The study of rock failure mechanisms is fundamental to geotechnical engineering,as it enhances design quality and mitigates disaster risks.This research employed in situ compression tests on 3D-printed rocklike sample...The study of rock failure mechanisms is fundamental to geotechnical engineering,as it enhances design quality and mitigates disaster risks.This research employed in situ compression tests on 3D-printed rocklike samples with a single flaw,combining Micro-CT scans and a specialized loading device to analyze their behavior.Mechanical properties and failure modes of these printed samples were compared to those of natural flawed sandstones,demonstrating the capability of 3D printing to replicate natural rock characteristics.By reconstructing 3D crack evolution from 2D CT images and applying digital volume correlation(DVC),the study visualized internal strain fields and established a relationship between strain patterns and rock failure.The results reveal that crack initiation consistently occurs at the flaw,advancing into tensile and secondary shear or mixed cracks.For flaw angles(α)ranging from 0°to 45°,the 3D-printed samples exhibited a higher number of newly formed cracks and a faster increase in crack volume with strain.In contrast,for flaw angles of 45°≤α≤90°,the opposite trend was observed.The internal strain field exhibited significant strain localization,with this uneven distribution playing a critical role in sample failure.When the flaw angle was in the range of 0°≤α≤30°,failure was primarily driven by tensile cracks,forming distinct tensile bands.Conversely,for 30°<α≤90°,a combination of tensile and shear cracks dominated the failure,producing both shear and tensile bands in the sample.Additionally,the strain field component ε_(yy) showed a strong correlation with the evolution of internal damage,providing valuable insights into the underlying rock failure mechanisms.展开更多
Cyclic deformation behavior of friction-stir-welded dissimilar AA2024-T351 to AA7075-T65 aluminum alloy joints was evaluated via stepwise tests at different strain rates,along with transmission electron microscopy exa...Cyclic deformation behavior of friction-stir-welded dissimilar AA2024-T351 to AA7075-T65 aluminum alloy joints was evaluated via stepwise tests at different strain rates,along with transmission electron microscopy examinations to characterize the precipitates required to assess internal stresses.Electron backscatter diffraction was employed to observe the inhomogeneous microstructures of the FSWed joints.Strain localization appeared in the heat affected zone(HAZ)of AA2024 side.After cyclic deformation of 500 cycles at a total strain amplitude of 0.5%,the strength of the dissimilar joints resumed basically to that of AA2024 base material.And the AA2024 HAZ was obviously hardened,which should be attributed to the introduced dislocations during cyclic deformation process.Cyclic hardening capacity of the joints increased with decreasing strain rate.展开更多
To address the problems of strain localization, the exact Mohr-Coulomb (MC) model is used based on second-order cone programming (mpcFEM-SOCP) in the framework of micropolar continuum finite element method. Using the ...To address the problems of strain localization, the exact Mohr-Coulomb (MC) model is used based on second-order cone programming (mpcFEM-SOCP) in the framework of micropolar continuum finite element method. Using the uniaxial compression test, we focused on the earth pressure problem of rigid wall segment involving non-associated plasticity. The numerical results reveal that when mpcFEM-SOCP is applied, the problems of mesh dependency can be effectively addressed. For geotechnical strain localization analysis involving non-associated MC plasticity, mpcFEM-SOCP in conjunction with the pseudo-time discrete scheme can improve the numerical stability and avoid the unreasonable softening issue in the pressure-displacement curves, which may be encountered in the conventional FEM. It also shows that the pressure-displacement responses calculated by mpcFEM-SOCP with the pseudo-time discrete scheme are higher than those calculated by mpcFEM-SOCP with the Davis scheme. The inclination angle of shear band predicted by mpcFEM-SOCP with the pseudo-time discrete scheme agrees well with the theoretical solution of non-associated MC plasticity.展开更多
Using elastic crystalline viscoplastic finite element (FE) annlysis, the formability of BCC steel sheets was assessed. An orientation probability assignment method in the FE modeling procedure, which can be categorize...Using elastic crystalline viscoplastic finite element (FE) annlysis, the formability of BCC steel sheets was assessed. An orientation probability assignment method in the FE modeling procedure, which can be categorized as an inhomogenized material modeling, was newly proposed. In the study, the crystal orientations of three materials, mild steel, dual phase steel and the high strength steel, were obtained by Xray diffraction and orientation distribution function (ODF) analyses. The measured ODF results have revealed clearly different textures in the sheets, featured by orientation fibers, skeleton lines and selected orientations in Euler angle space, which are closely related to the plastic anisotropy. Then, the crystal orientations were assigned to FE integration points by using this ODF data, individually. The FE analyses of the standard limiting dome height (LDH) test show how the fiber textures affect the extent of strain localization in the forming processes. It was confirmed by comparison with experimental results that this FE code could predict the extreme strain localization and assess the sheet formability.展开更多
Based on governing equations of saturated porous media and Liapunov＇ s stability here, onset conditions matrix of porous media used by solid stress and Terzaghi＇s effective stress constitutive description under seep...Based on governing equations of saturated porous media and Liapunov＇ s stability here, onset conditions matrix of porous media used by solid stress and Terzaghi＇s effective stress constitutive description under seepage flow state, are presented, which have different forms with different representation of the solid phase, matrix or skeleton, constitutive model of porous media. The main difference relates with how to describe the interaction between solid phase and liquid phase in constitutive model. The derived onset condition of strain localization under Terzaghi＇ s effective stress description can be used to interpret different failure types, piping effect, landslides and mudflows, by means of the type and the magnitude ratio of relative movement between solid phase and liquid phase. Examples here illuminate the onset condition of how to work.展开更多
