based on nanoregion switching processes under combined electromechanical loading were interpreted. Studies clearly showed that applied stress has a significant influence on the dielectric properties of PLZT ceramics.

Effect of sub-inhibitory antibacterial stress on bacterial surface properties and biofilm formation

Sub-inhibitory concentrations of antibacterial compounds do not effectively interfere with bacterial growth and only impart stress on them. Bacteria may react to external stress by abandoning planktonic life and form biofilms as the latter life-form offers superior resistance. This study on the effect of norfloxacin on biofilm formation by Staphylococcus aureus and Pseudomonas aeruginosa found that biofilm formation is enhanced under sub-inhibitory stress. Studies have reported increase in biofilm formation under the influence of external stress. In addition, the physicochemical properties of bacteria (i.e. zeta potential and contact angle) in the presence of antibacterial compounds were determined and its effect on initial attachment of bacteria to surfaces was examined. Single cell AFM force spectroscopy measurements were carried out to model the detachment force once the transient attachment takes place. The results indicate that once bacteria breach the physiochemical free energy barrier and come in direct contact with a surface, specific molecular interactions occur and detachment demands more energy than physicochemical forces alone can explain, especially at relatively higher separation distances.

Multiple, Simultaneous, Martensitic Transformations: Implications on Transformation Texture Intensities

A Theory is Developed for Martensite Variants that have Different Start Temperatures but Existin the same Steel. Themethod Enables the Volume Fractions of each Kind Ofmartensite to be Followed Asa Function of the Steel Temperature. the Problemis Relevant to the Calculation of Detail in Transformationtexture when Phase Changes Occur under the Influence of External Stress. it should Allow for the Firsttime, the Estimation of both the Location of Crystallographic Poles on a Stereographic Projection, Andthe Diffraction Intensity Associated with that Location. it is Found that the Increment of Transformationas a Function of Undercooling is Identical for all Variants, once Simultaneous Transformation Begins.Any Variance in the Absolute Fractions is due to the Differences in the Martensite-Start Temperature.

Ferroelasticity in a metal–organic framework perovskite; towards a new class of multiferroics

A metal–organic framework perovskite, [(CH2)3NH2][Mn(HCOO)3], exhibits a weakly first order ferroelastic phase transition at ∼272K, from orthorhombic Pnma to monoclinic P21/n, and a further transition associated with antiferromagnetic ordering at ∼8.5K. The main structural changes, through the phase transition, are orientational ordering of the azetidium groups and associated changes in hydrogen bonding. In marked contrast to conventional improper ferroelastic oxide perovskites, the driving mechanism is associated with the X-point of the cubic Brillouin zone rather than being driven by R- and M-point octahedral tilting. The total ferroelastic shear strain of up to ∼5% is substantially greater than found for typical oxide perovskites, and highlights the potential of the flexible framework to undergo large relaxations in response to local structural changes. Measurements of elastic and anelastic properties by resonant ultrasound spectroscopy show some of the characteristic features of ferroelastic materials. In particular, acoustic dissipation below the transition point can be understood in terms of mobility of twin walls under the influence of external stress with relaxation times on the order of ∼10−7s. Elastic softening as the transition is approached from above is interpreted in terms of coupling between acoustic modes and dynamic local ordering of the azetidium groups. Subsequent stiffening with further temperature reduction is interpreted in terms of classical strain–order parameter coupling at an improper ferroelastic transition which is close to being tricritical. By way of contrast, there are no overt changes in elastic or anelastic properties near 9K, implying that any coupling of the antiferromagnetic order parameter with strain is weak or negligible.

High-Energy Synchrotron X-Ray Diffraction for In Situ Study of Phase Transformation in Shape-Memory Alloys

This overview highlights very recent progress on the application of high-energy x-ray diffraction for in situ study of the phase transformation of shape-memory alloys. The advantages of the synchrotron-based high-energy x-ray diffraction method and the experimental setup for exploring the phase-transition behavior of single crystals or textured polycrystalline materials under multiple external fields are described. Experimental investigations on the influence of external stress, magnetic, and thermal fields on the phase-transformation behaviors of thermal and ferromagnetic shape-memory alloys, and nanowire-reinforced shape-memory composites are also summarized. Special attention is given to recent scientific issues related to the microscopic “memory” of martensite variants, transition kinetics, magnetic field-induced selection of variants, magnetic field-driven phase transition, and superelasticity.

LPCMO nano-templates grown using substrate induced strain

Abstract The phase diagram of mixed phase manganites exhibits an electronic soft matter (ESM) like state, where the coexisting metallic and insulating phases behave like a fluid under the influence of external stress and electric field. We present here the nano-template growth of (La0.5Pr0.5)0.67Ca0.33MnO3 on NdGaO3 (NGO) (1 1 0) and SrTiO3 (STO) (1 0 0) substrates using pulsed laser ablation technique. The films grown on STO have disconnected islands due to the large lattice mismatch of about 2%. These single crystalline islands are approximately 50 nm in size and also display the ESM state. The ESM state in these nano-templates is found to be sensitive to the substrate induced strain. On NGO, the ESM is formed near the insulator to metal transition temperature (TIM). When the film thickness is increased, i.e. the substrate strain is relaxed; the ESM region in the phase diagram shrinks, confirming the influence of strain on the ESM. Thus by engineering strain, we can create nano-templates which display electronic soft matter like behavior. Since the magnetism of the nano-templates can be manipulated by an electric field, novel magneto-electronic devices can be fabricated.

Influence of External Stress on Discontinuous Precipitation Behavior in a Cu-Ag Alloy

The influence of an applied stress on discontinuous precipitation (DP) has been investigated for a Cu-5 wt pct Ag alloy aged at 573 K. A tensile stress enhances the growth of DP cells in both the loading direction (LD) and transverse direction (TD), but the cell growth rate in the TD, v CT , is faster than that in the LD, v CL . A compressive stress suppresses the cell growth in the TD, but does not significantly influence it in the LD. The tensile or compressive stress tends to produce discontinuous silver precipitates elongated in a $$ \left\langle {110} \right\rangle_{\alpha } $$ direction of the copper matrix in a DP cell, nearly perpendicular to or parallel to the LD. This result, along with the dependence of the cell growth rate on the sense of the applied stress, can be understood through the interaction energy between the external stress and the misfit strains of silver precipitates. An analysis of length-change measurement results has enabled estimation of the ratio of the growth rate of silver precipitates in the TD, v PT , to that in the LD, v PL , under tension or compression. The estimated values of v PT /v PL are in good agreement with the values of v CT /v CL , experimentally obtained, indicating that the anisotropy of the cell growth rate is determined by the growth behavior of silver precipitates.

Influence of external stress and plastic strain on morphological evolution of precipitates in Ni-based superalloys

Abstract An analytical method is proposed to investigate the morphological evolution of γ ′ precipitates in Ni-based superalloys. Two types of superalloys are considered with different ratio between the Young’s moduli of the precipitates and the matrix. Based on Eshelby’s equivalent inclusion theory and Mori–Tanaka’s mean field method the elastic energy is calculated as a function of the particle shape. The plastic strain induced by the formation of dislocation networks at the phase interface is taken into account. The results show that the external stress and the plastic matrix strain play a significant role for shape stability and the rafting mechanism of the precipitates. The elastic–plastic analysis provides a satisfactory explanation for all available experimental observations superalloys undergoing plastic creep.