This work investigates how temperature and microstructural evolution affect the formability of face-centered cubic(fcc)structured CoCrFeNiMn_(0.75)Cu_(0.25) high entropy alloy(HEA)sheets under complex stress condition...This work investigates how temperature and microstructural evolution affect the formability of face-centered cubic(fcc)structured CoCrFeNiMn_(0.75)Cu_(0.25) high entropy alloy(HEA)sheets under complex stress conditions.Erichsen cupping tests were conducted to quantitatively evaluate the deformation capacity at room temperature(298 K)and cryogenic temperatures.The findings reveal a strong temperature dependence on the formability of the HEA.A decrease in the deformation temperature from 298 to 93 K causes a significant increase in both the Erichsen index(IE)(from 9.8 to 12.4 mm)and the expansion rate(δ)of surface area(from 51.6%to 76.3%),as well as a reduction in the average deviation(η)of thickness(from 55.1%to 44.4%),signifying its ultrahigh formability and uniform deformation capability at cryogenic temperature.This enhancement is attributed to the transition in the deformation mechanism from single dislocation slip at 298 K to a cooperative of plastic deformation mechanisms at 93 K,involving dislocation slip,stacking faults(SFs),Lomer-Cottrell(L-C)locks and multi-scale nanotwins.The lower stacking fault energy of the alloy facilitates these deformation mechanisms,particularly the formation of SFs and nanotwins,which enhance ductility and strength by providing additional pathways for plastic deformation.These mechanisms collectively contribute to delaying plastic instability,thereby improving the overall formability.This work provides a comprehensive understanding of the underlying reasons for the enhanced formability of HEAs at cryogenic temperatures,offering valuable insights for their practical use in challenging environments.展开更多
Stiffness degradation will occur due to the generation of accumulated pore pressure in saturated soft clays under cyclic loading. The soil static-dynamic multi-purpose triaxial and torsional shear apparatus in Dalian ...Stiffness degradation will occur due to the generation of accumulated pore pressure in saturated soft clays under cyclic loading. The soil static-dynamic multi-purpose triaxial and torsional shear apparatus in Dalian University of Technology was employed to perform different types of test on the saturated soft marine clay in the Yangtze Estuary. Undisturbed samples of the clay were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotropic consolidation with different initial consolidation parameters. Investigated were the effects of the initial orientation angle of the major principal stress, initial ratio of deviatoric stress, initial coefficient of intermediate principal stress and continuous rotation of principal stress axes on the stiffness degradation. It is found that the degradation index decreases （or degradation degree increases） significantly with increasing initial orientation angle of the major principal stress and initial ratio of deviatoric stress. Compared with the effects of the initial orientation angle of the major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate principal stress is less evident and this trend is more clearly reflected by the results of the cyclic torsional shear tests than those of the cyclic coupling shear tests. At the same cycle number, the degradation index obtained from the cyclic torsional shear test is higher than that from the cyclic coupling shear test. The main reason is that the continuous rotation in principal stress directions during cyclic coupling shear damages the original structure of the soil more than the cyclic torsional shear does.Based on a series of experiments, a mathematical model for stiffness degradation is proposed and the relevant parameters are determined.展开更多
The formation of shear bands in metallic glasses(MGs)was examined by tailoring localized complex stress fields(LCSFs).The findings have shown that the LCSFs in MGs can increase the localization of strained atoms and a...The formation of shear bands in metallic glasses(MGs)was examined by tailoring localized complex stress fields(LCSFs).The findings have shown that the LCSFs in MGs can increase the localization of strained atoms and accelerate the release of accumulated deformation energy for initiating a shear band in confined and thin-layered regions.The findings not only add more knowledge to the formation mechanisms of shear bands in MGs,but also provide possible rationale for the discrepancies in the mechanical properties of different-sized MGs.As compared with the bulk samples,the higher strength and larger elastic limits in nanoscaled MGs could be attributed to the elimination of stress-concentrators,which can serve as LCSFs.展开更多
To investigate the long-term stability of deep rocks,a three-dimensional(3D)time-dependent model that accounts for excavation-induced damage and complex stress state is developed.This model comprises three main compon...To investigate the long-term stability of deep rocks,a three-dimensional(3D)time-dependent model that accounts for excavation-induced damage and complex stress state is developed.This model comprises three main components:a 3D viscoplastic isotropic constitutive relation that considers excavation damage and complex stress state,a quantitative relationship between critical irreversible deformation and complex stress state,and evolution characteristics of strength parameters.The proposed model is implemented in a self-developed numerical code,i.e.CASRock.The reliability of the model is validated through experiments.It is indicated that the time-dependent fracturing potential index(xTFPI)at a given time during the attenuation creep stage shows a negative correlation with the extent of excavationinduced damage.The time-dependent fracturing process of rock demonstrates a distinct interval effect of the intermediate principal stress,thereby highlighting the 3D stress-dependent characteristic of the model.Finally,the influence of excavation-induced damage and intermediate principal stress on the time-dependent fracturing characteristics of the surrounding rocks around the tunnel is discussed.展开更多
A series of numerical simulations of conventional and true triaxial tests for soft rock materials using the three-dimensional finite difference code FLAC3D were presented. A hexahedral element and a strain hardening/s...A series of numerical simulations of conventional and true triaxial tests for soft rock materials using the three-dimensional finite difference code FLAC3D were presented. A hexahedral element and a strain hardening/softening constitutive model based on the unified strength theory(UST) were used to simulate both the consolidated-undrained(CU) triaxial and the consolidated-drained(CD) true triaxial tests. Based on the results of the true triaxial tests simulation, the effect of the intermediate principal stress on the strength of soft rock was investigated. Finally, an example of an axial compression test for a hard rock pillar with a soft rock interlayer was analyzed using the two-dimensional finite difference code FLAC. The CD true triaxial test simulations for diatomaceous soft rock suggest the peak and residual strengths increase by 30% when the effect of the intermediate principal stress is taken into account. The axial compression for a rock pillar indicated the peak and residual strengths increase six-fold when the soft rock interlayer approached the vertical and the effect of the intermediate principal stress is taken into account.展开更多