An investigation of computer simulation is presented to analyze the effectsof strain localization and damage evolution in large plastic deformation. The simulation is carriedout by using an elastic-plastic-damage coup...An investigation of computer simulation is presented to analyze the effectsof strain localization and damage evolution in large plastic deformation. The simulation is carriedout by using an elastic-plastic-damage coupling finite element program that is developed based onthe concept of mixed interpolation of displacement/pressure. This program has been incorporated intoa damage mechanics model as well as the corresponding damage criterion. To illustrate theperformance of the proposed approach, a typical strain localization problem has been simulated. Theresults show that the proposed approach is of good capability to capture strain localization andpredict the damage evolution.展开更多
This paper presents a numerical investigation on the strain localization of an idealized sand in biaxial compression tests using the distinct element method(DEM).In addition to the dilatancy and material frictional an...This paper presents a numerical investigation on the strain localization of an idealized sand in biaxial compression tests using the distinct element method(DEM).In addition to the dilatancy and material frictional angle,the principal stress field,and distributions of void ratio,particle velocity,and the averaged pure rotation rate(APR)in the DEM specimen are examined to illustrate the link between microscopic and macroscopic variables in the case of strain localization.The study shows that strain localization of the granular material in the tests proceeds with localizations of void ratio,strain and APR,and distortions of stress field and force chains.In addition,both thickness and inclination of the shear band change with the increasing of axial swain,with the former valued around 10-14 times of mean grain diameter and the later overall described by the Mohr-Coulomb theory.展开更多
Fracture strain becomes critical for the local formability and crash performance of carbody components when the tensile strength exceeds 1000 MPa.Regrettably,high-strength quenching and partitioning(Q&P)steels and...Fracture strain becomes critical for the local formability and crash performance of carbody components when the tensile strength exceeds 1000 MPa.Regrettably,high-strength quenching and partitioning(Q&P)steels and dual-phase(DP)steels always focus on improving the tensile ductility for stretch formability,while ignoring their limited fracture strain.In this work,we explored a novel strategy,i.e.,developing a high fracture strain ferrite-martensite dual-phase steel(HFS-DP)maintaining good strength–ductility balance by suppressing intense strain localization during deformation and enhancing martensite deformability via microstructure design including grain refinement,nano-precipitate hardening in soft ferrite phase,low-carbon and high fraction martensite.HFS-DP demonstrates a remarkable 26%and 47%improvement in tensile ductility and fracture strain,respectively,compared to commercial DP1180 steel with similar ultimate tensile strength.Furthermore,HFS-DP also exhibits a substantial 39%improvement in fracture strain compared to retained austenite-involved commercial QP1180 steel.The detailed processes of strain partitioning,strain localization,and damage formation during deformation were revealed through in-situ scanning electron microscopy(SEM)observation combined with digital image correlation(DIC).The results indicate that the excellent coordinated deformation between ferrite and martensite,coupled with microstructure refinement,effectively suppresses intense strain localization.Moreover,the excellent martensite deformability resulting from the low carbon content also aids in retarding crack formation.This combination effectively suppresses damage initiation and development during deformation,therefore the fracture strain is significantly improved.This study not only contributes to a deeper understanding of the strain localization and damage process during tensile deformation of DP steels,but also provides a new perspective on designing ultrahigh strength steels with high ductility and fracture strain.展开更多
Two-dimensional transition metal dichalcogenides(2D TMDCs)have received considerable attention in local strain engineering due to their extraordinary mechanical flexibility,electonic structure,and optical properties.T...Two-dimensional transition metal dichalcogenides(2D TMDCs)have received considerable attention in local strain engineering due to their extraordinary mechanical flexibility,electonic structure,and optical properties.The strain-induced out-of-plane deformations in 2D TMDCs lead to diverse excitonic behaviors and versatile modulations in optical properties,paving the way for the development of advanced quantum technologies,flexible optoelectronic materials,and straintronic devices.Research on local strain engineering on 2D TMDCs has been delved into fabrication techniques,electronic state variations,and quantum optical applications.This review begins by summarizing the state-of-the-art methods for introducing local strain into 2D TMDCs,followed by an exploration of the impact of local strain engineering on optical properties.The intriguing phenomena resulting from local strain,such as exciton funnelling and anti-funnelling,are also discussed.We then shift the focus to the application of locally strained 2D TMDCs as quantum emitters,with various strategies outlined for modulating the properties of TMDC-based quantum emitters.Finally,we discuss the remaining questions in this field and provide an outlook on the future of local strain engineering on 2D TMDCs.展开更多
Welded joints can be divided into different material zones,with considerable variation of material properties around the weld toe.The material inhomogeneity influences the local stress and strain of welded joints unde...Welded joints can be divided into different material zones,with considerable variation of material properties around the weld toe.The material inhomogeneity influences the local stress and strain of welded joints under monotonic and cyclic loading.This study aims to examine the local stress and strain characteristics of welded joints considering material inhomogeneity.Numerical models with various material zones were developed,and material properties were determined based on hardness.Smooth specimen models were used to analyze stress and strain distributions excluding notch effects.A detailed inhomogeneous model of a welded joint was established based on extensive microhardness measurements around the weld toe and the Kriging interpolation method.Additionally,a homogeneous model and a simplified inhomogeneous model,based on limited measured data,were generated and compared with the detailed inhomogeneous model.Fatigue life was estimated using the Smith,Watson,and Topper method based on the obtained stress and strain.For smooth specimen models,stress concentration occurs at a location where the strain is not significant,and fatigue cracks were most likely to initiate from the base metal.Results from the two simplified models showed deviations from those of the detailed inhomogeneous model,and the limitations of these simplified models are discussed.展开更多
