The deformation characteristics of silty soils under vibrational loads can easily change due to the wetting process,leading to the failure of roadbed structures.Commonly used methods for improving silty soils in engin...The deformation characteristics of silty soils under vibrational loads can easily change due to the wetting process,leading to the failure of roadbed structures.Commonly used methods for improving silty soils in engineering often yield unsatisfactory economic and ecological outcomes.As an environment-friendly soil improvement material,Xanthan gum has broad application prospects and is therefore considered a solidifying agent for enhancing silty soil properties in the Yellow River Basin.In this study,a series of tests is conducted using a scanning electron microscope and a dynamic triaxial testing apparatus to investigate the microstructure and dynamic deformation characteristics of unsaturated silty soil with varying xanthan gum contents during the wetting process.The results show that xanthan gum effectively fills voids between soil particles and adheres to their surfaces,forming fibrous and network structures.This modification enhances the inherent properties of the silty soil and significantly improves its stability under dynamic loading.Specifically,with increasing xanthan gum content,the dynamic shear modulus increases while the damping ratio decreases.During the wetting process,as suction decreases,the dynamic shear modulus decreases while the damping ratio increases.Xanthan gum reduces the sensitivity of the dynamic deformation characteristics of the treated silty soil to changes in suction levels.Finally,based on the modified Hardin-Drnevich hyperbolic model,a predictive model for the dynamic shear modulus and damping ratio of treated silty soil is proposed,considering the xanthan gum content.These research findings provide a theoretical basis for the construction and maintenance of water conservancy,slope stabilization,and roadbed projects in the Yellow River Basin.展开更多
The real-time dynamic deformation monitoring of offshore platforms under environmental excitation is crucial to their safe operation.Although Global Navigation Satellite System-Precise Point Positioning(GNSS-PPP)has b...The real-time dynamic deformation monitoring of offshore platforms under environmental excitation is crucial to their safe operation.Although Global Navigation Satellite System-Precise Point Positioning(GNSS-PPP)has been considered for this purpose,its monitoring accuracy is relatively low.Moreover,the influence of background noise on the dynamic monitoring accuracy of GNSS-PPP remains unclear.Hence,it is imperative to further validate the feasibility of GNSS-PPP for deformation monitoring of offshore platforms.To address these concerns,vibration table tests with different amplitudes and frequencies are conducted.The results demonstrate that GNSS-PPP can effectively monitor horizontal vibration displacement as low as±30 mm,which is consistent with GNSS-RTK.Furthermore,the spectral characteristic of background noise in GNSS-PPP is similar to that of GNSS-RTK(Real Time Kinematic).Building on this observation,an improved Complete Ensemble Empirical Mode Decomposition with Adaptive Noise(CEEMDAN)has been proposed to de-noise the data and enhance the dynamic monitoring accuracy of GNSS-PPP.Field monitoring application research is also undertaken,successfully extracting and analyzing the dynamic deformation of an offshore platform structure under environmental excitation using GNSS-PPP monitoring in conjunction with improved CEEMDAN de-noising.By comparing the de-noised dynamic deformation trajectories of the offshore platform during different periods,it is observed that the platform exhibits reversible alternating vibration responses under environmental excitation,with more pronounced displacement deformation in the direction of load action.The research results confirm the feasibility and potential of GNSS-PPP for dynamic deformation monitoring of offshore platforms.展开更多
The measurement of wing dynamic deformation in morphing aircraft is crucial for achieving closed-loop control and evaluating structural safety.For variable-sweep wings with active large deformation,this paper proposes...The measurement of wing dynamic deformation in morphing aircraft is crucial for achieving closed-loop control and evaluating structural safety.For variable-sweep wings with active large deformation,this paper proposes a novel videogrammetric method for full-field dynamic deformation measurement.A stereo matching method based on epipolar geometry constraint and topological constraint is presented to find the corresponding targets between stereo images.In addition,a new method based on affine transformation combined with adjacent closest point matching is developed,aiming to achieve fast and automatic tracking of targets in time-series images with large deformation.A calculation model for dynamic deformation parameters is established to obtain the displacement,sweep variable angle,and span variation.To verify the proposed method,a dynamic deformation measurement experiment is conducted on a variable-sweep wing model.The results indicate that the actual accuracy of the proposed method is approximately 0.02%of the measured area(e.g.,0.32 mm in a 1.6 m scale).During one morphing course,the sweep variable angle,the span variation and the displacement increase gradually,and then decrease.The maximum sweep variable angle is 36.6°,and the span variation is up to 101.13 mm.The overall configuration of the wing surface is effectively reconstructed under different morphing states.展开更多
Copper alloy is widely used in high-speed railway,aerospace and other fields due to its excellent electrical conductivity and mechanical properties.High speed deformation and dynamic loading under impact load is a com...Copper alloy is widely used in high-speed railway,aerospace and other fields due to its excellent electrical conductivity and mechanical properties.High speed deformation and dynamic loading under impact load is a complex service condition,which widely exists in the field of national defense,military and industrial application.Therefore,the dynamic deformation behavior of the Cu-20Ag alloy was investigated by Split Hopkinson Pressure Bar(SHPB)with the strain rates of 1000-25000 s^(-1),high-speed hydraulic servo material testing machine with the strain rates of 1-500 s^(-1).The effect of strain rate on flow stress and adiabatic shear sensitivity was analyzed.The results show that the increase of strain rate will increase the flow stress and critical strain,that is to say,the increase of strain rate will reduce the adiabatic shear sensitivity of the Cu-20Ag alloy.The Cu-Ag interface has obvious orientation relationship with;(111)_(Cu)//(111)_(Ag):(^(-)111)_(Cu)//(^(-)111)_(Ag):(^(-)200)_(Cu)//(^(-)200)_(Ag) and [0^(-)11]_(Cu)//[0^(-)11]_(Ag) with the increase of strain rate.The increase of strain rate promotes the precipitation of Ag and increases the number of interfaces in the microstructure,which hinders the movement of dislocations and improves the stress and yield strength of the Cu-20Ag alloy.The concentration and distribution density of dislocations and the precipitation of Ag were the main reasons improve the flow stress and yield strength of the Cu-20Ag alloy.展开更多