There exists a critical cyclic stress ratio when sand or clay is subjected to cyclic loading. It is an index dis-tinguishing stable state or failure state. The soil static and dynamic universal triaxial and torsional ...There exists a critical cyclic stress ratio when sand or clay is subjected to cyclic loading. It is an index dis-tinguishing stable state or failure state. The soil static and dynamic universal triaxial and torsional shear apparatus de-veloped by Dalian University of Technology in China was employed to perform different types of tests on saturated soft marine clay in the Yangtze estuary. Undisturbed samples were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotropic consolidation with different initial consoli-dation parameters. The effects of initial orientation angle of major principal stress, initial ratio of deviatoric stress,initial coefficient of intermediate principal stress and stress mode of cyclic shear on the critical cyclic stress ratio wereinvestigated. It is found that the critical cyclic stress ratio decreases significantly with increasing initial orientation angle of major principal stress and initial ratio of deviatoric stress. Compared with the effects of the initial orientationangle of major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate prin-cipal stress is less evident. Under the same consolidation condition, the critical cyclic stress ratio from the cyclic cou-pling shear test is lower than that from the cyclic torsional shear test, indicating that the stress mode of cyclic shear has an obvious effect on the critical cyclic stress ratio. The main reason is that the continuous rotation in principal stressdirections during cyclic coupling shear damages the original structure of soil more than the cyclic torsional shear does.展开更多
Taking cruciform welded joints under different corrosion degrees, together with 45° inclined angle and full penetration load-carrying fillet, as the research object, the stress intensity factor of a quarter-circu...Taking cruciform welded joints under different corrosion degrees, together with 45° inclined angle and full penetration load-carrying fillet, as the research object, the stress intensity factor of a quarter-circular comer crack of welded joints is calculated based on FRANC3D with ABAQUS. Effects of different corrosion pit sizes, crack aspect ratios, and crack depths on stress intensity factor are analyzed. The results show that pit depth plays a major role in stress intensity factor, while the effect of pit radius is relatively small. The cracking modes of the surface and the deepest point are mode I, and mixed modes I and II, respectively. Effects of pit depths, crack aspect ratios, and crack depths on the stress intensity factor at the surface point are greater than at the deepest point.展开更多
Complex posttraumatic stress disorder(Complex PTSD)has been recently proposed as a distinct clinical entity in the WHO International Classification of Diseases,11^(th)version,due to be published,two decades after its ...Complex posttraumatic stress disorder(Complex PTSD)has been recently proposed as a distinct clinical entity in the WHO International Classification of Diseases,11^(th)version,due to be published,two decades after its first initiation.It is described as an enhanced version of the current definition of PTSD,with clinical features of PTSD plus three additional clusters of symptoms namely emotional dysregulation,negative self-cognitions and interpersonal hardship,thus resembling the clinical features commonly encountered in borderline personality disorder(BPD).Complex PTSD is related to complex trauma which is defined by its threatening and entrapping context,generally interpersonal in nature.In this manuscript,we review the current findings related to traumatic events predisposing the above-mentioned disorders as well as the biological correlates surrounding them,along with their clinical features.Furthermore,we suggest that besides the present distinct clinical diagnoses(PTSD;Complex PTSD;BPD),there is a cluster of these comorbid disorders,that follow a continuum of trauma and biological severity on a spectrum of common or similar clinical features and should be treated as such.More studies are needed to confirm or reject this hypothesis,particularly in clinical terms and how they correlate to clinical entities'biological background,endorsing a shift from the phenomenologically only classification of psychiatric disorders towards a more biologically validated classification.展开更多
Classical plate theory has been used to find out interfacial stress intensity factors in composite laminates. By using a well-known relation between the crack-tip energy release rate and the complex stress intensity f...Classical plate theory has been used to find out interfacial stress intensity factors in composite laminates. By using a well-known relation between the crack-tip energy release rate and the complex stress intensity factor. a closed-form solution for complex. Stress intensity in terms of external loading and a mode mix parameter for fairly. general composite laminates is given. Then a procedure for determining this mode mix. parameter is presented. followed by numerical results for some laminates. Small scale contact condition is expressed in terms of external loading In particular, a symmetric property of interfacial toughness curye is proven. Finally. the accuracy of failure load predicled by elininating oscllation index is discussed. and an example is presented to show the validity and limitation of β=0 approximation.展开更多
BACKGROUND The debate regarding diagnostic classification systems in psychiatry(categorial vs dimensional systems)has essential implications for the diagnosis,prevention and treatment of stress reactions.We previously...BACKGROUND The debate regarding diagnostic classification systems in psychiatry(categorial vs dimensional systems)has essential implications for the diagnosis,prevention and treatment of stress reactions.We previously found a unique pattern of stress reaction in a study executed during the coronavirus disease 2019 pandemic using large representative samples in two countries,and termed it the Complex Stress Reaction Syndrome(CSRS).AIM To investigate CSRS,Type A(psychiatric symptoms,spanning anxiety,depression,stress symptoms,and posttraumatic stress disorder(PTSD)),with or without long-coronavirus disease(COVID)residuals(CSRS,Type B,neuropsychiatric symptoms spanning cognitive deficits and fatigue,excluding systemic symptoms).Our two-tailed hypothesis was that CSRS is a condition related to an unrecognized type of stress reaction in daily life in the general population(Type A)or that it is related to the severe acute respiratory syndrome coronavirus 2 infection and its long-COVID residuals(Type B).METHODS 977 individuals in four continents(North America,Europe,Australia and the Middle East)completed the online study questionnaire in six languages using the Qualtrics platform.The study was managed by six teams in six countries that promoted the study on social media.The questionnaire assessed anxiety,depression,stress symptoms and PTSD(CSRS,Type A),cognitive deficits and fatigue(CSRS,Type B).The data were analyzed using Proportion Analyses,Multivariate Analysis of Co-Variance(MANCOVA),linear regression analyses and validated clinical cutoff points.RESULTS The results of the Proportion Analyses showed that the prevalence of 4 symptoms spanning anxiety,depression,stress symptoms,and PTSD was significantly higher than the most prevalent combinations of fewer symptoms across 4 continents,age groups,and gender.This supports the