Geotechnical stability analyses based on classical continuum may lead to remarkable underestimations on geotechnical safety.To attain better estimations on geotechnical stability,the micro-polar continuum is employed ...Geotechnical stability analyses based on classical continuum may lead to remarkable underestimations on geotechnical safety.To attain better estimations on geotechnical stability,the micro-polar continuum is employed so that its internal characteristic length(lc)can be utilized to model the shear band width.Based on two soil slope examples,the role of internal characteristic length in modeling the shear band width of geomaterial is investigated by the second-order cone programming optimized micro-polar continuum finite element method.It is recognized that the underestimation on factor of safety(FOS)calculated from the classical continuum tends to be more pronounced with the increase of lc.When the micro-polar continuum is applied,the shear band dominated by lc is almost kept unaffected as long as the adopted meshes are fine enough,but it does not generally present a slip surface like in the cases from the classical continuum,indicating that the micro-polar continuum is capable of capturing the non-local geotechnical failure characteristic.Due to the coupling effects of lc and strain softening,softening behavior of geomaterial tends to be postponed.Additionally,the bearing capacity of a geotechnical system may be significantly underestimated,if the effects of lc are not modeled or considered in numerical analyses.展开更多
It is always desirable to know the interior deformation pattern when a rock is subjected to mechanicalload. Few experimental techniques exist that can represent full-field three-dimensional （3D） straindistribution i...It is always desirable to know the interior deformation pattern when a rock is subjected to mechanicalload. Few experimental techniques exist that can represent full-field three-dimensional （3D） straindistribution inside a rock specimen. And yet it is crucial that this information is available for fully understandingthe failure mechanism of rocks or other geomaterials. In this study, by using the newlydeveloped digital volumetric speckle photography （DVSP） technique in conjunction with X-ray computedtomography （CT） and taking advantage of natural 3D speckles formed inside the rock due to materialimpurities and voids, we can probe the interior of a rock to map its deformation pattern under load andshed light on its failure mechanism. We apply this technique to the analysis of a red sandstone specimenunder increasing uniaxial compressive load applied incrementally. The full-field 3D displacement fieldsare obtained in the specimen as a function of the load, from which both the volumetric and the deviatoricstrain fields are calculated. Strain localization zones which lead to the eventual failure of the rock areidentified. The results indicate that both shear and tension are contributing factors to the failuremechanism. 2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.展开更多
This paper investigates the deformation and fracture propagation of sandstone specimen under uniaxial compression using the distributed fiber optic strain sensing(DFOSS)technology.It shows that the DFOSS-based circumf...This paper investigates the deformation and fracture propagation of sandstone specimen under uniaxial compression using the distributed fiber optic strain sensing(DFOSS)technology.It shows that the DFOSS-based circumferential strains are in agreement with the data monitored with the traditional strain gage.The DFOSS successfully scans the full-field view of axial and circumferential strains on the specimen surface.The spatiotemporal strain measurement based on DFOSS manifests crack closure and elastoplastic deformation,detects initialization of microcrack nucleation,and identifies strain localization within the specimen.The DFOSS well observes the effects of rock heterogeneity on rock deformation.The advantage of DFOSS-based strain acquisition includes the high spatiotemporal resolution of signals and the ability of full-surface strain scanning.The introduction to the DFOSS technology yields a better understanding of the rock damage process under uniaxial compression.展开更多
Influence of confining pressure from 0 to 28 MPa, which acts on the two lateral edges of rock specimen in plane strain compression, on the shear failure processes and patterns as well as on the macroscopically mechani...Influence of confining pressure from 0 to 28 MPa, which acts on the two lateral edges of rock specimen in plane strain compression, on the shear failure processes and patterns as well as on the macroscopically mechanical responses were numerically modeled by use of FLAC. A material imperfection with lower strength in comparison with the intact rock, which is close to the lower-left corner of the specimen, was prescribed. In elastic stage, the adopted constitutive relation of rock was linear elastic; in strain-softening stage, a composite Mohr-Coulomb criterion with tension cut-off and a post-peak linear constitutive relation were adopted. The numerical results show that with an increase of confining pressure the peak strength of axial stress-axial strain curve and the corresponding axial strain linearly increase; the residual strength and the stress drop from the peak strength to the residual strength increase; the failure modes of rock transform form the multiple shear bands close to the loading end of the specimen （confining pressure=0-0.1 MPa）, to the conjugate shear bands （0.5-2.0 MPa）, and then to the single shear band （4-28 MPa）. Once the tip of the band reaches the loading end of the specimen, the direction of the band changes so that the reflection of the band occurs. At higher confining pressure, the new-formed shear band does not intersect the imperfection, bringing extreme difficulties in prediction of the failure of rock structure, such as rock burst. The present results enhance the understanding of the shear failure processes and patterns of rock specimen in higher confining pressure and higher loading strain rate.展开更多
A mechanical model is proposed for the system of elastic beam and strain-softening pillar where strain localization is initiated at peak shear stress. To obtain the plastic deformation of the pillar due to the shear s...A mechanical model is proposed for the system of elastic beam and strain-softening pillar where strain localization is initiated at peak shear stress. To obtain the plastic deformation of the pillar due to the shear slips of multiple shear bands, the pillar is divided into several narrow slices where compressive deformation is treated as uniformity. In the light of the compatibility condition of deformation, the total compressive displacement of the pillar is equal to the displacement of the beam in the middle span. An instability criterion is derived analytically based on the energy principle using a known size of localization band according to gradient dependent plasticity. The main advantage of the present model is that the effects of the constitutive parameters of rock and the geometrical size of structure are reflected in the criterion. The condition that the derivative of distributed load with respect to the deflection of the beam in the middle span is less than zero is not only equivalent to, but also even more concise in form than the instability criterion. To study the influences of constitutive parameters and geometrical size on stability, some examples are presented.展开更多
