Negative Strain Research Articles

Effect of subsurface damage on tensile behavior and fracture mechanism of SiCp/Al composites: Experimental analysis and RVE modeling

Machining-induced subsurface damage (SSD) is crucial for the reliable application of composite components. This paper investigated the SSD characteristics and its effect mechanism on tensile behavior and fracture mechanism for SiCp/Al/45%p based on experimental analysis and numerical modeling. Specifically, a representative volume element (RVE) model considering SSD was established to reveal the crack initiation and propagation in uniaxial tension. The digital image correlation (DIC) technique was used for monitoring the tensile strength and full-field strain of specimens containing SSD. The results showed that the increase in SSD depth decreases the tensile strength, which declined by 16.3% from 258 MPa to 216 MPa when SSD depth increased from 60 μm to 210 μm. The εxx maximum negative strain in the high-stress state and the εyy maximum positive strain in the low-stress state were susceptible to increased SSD depth. The fractography characteristics analysis showed the initial fracture position of the specimens was within the SSD area. The brittle fracture of particles and ductile fracture of the matrix are the main fracture mechanisms of SiCp/Al/45%p. A few particle-matrix interface failure was observed. Moreover, the RVE model indicates that the location of particle fracture and particle debonding damage is prone to generate stress concentrations, leading to crack initiation and propagation. This study provides a new sight and theoretical guidance for the reliability application SiCp/Al composite.

A direct numerical simulation study on the structures and turbulence–flame interactions of a laboratory-scale lean premixed jet flame in cross-flow

In the present work, direct numerical simulation of a laboratory-scale lean premixed reacting jet in cross-flow was performed to explore the flow–flame structures and turbulence–flame interactions. A jet of lean premixed ethylene–air mixtures (equivalence ratio $\phi = 0.6$ ) was injected into a hot vitiated cross-flow. Both non-reacting and reacting cases were simulated. It was found that the reacting jet penetrates deeper in the cross-flow with a weaker shear layer compared with the non-reacting one. The wake of the non-reacting and reacting jet is characterized by vertical vortices and recirculation zones, respectively. As for the flame structure of the reacting case, the reaction intensity varies considerably in different flame zones. The heat release rate on the leeward side is higher than that on the windward side, but lower than that of the corresponding laminar flame. The analysis of the turbulence–flame interactions of the reacting case showed that the large local Damköhler number ( $Da$ ) related to reaction-induced dilatations results in an increased tendency of the scalar gradient to align with the most extensive strain rate, which is more evident in the regions with high heat release rate on the leeward side. Negative dilatation regions with positive tangential strain rate and negative normal strain rate are observed on the windward side. High positive dilatations appear on the flame front of the leeward side. The tangential strain rate is negatively correlated with the normal strain rate and curvature. Regions with a high local $Da$ on the windward side correspond with high positive curvature regions.

Crossing the line: The violating effects of illegitimate interruptions from work and the differential impact on work‐to‐family conflict by gender

SummaryDespite interruptions from work being increasingly common for many employees, their inherently disruptive nature induces strain on the work–life interface; yet, it remains unclear why the experienced strain is not universal. Drawing on role identity and Stress‐as‐Offense‐to‐Self theories, illegitimate interruptions from work (IIWs) are inappropriate, avoidable, unnecessary, or unreasonable interruptions that carry an added meaning of disrespect, thereby presenting a threat to the self and potentially inducing additional unnecessary strain. Differential value placed on professional and personal roles likely shapes attributions of illegitimacy. We collected event‐based data over 5 days from 182 employees (432 interruptions). Our multilevel moderated mediation model established IIW's indirect effect on work‐to‐family conflict (WFC) via boundary violation, above and beyond the negative effects of interruptions themselves. Thus, subjectively ascribed illegitimacy induces further but potentially unnecessary negative strain. Men were more likely to experience boundary violation in reaction to IIWs and subsequently reported more WFC as compared to women. Yet, although results suggest that IIWs may be a more salient immediate threat to men, it is possible that women's higher threshold for IIWs may present a more distal threat for gender parity. We offer guidance for developing strategies to reduce IIWs and mitigate their impact.

A Klebsiella pneumoniae NDM-1+ bacteriophage: Adaptive polyvalence and disruption of heterogenous biofilms.