The deformation behavior of the dual phase steel （DP1000 steel） was studied by the quasi-static tensile ex-periment and the dynamic tensile experiment. The experiments were carried out at strain rates ranging from 1...The deformation behavior of the dual phase steel （DP1000 steel） was studied by the quasi-static tensile ex-periment and the dynamic tensile experiment. The experiments were carried out at strain rates ranging from 10^-4 to 2 000 s^-1 at room temperature. Then the stress-strain curves of DP1000 steel in the strain rate range of 10^-4-2000 s^-1 were measured. By introducing the strain rate sensitivity factor m, Zerilli Armstrong model was optimized. The con- stitutive equation parameters which formulate the mechanical behavior of DP1000 steel were fitted based on the John-son-Cook （JC） constitutive model and the optimized Zerilli-Armstrong （ZA） constitutive model, respectively. By comparing indicators of ＂accuracy-of-fit＂, Rz terms, for the two models, the optimized Zerilli-Armstrong constitu-tive model can reflect plastic deformation behavior both at the low and high strain rates more accurately. The reasons why the optimized Zerilli-Armstrong constitutive model is more advantageous than the Johnson Cook model were discussed by using the yield strength and ultimate tensile strength （UTS） versus strain rates, and strain hardening rate versus effective plastic strain analytical methods.展开更多
-This paper presents the research results of dynamic pore water pressure and the characteristics of dynamic deformation of saturated soft clay and the factors affecting the dynamic pore water pressure and dynamic defo...-This paper presents the research results of dynamic pore water pressure and the characteristics of dynamic deformation of saturated soft clay and the factors affecting the dynamic pore water pressure and dynamic deformation. Dynamic triaxial compression tests are carried out and the soil samples used in the tests are remoulded clay from the seabed of the Bohai Bay. The paper also deals with the dynamic deformation mechanism of saturated soft clay foundation without drain. A calculation model for permanent dynamic deformation of saturated soft clay foundation has been established.展开更多
ABSTRACT The multipath has long been considered a major error source in GPS applications .The characteristics 0f the GPS signal multipath effects are analyzed. based on which an experiment that considers the characte...ABSTRACT The multipath has long been considered a major error source in GPS applications .The characteristics 0f the GPS signal multipath effects are analyzed. based on which an experiment that considers the characteristics of dynamic deformation monitoring has been carried out. The solution results of observation data in two successive days are processed by a method,which combines the wavelet filtering and the differential correction betweentwo successive days. The research demonstrates that the multipath errors have stronger repeatability on successive days;after significantly mitigating the influence of multipath effects,the accuracy of three-dimensional positioning for GPS dynamic deformation monitoring can attain the mm level,an obvious accuracy improving particularly invertical component.The characteristics of GPS signal multipath,th eexperimental scheme and the qualitative and quantitative analysis of results are detailed.展开更多
Construction progress of long-span bridge is complicated and the quality control is strict. Any disadvantage during construction may potentially affect the internal forces and deck alignments after it is open to traff...Construction progress of long-span bridge is complicated and the quality control is strict. Any disadvantage during construction may potentially affect the internal forces and deck alignments after it is open to traffic. To exactly evaluate the periodic alignments, internal forces and safety, geometrical and physical monitoring are needed during construction. This study aims at the requirement of dynamic geometric monitoring during Sutong Bridge construction, and introduces the realization and observing schemes of the self-developed GPS real-time dynamic geometrical deformation monitoring system. Affected by wind load and construction circumstance, GPS （global positioning system） monitoring signal contains a variety of noise. And the useful signal can be extracted from the signal after de-noising the noises. A de-noising method based on EMD （empirical mode decomposition） model is introduced here to process the bridge dynamic monitoring data, and with the wavelet threshold de-noising method are compared. The result shows that the EMD method has good adaptability, is free from the choice of wavelet bases and the number of decomposition layer. The method is an effective de-noising method for dynamic deformation monitoring to large-span bridges.展开更多
A new dimensionless number is proposed for dynamic plastic deformation analysis of clamped circular plates under underwater explosion loads by introducing dimensional analysis method to the basic dynamical governing e...A new dimensionless number is proposed for dynamic plastic deformation analysis of clamped circular plates under underwater explosion loads by introducing dimensional analysis method to the basic dynamical governing equations of circular plates.The relation between dimensionless final plastic deformation of circular plates and the new dimensionless number is established based on massive underwater explosion test data.Meanwhile,comparative analysis was discussed with two other published dimensionless parameters which indicated the new dimensionless number proposed in this paper is more effective and extensive to predict the dynamic plastic response of circular plates under underwater explosion condition.展开更多
Premature adiabatic shear localization caused by strain softening is a roadblock for the application of body-centered cubic(BCC)structured high-entropy alloy(HEAs)in the impact field.A micron-scale orthorhombic-phase(...Premature adiabatic shear localization caused by strain softening is a roadblock for the application of body-centered cubic(BCC)structured high-entropy alloy(HEAs)in the impact field.A micron-scale orthorhombic-phase(O-phase)strengthened TiZrVNbAl alloy was developed to delay adiabatic shear failure and enhance dynamic ductility.The O-phase can not only reduce the slip length,but also promote the pinning and tangling of the dislocations near the phase boundaries.The introduction of the O-phase transformed the strain hardening rate from negative to positive,resulting in a significantly improved dynamic shear resistance.Meanwhile,slip transfer across the O-phase via dislocation cutting mechanisms and a reduction of slip band spacing guaranteed dynamic deformation uniformity.Benefiting from the introduction of the O-phase,the alloy exhibits an excellent stored energy density(∼446 J/cm^(3),surpass the reported BCC-HEAs and typical titanium alloys),a large dynamic fracture strain(∼42%)and a considerable dynamic specific yield strength(∼241 MPa cm^(3)g^(-1)).The present study presents an effective approach for developing BCC-HEAs with excellent dynamic shear resistance and plasticity.展开更多