A continental-scale strike-slip shear zone frequently presents a long-lasting deformation and physical expression of strain localization in a middle to lower crustal level.However,the deformation evolution of strain l...A continental-scale strike-slip shear zone frequently presents a long-lasting deformation and physical expression of strain localization in a middle to lower crustal level.However,the deformation evolution of strain localization at a small-scale remains unclear.This study investigated<10 cm wide shear zones developing in undeformed granodiorites exposed at the boundary of the continental-scale Gaoligong strike-slip shear zone.The small-scale ductile shear zones exhibit a typical transition from protomylonite,mylonite to extremely deformed ultramylonite,and decreasing mineral size from coarse-grained aggregates to extremely fine-grained mixed phases.Shearing sense indicators such as hornblende and feldspar porphyroclasts in the shear zone are the more significantly low-strain zone of mylonite.The microstructure and EBSD results revealed that the small-scale shear zone experienced ductile deformation under medium-high temperature conditions.Quartz aggregates suggested a consistent temperature with an irregular feature,exhibiting a dominated high-temperature prism <a> slip system.Additionally,coarse-grained aggregates in the mylonite of the shear zone were deformed predominantly by dislocation creep,while ultra-plastic flow by viscous grain boundary sliding was an essential deformation process in the extremely fine-grained(~50μm)mixed-phases in the ultramylonite.Microstructural-derived strain rates calculated from quartz paleopiezometry were on the order of 10^(-15) to 10^(-13) s^(-1)from low-strain mylonite to high strained ultramylonite.The localization and strain ratelimited process was fluid-assisted precipitation presenting transitions of compositions as hydrous retrogression of hornblende to mica during increasing deformation and exhumation.Furthermore,the potential occurrence of the small-scale shear zone was initiated at a middle-deep crust seated crustal condition dominated by the temperature-controlled formation and rheological weakening.展开更多
A three-stage model is introduced to describe the tensile failure process of rock and concrete materials.Failure of the material is defined to contain three stages in the model,which include elastic deformation stage,...A three-stage model is introduced to describe the tensile failure process of rock and concrete materials.Failure of the material is defined to contain three stages in the model,which include elastic deformation stage,body damage stage and localization damage stage.The failure mode change from uniform body damage to localization damage is expressed.The heterogeneity of material is described with strain strength distribution.The fracture factor and intact factor,defined as the distribution function of strain strength,are used to express the fracture state in the failure process.And the distributive parameters can be determined through the experimental stress-strain curve.展开更多
Detection of local strain at the nanometer scale with high sensitivity remains challenging.Here we report near-field infrared nano-imaging of local strains in bilayer graphene by probing strain-induced shifts of phono...Detection of local strain at the nanometer scale with high sensitivity remains challenging.Here we report near-field infrared nano-imaging of local strains in bilayer graphene by probing strain-induced shifts of phonon frequency.As a non-polar crystal,intrinsic bilayer graphene possesses little infrared response at its transverse optical phonon frequency.The reported optical detection of local strain is enabled by applying a vertical electrical field that breaks the symmetry of the two graphene layers and introduces finite electrical dipole moment to graphene phonon.The activated phonon further interacts with continuum electronic transitions,and generates a strong Fano resonance.The resulted Fano resonance features a very sharp near-field infrared scattering peak,which leads to an extraordinary sensitivity of-0.002%for the strain detection.Our results demonstrate the first nano-scale near-field Fano resonance,provide a new way to probe local strains with high sensitivity in non-polar crystals,and open exciting possibilities for studying strain-induced rich phenomena.展开更多
The coupling effects of the metastable austenitic phase and the amorphous matrix in a transformation-induced plasticity(TRIP)-reinforced bulk metallic glass(BMG)composite under compressive loading were investigated by...The coupling effects of the metastable austenitic phase and the amorphous matrix in a transformation-induced plasticity(TRIP)-reinforced bulk metallic glass(BMG)composite under compressive loading were investigated by employing the digital image correlation(DIC)technique.The evolution of local strain field in the crystalline phase and the amorphous matrix was directly monitored,and the contribution from the phase transformation of the metastable austenitic phase was revealed.Local shear strain was found to be effectively consumed by the displacive phase transformation of the metastable austenitic phase,which relaxed the local strain/stress concentration at the interface and thus greatly enhanced the plasticity of the TRIP-reinforced BMG composites.Our current study sheds light on in-depth understanding of the underlying deformation mechanism and the interplay between the amorphous matrix and the metastable crystalline phase during deformation,which is helpful for design of advanced BMG composites with further improved properties.展开更多
We reported a low-cost and easy-to-make method to effectively generate quantum dot(QD)states in 2D hBN films for quantum emissions at room temperature by utilizing silica nanospheres,in comparison with the sophisticat...We reported a low-cost and easy-to-make method to effectively generate quantum dot(QD)states in 2D hBN films for quantum emissions at room temperature by utilizing silica nanospheres,in comparison with the sophisticated nanofabrication method reported in previous studies.The QDs created in 2D hBN films using silica nanospheres exhibit pronounced photon emissions with a good photo-stability in air,a narrow distribution of the emission peaks within the range of 580-620 nm,and a directional emission pattern,behaving as a single electric dipole.Our work develops the method of controllable fabrication of quantum emitters in 2D materials by using nano materials and structures.展开更多
基金supported by the Korea Institute of Energy Technology Evaluation and Planning(KETEP)grant funded by the Korea Government(MOTIE)(Grant No.20214000000500,Training program of CCUS for the green growth)by the National Research Foundation of Korea(NRF)grant funded by the Korea Government(MSIT)(Grant No.2022R1F1A1076409)the support from the Chinese Scholarship Council for awarding a scholarship(CSC No.202106820011).