Bacteriophage KL-2146 is a lytic virus isolated to infect Klebsiella pneumoniae BAA2146, a pathogen carrying the broad range antibiotic resistance gene New Delhi metallo-betalactamase-1 (NDM-1). Upon complete characterization, the virus is shown to belong to the Drexlerviridae family and is a member of the Webervirus genus located within the (formerly) T1-like cluster of phages. Its double-stranded (dsDNA) genome is 47,844 bp long and is predicted to have 74 protein-coding sequences (CDS). After challenging a variety of K. pneumoniae strains with phage KL-2146, grown on the NDM-1 positive strain BAA-2146, polyvalence was shown for a single antibiotic-sensitive strain, K. pneumoniae 13,883, with a very low initial infection efficiency in liquid culture. However, after one or more cycles of infection in K. pneumoniae 13,883, nearly 100% infection efficiency was achieved, while infection efficiency toward its original host, K. pneumoniae BAA-2146, was decreased. This change in host specificity is reversible upon re-infection of the NDM-1 positive strain (BAA-2146) using phages grown on the NDM-1 negative strain (13883). In biofilm infectivity experiments, the polyvalent nature of KL-2146 was demonstrated with the killing of both the multidrug-resistant K. pneumoniae BAA-2146 and drug-sensitive 13,883 in a multi-strain biofilm. The ability to infect an alternate, antibiotic-sensitive strain makes KL-2146 a useful model for studying phages infecting the NDM-1+ strain, K. pneumoniae BAA-2146. GRAPHICAL ABSTRACT.

Substructure evolution in two phases based constitutive model for hot deformation of TC18 in α + β phase region

The α + β dual phase titanium alloys are key structural materials in aviation and aerospace industries, and the complicated flow behavior of these titanium alloys during hot deformation requires to establish a constitutive model incorporating physical mechanism for optimizing processing parameters and designing forming tools. This work aims to establish a constitutive model incorporating physical mechanism for hot deformation of TC18 in α + β phase region. Firstly, the flow behavior and microstructure evolution for hot deformation of TC18 in α + β phase region are characterized. The TC18 shows significant strain hardening rate and negative strain hardening exponent around and after peak flow stress, respectively. After peak flow stress, Dynamic Recovery (DRV) mechanism dominates the evolution of α and β phases according to the results of substructure evolution. Then, the internal state variables method is applied to establish a constitutive model incorporating physical mechanism for hot deformation of dual phase titanium alloys. The variation of dislocation density during the hot deformation of titanium alloys is modeled by considering the accumulation of dislocation due to the impediment to dislocation movement by substructure obstacles and the annihilation of dislocation due to the dynamic restoration effect. The interaction between dislocations, the subgrain boundaries and the grain/phase boundaries obstruct the dislocation movement in the α phase, and the first two obstructs the dislocation movement in the β phase during the hot deformation of TC18. The dislocation annihilation process in the α and β phases during the hot deformation of TC18 is dominated by DRV. Finally, the substructure evolution in the two phases based constitutive model for hot deformation of TC18 in α + β phase region is presented. This model is well applied to predict the flow stress and quantitively analyze the role of DRV effect in the evolution of α and β phases during the hot deformation of TC18.

Anti-Oomycete Activity and Pepper Root Colonization of Pseudomonas plecoglossicida YJR13 and Pseudomonas putida YJR92 against Phytophthora capsici

Previously, Pseudomonas plecoglossicida YJR13 and Pseudomonas putida YJR92 from a sequential screening procedure were proven to effectively control Phytophthora blight caused by Phytophthora capsici. In this study, we further investigated the anti-oomycete activities of these strains against mycelial growth, zoospore germination, and germ tube elongation of P. capsici. We also investigated root colonization ability of the bacterial strains in square dishes, including cell motility (swimming and swarming motilities) and biofilm formation. Both strains significantly inhibited mycelial growth in liquid and solid V8 juice media and M9 minimal media, zoospore germination, and germ tube elongation compared with Bacillus vallismortis EXTN-1 (positive biocontrol strain), Sphingomonas aquatilis KU408 (negative biocontrol strain), and MgSO4 solution (untreated control). In diluted (nutrient-deficient) V8 juice broth, the tested strain populations were maintained at >108 cells/ml, simultaneously providing mycelial inhibitory activity. Additionally, these strains colonized pepper roots at a 106 cells/ml concentration for 7 days. The root colonization of the strains was supported by strong swimming and swarming activities, biofilm formation, and chemotactic activity towards exudate components (amino acids, organic acids, and sugars) of pepper roots. Collectively, these results suggest that strains YJR13 and YJR92 can effectively suppress Phytophthora blight of pepper through direct anti-oomycete activities against mycelial growth, zoospore germination and germ tube elongation. Bacterial colonization of pepper roots may be mediated by cell motility and biofilm formation together with chemotaxis to root exudates.