transdiagnostic argument embedded in the CSRS(Type A).The same pattern of results was found in infected/recovered individuals.The prevalence of the 4 psychiatric symptoms combination was significantly greater than that of 5 and 6 symptoms,when adding cognitive deficits and fatigue,respectively.MANCOVA showed a significant three-way interaction(age×gender×continent).Further analyses showed that the sources of this three-way interaction were threefold relating to two sub-populations at-risk:(1)Individuals that self-identified as non-binary gender scored significantly higher on all 4 psychiatric symptoms of the CSRS,Type A at young age groups(<50 years old)in North America compared to(self-identified)women and men located in the 4 continents studied,and to other ages across the adult life span;and(2)This pattern of results(CSRS,Type A)was found also in women at young ages(<40 years old)in North America who scored higher compared to men and women in other continents and other ages.Linear regression analyses confirmed the MANCOVA results.CONCLUSION These results show a combined mental health risk factor related to stress reactivity,suggesting that the CSRS is sensitive to populations at risk and may be applied to future identification of other vulnerable sub-populations.It also supports the transdiagnostic approach for more accurate prevention and treatment.Time will tell if such transdiagnostic syndromes will be part of the discussions on the next revisions of the traditional classification systems or whether the crisis in psychiatry further evolves.展开更多
Background Non-suicidal self-injury(NSSI)is a significant health concern among adolescents and young adults,often resulting from adverse childhood experiences(ACEs).Dissociation,post-traumatic symptoms and attachment ...Background Non-suicidal self-injury(NSSI)is a significant health concern among adolescents and young adults,often resulting from adverse childhood experiences(ACEs).Dissociation,post-traumatic symptoms and attachment style may have a role in shaping such associations.Aims This study aims to provide a unified model of the impact of ACEs on NSSI,exploring complex post-traumatic stress disorder(cPTSD)symptoms and dissociation as potential mediators and the role of the predominant attachment style in affecting such associations.Methods 1010 young individuals attending the last year of high school participated in this cross-sectional study.ACEs,cPTSD,dissociation and NSSI were evaluated using self-report questionnaires.We fitted a path model of NSSI,with ACEs as exogenous variables and cPTSD and dissociation as sequential mediators.Secure,fearful and preoccupied attachment styles were modelled as grouping variables.Results Our findings showed that dissociation mediated the impact of ACEs on NSSI in subjects with a fearful attachment style,as opposed to those with a preoccupied attachment for whom cPTSD symptoms mediated the ACEs-NSSI association.Conclusions Attachment styles moderate the relationship between ACEs and NSSI,with either dissociation or post-traumatic symptomatology mediating the impact of ACEs on NSSI,depending on the predominant attachment style.Our results highlight the importance of attachment as a pathway modifier in the relationships between different psychopathology dimensions,providing a useful framework to better conceptualise the ACEs-NSSI association.展开更多
The cooling curves of 6061 aluminum alloy were acquired through water quenching experiment. The heat transfer coefficient was accurately calculated based on the cooling curves and the law of cooling. The online quench...The cooling curves of 6061 aluminum alloy were acquired through water quenching experiment. The heat transfer coefficient was accurately calculated based on the cooling curves and the law of cooling. The online quenching process of complex cross-section profile was dynamically simulated by the ABAQUS software. The results suggest that the heat transfer coefficient changes during online quenching process. Different parts of the profile have different cooling velocity, and it was verified by water quenching experiment. The maximum residual stress of the profile was predicted using FEM simulation based on ABAQUS software The relations between the temperature and stress were presented by analyzing the data of key points.展开更多
Aero-engine spindle ball bearings work in harsh conditions which are affected by relatively complex stresses. One of the key factors which affects bearing performance is its structure. In this paper,we used reliabilit...Aero-engine spindle ball bearings work in harsh conditions which are affected by relatively complex stresses. One of the key factors which affects bearing performance is its structure. In this paper,we used reliability based design optimization method to solve the structure design problem of aero-engine spindle ball bearings.Compared with the optimization design method, the value of equivalent dynamic load using reliability optimization design method was the least by MATLAB simulation. Also the design solutions show that the optimized structure possesses higher reliability than the original solution.展开更多
Soil behavior can reflect the characteristics of principal stress rotation under dynamic wave and traffic loads. Unequal amplitudes of tensile and compressive stresses applied to soils have complex effects on foundati...Soil behavior can reflect the characteristics of principal stress rotation under dynamic wave and traffic loads. Unequal amplitudes of tensile and compressive stresses applied to soils have complex effects on foundation soils in comparison with the pure principal stress rotation path. A series of undrained cyclic hollow torsional shear tests were performed on typical remolded soft clay from the Hexi area of Nanjing, China. The main control parameters were the tensile and compressive stress amplitude ratio(α) and the cyclic dynamic stress ratio(η). It was found that the critical η tended to remain constant at 0.13, when the value of the compressive stress amplitude was higher than the tensile stress amplitude. However, the influence of the tensile stress was limited by the dynamic stress level when α= 1.For obvious structural change in the soil, the corresponding numbers of cyclic vibration cycles were found to be independent of α at low stress levels and were only related to η. Finally, a new method for evaluating the failure of remolded soft clay was presented. It considers the influence of the tensile and compressive stresses which caused by complex stress paths of the principal stress rotation. This criterion can distinguish stable, critical, and destructive states based on the pore-water-pressure-strain coupling curve while also providing a range of failure strain and vibration cycles. These results provide the theoretical support for systematic studies of principal stress rotation using constitutive models.展开更多