The tensile properties and deformation mechanisms of the reduced activation ferritic/martensitic steel—China low activation martensitic(CLAM)steel are determined from tests carried out over a wider range of strain ra...The tensile properties and deformation mechanisms of the reduced activation ferritic/martensitic steel—China low activation martensitic(CLAM)steel are determined from tests carried out over a wider range of strain rate and temperature.During high-temperature deformation,the plastic deformation modes involve dynamic recrystallization(DRX)and dynamic recovery(DRV)processes,which govern the mechanical behaviors of CLAM steel under different loading conditions.This work systematically explored the effects of increasing strain rates and temperatures,finding that the microstructure evolution process is facilitated by nano-sized M_(23)C_(6)precipitates and the grain boundaries of the initial microstructure.Under quasi-static loading conditions,DRX grains preferentially nucleate around M_(23)C_(6) precipitates,and the dominant deformation mechanism is DRX.However,under dynamic loading conditions,the number of DRX grains decreases significantly,and the dominant deformation mechanism converts to DRV.It was concluded that the coupling effects of strain rates and temperatures strongly influence DRX and DRV processes,which ultimately determine the mechanical properties and microstructure evolution.Moreover,dynamic deformation at elevated temperatures achieves much finer grain sizes,offering a novel method for grain refinement through dynamic straining processes.展开更多
Differential interferometric synthetic aperture radar （DInSAR） technology is a new method to monitor the dynamic surface subsidence. It can monitor the large scope of dynamic deformation process of surface subsidenc...Differential interferometric synthetic aperture radar （DInSAR） technology is a new method to monitor the dynamic surface subsidence. It can monitor the large scope of dynamic deformation process of surface subsidence basin and better reflect the surface subsidence form in different stages. But under the influence of factors such as noise and other factors, the tilt and horizontal deformation curves regularity calculated by DInSAR data are poorer and the actual deviation is larger. The tilt and horizontal deformations are the important indices for the safety of surface objects protection. Numerical simulation method was used to study the dynamic deformation of LW32 of West Cliff colliery in Australia based on the DInSAR monitoring data. The result indicates that the subsidence curves of two methods fit well and the correlation coefficient is more than 95%. The other deformations calculated by numerical simulation results are close to the theory form. Therefore, considering the influence, the surface and its subsidiary structures and buildings due to mining, the numerical simulation method based on the DInSAR data can reveal the distribution rules of the surface dynamic deformation values and supply the shortcomings of DInSAR technology. The research shows that the method has good applicability and can provide reference for similar situation.展开更多
Based on the recently proposed mirror-assisted multi-view digital image correlation(MV-DIC),we establish a cost-effective and easy-to-implement mirror-assisted multi-view high-speed digital image correlation(MVHS-DIC)...Based on the recently proposed mirror-assisted multi-view digital image correlation(MV-DIC),we establish a cost-effective and easy-to-implement mirror-assisted multi-view high-speed digital image correlation(MVHS-DIC)method and explore its applications for dual-surface full-field dynamic deformation measurement.In contrast to the general requirement of four expensive high-speed cameras for dual-surface dynamic deformation field measurement,the established mirror-assisted MVHS-DIC halves the cost by involving only two synchronized high-speed cameras and two planar mirrors.The two synchronized high-speed cameras can dynamically measure the front and rear surfaces of a sheet sample simultaneously through the reflection of the two mirrors.The results on the two surfaces are then transformed into the same coordinate system,leading to the required dual-surface 3D dynamical deformation fields.The effectiveness and accuracy of the established system are validated through modal tests of a cantilever aluminum sheet.The vibration measurement of a drum and dual-surface transient deformation measurement of a smartphone in the drop-collision process further prove its practicability.Benefiting from the attractive advantages of multi-view dynamic deformation measurement in a cost-efficient way,the established mirror-assisted MVHS-DIC is expected to encourage more comprehensive dynamic mechanical behavior characterization of regular-sized materials and structures in vibration and impact engineering fields.展开更多
In this study, mechanical tests were conducted oil a face-centered cubic FeCoNiCrMn high-entropy alloy, both in tension and compression, in a wide range of strain rates （10^-4-10^4 s^-1） to systematically investigat...In this study, mechanical tests were conducted oil a face-centered cubic FeCoNiCrMn high-entropy alloy, both in tension and compression, in a wide range of strain rates （10^-4-10^4 s^-1） to systematically investigate its dynamic response and underlying deformation mechanism. Materials with different grain sizes were tested to understand the effect of grain size, thus grain boundary volume, on the mechanical prop-erties. Microstructures of various samples both before and after deformation were examined using elec-tron backscatter diffraction and transmission electron microscopy. The dislocation structure as well as deformation-induced twins were analyzed and correlated with the measured mechanical properties. Plastic stability during tension of the current high-entropy alloy （HEA）, in particular, at dynamic strain rates, was discussed in lights of strain-rate sensitivity and work hardening rate. It was found that, under dynamic conditions, the strength and uniform ductility increased simultaneously as a result of the mas-sive formation of deformation twins. Specifically, an ultimate tensile strength of 734 MPa and uniform elongation of-63% are obtained at 2.3×10^3 s^-1, indicating that the alloy has great potential for energy absorption upon impact loading.展开更多
Hollow porcelain insulators in substations are frequently confronted with rain flashovers under extreme rainfall.This study aims to investigate the spatial and temporal variation of electric fields between hollow porc...Hollow porcelain insulators in substations are frequently confronted with rain flashovers under extreme rainfall.This study aims to investigate the spatial and temporal variation of electric fields between hollow porcelain insulator sheds affected by dynamic deformation of pendant water drops and effects of the dimensionless number of fluids,the Weber number(We)and the electric Bond number(BoE),on it for influencing factors'analysis.Flow‐electric field coupling simulations were carried out to compute the magnitude and the position of AC electric fields between the sheds.The results show that the maximum electric field at a point in time(Etmax)increases significantly after the breakup of the pendant water drop,and its position alters accordingly.For low We and BoE,the global maximum electric field(Egmax)increases with increasing We and BoE,respectively.It is much closer to the adjacent sheds and occurs later than Etmax at the breakup of the pendant water drop(Ebmax).By contrast,Egmax decreases in different degrees at high We and BoE,respectively.There is little difference between Egmax and Ebmax in the position and the occurring time.The influence mechanism on the maximum electric field and discharges and the relationship between discharges induced by the pendant water drop and rain flashover are discussed.展开更多