Reverse remodeling of left atrium assessed by cardiovascular magnetic resonance feature tracking in hypertrophic obstructive cardiomyopathy after septal myectomy

BackgroundAssessing the structure and function of left atrium (LA) is crucial in hypertrophic obstructive cardiomyopathy (HOCM) because LA remodeling correlates with atrial fibrillation. However, few studies have investigated the potential effect of myomectomy on LA phasic remodeling in HOCM after myectomy using cardiovascular magnetic resonance (CMR) feature tracking (FT). This study aims to evaluate the LA structural and functional remodeling with HOCM after myectomy by CMR-FT and to further investigate the determinants of LA reverse remodeling. MethodsIn this single-center study, we retrospectively studied 88 patients with HOCM who received CMR before and after myectomy between January 2011 and June 2021. Preoperative and postoperative LA parameters derived from CMR-FT were compared, including LA reservoir function (total ejection fraction [EF], total strain [εs], peak positive strain rate [SRs]), conduit function (passive EF, passive strain [εe], peak early negative strain rate [SRe]) and booster function (booster EF, active strain [εa], late peak negative strain rate [SRa]). Eighty-six healthy participants were collected for comparison. Univariate and multivariate linear regression identified variables associated with the rate of change of εa. ResultsCompared with preoperative parameters, LA reservoir function (total EF, εs, SRs), booster function (booster EF, εa, SRa), and SRe were significantly improved after myectomy (all P < 0.05), while no significant differences were observed in passive EF and εe. Postoperative patients with HOCM still had larger LA and worse LA function than healthy controls (all P < 0.05). After analyzing the rates of change in LA parameters, LA boost function, especially εa, showed the most dramatic improvement beyond the improvements in reservoir function, conduit function, and volume. In multivariable regression analysis, minimum LA volume index (adjusted β = − 0.39, P < 0.001) and Δleft ventricular outflow tract (LVOT) pressure gradient (adjusted β = − 0.29, P = 0.003) were significantly related to the rate of change of εa. ConclusionsPatients with HOCM after septal myectomy showed LA reverse remodeling with a reduction in LA size and restoration in LA reservoir and booster function but unchanged LA conduit function. Among volumetric and functional changes, booster function had the greatest improvement postoperatively. Besides, preoperative LAVmin index and ΔLVOT might be potential factors associated with the degree of improvement in εa.

Molecular characterization of virulence genes in poultry-originated Salmonella Enteritidis and Salmonella Typhimurium

Salmonella Enteritidis and Salmonella Typhimurium are the most common serovars observed in human salmonellosis while contaminated poultry products are the major source of Salmonella transmission to humans. Therefore, high pathogenicity of poultry-originated S. Enteritidis and S. Typhimurium strains poses a serious risk to human health. This study analyzed the virulence genes of broiler chicken-originated S. Enteritidis and S. Typhimurium strains. SipA, sipD, sopB, sopD, sopE, sopE2, sitC, sifA, ssaR, spvC and pefA genes were investigated in a total of 137 strains consisting of 105 S. Enteritidis and 32 S. Typhimurium. Nine strains (6.6%) had all genes. No negative strain was detected for all genes. SopE was found in all strains (100%). SitC (89.1%), ssaR (83.9%), sipA (70.1%), sipD (73.0%), sopE2 (68.6%), spvC (68.6%) and pefA (73.0%) were also highly prevalent. Noticeable differences were observed between serovars in terms of sopE2, spvC and pefA prevalence: 77.1%, 80% and 82.9%, respectively, of S. Enteritidis strains were sopE2, spvC and pefA positive while 40.6%, 31.3% and 40.6% of S. Typhimurium strains were positive. This finding indicates that S. Enteritidis is more frequent than S. Typhimurium in poultry populations thanks to higher virulence. Based on virulence gene distribution, the strains were divided into 44 different virulence genotypes, with the major genotype 4 (15.3%) carrying 8 of the 11 genes. The majority of strains (75.9%) were positive for at least 6 genes. S. Enteritidis and S. Typhimurium strains were highly virulent and pose a threat as a zoonotic infection.

