The Steel Catenary Riser(SCR)is a vital component for transporting oil and gas from the seabed to the floating platform.The harsh environmental conditions and complex platform motion make the SCR’s girth-weld prone t...The Steel Catenary Riser(SCR)is a vital component for transporting oil and gas from the seabed to the floating platform.The harsh environmental conditions and complex platform motion make the SCR’s girth-weld prone to fatigue failure.The structural stress fatigue theory and Master S-N curve method provide accurate predictions for the fatigue damage on the welded joints,which demonstrate significant potential and compatibility in multi-axial and random fatigue evaluation.Here,we propose a new frequency fatigue model subjected to welded joints of SCR under multiaxial stress,which fully integrates the mesh-insensitive structural stress and frequency domain random process and transforms the conventional welding fatigue technique of SCR into a spectrum analysis technique utilizing structural stress.Besides,a full-scale FE model of SCR with welds is established to obtain the modal structural stress of the girth weld and the frequency response function(FRF)of modal coordinate,and a biaxial fatigue evaluation about the girth weld of the SCR can be achieved by taking the effects of multi-load correlation and pipe-soil interaction into account.The research results indicate that the frequency-domain fatigue results are aligned with the time-domain results,meeting the fatigue evaluation requirements of the SCR.展开更多
ΔF-N curves are usually used to predict the fatigue life of spot welding in engineering,but they are time-consuming and laborious and not universal.For the purpose of predicting the fatigue life of spot welding accur...ΔF-N curves are usually used to predict the fatigue life of spot welding in engineering,but they are time-consuming and laborious and not universal.For the purpose of predicting the fatigue life of spot welding accurately and efficiently,tensile-shear fatigue tests were conducted to obtain the fatigue life of spot-welded specimens with different sheet thicknesses combinations.These specimens were simulated by using the finite element method,and the structural stress was theoretically calculated.In the double logarithmic coordinate system,the structural stress-fatigue life(S-N)curve of spot welding was fitted by the least-squares method,based on the quasi-Newton method.The square of the correlation coefficient of the S-N curve was taken as the optimization objective,with the correction coefficients of force,bending moment,spot welding diameter,and sheet thickness as the variables.During the optimization process,three different ways were utilized to get three optimized spot welding S-N curves,which are suitable for different situations.The results show that the fitting effect of the S-N curve is improved,the data points are more compact,and the optimization effect is significant.These S-N curves can be used to predict the fatigue life,which provide the basis for practical engineering application.展开更多
Most existing studies on the vibration analysis of cylindrical shells with structural stress are limited to uniform stress distribution. However, non-uniform stress distributions are encountered in many engineering ap...Most existing studies on the vibration analysis of cylindrical shells with structural stress are limited to uniform stress distribution. However, non-uniform stress distributions are encountered in many engineering applications. In this study, a unified solution for the vibration analysis of cylindrical shells with a general stress distribution is presented using the Fliigge shell theory and modal orthogonality simplification. The obtained analytical solution can be applied to a structure with arbitrary distributed stress, thus it has a wider range of applications than previous methods. The accuracy and advantage of the proposed method are validated by comparing with the finite element method results.展开更多
Based on the study about the geological background of Beiya Gold Deposit, numerical simulation was conducted about the three-dimensional structural stress field for Beiya Gold Deposit by applying finite element theory...Based on the study about the geological background of Beiya Gold Deposit, numerical simulation was conducted about the three-dimensional structural stress field for Beiya Gold Deposit by applying finite element theory and by employing a linear elasticity model. Results of the simulation indicate that the Beiya syncline is a faulted basin, and a hidden fracture occurs in the west wing of the syncline.Under the action of the EW-trending compressive force, four nearly NS-trending fractures (groups) were generated in the stress stretching areas of the two wings of the syncline, and these fractures constitute favorable tectonic positions for the upward intrusion of porphyry magma and the occurrence of Au-Pb-Zn polymetallic deposits.展开更多