文摘The study of rock failure mechanisms is fundamental to geotechnical engineering,as it enhances design quality and mitigates disaster risks.This research employed in situ compression tests on 3D-printed rocklike samples with a single flaw,combining Micro-CT scans and a specialized loading device to analyze their behavior.Mechanical properties and failure modes of these printed samples were compared to those of natural flawed sandstones,demonstrating the capability of 3D printing to replicate natural rock characteristics.By reconstructing 3D crack evolution from 2D CT images and applying digital volume correlation(DVC),the study visualized internal strain fields and established a relationship between strain patterns and rock failure.The results reveal that crack initiation consistently occurs at the flaw,advancing into tensile and secondary shear or mixed cracks.For flaw angles(α)ranging from 0°to 45°,the 3D-printed samples exhibited a higher number of newly formed cracks and a faster increase in crack volume with strain.In contrast,for flaw angles of 45°≤α≤90°,the opposite trend was observed.The internal strain field exhibited significant strain localization,with this uneven distribution playing a critical role in sample failure.When the flaw angle was in the range of 0°≤α≤30°,failure was primarily driven by tensile cracks,forming distinct tensile bands.Conversely,for 30°<α≤90°,a combination of tensile and shear cracks dominated the failure,producing both shear and tensile bands in the sample.Additionally,the strain field component ε_(yy) showed a strong correlation with the evolution of internal damage,providing valuable insights into the underlying rock failure mechanisms.
基金financially supported by the National Natural Science Foundation of China(No.51574196)the Natural Sciences and Engineering Research Council of Canada(NSERC)in the form of an international research collaboration+3 种基金the financial support by Premier’s Research Excellence Award(PREA)NSERC-Discovery Accelerator Supplement(DAS)AwardCanada Foundation for Innovation(CFI)Ryerson Research Chair(RRC)program。
文摘Cyclic deformation behavior of friction-stir-welded dissimilar AA2024-T351 to AA7075-T65 aluminum alloy joints was evaluated via stepwise tests at different strain rates,along with transmission electron microscopy examinations to characterize the precipitates required to assess internal stresses.Electron backscatter diffraction was employed to observe the inhomogeneous microstructures of the FSWed joints.Strain localization appeared in the heat affected zone(HAZ)of AA2024 side.After cyclic deformation of 500 cycles at a total strain amplitude of 0.5%,the strength of the dissimilar joints resumed basically to that of AA2024 base material.And the AA2024 HAZ was obviously hardened,which should be attributed to the introduced dislocations during cyclic deformation process.Cyclic hardening capacity of the joints increased with decreasing strain rate.
基金support from National Natural Science Foundation of China(Grant No.52178309)the National Key R&D Program of China(Grant No.2017YFC0804602)the Fundamental Research Funds for the Central Universities(Grant No.2019JBM092)。
文摘To address the problems of strain localization, the exact Mohr-Coulomb (MC) model is used based on second-order cone programming (mpcFEM-SOCP) in the framework of micropolar continuum finite element method. Using the uniaxial compression test, we focused on the earth pressure problem of rigid wall segment involving non-associated plasticity. The numerical results reveal that when mpcFEM-SOCP is applied, the problems of mesh dependency can be effectively addressed. For geotechnical strain localization analysis involving non-associated MC plasticity, mpcFEM-SOCP in conjunction with the pseudo-time discrete scheme can improve the numerical stability and avoid the unreasonable softening issue in the pressure-displacement curves, which may be encountered in the conventional FEM. It also shows that the pressure-displacement responses calculated by mpcFEM-SOCP with the pseudo-time discrete scheme are higher than those calculated by mpcFEM-SOCP with the Davis scheme. The inclination angle of shear band predicted by mpcFEM-SOCP with the pseudo-time discrete scheme agrees well with the theoretical solution of non-associated MC plasticity.
基金the National Natural Science Foundation of China for financial support(Grant No.59875025) to the research cooperation with OIT,Japan
文摘Using elastic crystalline viscoplastic finite element (FE) annlysis, the formability of BCC steel sheets was assessed. An orientation probability assignment method in the FE modeling procedure, which can be categorized as an inhomogenized material modeling, was newly proposed. In the study, the crystal orientations of three materials, mild steel, dual phase steel and the high strength steel, were obtained by Xray diffraction and orientation distribution function (ODF) analyses. The measured ODF results have revealed clearly different textures in the sheets, featured by orientation fibers, skeleton lines and selected orientations in Euler angle space, which are closely related to the plastic anisotropy. Then, the crystal orientations were assigned to FE integration points by using this ODF data, individually. The FE analyses of the standard limiting dome height (LDH) test show how the fiber textures affect the extent of strain localization in the forming processes. It was confirmed by comparison with experimental results that this FE code could predict the extreme strain localization and assess the sheet formability.
文摘Based on governing equations of saturated porous media and Liapunov＇ s stability here, onset conditions matrix of porous media used by solid stress and Terzaghi＇s effective stress constitutive description under seepage flow state, are presented, which have different forms with different representation of the solid phase, matrix or skeleton, constitutive model of porous media. The main difference relates with how to describe the interaction between solid phase and liquid phase in constitutive model. The derived onset condition of strain localization under Terzaghi＇ s effective stress description can be used to interpret different failure types, piping effect, landslides and mudflows, by means of the type and the magnitude ratio of relative movement between solid phase and liquid phase. Examples here illuminate the onset condition of how to work.
基金The work was financially supported by a research grant from University of Science and Technology Beijing (No.20020611590).