The effects of spin-orbit coupling on optical properties of monolayer text {MoS}_{2} due to mechanical strains

We have studied the optical conductivity of a quasi two-dimensional text {MoS}_{2} in the presence of external magnetic field and spin-orbit coupling. Specially, we address the frequency dependence of optical conductivity due to spin-orbit interaction. Using linear response theory the behavior of optical conductivity has been obtained within Green’s function method. We have also considered the effects of uniaxial and biaxial in-plane strain on the optical absorption of text {MoS}_{2} layer. In the absence of external magnetic field with negative uniaxial strain parameter, optical conductivity includes Drude weight at zero frequency limit while Drude weight vanishes for text {MoS}_{2} layer under positive uniaxial strain. Our results show that the increase of uniaxial positive strain parameter causes to move the position peak to the higher frequencies. In contrast to uniaxial strain case, the Drude weight in optical conductivity appears at positive biaxial strain value 0.15. Also we have studied the effects of magnetic field, electron doping, hole doping in the presence of spin-orbit coupling on frequency dependence of optical conductivity of text {MoS}_{2} in details. The magnetic field dependence of optical absorption shows a monotonic decreasing behavior for each value of temperature in the absence of strain parameter.

Influence of particle size on the electrocatalytic activity and optical properties of NiO nanoparticles

The study of nanoparticles becomes increasingly fascinating since their size can give them unusual behaviors, changing their properties. Due to their outstanding properties, nickel oxide nanoparticles have been applied in several research fields, such as catalysis and optical electronics. In this work, we have investigated the influence of particle size on the optical and electrocatalytic properties of NiO obtained through coprecipitation synthesis (Cp). Thermogravimetric analysis (TG/DTG) measurements reveal that the total decomposition of the precursors occurs at ≈ 545 °C. The X-ray diffraction measurements (XRD) show that it is possible for the formation of only one phase of NiO at 350 °C. Rietveld refinement indicates an increase in crystallite size with the rise of temperature and negative strain values associated with shrinkage of the crystalline lattice. Vibrational spectroscopy (infrared and Raman) data showed a symmetry break and imperfections/defects in the synthesized NiO nanoparticles. The optical properties of these samples were studied by spectrophotometry in the ultraviolet–visible and near-infrared region measurements (UV–vis-NIR). Band gap values decreased with increasing nanoparticle size. The Urbach tail energy estimates corroborate the vibrational spectroscopy measurements, indicating the presence of imperfections/defects in the samples. Density Functional Theory (DFT) studies have been applied from the XRD parameters implemented by the Spanish Initiative for Electronic Simulations with Thousands of Atom (SIESTA) to understand the experimental results better. Despite the computational limitations and the difficulty of describing the dynamic effect presented by the 3d orbitals of Ni, it was possible to obtain satisfactory results within the order of magnitude desired. Also, under the effect of the size of the nanoparticles, all samples present excellent electrocatalytic performance (overpotential of 312–335 mV for a current density of 10 mA/cm2) for Oxygen Evolution Reaction (OER) in alkaline medium.

3D-strain-induced multiple semiconductor–metallic phase transition in monolayer SrTiO3

The recent discovery of monolayer perovskite has attracted much attention due to its abundant physical properties and extreme flexible properties. However, multiple strain effects on its physical properties are not clear. Herein, by means of first-principles calculations, we show that under 3D-multiple strains, the monolayer SrTiO3 (STO) can be tuned from the semiconductor into metallic phases via the in-plane strain engineering. The bandgap of the monolayer STO increases with increasing positive biaxial strain and reduces to zero when a negative biaxial strain is applied. In addition, we found that the metallic phase of the monolayer STO under the in-plane biaxial strain will drop back into the semiconductor phase when an out-of-plane compressive strain is added. By analyzing the electronic band structure, density of states, and orbital-projected band structures, we found that the p-orbitals of Sr and O atoms as well as the d-orbitals of Sr atoms make significant effects on the multiple semiconductor–metallic phase transition. In summary, the abundant semiconductor–metallic phase transition of the monolayer STO under 3D-strain conditions opens up an opportunity for its application in modulating the electronic properties of 2D materials.