The constant amplitude loading fatigue tests were carried out on the 6061/7075 aluminum alloy TIG fillet welded lap specimens in this study,and the weld seam cross-section hardness was measured.The experimental result...The constant amplitude loading fatigue tests were carried out on the 6061/7075 aluminum alloy TIG fillet welded lap specimens in this study,and the weld seam cross-section hardness was measured.The experimental results show that most specimens mainly failed at the 7075 side weld toes even though the base material tensile strength of 7075 is higher than that of 6061.The maximum stress-strain concentration in the two finite element models is located at the 7075 side weld toe,which is basically consistent with the actual fracture location.The weld zone on the 7075 side experiences severe material softening,with a large gradient.However,the Vickers hardness value on the 6061 side negligibly changes and fluctuates around 70 HV.No obvious defects are found on the fatigue fracture,but a large number of secondary cracks appear.Cracks germinate from the weld toe and propagate in the direction of the plate thickness.Weld reinforcement has a serious impact on fatigue life.Fatigue life will decrease exponentially as the weld reinforcement increases under low stress.It is found that the notch stress method can give a better fatigue life prediction for TIG weldments,and the errors of the predicted results are within the range of two factors,while the prediction accuracy decreases under low stress.The equivalent structural stress method can also be used for fatigue life prediction of TIG weldments,but the errors of prediction results are within the range of three factors,and the accuracy decreases under high stress.展开更多
Quartz vein-type tungsten deposits are a common W deposit type.Their ore vein distribution was previously considered to be controlled by regional horizontal tectonic stress.In this paper,14 tungsten deposits with fan-...Quartz vein-type tungsten deposits are a common W deposit type.Their ore vein distribution was previously considered to be controlled by regional horizontal tectonic stress.In this paper,14 tungsten deposits with fan-shaped mineralization in SE China are summarized,and the relations between their ore veins and granite and the ore-forming structural stress field are analyzed.These deposits have a post-magmatic hydrothermal genesis and involve the formation of two sets of veins with similar strike and opposite dips at the top of the ore-causative granite bodies,forming a vertical fan-shaped profile.Their ore veins were coeval with the underlying granite bodies,and generally extend along the long axis of the granite.In such fan-shaped ore formation,the stress is highly focused at the top of the granite and gradually weakens outward.The maximum principal stress(σ1)is perpendicular to the granite contact surface,and radiates outward from the pluton.Meanwhile,the minimum principal stress(σ3)forms an arc-shaped band parallel to the contact surface.Our findings,together with published numerical modeling indicate that the emplacement dynamics of granitic magma(rather than regional horizontal tectonic stress)are essential controls on the distribution of ore veins in quartz vein-type tungsten deposits.展开更多
Experimental tests are essential for evaluating S-N curves and assessing the fatigue life of welded joints.However,in the case of complex geometries,experimental tests often cannot provide the necessary stress-strain ...Experimental tests are essential for evaluating S-N curves and assessing the fatigue life of welded joints.However,in the case of complex geometries,experimental tests often cannot provide the necessary stress-strain data for specific materials and welded joints.Therefore,finite element(FE)analyses are frequently utilized to assess fatigue behavior in complex geometries and address the discontinuities induced by welding processes.In this study,the fatigue properties of titanium welded joints,produced using an innovative laser source and welded without the use of filler materials,were analyzed through numerical methods.Two different FEmethodswere applied to T-specimens fabricated from Ti6Al4V sheets:the hot-spot stress and notch-stress approach.The FE fatigue life predictions were validated using experimental fatigue test results.The Hot-Spot Stress method yielded a fatigue limit slightly below 100 MPa,demonstrating a consistent slope in the S-N response.Conversely,the Notch Stress method,using a 1 mm fictitious notch radius,indicated a higher fatigue strength corresponding to a range between 225 and 250MPa,providing amore conservative and localized fatigue estimate.Fatigue resistance in welded joints of steel and