The apparatus for static and dynamic universal triaxial and torsional shear soil testing is employed to perform stress-controlled cyclic single-direction torsional shear tests and two-direction coupled shear tests und...The apparatus for static and dynamic universal triaxial and torsional shear soil testing is employed to perform stress-controlled cyclic single-direction torsional shear tests and two-direction coupled shear tests under unconsolidated-undrained conditions. Through a series of tests on saturated clay, the effects of initial shear stress and stress reversal on the clay’s strain-stress behavior are examined, and the behavior of pore water pressure is studied. The experimental results indicate that the patterns of stress-strain relations are distinctly influenced by the initial shear stress in the cyclic single-direction shear tests. When the initial shear stress is large and no stress reversal occurs, the predominant deformation behavior is characterized by an accumulative effect. When the initial shear stress is zero and symmetrical cyclic stress occurs, the predominant deformation behavior is characterized by a cyclic effect. The pore water pressure fluctuates around the confining pressure with the increase of cycle number. It seems that the fluctuating amplitude increases with the increase of the cyclic stress. But a buildup of pore water pressure does not occur. The de- formations of clay samples under the complex initial and the cyclic coupled stress conditions include the normal deviatoric deforma- tion and horizontal shear deformation, the average deformation and cyclic deformation. A general strain failure criterion taking into account these deformations is recommended and is proved more stable and suitable compared to the strain failure criteria currently used.展开更多
The conservation law of J-integral in two-media with a crack paralleling to the interface of the two media was firstly proved by analytical and numerical finite element method. Then a schedule model was established th...The conservation law of J-integral in two-media with a crack paralleling to the interface of the two media was firstly proved by analytical and numerical finite element method. Then a schedule model was established that an interface crack is inserted in four media. According to the J-integral conservation law on multi-media, the energy release ratio of Ⅰ-type crack was considered to be conservation when the middle medium layers are very thin. And the conservation law was also convinced by numerical method. By means of the dimension analysis on the model, the asymptotic results and formula calculating the energy release ratio and complex stress intensity factor are presented.展开更多
The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material.The holes will lead to mutations and discontinuity to ...The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material.The holes will lead to mutations and discontinuity to the structure.So the hole-edge stress concentration is always a serious phenomenon.And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points.Most partial damage begins from these weak points.According to the complex variable functions theory,the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes.Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction.The boundary integral equations are founded based on exact boundary conditions.Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved.Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed.And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made.It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient;and smaller angle of outer load and fiber can decrease the stress peak value.展开更多
Stimulation of hydraulic fracturing of horizontal shale gas wells in Weirong Block has always been facing many difficulties due to many factors such as complicated geological conditions,small differences between the h...Stimulation of hydraulic fracturing of horizontal shale gas wells in Weirong Block has always been facing many difficulties due to many factors such as complicated geological conditions,small differences between the horizontal principal stress and the vertical principal stress,high working pump pressures,and low sensitive sand ratios.In view of this,by combing the geological structure,engineering geological characteristics and the difficulties of fracturing of deep shale gas wells in Weirong Block,learning from the general idea of volumetric fracturing for shale gas reservoirs at home and abroad,we determined the main ideas and technical countermeasures for fracturing in the area and applied them to the subsequent fracturing practices of shale gas wells.And the following achievements were obtained.First,the conventional fracturing technology applied to the shale gas wells in Weirong Block resulted in low fracture complexity,small stimulated reservoir volume(SRV),difficulties in guaranteeing the effectiveness of perforation clusters,low strength of proppant adding,difficulties in obtaining higher conductivity,poor stable production capacity after stimulation,and difficulties in meeting the need of well fracturing with casing deformation.Second,in view of the difficulties of fracturing stimulation in deep shale gas wells of Weirong Block,super high pressure,huge displacement,large fluid volume,temporary plugging and diverting in fracturing,and variable displacement technology can effectively increase SRV and the complexity of fractures in distant wells.The effectiveness of multi-cluster perforation can be guaranteed by comprehensive utilization of multi-cluster perforation optimization technology,big displacement technology and temporary plugging and diverting&fracturing technology at slots.The continuous proppant-adding technology with huge displacement,high viscosity,low sand ratio,low density and small particle size can improve sand adding strength and fracture conductivity.Besides,the stimulation technology for casing deformed wells using coiled tubing fast processing+small diameter bridge plug and separate pumping technology of perforating gun have been formed.Third,after the above fracturing technologies have been applied in five shale gas horizontal wells in Weirong Block,the average absolute open flow(QAOF)reached 26.11×10^(4)m^(3)/d,indicating a good stimulation effect.In conclusion,this paper can provide meaningful reference for the development of deep shale gas wells of the similar type.展开更多
This paper discusses the stability of the welding problems under different materials with same shearing modulus. Using the stability of Cauchy type integral while the smooth perturbation for the integral curve and Sob...This paper discusses the stability of the welding problems under different materials with same shearing modulus. Using the stability of Cauchy type integral while the smooth perturbation for the integral curve and Sobolev perturbation for the kernel density happening, the stability of complex stress functions are studied and errors of stress and displacement are given.展开更多
In order to make the fracture cross-section of rock smooth in controlled cutting-blast, generally, two V-shape-notches on the inner wall of a shot hole are notched in symmetry along the design direction. A V-shape not...In order to make the fracture cross-section of rock smooth in controlled cutting-blast, generally, two V-shape-notches on the inner wall of a shot hole are notched in symmetry along the design direction. A V-shape notch approximately be considered as V-shape-fracture under certain condition. This paper gave the complex stress function of preformed V-shape-fracture under a blasting load. The stress field and displacement field at the tip of a preformed V-shape-fracture were derived with Westergaard's method, hence its stressintensity factor was obtained. To verify the derived results, blasting tests were made with concrete samples of 400mm×400mm×300mm, and all having, in the center, a drilled hole of 25mm in diameter and 200mm in height. The test result showed that the formulas derived are correct and effective.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52371025 and 52371106)Guangdong Major Project of Basic and Applied Basic Research(No.2020B0301030001)Shenzhen Fund 2021 Basic Research General Programme(No.JCYJ20210324115400002).