Prognostic Significance of Cardiac Magnetic Resonance in Left Atrial and Biventricular Strain Analysis during the Follow-Up of Suspected Myocarditis.

To assess the variation in left atrial (LA) and biventricular strain and its prognostic value in the course of suspected myocarditis, this retrospective study included 55 patients with clinically suspected myocarditis who underwent cardiac magnetic resonance (CMR) examinations at baseline and follow-up periods. Cine images were used for feature tracking analysis. Paired Student's t test, McNemar's test, and Cox proportional hazard regression were used for statistical analysis. The LA total emptying fraction was the only functional index that showed a statistically significant improvement. The initial LA peak's late negative strain rate (SRa) was the only parameter with a significant predictive power of major adverse cardiac events under univariable (hazard ratio [HR] 2.396, 95% confidence interval [CI] 1.044-5.498, p = 0.039) and multivariable Cox survival analysis when adjusted by LA strain parameters (HR 5.072, 95% CI 1.478-17.404, p = 0.010), LA strain and functional parameters (HR 7.197, 95% CI 1.679-30.846, p = 0.008), and LA and biventricular strain and functional parameters (HR 10.389, 95% CI 2.250-47.977, p = 0.003). Thus, our findings indicate that CMR strain is useful for monitoring LA and ventricular function in suspected myocarditis, that LA function may recover preceding ventricular function changes, and that LA strain may serve as an incremental tool to predict adverse outcomes.

Constitutive model research on the hot deformation behavior of Ti6Al4V alloy under wide temperatures

The hot compression tests of Ti6Al4V alloy were carried out at different temperatures (500, 600, 700, 800, and 900 °C) and different strain rates (0.01 s−1, 0.1 s−1, and 1 s−1). The hot deformation behavior of Ti6Al4V alloy is complex in a wide temperature range, and the phenomenon of negative strain rate sensitivity even appears at low temperature (500 °C and 600 °C). The phenomenological Arrhenius model, modified Fields-Backofen model (m-FB) and Gray Wolf Optimization Algorithm optimizing BP artificial neural network model (GWO-BPNN) were established. A new FB model (n-FB) was proposed based on m-FB model. The prediction accuracy and computational cost of these constitutive models were evaluated by mean absolute percentage error (MAPE), correlation coefficient (R) and the number of parameters. The comparison results show that the m-FB model, the GWO-BPNN model, and the n-FB model can predict the flow stress at all temperatures, but the Arrhenius model cannot be fitted at low temperature conditions, and the fitting effect of the Arrhenius model is the worst. The GWO-BPNN has the highest prediction accuracy based on that it has the maximum number of parameters. The MAPE and R values of n-FB model are 1.9093% and 0.993 respectively. Compared with the m-FB model, the MAPE value of n-FB is reduced by 64.64%.

Young adults’ protest participation and mental health

Summary This article explores how political fluctuations can negatively affect young adults’ psychosocial well-being, by using the case of Hong Kong's Anti-Extradition Law Amendment Bill Movement. The study included both individual and focus group interviews to collect the experiences and perspectives of 25 youths, 13 teachers, and 12 social workers within a qualitative paradigm. The data were coded independently by the author and research assistant. Findings Four major themes related to young adults’ psychosocial well-being: (a) mental health deterioration, (b) tension in family relations, (c) problems in peer relations, and (d) decreasing trust in teachers and social workers. The findings not only reveal the relevance of political issues to contemporary youths’ well-being, but also display a possible vicious circle among negative psychosocial environment, psychosocial strain, and poor environment. Applications There is a pressing need for social workers to be better prepared for dealing with young adults’ psychosocial issues that arise from political conflicts. This article contributes to the literature by considering the role of psychosocial factors in maintaining or reinforcing youth participation in protests. Unconventional strategies should be developed by social workers to reach youth activists and help relieve emotional and psychological pressures caused by political unrest. Suggestions for fostering post-conflict reconciliation in the community are also offered.

Evaluation of right ventricular strain in two separate cohorts with precapillary pulmonary hypertension.