Coral sandy soils widely exist in coral island reefs and seashores in tropical and subtropical regions.Due to the unique marine depositional environment of coral sandy soils,the engineering characteristics and respons...Coral sandy soils widely exist in coral island reefs and seashores in tropical and subtropical regions.Due to the unique marine depositional environment of coral sandy soils,the engineering characteristics and responses of these soils subjected to monotonic and cyclic loadings have been a subject of intense interest among the geotechnical and earthquake engineering communities.This paper critically reviews the progress of experimental investigations on the undrained behavior of coral sandy soils under monotonic and cyclic loadings over the last three decades.The focus of coverage includes the contractive-dilative behavior,the pattern of excess pore-water pressure(EPWP)generation and the liquefaction mechanism and liquefaction resistance,the small-strain shear modulus and strain-dependent shear modulus and damping,the cyclic softening feature,and the anisotropic characteristics of undrained responses of saturated coral sandy soils.In particular,the advances made in the past decades are reviewed from the following aspects:(1)the characterization of factors that impact the mechanism and patterns of EPWP build-up;(2)the identification of liquefaction triggering in terms of the apparent viscosity and the average flow coefficient;(3)the establishment of the invariable form of strain-based,stress-based,or energy-based EPWP ratio formulas and the unique relationship between the new proxy of liquefaction resistance and the number of cycles required to reach liquefaction;(4)the establishment of the invariable form of the predictive formulas of small strain modulus and strain-dependent shear modulus;and(5)the investigation on the effects of stress-induced anisotropy on liquefaction susceptibility and dynamic deformation characteristics.Insights gained through the critical review of these advances in the past decades offer a perspective for future research to further resolve the fundamental issues concerning the liquefaction mechanism and responses of coral sandy sites subjected to cyclic loadings associated with seismic events in marine environments.展开更多
Compressive properties of AZ31 alloy were investigated at temperatures from room temperature to 543 K and at strain rates from 10-3to 2×10 4s-1.The results show that the compressive behavior and deformation mecha...Compressive properties of AZ31 alloy were investigated at temperatures from room temperature to 543 K and at strain rates from 10-3to 2×10 4s-1.The results show that the compressive behavior and deformation mechanism of AZ31 depend largely on the temperature and strain rate.The flow stress increases with the increase of strain rate at fixed temperature,while decreases with the increase of deformation temperature at fixed strain rate.At low temperature and quasi-static condition,the true stress-true strain curve of AZ31 alloy can be divided into three stages(strain hardening,softening and stabilization) after yielding.However,at high temperature and high strain rate,the AZ31 alloy shows ideal elastic-plastic properties.It is therefore suggested that the change in loading conditions(temperature and strain rate) plays an important role in deformation mechanisms of AZ31 alloy.展开更多
Lamellar nanostructures were induced in a plain martensitic low-carbon steel by using dynamic plastic deformation at room temperature.The nanostructured steel was hardened after annealing at 673 K for20 min,with a ten...Lamellar nanostructures were induced in a plain martensitic low-carbon steel by using dynamic plastic deformation at room temperature.The nanostructured steel was hardened after annealing at 673 K for20 min,with a tensile strength increased from 1.2 GPa to 1.6 GPa.Both the remained nanostructures and annealing-induced precipitates in nano-scale play key roles in the hardening.展开更多
A pure Cu （99.995 wt%） has been subjected to dynamic plastic deformation at cryogenic temperature to a strain of 2.1. Three types of microstructures that are related to dislocation slip, twinning and shear banding h...A pure Cu （99.995 wt%） has been subjected to dynamic plastic deformation at cryogenic temperature to a strain of 2.1. Three types of microstructures that are related to dislocation slip, twinning and shear banding have been quantitatively characterized by transmission electron microscopy （TEM） assisted by convergent beam electron diffraction （CBED） analysis. Microstructures originated from dislocation slip inside or outside the shear bands are characterized by low angle boundaries （〈15°） that are spaced in the nanometer scale, whereas most deformation twins are deviated from the perfect ∑3 coincidence （60°/〈111〉） up to the maximum angle of 9°. The quantitative structural characteristics are compared with those in conventionally deformed Cu at low strain rates, and allowed a quantitative analysis of the flow stress-structural parameter relationship.展开更多
Molecular dynamics simulation is employed to study the tension and compression deformation behaviors of magnesium single crystals with different orientations.The angle between the loading axis and the basal direction ...Molecular dynamics simulation is employed to study the tension and compression deformation behaviors of magnesium single crystals with different orientations.The angle between the loading axis and the basal direction ranges from 0° to 90°.The simulation results show that the initial defects usually nucleate at free surfaces,but the initial plastic deformation and the subsequent microstructural evolutions are various due to different loading directions.The tension simulations exhibit the deformation mechanisms of twinning,slip,crystallographic reorientation and basal/prismatic transformation.The twinning,crystallographic reorientation and basal/prismatic transformation can only appear in the crystal model loaded along or near the a-axis or c-axis.For the compression simulations,the basal,prismatic and pyramidal slips are responsible for the initial plasticity,and no twinning is observed.Moreover,the plastic deformation models affect the yield strengths for the samples with different orientations.The maximum yield stresses for the samples loaded along the c-axis or a-axis are much higher than those loaded in other directions.展开更多
基金supported by the Postgraduate Education Reform and Quality Improvement Project of Henan Province,China(Grant No.YJS2023AL004)the Graduate Innovation Project of North China University of Water Resources and Electric Power(Grant No.NCWUYC-202315069)the China National Scholarship Fund organized by the China Scholarship Council(Grant No.202208410337).