文摘This work investigates how temperature and microstructural evolution affect the formability of face-centered cubic(fcc)structured CoCrFeNiMn_(0.75)Cu_(0.25) high entropy alloy(HEA)sheets under complex stress conditions.Erichsen cupping tests were conducted to quantitatively evaluate the deformation capacity at room temperature(298 K)and cryogenic temperatures.The findings reveal a strong temperature dependence on the formability of the HEA.A decrease in the deformation temperature from 298 to 93 K causes a significant increase in both the Erichsen index(IE)(from 9.8 to 12.4 mm)and the expansion rate(δ)of surface area(from 51.6%to 76.3%),as well as a reduction in the average deviation(η)of thickness(from 55.1%to 44.4%),signifying its ultrahigh formability and uniform deformation capability at cryogenic temperature.This enhancement is attributed to the transition in the deformation mechanism from single dislocation slip at 298 K to a cooperative of plastic deformation mechanisms at 93 K,involving dislocation slip,stacking faults(SFs),Lomer-Cottrell(L-C)locks and multi-scale nanotwins.The lower stacking fault energy of the alloy facilitates these deformation mechanisms,particularly the formation of SFs and nanotwins,which enhance ductility and strength by providing additional pathways for plastic deformation.These mechanisms collectively contribute to delaying plastic instability,thereby improving the overall formability.This work provides a comprehensive understanding of the underlying reasons for the enhanced formability of HEAs at cryogenic temperatures,offering valuable insights for their practical use in challenging environments.
基金supported bythe National Natural Science Foundation of China(Grant Nos.50579006,50639010 and 50909014)
文摘Stiffness degradation will occur due to the generation of accumulated pore pressure in saturated soft clays under cyclic loading. The soil static-dynamic multi-purpose triaxial and torsional shear apparatus in Dalian University of Technology was employed to perform different types of test on the saturated soft marine clay in the Yangtze Estuary. Undisturbed samples of the clay were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotropic consolidation with different initial consolidation parameters. Investigated were the effects of the initial orientation angle of the major principal stress, initial ratio of deviatoric stress, initial coefficient of intermediate principal stress and continuous rotation of principal stress axes on the stiffness degradation. It is found that the degradation index decreases （or degradation degree increases） significantly with increasing initial orientation angle of the major principal stress and initial ratio of deviatoric stress. Compared with the effects of the initial orientation angle of the major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate principal stress is less evident and this trend is more clearly reflected by the results of the cyclic torsional shear tests than those of the cyclic coupling shear tests. At the same cycle number, the degradation index obtained from the cyclic torsional shear test is higher than that from the cyclic coupling shear test. The main reason is that the continuous rotation in principal stress directions during cyclic coupling shear damages the original structure of the soil more than the cyclic torsional shear does.Based on a series of experiments, a mathematical model for stiffness degradation is proposed and the relevant parameters are determined.
基金financially supported by the National Natural Science Foundation of China(Nos.51801049 and 51801174)the State Key Laboratory of Metastable Materials Science and Technology,Yanshan University(No.201809)the Fundamental Research Funds for the Central Universities of China(Nos.PA2019GDZC0096 and JD2019JGPY0015)。
文摘The formation of shear bands in metallic glasses(MGs)was examined by tailoring localized complex stress fields(LCSFs).The findings have shown that the LCSFs in MGs can increase the localization of strained atoms and accelerate the release of accumulated deformation energy for initiating a shear band in confined and thin-layered regions.The findings not only add more knowledge to the formation mechanisms of shear bands in MGs,but also provide possible rationale for the discrepancies in the mechanical properties of different-sized MGs.As compared with the bulk samples,the higher strength and larger elastic limits in nanoscaled MGs could be attributed to the elimination of stress-concentrators,which can serve as LCSFs.
基金supported by the National Natural Science Foundation of China(Grant No.52125903)the China Postdoctoral Science Foundation(Grant No.2023M730367)the Fundamental Research Funds for Central Public Welfare Research Institutes of China(Grant No.CKSF2023323/YT).
文摘To investigate the long-term stability of deep rocks,a three-dimensional(3D)time-dependent model that accounts for excavation-induced damage and complex stress state is developed.This model comprises three main components:a 3D viscoplastic isotropic constitutive relation that considers excavation damage and complex stress state,a quantitative relationship between critical irreversible deformation and complex stress state,and evolution characteristics of strength parameters.The proposed model is implemented in a self-developed numerical code,i.e.CASRock.The reliability of the model is validated through experiments.It is indicated that the time-dependent fracturing potential index(xTFPI)at a given time during the attenuation creep stage shows a negative correlation with the extent of excavationinduced damage.The time-dependent fracturing process of rock demonstrates a distinct interval effect of the intermediate principal stress,thereby highlighting the 3D stress-dependent characteristic of the model.Finally,the influence of excavation-induced damage and intermediate principal stress on the time-dependent fracturing characteristics of the surrounding rocks around the tunnel is discussed.