文摘An investigation of computer simulation is presented to analyze the effectsof strain localization and damage evolution in large plastic deformation. The simulation is carriedout by using an elastic-plastic-damage coupling finite element program that is developed based onthe concept of mixed interpolation of displacement/pressure. This program has been incorporated intoa damage mechanics model as well as the corresponding damage criterion. To illustrate theperformance of the proposed approach, a typical strain localization problem has been simulated. Theresults show that the proposed approach is of good capability to capture strain localization andpredict the damage evolution.
基金This research was financially supported by the National Natural Science Foundation of China(Grant Nos.50679057 and 10972158).
文摘This paper presents a numerical investigation on the strain localization of an idealized sand in biaxial compression tests using the distinct element method(DEM).In addition to the dilatancy and material frictional angle,the principal stress field,and distributions of void ratio,particle velocity,and the averaged pure rotation rate(APR)in the DEM specimen are examined to illustrate the link between microscopic and macroscopic variables in the case of strain localization.The study shows that strain localization of the granular material in the tests proceeds with localizations of void ratio,strain and APR,and distortions of stress field and force chains.In addition,both thickness and inclination of the shear band change with the increasing of axial swain,with the former valued around 10-14 times of mean grain diameter and the later overall described by the Mohr-Coulomb theory.
基金supported by the National Natural Science Foundation of China(No.52101128)the Jiangsu Provincial Key Research and Development Program(No.BE023059)+1 种基金the Post-doctoral Science Foundation of China(No.2022M710021)the Northeastern University Postdoctoral Research Fund of China(No.20220202).
文摘Fracture strain becomes critical for the local formability and crash performance of carbody components when the tensile strength exceeds 1000 MPa.Regrettably,high-strength quenching and partitioning(Q&P)steels and dual-phase(DP)steels always focus on improving the tensile ductility for stretch formability,while ignoring their limited fracture strain.In this work,we explored a novel strategy,i.e.,developing a high fracture strain ferrite-martensite dual-phase steel(HFS-DP)maintaining good strength–ductility balance by suppressing intense strain localization during deformation and enhancing martensite deformability via microstructure design including grain refinement,nano-precipitate hardening in soft ferrite phase,low-carbon and high fraction martensite.HFS-DP demonstrates a remarkable 26%and 47%improvement in tensile ductility and fracture strain,respectively,compared to commercial DP1180 steel with similar ultimate tensile strength.Furthermore,HFS-DP also exhibits a substantial 39%improvement in fracture strain compared to retained austenite-involved commercial QP1180 steel.The detailed processes of strain partitioning,strain localization,and damage formation during deformation were revealed through in-situ scanning electron microscopy(SEM)observation combined with digital image correlation(DIC).The results indicate that the excellent coordinated deformation between ferrite and martensite,coupled with microstructure refinement,effectively suppresses intense strain localization.Moreover,the excellent martensite deformability resulting from the low carbon content also aids in retarding crack formation.This combination effectively suppresses damage initiation and development during deformation,therefore the fracture strain is significantly improved.This study not only contributes to a deeper understanding of the strain localization and damage process during tensile deformation of DP steels,but also provides a new perspective on designing ultrahigh strength steels with high ductility and fracture strain.
基金support from National Natural Science Foundation of China(Grant Nos.62205223)Natural Science Foundation of Guangdong Province(Grant Nos.2023A1515011455)+6 种基金Science and Technology Innovation Commission of Shenzhen(Grant Nos.20231121120748002)support from Guangdong Introducing Innovative and Entrepreneurial Teams(Grant Nos.2019ZT08L101)Natural Science Foundation of Guangdong Province(Grant Nos.2023A1515110091)Science and Technology Innovation Commission of Shenzhen(Grant Nos.JSGGKQTD20221101115701006)support from National Key R&D Program of China(Grant Nos.2021YFA1401100)National Natural Science Foundation of China(Grant Nos.12104317)Scientific Instrument Developing Project of Shenzhen University(Grant Nos.2023YQ003)。
文摘Two-dimensional transition metal dichalcogenides(2D TMDCs)have received considerable attention in local strain engineering due to their extraordinary mechanical flexibility,electonic structure,and optical properties.The strain-induced out-of-plane deformations in 2D TMDCs lead to diverse excitonic behaviors and versatile modulations in optical properties,paving the way for the development of advanced quantum technologies,flexible optoelectronic materials,and straintronic devices.Research on local strain engineering on 2D TMDCs has been delved into fabrication techniques,electronic state variations,and quantum optical applications.This review begins by summarizing the state-of-the-art methods for introducing local strain into 2D TMDCs,followed by an exploration of the impact of local strain engineering on optical properties.The intriguing phenomena resulting from local strain,such as exciton funnelling and anti-funnelling,are also discussed.We then shift the focus to the application of locally strained 2D TMDCs as quantum emitters,with various strategies outlined for modulating the properties of TMDC-based quantum emitters.Finally,we discuss the remaining questions in this field and provide an outlook on the future of local strain engineering on 2D TMDCs.
基金Supported by the National Natural Science Foundation of China(52101350).
文摘Welded joints can be divided into different material zones,with considerable variation of material properties around the weld toe.The material inhomogeneity influences the local stress and strain of welded joints under monotonic and cyclic loading.This study aims to examine the local stress and strain characteristics of welded joints considering material inhomogeneity.Numerical models with various material zones were developed,and material properties were determined based on hardness.Smooth specimen models were used to analyze stress and strain distributions excluding notch effects.A detailed inhomogeneous model of a welded joint was established based on extensive microhardness measurements around the weld toe and the Kriging interpolation method.Additionally,a homogeneous model and a simplified inhomogeneous model,based on limited measured data,were generated and compared with the detailed inhomogeneous model.Fatigue life was estimated using the Smith,Watson,and Topper method based on the obtained stress and strain.For smooth specimen models,stress concentration occurs at a location where the strain is not significant,and fatigue cracks were most likely to initiate from the base metal.Results from the two simplified models showed deviations from those of the detailed inhomogeneous model,and the limitations of these simplified models are discussed.