文摘The deformation characteristics of silty soils under vibrational loads can easily change due to the wetting process,leading to the failure of roadbed structures.Commonly used methods for improving silty soils in engineering often yield unsatisfactory economic and ecological outcomes.As an environment-friendly soil improvement material,Xanthan gum has broad application prospects and is therefore considered a solidifying agent for enhancing silty soil properties in the Yellow River Basin.In this study,a series of tests is conducted using a scanning electron microscope and a dynamic triaxial testing apparatus to investigate the microstructure and dynamic deformation characteristics of unsaturated silty soil with varying xanthan gum contents during the wetting process.The results show that xanthan gum effectively fills voids between soil particles and adheres to their surfaces,forming fibrous and network structures.This modification enhances the inherent properties of the silty soil and significantly improves its stability under dynamic loading.Specifically,with increasing xanthan gum content,the dynamic shear modulus increases while the damping ratio decreases.During the wetting process,as suction decreases,the dynamic shear modulus decreases while the damping ratio increases.Xanthan gum reduces the sensitivity of the dynamic deformation characteristics of the treated silty soil to changes in suction levels.Finally,based on the modified Hardin-Drnevich hyperbolic model,a predictive model for the dynamic shear modulus and damping ratio of treated silty soil is proposed,considering the xanthan gum content.These research findings provide a theoretical basis for the construction and maintenance of water conservancy,slope stabilization,and roadbed projects in the Yellow River Basin.
基金financially supported by the National Key R&D Program of China(Grant No.2022YFB4200705)the National Natural Science Foundation of China(Grant No.52109146)。
文摘The real-time dynamic deformation monitoring of offshore platforms under environmental excitation is crucial to their safe operation.Although Global Navigation Satellite System-Precise Point Positioning(GNSS-PPP)has been considered for this purpose,its monitoring accuracy is relatively low.Moreover,the influence of background noise on the dynamic monitoring accuracy of GNSS-PPP remains unclear.Hence,it is imperative to further validate the feasibility of GNSS-PPP for deformation monitoring of offshore platforms.To address these concerns,vibration table tests with different amplitudes and frequencies are conducted.The results demonstrate that GNSS-PPP can effectively monitor horizontal vibration displacement as low as±30 mm,which is consistent with GNSS-RTK.Furthermore,the spectral characteristic of background noise in GNSS-PPP is similar to that of GNSS-RTK(Real Time Kinematic).Building on this observation,an improved Complete Ensemble Empirical Mode Decomposition with Adaptive Noise(CEEMDAN)has been proposed to de-noise the data and enhance the dynamic monitoring accuracy of GNSS-PPP.Field monitoring application research is also undertaken,successfully extracting and analyzing the dynamic deformation of an offshore platform structure under environmental excitation using GNSS-PPP monitoring in conjunction with improved CEEMDAN de-noising.By comparing the de-noised dynamic deformation trajectories of the offshore platform during different periods,it is observed that the platform exhibits reversible alternating vibration responses under environmental excitation,with more pronounced displacement deformation in the direction of load action.The research results confirm the feasibility and potential of GNSS-PPP for dynamic deformation monitoring of offshore platforms.
基金supported by the National Natural Science Foundation of China(Grant No.12202282).
文摘The measurement of wing dynamic deformation in morphing aircraft is crucial for achieving closed-loop control and evaluating structural safety.For variable-sweep wings with active large deformation,this paper proposes a novel videogrammetric method for full-field dynamic deformation measurement.A stereo matching method based on epipolar geometry constraint and topological constraint is presented to find the corresponding targets between stereo images.In addition,a new method based on affine transformation combined with adjacent closest point matching is developed,aiming to achieve fast and automatic tracking of targets in time-series images with large deformation.A calculation model for dynamic deformation parameters is established to obtain the displacement,sweep variable angle,and span variation.To verify the proposed method,a dynamic deformation measurement experiment is conducted on a variable-sweep wing model.The results indicate that the actual accuracy of the proposed method is approximately 0.02%of the measured area(e.g.,0.32 mm in a 1.6 m scale).During one morphing course,the sweep variable angle,the span variation and the displacement increase gradually,and then decrease.The maximum sweep variable angle is 36.6°,and the span variation is up to 101.13 mm.The overall configuration of the wing surface is effectively reconstructed under different morphing states.
基金financially supported by the Innovation Leading Project of Henan Province (No. 191110210400)the Key Scientific Research Projects of Colleges and Universities in Henan Province (No. 19A430012)+3 种基金the Luoyang Science and Technology Major Project (No. 1901006A)the Henan Outstanding Talents Innovation Fund (182101510003)National Key R&D Plan (No. 2016YFB0301400)National Key R&D Plan (No.2017YFB0306400)
文摘Copper alloy is widely used in high-speed railway,aerospace and other fields due to its excellent electrical conductivity and mechanical properties.High speed deformation and dynamic loading under impact load is a complex service condition,which widely exists in the field of national defense,military and industrial application.Therefore,the dynamic deformation behavior of the Cu-20Ag alloy was investigated by Split Hopkinson Pressure Bar(SHPB)with the strain rates of 1000-25000 s^(-1),high-speed hydraulic servo material testing machine with the strain rates of 1-500 s^(-1).The effect of strain rate on flow stress and adiabatic shear sensitivity was analyzed.The results show that the increase of strain rate will increase the flow stress and critical strain,that is to say,the increase of strain rate will reduce the adiabatic shear sensitivity of the Cu-20Ag alloy.The Cu-Ag interface has obvious orientation relationship with;(111)_(Cu)//(111)_(Ag):(^(-)111)_(Cu)//(^(-)111)_(Ag):(^(-)200)_(Cu)//(^(-)200)_(Ag) and [0^(-)11]_(Cu)//[0^(-)11]_(Ag) with the increase of strain rate.The increase of strain rate promotes the precipitation of Ag and increases the number of interfaces in the microstructure,which hinders the movement of dislocations and improves the stress and yield strength of the Cu-20Ag alloy.The concentration and distribution density of dislocations and the precipitation of Ag were the main reasons improve the flow stress and yield strength of the Cu-20Ag alloy.