基金Projects(41172276,51279155)supported by the National Natural Science Foundation of ChinaProjects(106-00X101,106-5X1205)supported by the Central Financial Funds for the Development of Characteristic Key Disciplines in Local University,China
文摘A series of numerical simulations of conventional and true triaxial tests for soft rock materials using the three-dimensional finite difference code FLAC3D were presented. A hexahedral element and a strain hardening/softening constitutive model based on the unified strength theory(UST) were used to simulate both the consolidated-undrained(CU) triaxial and the consolidated-drained(CD) true triaxial tests. Based on the results of the true triaxial tests simulation, the effect of the intermediate principal stress on the strength of soft rock was investigated. Finally, an example of an axial compression test for a hard rock pillar with a soft rock interlayer was analyzed using the two-dimensional finite difference code FLAC. The CD true triaxial test simulations for diatomaceous soft rock suggest the peak and residual strengths increase by 30% when the effect of the intermediate principal stress is taken into account. The axial compression for a rock pillar indicated the peak and residual strengths increase six-fold when the soft rock interlayer approached the vertical and the effect of the intermediate principal stress is taken into account.
基金Supported by National Natural Science Foundation of China (No. 50639010, 50779003 and 50909014)
文摘There exists a critical cyclic stress ratio when sand or clay is subjected to cyclic loading. It is an index dis-tinguishing stable state or failure state. The soil static and dynamic universal triaxial and torsional shear apparatus de-veloped by Dalian University of Technology in China was employed to perform different types of tests on saturated soft marine clay in the Yangtze estuary. Undisturbed samples were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotropic consolidation with different initial consoli-dation parameters. The effects of initial orientation angle of major principal stress, initial ratio of deviatoric stress,initial coefficient of intermediate principal stress and stress mode of cyclic shear on the critical cyclic stress ratio wereinvestigated. It is found that the critical cyclic stress ratio decreases significantly with increasing initial orientation angle of major principal stress and initial ratio of deviatoric stress. Compared with the effects of the initial orientationangle of major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate prin-cipal stress is less evident. Under the same consolidation condition, the critical cyclic stress ratio from the cyclic cou-pling shear test is lower than that from the cyclic torsional shear test, indicating that the stress mode of cyclic shear has an obvious effect on the critical cyclic stress ratio. The main reason is that the continuous rotation in principal stressdirections during cyclic coupling shear damages the original structure of soil more than the cyclic torsional shear does.
基金supported by the National Natural Science Foundation of China(51378430 and 51378431)
文摘Taking cruciform welded joints under different corrosion degrees, together with 45° inclined angle and full penetration load-carrying fillet, as the research object, the stress intensity factor of a quarter-circular comer crack of welded joints is calculated based on FRANC3D with ABAQUS. Effects of different corrosion pit sizes, crack aspect ratios, and crack depths on stress intensity factor are analyzed. The results show that pit depth plays a major role in stress intensity factor, while the effect of pit radius is relatively small. The cracking modes of the surface and the deepest point are mode I, and mixed modes I and II, respectively. Effects of pit depths, crack aspect ratios, and crack depths on the stress intensity factor at the surface point are greater than at the deepest point.
文摘Complex posttraumatic stress disorder(Complex PTSD)has been recently proposed as a distinct clinical entity in the WHO International Classification of Diseases,11^(th)version,due to be published,two decades after its first initiation.It is described as an enhanced version of the current definition of PTSD,with clinical features of PTSD plus three additional clusters of symptoms namely emotional dysregulation,negative self-cognitions and interpersonal hardship,thus resembling the clinical features commonly encountered in borderline personality disorder(BPD).Complex PTSD is related to complex trauma which is defined by its threatening and entrapping context,generally interpersonal in nature.In this manuscript,we review the current findings related to traumatic events predisposing the above-mentioned disorders as well as the biological correlates surrounding them,along with their clinical features.Furthermore,we suggest that besides the present distinct clinical diagnoses(PTSD;Complex PTSD;BPD),there is a cluster of these comorbid disorders,that follow a continuum of trauma and biological severity on a spectrum of common or similar clinical features and should be treated as such.More studies are needed to confirm or reject this hypothesis,particularly in clinical terms and how they correlate to clinical entities'biological background,endorsing a shift from the phenomenologically only classification of psychiatric disorders towards a more biologically validated classification.
文摘Classical plate theory has been used to find out interfacial stress intensity factors in composite laminates. By using a well-known relation between the crack-tip energy release rate and the complex stress intensity factor. a closed-form solution for complex. Stress intensity in terms of external loading and a mode mix parameter for fairly. general composite laminates is given. Then a procedure for determining this mode mix. parameter is presented. followed by numerical results for some laminates. Small scale contact condition is expressed in terms of external loading In particular, a symmetric property of interfacial toughness curye is proven. Finally. the accuracy of failure load predicled by elininating oscllation index is discussed. and an example is presented to show the validity and limitation of β=0 approximation.