Evaluation for right ventricular (RV)dysfunction is an important part of risk assessment in care of patients with pulmonary hypertension (PH) as it is associated with morbidity and mortality. Echocardiography provides a widely available and acceptable method to assess RV function. RV global longitudinal strain (RVGLS), a measure of longitudinal shortening of RV deep muscle fibers obtained by two-dimensional echocardiography, was previously shown to predict short-term mortality in patients with PH. The purpose of the current study was to assess the performance of RVGLS in predicting 1-year outcomes in PH. We retrospectively identified 83 subjects with precapillary PH and then enrolled 50 consecutive prevalent pulmonary arterial hypertension (PAH) subjects into a prospective validation cohort. Death as well as combined morbidity and mortality events at 1 year were assessed as outcomes. In the retrospective cohort, 84% of patients had PAH and the overall 1-year mortality rate was 16%. Less negative RVGLS was marginally better than tricuspid annular plane systolic excursion(TAPSE)as a predictor for death. However, in the prospective cohort, 1-year mortality was only 2%, and RVGLS was not predictive of death or a combined morbidity and mortality outcome. This study supports that RV strain and TAPSE have similar 1-year outcome predictions but highlights that low TAPSE or less negative RV strain measures are often false-positive in a cohort with low baseline mortality risk. While RV failure is considered the final common pathway for disease progression in PAH, echocardiographic measures of RV function may be less informative of risk in serial follow-up of treated PAH patients.

Скоростная чувствительность механических свойств сплава ZK60 с высокой степенью коррозионных повреждений

According to the stable opinion, hydrogen absorbed by magnesium alloys during corrosion can cause their stress corrosion cracking. One of the characteristic markers indicating the involvement of diffusible hydrogen into the fracture mechanism of metals is the negative strain rate dependence of the embrittlement degree. Recent studies show that the loss of ductility of the ZK60 alloy specimens subjected to a short-term (1.5 h) pre-exposure in a corrosive medium actually decreases with the increasing strain rate. However, after the removal of corrosion products from the surface of specimens, the strain rate dependence of the ductility loss becomes positive, which indicates the absence of hydrogen in the bulk of a metal. At a short-term exposure in a corrosive environment, the deep penetration of hydrogen into a metal could be limited due to the insufficient time for hydrogen diffusion. The paper studies the mechanical behavior of the ZK60 alloy subjected to a longer (12 h) pre-exposure in a corrosive medium followed by tensile testing in air at various strain rates. The authors consider the effect of strain rate, long-term pre-exposure in a corrosive medium, and subsequent removal of corrosion products on the strength, ductility, stages of work hardening, and localized deformation, as well as on the state of the side and fracture surfaces of specimens. The study identified that the ductility loss of specimens pre-exposed in a corrosive medium for 12 h decreases with the increasing strain rate, regardless of whether the corrosion products have been removed from their surface or not. It is shown that in this case, the negative strain rate dependence of the ductility loss is associated not with hydrogen dissolved in the bulk of a metal but with the presence of severe corrosion damage of the specimens’ surface. The authors proposed an explanation for the effect of corrosion damage on the mechanical properties and their strain rate sensitivity.

Investigation on torsional performance of wind turbine blades under pure torsion through subcomponent test

Torsional performance has received little attention in the process of blade design. Furthermore, the mechanical response of main structural components is unknown under pure torsion. This paper studies the torsional performance of the blade segment through the latest subcomponent test method. The blade segment, which length is 5m, is cut off from the blade in service. The subcomponent test rig is designed specifically to apply pure torsion force to a blade segment. The structure response of the blade segment under pure torque is recorded through a preset data acquisition system. This study also used the finite element model established with combined shell/solid mesh to predict the test. Finally, it is compared with the test results, and the two have achieved a good agreement. It is found that the blade segments show apparent nonlinear behavior after being subjected to pure torsional force, including inclination response, stress response, and strain response. The inclination angle increases faster in the early stage and slower in the later stage with the addition of load. The maximum stress region is the sandwich and adhesive joint. Moreover, the stress of specimen near the fixed side is higher. The strain results show that the pure torsional force on the specimen is transformed into a positive and negative strain of the sandwich and adhesive joint. Both ends of the specimen are the dangerous region of it. These novel conclusions provide a valuable reference for the design of the blade.