基金Projects(2017YFC0804602,2017YFC0404802)supported by the National Key R&D Program of ChinaProject(2019JBM092)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Geotechnical stability analyses based on classical continuum may lead to remarkable underestimations on geotechnical safety.To attain better estimations on geotechnical stability,the micro-polar continuum is employed so that its internal characteristic length(lc)can be utilized to model the shear band width.Based on two soil slope examples,the role of internal characteristic length in modeling the shear band width of geomaterial is investigated by the second-order cone programming optimized micro-polar continuum finite element method.It is recognized that the underestimation on factor of safety(FOS)calculated from the classical continuum tends to be more pronounced with the increase of lc.When the micro-polar continuum is applied,the shear band dominated by lc is almost kept unaffected as long as the adopted meshes are fine enough,but it does not generally present a slip surface like in the cases from the classical continuum,indicating that the micro-polar continuum is capable of capturing the non-local geotechnical failure characteristic.Due to the coupling effects of lc and strain softening,softening behavior of geomaterial tends to be postponed.Additionally,the bearing capacity of a geotechnical system may be significantly underestimated,if the effects of lc are not modeled or considered in numerical analyses.
基金financially supported by National Basic Research Program of China (973 Program) (No. 2010CB732002)National Natural Science Foundation of China (Nos. 51374211, 51374215)+1 种基金National Key Foundation for Exploring Scientific Instrument of China (No. 2013YQ240803)Fundamental Research Funds for the Central Universities (No. 2009QM02)
文摘It is always desirable to know the interior deformation pattern when a rock is subjected to mechanicalload. Few experimental techniques exist that can represent full-field three-dimensional （3D） straindistribution inside a rock specimen. And yet it is crucial that this information is available for fully understandingthe failure mechanism of rocks or other geomaterials. In this study, by using the newlydeveloped digital volumetric speckle photography （DVSP） technique in conjunction with X-ray computedtomography （CT） and taking advantage of natural 3D speckles formed inside the rock due to materialimpurities and voids, we can probe the interior of a rock to map its deformation pattern under load andshed light on its failure mechanism. We apply this technique to the analysis of a red sandstone specimenunder increasing uniaxial compressive load applied incrementally. The full-field 3D displacement fieldsare obtained in the specimen as a function of the load, from which both the volumetric and the deviatoricstrain fields are calculated. Strain localization zones which lead to the eventual failure of the rock areidentified. The results indicate that both shear and tension are contributing factors to the failuremechanism. 2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.
基金support from the Institute of Crustal Dynamics,China Earthquake Administration(Grant No.ZDJ2016-20 and ZDJ2019-15)。
文摘This paper investigates the deformation and fracture propagation of sandstone specimen under uniaxial compression using the distributed fiber optic strain sensing(DFOSS)technology.It shows that the DFOSS-based circumferential strains are in agreement with the data monitored with the traditional strain gage.The DFOSS successfully scans the full-field view of axial and circumferential strains on the specimen surface.The spatiotemporal strain measurement based on DFOSS manifests crack closure and elastoplastic deformation,detects initialization of microcrack nucleation,and identifies strain localization within the specimen.The DFOSS well observes the effects of rock heterogeneity on rock deformation.The advantage of DFOSS-based strain acquisition includes the high spatiotemporal resolution of signals and the ability of full-surface strain scanning.The introduction to the DFOSS technology yields a better understanding of the rock damage process under uniaxial compression.
基金Supported by the National Natural Science Foundation of China(50490275,50309004)
文摘Influence of confining pressure from 0 to 28 MPa, which acts on the two lateral edges of rock specimen in plane strain compression, on the shear failure processes and patterns as well as on the macroscopically mechanical responses were numerically modeled by use of FLAC. A material imperfection with lower strength in comparison with the intact rock, which is close to the lower-left corner of the specimen, was prescribed. In elastic stage, the adopted constitutive relation of rock was linear elastic; in strain-softening stage, a composite Mohr-Coulomb criterion with tension cut-off and a post-peak linear constitutive relation were adopted. The numerical results show that with an increase of confining pressure the peak strength of axial stress-axial strain curve and the corresponding axial strain linearly increase; the residual strength and the stress drop from the peak strength to the residual strength increase; the failure modes of rock transform form the multiple shear bands close to the loading end of the specimen （confining pressure=0-0.1 MPa）, to the conjugate shear bands （0.5-2.0 MPa）, and then to the single shear band （4-28 MPa）. Once the tip of the band reaches the loading end of the specimen, the direction of the band changes so that the reflection of the band occurs. At higher confining pressure, the new-formed shear band does not intersect the imperfection, bringing extreme difficulties in prediction of the failure of rock structure, such as rock burst. The present results enhance the understanding of the shear failure processes and patterns of rock specimen in higher confining pressure and higher loading strain rate.
文摘A mechanical model is proposed for the system of elastic beam and strain-softening pillar where strain localization is initiated at peak shear stress. To obtain the plastic deformation of the pillar due to the shear slips of multiple shear bands, the pillar is divided into several narrow slices where compressive deformation is treated as uniformity. In the light of the compatibility condition of deformation, the total compressive displacement of the pillar is equal to the displacement of the beam in the middle span. An instability criterion is derived analytically based on the energy principle using a known size of localization band according to gradient dependent plasticity. The main advantage of the present model is that the effects of the constitutive parameters of rock and the geometrical size of structure are reflected in the criterion. The condition that the derivative of distributed load with respect to the deflection of the beam in the middle span is less than zero is not only equivalent to, but also even more concise in form than the instability criterion. To study the influences of constitutive parameters and geometrical size on stability, some examples are presented.