基金Item Sponsored by National High Technology Research and Development Program(863Program)of China(2009AA03Z518)Basic Theory Research Fund of Engineering Research Institute of USTB of China(YJ2010-006)
文摘The deformation behavior of the dual phase steel （DP1000 steel） was studied by the quasi-static tensile ex-periment and the dynamic tensile experiment. The experiments were carried out at strain rates ranging from 10^-4 to 2 000 s^-1 at room temperature. Then the stress-strain curves of DP1000 steel in the strain rate range of 10^-4-2000 s^-1 were measured. By introducing the strain rate sensitivity factor m, Zerilli Armstrong model was optimized. The con- stitutive equation parameters which formulate the mechanical behavior of DP1000 steel were fitted based on the John-son-Cook （JC） constitutive model and the optimized Zerilli-Armstrong （ZA） constitutive model, respectively. By comparing indicators of ＂accuracy-of-fit＂, Rz terms, for the two models, the optimized Zerilli-Armstrong constitu-tive model can reflect plastic deformation behavior both at the low and high strain rates more accurately. The reasons why the optimized Zerilli-Armstrong constitutive model is more advantageous than the Johnson Cook model were discussed by using the yield strength and ultimate tensile strength （UTS） versus strain rates, and strain hardening rate versus effective plastic strain analytical methods.
文摘-This paper presents the research results of dynamic pore water pressure and the characteristics of dynamic deformation of saturated soft clay and the factors affecting the dynamic pore water pressure and dynamic deformation. Dynamic triaxial compression tests are carried out and the soil samples used in the tests are remoulded clay from the seabed of the Bohai Bay. The paper also deals with the dynamic deformation mechanism of saturated soft clay foundation without drain. A calculation model for permanent dynamic deformation of saturated soft clay foundation has been established.
文摘ABSTRACT The multipath has long been considered a major error source in GPS applications .The characteristics 0f the GPS signal multipath effects are analyzed. based on which an experiment that considers the characteristics of dynamic deformation monitoring has been carried out. The solution results of observation data in two successive days are processed by a method,which combines the wavelet filtering and the differential correction betweentwo successive days. The research demonstrates that the multipath errors have stronger repeatability on successive days;after significantly mitigating the influence of multipath effects,the accuracy of three-dimensional positioning for GPS dynamic deformation monitoring can attain the mm level,an obvious accuracy improving particularly invertical component.The characteristics of GPS signal multipath,th eexperimental scheme and the qualitative and quantitative analysis of results are detailed.
文摘Construction progress of long-span bridge is complicated and the quality control is strict. Any disadvantage during construction may potentially affect the internal forces and deck alignments after it is open to traffic. To exactly evaluate the periodic alignments, internal forces and safety, geometrical and physical monitoring are needed during construction. This study aims at the requirement of dynamic geometric monitoring during Sutong Bridge construction, and introduces the realization and observing schemes of the self-developed GPS real-time dynamic geometrical deformation monitoring system. Affected by wind load and construction circumstance, GPS （global positioning system） monitoring signal contains a variety of noise. And the useful signal can be extracted from the signal after de-noising the noises. A de-noising method based on EMD （empirical mode decomposition） model is introduced here to process the bridge dynamic monitoring data, and with the wavelet threshold de-noising method are compared. The result shows that the EMD method has good adaptability, is free from the choice of wavelet bases and the number of decomposition layer. The method is an effective de-noising method for dynamic deformation monitoring to large-span bridges.
基金supported by the National Natural Science Foundation of China(12402444)。
文摘A new dimensionless number is proposed for dynamic plastic deformation analysis of clamped circular plates under underwater explosion loads by introducing dimensional analysis method to the basic dynamical governing equations of circular plates.The relation between dimensionless final plastic deformation of circular plates and the new dimensionless number is established based on massive underwater explosion test data.Meanwhile,comparative analysis was discussed with two other published dimensionless parameters which indicated the new dimensionless number proposed in this paper is more effective and extensive to predict the dynamic plastic response of circular plates under underwater explosion condition.
基金supported by the YEQISUN Joint Funds of the National Natural Science Foundation of China(Grant No.U2241234)the National Natural Science Foundation of China(Grant No.52301127).
文摘Premature adiabatic shear localization caused by strain softening is a roadblock for the application of body-centered cubic(BCC)structured high-entropy alloy(HEAs)in the impact field.A micron-scale orthorhombic-phase(O-phase)strengthened TiZrVNbAl alloy was developed to delay adiabatic shear failure and enhance dynamic ductility.The O-phase can not only reduce the slip length,but also promote the pinning and tangling of the dislocations near the phase boundaries.The introduction of the O-phase transformed the strain hardening rate from negative to positive,resulting in a significantly improved dynamic shear resistance.Meanwhile,slip transfer across the O-phase via dislocation cutting mechanisms and a reduction of slip band spacing guaranteed dynamic deformation uniformity.Benefiting from the introduction of the O-phase,the alloy exhibits an excellent stored energy density(∼446 J/cm^(3),surpass the reported BCC-HEAs and typical titanium alloys),a large dynamic fracture strain(∼42%)and a considerable dynamic specific yield strength(∼241 MPa cm^(3)g^(-1)).The present study presents an effective approach for developing BCC-HEAs with excellent dynamic shear resistance and plasticity.
基金financially supported by National Natural Science Foundation of China(Grant Nos.12025205 and 12141203)Natural Science Basic Research Program of Shaanxi(Program No.S2023-JC-QN-0614)Fund for Basic Research(No.2021T019)from the Analytical&Testing Center of Northwestern Polytechnical University.