Insight into the effect of biaxial compression strain on adsorption structure of bituminous coal matrix as well as gas diffusion and permeability properties by macromolecule simulation

The concentrated stress induced by mining activities leads to deformation of the coal, especially the coal matrix, which affects the production of coalbed methane (CBM). Therefore, grand canonical Monte Carlo and molecular dynamics methods were used to study the effect of biaxial compression strain on the adsorption structure of the bituminous coal matrix as well as the CH4/CO2/N2 diffusion and permeability properties based on the constructed macromolecular coal model. The results show that the dual-mode equation fits the gas adsorption isotherm and the order of influence of adsorption concentration on the model structure is N2 > CO2 > CH4. For the diffusion models, the orders of swelling rate and specific volume are CH4 > N2 > CO2, while those of the fractional free volume and pore volume are opposite. Compression (negative) strain (0.00 ∼ −0.20) reduces the bulk modulus but has a negligible effect on the shear modulus and wave velocity. Also the Poisson’s ratio of the CH4 diffusion model is smaller compared to the CO2/N2 diffusion model. The cohesive energy density (CED) order is CO2 > N2 > CH4 and its van der Waals component accounts for the major part. The mean square displacement distribution of gases successively increases in the power function and linearity with time. The self-diffusion coefficient of CH4 is larger than that of CO2/N2, which is greatly affected by strain. The (negative) interaction energy order between gas and coal matrix is CH4 > N2 > CO2, and the order of intermolecular interaction distance of gases is N2 > CO2 > CH4. Most importantly, the solubility order of gases is CO2 > CH4 > N2, and the strain has the dual effect of promoting and inhibiting the permeability of the coal matrix. The research results provide molecular-level insights into CBM recoveries in coal reservoirs with different strain degrees, with some technical value and theoretical importance.

Experimental and numerical analysis of the Portevin–Le Chatelier effect in a nickel-base superalloy for turbine disks application

High-pressure turbine disks are subjected to extreme mechanical and thermal loadings throughout their lifetime. This is the reason why during the design of turboshaft engines, regulation rules impose on manufacturers to demonstrate the integrity of rotating parts, especially turbine disks, with over-speed experiments. To improve the prediction of rotation speed at burst, it is essential to study the viscoplastic behavior and the fracture of the material. The present work focuses on the approach used to calibrate accurately a viscoplastic behavior model at high temperature (500 °C) of nickel-based superalloy Inconel718. The experimental testing campaign includes standard tensile tests on axisymmetric and flat specimens with and without notches. The behavior is described using the McCormick model for dynamic strain aging. This model accounts for the viscoplastic behavior including the range of negative strain rate sensitivity and the Portevin–Le Chatelier (PLC) effect. In addition to global measurements, digital image correlation at high temperature using a speckle directly engraved on the specimen is used to detect and measure the strain carried by the PLC bands. This information is used in the parameter calibration. The consideration of the machine stiffness is shown to be essential in the analysis for a correct description of serrations and of the critical strain for PLC effects. 3D simulations on full specimen geometries samples are performed to validate the finite element model. Finally, a full 3D representative disk geometry simulation is performed to detect instabilities and their propagation due to geometrical singularities.

Aerodynamic Force and Aeroelastic Response Characteristics Analyses for the Galloping of Ice-Covered Four-Split Transmission Lines in Oblique Flows

In order to study the galloping mechanism of ice-covered four-split transmission lines in oblique flows, the aerodynamic forces and aero-elastic response characteristics of the crescent-shaped four-split ice-covered transmission lines are investigated through wind tunnel tests on rigid and aero-elastic models. According to Den Hartog and Nigel’s galloping theories, the damping coefficients are calculated based on the experimental data. The results show that the crescent-shaped ice-covered four-split transmission lines usually suffer from torsional galloping. Furthermore, based on the aero-elastic wind tunnel data, the galloping is characterized by an elliptical trajectory, negative damping ratio, and a negative strain at hanging position. In addition, the galloping appears to be more prone to occur under oblique flows, with a larger galloping amplitude and a lower critical wind speed. This might be because an out-of-plane vibration of the third-order mode is excited at a lower wind speed, leading to a coupled resonance between in-plane and out-of-plane vibrations at the third-order mode with a frequency ratio of 1:1. The experimental results in this paper can also be used to verify the fluid-structure interaction simulation method of ice-covered transmission lines.