文摘BACKGROUND The debate regarding diagnostic classification systems in psychiatry(categorial vs dimensional systems)has essential implications for the diagnosis,prevention and treatment of stress reactions.We previously found a unique pattern of stress reaction in a study executed during the coronavirus disease 2019 pandemic using large representative samples in two countries,and termed it the Complex Stress Reaction Syndrome(CSRS).AIM To investigate CSRS,Type A(psychiatric symptoms,spanning anxiety,depression,stress symptoms,and posttraumatic stress disorder(PTSD)),with or without long-coronavirus disease(COVID)residuals(CSRS,Type B,neuropsychiatric symptoms spanning cognitive deficits and fatigue,excluding systemic symptoms).Our two-tailed hypothesis was that CSRS is a condition related to an unrecognized type of stress reaction in daily life in the general population(Type A)or that it is related to the severe acute respiratory syndrome coronavirus 2 infection and its long-COVID residuals(Type B).METHODS 977 individuals in four continents(North America,Europe,Australia and the Middle East)completed the online study questionnaire in six languages using the Qualtrics platform.The study was managed by six teams in six countries that promoted the study on social media.The questionnaire assessed anxiety,depression,stress symptoms and PTSD(CSRS,Type A),cognitive deficits and fatigue(CSRS,Type B).The data were analyzed using Proportion Analyses,Multivariate Analysis of Co-Variance(MANCOVA),linear regression analyses and validated clinical cutoff points.RESULTS The results of the Proportion Analyses showed that the prevalence of 4 symptoms spanning anxiety,depression,stress symptoms,and PTSD was significantly higher than the most prevalent combinations of fewer symptoms across 4 continents,age groups,and gender.This supports the transdiagnostic argument embedded in the CSRS(Type A).The same pattern of results was found in infected/recovered individuals.The prevalence of the 4 psychiatric symptoms combination was significantly greater than that of 5 and 6 symptoms,when adding cognitive deficits and fatigue,respectively.MANCOVA showed a significant three-way interaction(age×gender×continent).Further analyses showed that the sources of this three-way interaction were threefold relating to two sub-populations at-risk:(1)Individuals that self-identified as non-binary gender scored significantly higher on all 4 psychiatric symptoms of the CSRS,Type A at young age groups(<50 years old)in North America compared to(self-identified)women and men located in the 4 continents studied,and to other ages across the adult life span;and(2)This pattern of results(CSRS,Type A)was found also in women at young ages(<40 years old)in North America who scored higher compared to men and women in other continents and other ages.Linear regression analyses confirmed the MANCOVA results.CONCLUSION These results show a combined mental health risk factor related to stress reactivity,suggesting that the CSRS is sensitive to populations at risk and may be applied to future identification of other vulnerable sub-populations.It also supports the transdiagnostic approach for more accurate prevention and treatment.Time will tell if such transdiagnostic syndromes will be part of the discussions on the next revisions of the traditional classification systems or whether the crisis in psychiatry further evolves.
基金supported by #NEXTGENERATIONEU(NGEU)and funded by the Ministry of University and Research(MUR),National Recovery and Resilience Plan(NRRP),project MNESYS(PE0000006)-(DN.155311.10.2022)supported by Sapienza Grant 2021(RM12117A60BDF685).
文摘Background Non-suicidal self-injury(NSSI)is a significant health concern among adolescents and young adults,often resulting from adverse childhood experiences(ACEs).Dissociation,post-traumatic symptoms and attachment style may have a role in shaping such associations.Aims This study aims to provide a unified model of the impact of ACEs on NSSI,exploring complex post-traumatic stress disorder(cPTSD)symptoms and dissociation as potential mediators and the role of the predominant attachment style in affecting such associations.Methods 1010 young individuals attending the last year of high school participated in this cross-sectional study.ACEs,cPTSD,dissociation and NSSI were evaluated using self-report questionnaires.We fitted a path model of NSSI,with ACEs as exogenous variables and cPTSD and dissociation as sequential mediators.Secure,fearful and preoccupied attachment styles were modelled as grouping variables.Results Our findings showed that dissociation mediated the impact of ACEs on NSSI in subjects with a fearful attachment style,as opposed to those with a preoccupied attachment for whom cPTSD symptoms mediated the ACEs-NSSI association.Conclusions Attachment styles moderate the relationship between ACEs and NSSI,with either dissociation or post-traumatic symptomatology mediating the impact of ACEs on NSSI,depending on the predominant attachment style.Our results highlight the importance of attachment as a pathway modifier in the relationships between different psychopathology dimensions,providing a useful framework to better conceptualise the ACEs-NSSI association.
基金Project(zzyjkt2013-10B)supported by the Foundation of State Key Laboratory of High-performance&Complicated Manufacturing,ChinaProject(51275533)supported by the National Natural Science Foundation of China
文摘The cooling curves of 6061 aluminum alloy were acquired through water quenching experiment. The heat transfer coefficient was accurately calculated based on the cooling curves and the law of cooling. The online quenching process of complex cross-section profile was dynamically simulated by the ABAQUS software. The results suggest that the heat transfer coefficient changes during online quenching process. Different parts of the profile have different cooling velocity, and it was verified by water quenching experiment. The maximum residual stress of the profile was predicted using FEM simulation based on ABAQUS software The relations between the temperature and stress were presented by analyzing the data of key points.
文摘Aero-engine spindle ball bearings work in harsh conditions which are affected by relatively complex stresses. One of the key factors which affects bearing performance is its structure. In this paper,we used reliability based design optimization method to solve the structure design problem of aero-engine spindle ball bearings.Compared with the optimization design method, the value of equivalent dynamic load using reliability optimization design method was the least by MATLAB simulation. Also the design solutions show that the optimized structure possesses higher reliability than the original solution.
基金financial support of the National Natural Science Foundation of China(51420105013 and 51479060)Fundamental Research Funds for the Central Universities(2015B17114)Science and Technology Project of Shandong Housing and Urban-Rural Development(2014QG009)
文摘Soil behavior can reflect the characteristics of principal stress rotation under dynamic wave and traffic loads. Unequal amplitudes of tensile and compressive stresses applied to soils have complex effects on foundation soils in comparison with the pure principal stress rotation path. A series of undrained cyclic hollow torsional shear tests were performed on typical remolded soft clay from the Hexi area of Nanjing, China. The main control parameters were the tensile and compressive stress amplitude ratio(α) and the cyclic dynamic stress ratio(η). It was found that the critical η tended to remain constant at 0.13, when the value of the compressive stress amplitude was higher than the tensile stress amplitude. However, the influence of the tensile stress was limited by the dynamic stress level when α= 1.For obvious structural change in the soil, the corresponding numbers of cyclic vibration cycles were found to be independent of α at low stress levels and were only related to η. Finally, a new method for evaluating the failure of remolded soft clay was presented. It considers the influence of the tensile and compressive stresses which caused by complex stress paths of the principal stress rotation. This criterion can distinguish stable, critical, and destructive states based on the pore-water-pressure-strain coupling curve while also providing a range of failure strain and vibration cycles. These results provide the theoretical support for systematic studies of principal stress rotation using constitutive models.