文摘The tensile properties and deformation mechanisms of the reduced activation ferritic/martensitic steel—China low activation martensitic(CLAM)steel are determined from tests carried out over a wider range of strain rate and temperature.During high-temperature deformation,the plastic deformation modes involve dynamic recrystallization(DRX)and dynamic recovery(DRV)processes,which govern the mechanical behaviors of CLAM steel under different loading conditions.This work systematically explored the effects of increasing strain rates and temperatures,finding that the microstructure evolution process is facilitated by nano-sized M_(23)C_(6)precipitates and the grain boundaries of the initial microstructure.Under quasi-static loading conditions,DRX grains preferentially nucleate around M_(23)C_(6) precipitates,and the dominant deformation mechanism is DRX.However,under dynamic loading conditions,the number of DRX grains decreases significantly,and the dominant deformation mechanism converts to DRV.It was concluded that the coupling effects of strain rates and temperatures strongly influence DRX and DRV processes,which ultimately determine the mechanical properties and microstructure evolution.Moreover,dynamic deformation at elevated temperatures achieves much finer grain sizes,offering a novel method for grain refinement through dynamic straining processes.
基金Project (20110023110014) supported by Specialized Research Fund for the Doctoral Program of Higher Education of ChinaProject (2010QD01) supported by Fundamental Research Funds for the Central Universities,China
文摘Differential interferometric synthetic aperture radar （DInSAR） technology is a new method to monitor the dynamic surface subsidence. It can monitor the large scope of dynamic deformation process of surface subsidence basin and better reflect the surface subsidence form in different stages. But under the influence of factors such as noise and other factors, the tilt and horizontal deformation curves regularity calculated by DInSAR data are poorer and the actual deviation is larger. The tilt and horizontal deformations are the important indices for the safety of surface objects protection. Numerical simulation method was used to study the dynamic deformation of LW32 of West Cliff colliery in Australia based on the DInSAR monitoring data. The result indicates that the subsidence curves of two methods fit well and the correlation coefficient is more than 95%. The other deformations calculated by numerical simulation results are close to the theory form. Therefore, considering the influence, the surface and its subsidiary structures and buildings due to mining, the numerical simulation method based on the DInSAR data can reveal the distribution rules of the surface dynamic deformation values and supply the shortcomings of DInSAR technology. The research shows that the method has good applicability and can provide reference for similar situation.
基金supported by the National Natural Science Foundation of China(Grant Nos.11925202 and 11872009)National Science and Technology Major Project(Grant No.J2019-V-0006-0099)。
文摘Based on the recently proposed mirror-assisted multi-view digital image correlation(MV-DIC),we establish a cost-effective and easy-to-implement mirror-assisted multi-view high-speed digital image correlation(MVHS-DIC)method and explore its applications for dual-surface full-field dynamic deformation measurement.In contrast to the general requirement of four expensive high-speed cameras for dual-surface dynamic deformation field measurement,the established mirror-assisted MVHS-DIC halves the cost by involving only two synchronized high-speed cameras and two planar mirrors.The two synchronized high-speed cameras can dynamically measure the front and rear surfaces of a sheet sample simultaneously through the reflection of the two mirrors.The results on the two surfaces are then transformed into the same coordinate system,leading to the required dual-surface 3D dynamical deformation fields.The effectiveness and accuracy of the established system are validated through modal tests of a cantilever aluminum sheet.The vibration measurement of a drum and dual-surface transient deformation measurement of a smartphone in the drop-collision process further prove its practicability.Benefiting from the attractive advantages of multi-view dynamic deformation measurement in a cost-efficient way,the established mirror-assisted MVHS-DIC is expected to encourage more comprehensive dynamic mechanical behavior characterization of regular-sized materials and structures in vibration and impact engineering fields.
基金supported by the National Natural Science Foundation of China(51671018,51531001,51422101,51371003,and 51671021)111 Project(B07003)+5 种基金International S&T Cooperation Program of China(2015DFG52600)Program for Changjiang Scholars and Innovative Research Team in University of China(IRT_14R05)the Projects of SKL-AMM-USTB(2016Z-04,2016-09,2016Z-16)the financial support from the Top-Notch Young Talents Programthe Fundamental Research Funds for the Central Universitiesthe financial support by US-NSF under contract DMR-1408722
文摘In this study, mechanical tests were conducted oil a face-centered cubic FeCoNiCrMn high-entropy alloy, both in tension and compression, in a wide range of strain rates （10^-4-10^4 s^-1） to systematically investigate its dynamic response and underlying deformation mechanism. Materials with different grain sizes were tested to understand the effect of grain size, thus grain boundary volume, on the mechanical prop-erties. Microstructures of various samples both before and after deformation were examined using elec-tron backscatter diffraction and transmission electron microscopy. The dislocation structure as well as deformation-induced twins were analyzed and correlated with the measured mechanical properties. Plastic stability during tension of the current high-entropy alloy （HEA）, in particular, at dynamic strain rates, was discussed in lights of strain-rate sensitivity and work hardening rate. It was found that, under dynamic conditions, the strength and uniform ductility increased simultaneously as a result of the mas-sive formation of deformation twins. Specifically, an ultimate tensile strength of 734 MPa and uniform elongation of-63% are obtained at 2.3×10^3 s^-1, indicating that the alloy has great potential for energy absorption upon impact loading.
基金supported by the National Natural Science Foundation of China under Grant No.52077084.