基金financially supported by the National Natural Science Foundations of China(Nos.41972220,4188810)the National Key Research and Development Program(No.2017YFC0602401)the Excellent Youth Fund of the National Natural Science Foundation of China(No.41722207)。
文摘A continental-scale strike-slip shear zone frequently presents a long-lasting deformation and physical expression of strain localization in a middle to lower crustal level.However,the deformation evolution of strain localization at a small-scale remains unclear.This study investigated<10 cm wide shear zones developing in undeformed granodiorites exposed at the boundary of the continental-scale Gaoligong strike-slip shear zone.The small-scale ductile shear zones exhibit a typical transition from protomylonite,mylonite to extremely deformed ultramylonite,and decreasing mineral size from coarse-grained aggregates to extremely fine-grained mixed phases.Shearing sense indicators such as hornblende and feldspar porphyroclasts in the shear zone are the more significantly low-strain zone of mylonite.The microstructure and EBSD results revealed that the small-scale shear zone experienced ductile deformation under medium-high temperature conditions.Quartz aggregates suggested a consistent temperature with an irregular feature,exhibiting a dominated high-temperature prism <a> slip system.Additionally,coarse-grained aggregates in the mylonite of the shear zone were deformed predominantly by dislocation creep,while ultra-plastic flow by viscous grain boundary sliding was an essential deformation process in the extremely fine-grained(~50μm)mixed-phases in the ultramylonite.Microstructural-derived strain rates calculated from quartz paleopiezometry were on the order of 10^(-15) to 10^(-13) s^(-1)from low-strain mylonite to high strained ultramylonite.The localization and strain ratelimited process was fluid-assisted precipitation presenting transitions of compositions as hydrous retrogression of hornblende to mica during increasing deformation and exhumation.Furthermore,the potential occurrence of the small-scale shear zone was initiated at a middle-deep crust seated crustal condition dominated by the temperature-controlled formation and rheological weakening.
基金Project supported by the National Program on Key Basic Research Project of China(973 Program,No.2015CB250903)CAS Strategic Priority Research Program(B)(No.XDB10030303)
文摘A three-stage model is introduced to describe the tensile failure process of rock and concrete materials.Failure of the material is defined to contain three stages in the model,which include elastic deformation stage,body damage stage and localization damage stage.The failure mode change from uniform body damage to localization damage is expressed.The heterogeneity of material is described with strain strength distribution.The fracture factor and intact factor,defined as the distribution function of strain strength,are used to express the fracture state in the failure process.And the distributive parameters can be determined through the experimental stress-strain curve.
基金Supported by the National Key Research and Development Program of China (Grant No.2016YFA0302001)the National Natural Science Foundation of China (Grant Nos.11774224,12074244,11521404,and 61701394)+1 种基金support from the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learningadditional support from a Shanghai talent program。
文摘Detection of local strain at the nanometer scale with high sensitivity remains challenging.Here we report near-field infrared nano-imaging of local strains in bilayer graphene by probing strain-induced shifts of phonon frequency.As a non-polar crystal,intrinsic bilayer graphene possesses little infrared response at its transverse optical phonon frequency.The reported optical detection of local strain is enabled by applying a vertical electrical field that breaks the symmetry of the two graphene layers and introduces finite electrical dipole moment to graphene phonon.The activated phonon further interacts with continuum electronic transitions,and generates a strong Fano resonance.The resulted Fano resonance features a very sharp near-field infrared scattering peak,which leads to an extraordinary sensitivity of-0.002%for the strain detection.Our results demonstrate the first nano-scale near-field Fano resonance,provide a new way to probe local strains with high sensitivity in non-polar crystals,and open exciting possibilities for studying strain-induced rich phenomena.
基金financially supported by the National Natural Science Foundation of China(Nos.52061135207,51871016,51921001,11790293,and 51971017)111 Project(No.B07003)the Projects of SKL-AMM-USTB(Nos.2019Z-01 and 2018Z-19)。
文摘The coupling effects of the metastable austenitic phase and the amorphous matrix in a transformation-induced plasticity(TRIP)-reinforced bulk metallic glass(BMG)composite under compressive loading were investigated by employing the digital image correlation(DIC)technique.The evolution of local strain field in the crystalline phase and the amorphous matrix was directly monitored,and the contribution from the phase transformation of the metastable austenitic phase was revealed.Local shear strain was found to be effectively consumed by the displacive phase transformation of the metastable austenitic phase,which relaxed the local strain/stress concentration at the interface and thus greatly enhanced the plasticity of the TRIP-reinforced BMG composites.Our current study sheds light on in-depth understanding of the underlying deformation mechanism and the interplay between the amorphous matrix and the metastable crystalline phase during deformation,which is helpful for design of advanced BMG composites with further improved properties.
基金National Natural Science Foundation of China(No.11874067)。
文摘We reported a low-cost and easy-to-make method to effectively generate quantum dot(QD)states in 2D hBN films for quantum emissions at room temperature by utilizing silica nanospheres,in comparison with the sophisticated nanofabrication method reported in previous studies.The QDs created in 2D hBN films using silica nanospheres exhibit pronounced photon emissions with a good photo-stability in air,a narrow distribution of the emission peaks within the range of 580-620 nm,and a directional emission pattern,behaving as a single electric dipole.Our work develops the method of controllable fabrication of quantum emitters in 2D materials by using nano materials and structures.