基金This work is supported by the National Natural Science Foundation of China （Grant Nos. 50579006, 50639010 and 50179006）.
文摘The apparatus for static and dynamic universal triaxial and torsional shear soil testing is employed to perform stress-controlled cyclic single-direction torsional shear tests and two-direction coupled shear tests under unconsolidated-undrained conditions. Through a series of tests on saturated clay, the effects of initial shear stress and stress reversal on the clay’s strain-stress behavior are examined, and the behavior of pore water pressure is studied. The experimental results indicate that the patterns of stress-strain relations are distinctly influenced by the initial shear stress in the cyclic single-direction shear tests. When the initial shear stress is large and no stress reversal occurs, the predominant deformation behavior is characterized by an accumulative effect. When the initial shear stress is zero and symmetrical cyclic stress occurs, the predominant deformation behavior is characterized by a cyclic effect. The pore water pressure fluctuates around the confining pressure with the increase of cycle number. It seems that the fluctuating amplitude increases with the increase of the cyclic stress. But a buildup of pore water pressure does not occur. The de- formations of clay samples under the complex initial and the cyclic coupled stress conditions include the normal deviatoric deforma- tion and horizontal shear deformation, the average deformation and cyclic deformation. A general strain failure criterion taking into account these deformations is recommended and is proved more stable and suitable compared to the strain failure criteria currently used.
文摘The conservation law of J-integral in two-media with a crack paralleling to the interface of the two media was firstly proved by analytical and numerical finite element method. Then a schedule model was established that an interface crack is inserted in four media. According to the J-integral conservation law on multi-media, the energy release ratio of Ⅰ-type crack was considered to be conservation when the middle medium layers are very thin. And the conservation law was also convinced by numerical method. By means of the dimension analysis on the model, the asymptotic results and formula calculating the energy release ratio and complex stress intensity factor are presented.
基金supported by National Natural Science Foundation of China(No.50675209)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,Ministry of Education of China(No.200724).
文摘The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material.The holes will lead to mutations and discontinuity to the structure.So the hole-edge stress concentration is always a serious phenomenon.And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points.Most partial damage begins from these weak points.According to the complex variable functions theory,the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes.Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction.The boundary integral equations are founded based on exact boundary conditions.Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved.Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed.And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made.It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient;and smaller angle of outer load and fiber can decrease the stress peak value.
基金supported by the Scientific Research Project of Sinopec Oilfield Service Corporation“Key technologies for deep shale gas fracturing and gas testing in Weiyuan-Yongchuan”(No.:SG1704-02K).
文摘Stimulation of hydraulic fracturing of horizontal shale gas wells in Weirong Block has always been facing many difficulties due to many factors such as complicated geological conditions,small differences between the horizontal principal stress and the vertical principal stress,high working pump pressures,and low sensitive sand ratios.In view of this,by combing the geological structure,engineering geological characteristics and the difficulties of fracturing of deep shale gas wells in Weirong Block,learning from the general idea of volumetric fracturing for shale gas reservoirs at home and abroad,we determined the main ideas and technical countermeasures for fracturing in the area and applied them to the subsequent fracturing practices of shale gas wells.And the following achievements were obtained.First,the conventional fracturing technology applied to the shale gas wells in Weirong Block resulted in low fracture complexity,small stimulated reservoir volume(SRV),difficulties in guaranteeing the effectiveness of perforation clusters,low strength of proppant adding,difficulties in obtaining higher conductivity,poor stable production capacity after stimulation,and difficulties in meeting the need of well fracturing with casing deformation.Second,in view of the difficulties of fracturing stimulation in deep shale gas wells of Weirong Block,super high pressure,huge displacement,large fluid volume,temporary plugging and diverting in fracturing,and variable displacement technology can effectively increase SRV and the complexity of fractures in distant wells.The effectiveness of multi-cluster perforation can be guaranteed by comprehensive utilization of multi-cluster perforation optimization technology,big displacement technology and temporary plugging and diverting&fracturing technology at slots.The continuous proppant-adding technology with huge displacement,high viscosity,low sand ratio,low density and small particle size can improve sand adding strength and fracture conductivity.Besides,the stimulation technology for casing deformed wells using coiled tubing fast processing+small diameter bridge plug and separate pumping technology of perforating gun have been formed.Third,after the above fracturing technologies have been applied in five shale gas horizontal wells in Weirong Block,the average absolute open flow(QAOF)reached 26.11×10^(4)m^(3)/d,indicating a good stimulation effect.In conclusion,this paper can provide meaningful reference for the development of deep shale gas wells of the similar type.
基金Supported by the National Natural Science Foundation of China(11171260)Science and Technology Foundation of Education Department of Fujian Province(JA11341)
文摘This paper discusses the stability of the welding problems under different materials with same shearing modulus. Using the stability of Cauchy type integral while the smooth perturbation for the integral curve and Sobolev perturbation for the kernel density happening, the stability of complex stress functions are studied and errors of stress and displacement are given.
文摘In order to make the fracture cross-section of rock smooth in controlled cutting-blast, generally, two V-shape-notches on the inner wall of a shot hole are notched in symmetry along the design direction. A V-shape notch approximately be considered as V-shape-fracture under certain condition. This paper gave the complex stress function of preformed V-shape-fracture under a blasting load. The stress field and displacement field at the tip of a preformed V-shape-fracture were derived with Westergaard's method, hence its stressintensity factor was obtained. To verify the derived results, blasting tests were made with concrete samples of 400mm×400mm×300mm, and all having, in the center, a drilled hole of 25mm in diameter and 200mm in height. The test result showed that the formulas derived are correct and effective.