文摘Hollow porcelain insulators in substations are frequently confronted with rain flashovers under extreme rainfall.This study aims to investigate the spatial and temporal variation of electric fields between hollow porcelain insulator sheds affected by dynamic deformation of pendant water drops and effects of the dimensionless number of fluids,the Weber number(We)and the electric Bond number(BoE),on it for influencing factors'analysis.Flow‐electric field coupling simulations were carried out to compute the magnitude and the position of AC electric fields between the sheds.The results show that the maximum electric field at a point in time(Etmax)increases significantly after the breakup of the pendant water drop,and its position alters accordingly.For low We and BoE,the global maximum electric field(Egmax)increases with increasing We and BoE,respectively.It is much closer to the adjacent sheds and occurs later than Etmax at the breakup of the pendant water drop(Ebmax).By contrast,Egmax decreases in different degrees at high We and BoE,respectively.There is little difference between Egmax and Ebmax in the position and the occurring time.The influence mechanism on the maximum electric field and discharges and the relationship between discharges induced by the pendant water drop and rain flashover are discussed.
基金National Natural Science Foundation of China under Grant No.52278503。
文摘Coral sandy soils widely exist in coral island reefs and seashores in tropical and subtropical regions.Due to the unique marine depositional environment of coral sandy soils,the engineering characteristics and responses of these soils subjected to monotonic and cyclic loadings have been a subject of intense interest among the geotechnical and earthquake engineering communities.This paper critically reviews the progress of experimental investigations on the undrained behavior of coral sandy soils under monotonic and cyclic loadings over the last three decades.The focus of coverage includes the contractive-dilative behavior,the pattern of excess pore-water pressure(EPWP)generation and the liquefaction mechanism and liquefaction resistance,the small-strain shear modulus and strain-dependent shear modulus and damping,the cyclic softening feature,and the anisotropic characteristics of undrained responses of saturated coral sandy soils.In particular,the advances made in the past decades are reviewed from the following aspects:(1)the characterization of factors that impact the mechanism and patterns of EPWP build-up;(2)the identification of liquefaction triggering in terms of the apparent viscosity and the average flow coefficient;(3)the establishment of the invariable form of strain-based,stress-based,or energy-based EPWP ratio formulas and the unique relationship between the new proxy of liquefaction resistance and the number of cycles required to reach liquefaction;(4)the establishment of the invariable form of the predictive formulas of small strain modulus and strain-dependent shear modulus;and(5)the investigation on the effects of stress-induced anisotropy on liquefaction susceptibility and dynamic deformation characteristics.Insights gained through the critical review of these advances in the past decades offer a perspective for future research to further resolve the fundamental issues concerning the liquefaction mechanism and responses of coral sandy sites subjected to cyclic loadings associated with seismic events in marine environments.
基金Project(10932008)supported by the National Natural Science Foundation of ChinaProject(2008ZF53050)supported by Aviation Science Foundation of China Aviation Industry Corporation I
文摘Compressive properties of AZ31 alloy were investigated at temperatures from room temperature to 543 K and at strain rates from 10-3to 2×10 4s-1.The results show that the compressive behavior and deformation mechanism of AZ31 depend largely on the temperature and strain rate.The flow stress increases with the increase of strain rate at fixed temperature,while decreases with the increase of deformation temperature at fixed strain rate.At low temperature and quasi-static condition,the true stress-true strain curve of AZ31 alloy can be divided into three stages(strain hardening,softening and stabilization) after yielding.However,at high temperature and high strain rate,the AZ31 alloy shows ideal elastic-plastic properties.It is therefore suggested that the change in loading conditions(temperature and strain rate) plays an important role in deformation mechanisms of AZ31 alloy.
基金Financial supports from the National Basic Research Program of China(Grant No.2012CB932201)the National Natural Science Foundation of China(Grant No.51371172)+1 种基金Bosch (China) Investment Ltd.,the MOST of China(2010DFB54010)the CAS International Cooperation Project(GJHZ1033)
文摘Lamellar nanostructures were induced in a plain martensitic low-carbon steel by using dynamic plastic deformation at room temperature.The nanostructured steel was hardened after annealing at 673 K for20 min,with a tensile strength increased from 1.2 GPa to 1.6 GPa.Both the remained nanostructures and annealing-induced precipitates in nano-scale play key roles in the hardening.
基金the Danish National Research Foundation and the National Natural Science Foundation of China (Grant No. 50911130230)for the Danish-Chinese center for Nanometals, within which this study was performedsponsored by MOST international S&T project(2010DFB54010), SRF for ROCS, SEM, and the Young Merit Scholar of Institute of Metal Research, Chinese Academy of Science, China
文摘A pure Cu （99.995 wt%） has been subjected to dynamic plastic deformation at cryogenic temperature to a strain of 2.1. Three types of microstructures that are related to dislocation slip, twinning and shear banding have been quantitatively characterized by transmission electron microscopy （TEM） assisted by convergent beam electron diffraction （CBED） analysis. Microstructures originated from dislocation slip inside or outside the shear bands are characterized by low angle boundaries （〈15°） that are spaced in the nanometer scale, whereas most deformation twins are deviated from the perfect ∑3 coincidence （60°/〈111〉） up to the maximum angle of 9°. The quantitative structural characteristics are compared with those in conventionally deformed Cu at low strain rates, and allowed a quantitative analysis of the flow stress-structural parameter relationship.
基金supported by the National Natural Science Foundation of China(No.11372032)The Open Project of Key Laboratory of Computational Physics in China
文摘Molecular dynamics simulation is employed to study the tension and compression deformation behaviors of magnesium single crystals with different orientations.The angle between the loading axis and the basal direction ranges from 0° to 90°.The simulation results show that the initial defects usually nucleate at free surfaces,but the initial plastic deformation and the subsequent microstructural evolutions are various due to different loading directions.The tension simulations exhibit the deformation mechanisms of twinning,slip,crystallographic reorientation and basal/prismatic transformation.The twinning,crystallographic reorientation and basal/prismatic transformation can only appear in the crystal model loaded along or near the a-axis or c-axis.For the compression simulations,the basal,prismatic and pyramidal slips are responsible for the initial plasticity,and no twinning is observed.Moreover,the plastic deformation models affect the yield strengths for the samples with different orientations.The maximum yield stresses for the samples loaded along the c-axis or a-axis are much higher than those loaded in other directions.