aluminum is commonly assessed using specific fatigue classes called“Fatigue Strength Classes(FAT)curves”and their associated S-N curves as recommended by the International Institute of Welding(IIW).However,no such FAT class assignments currently exist for titanium alloys.To address this gap,strain-based FAT curves were proposed by normalizing steel FAT curves using titanium’s elastic properties.This strain-based framework enables direct comparison across materials and provides a foundation for fatigue evaluation of titanium weldments.The author proposed a procedure to normalize steel FAT curves considering the different elastic material properties,enabling a comparison with Ti6Al4V data in terms of hot spot strain or notch strain.This approach facilitates the development of a universal framework for strain-based fatigue evaluation across different materials.展开更多
The Shangzhuang altered-rock type gold ore deposit is located in the middle segment of and controlled by the Wang＇ershan fault zone in the northwestern part of the Jiaodong gold province, China. The deformation evolu...The Shangzhuang altered-rock type gold ore deposit is located in the middle segment of and controlled by the Wang＇ershan fault zone in the northwestern part of the Jiaodong gold province, China. The deformation evolution, the structure of strain and stress fields and its ore-controlling effect in the Shangzhuang deposit are discussed in this paper. It is revealed that the deformation evolution has mainly undergone four phases： the early ductile deformation, the second NE-striking horizontal simple shear, the third NE-striking compression-shear and the final NW-striking compression. The mineralization happened during the third stage in which the maximum principal stress gradually transited from NE to NW. The 3-D numerical simulations of the stress field show that, on the condition that the maximum principal stress is NE-striking, the fracture development in the fault zone is favored, while when the maximum principal stress is NW-striking, the fault zone is relatively extensional and it is suitable for the influx and emplacement of ore-forming fluids. The compression-shear strain field during the mineralization is characterized by the λ-type structure, the positive flower structure, etc. Orebodies are mostly equidistantly located in the dilatational spaces, which are distributed in the integral compressional circumstances. And the dilatational spaces are developed where the fault attitude changes or shear joint systems develop. In the overall compression-shear stress field, the strain field bears self-similarity at multiple scales, including the orebody, ore deposit and orefield. The selfsimilarity of the structure comprises the subequidistant distribution of fractures at the same scale and the similar shape of the fractures at various scales. Yet, due to the special geological structure, the orebodies are mostly located in the hanging wall in the Shangzhuang deposit, which is different from most deposits in the Jiaodong gold province. Analyses of the ore-controlling stress and strain fields in the deposit provide an important basis for deposit seeking.展开更多
The measurement on radial profile of electrostatic Reynolds stress, plasma poloidal rotations, radial and poloidal electric field have been performed in the plasma boundary region of the HL-IM Tokamak using a multi-ar...The measurement on radial profile of electrostatic Reynolds stress, plasma poloidal rotations, radial and poloidal electric field have been performed in the plasma boundary region of the HL-IM Tokamak using a multi-array of Mach/Langmuir probes. In the experiments of Lower Hybrid Current Drive (LHCD), Supersonic Molecular Beam injection (SMBI), Multi-shot Pellet Injection (MPI) and Neutral Beam injection (NBI), the correlation between the Reynolds stress and poloidal flow in the edge plasma is presented. The results indicate that a sheared poloidal flow can be generated in Tokamak plasma due to radially varying Reynolds stress.展开更多
This study proposes a parameterized model of a uniaxial symmetry non-circular hole, to improve conventional circular bolt clearance holes on turbine disks. The profile of the model consists of eight smoothly connected...This study proposes a parameterized model of a uniaxial symmetry non-circular hole, to improve conventional circular bolt clearance holes on turbine disks. The profile of the model consists of eight smoothly connected arcs, the radiuses of which are determined by 5 design variables.By changing the design variables, the profile of the non-circular hole can be transformed to accommodate different load ratios, thereby improving the stress concentration of the area near the hole and that of the turbine disk. The uniaxial symmetry non-circular hole is optimized based on finite element method（FEM）, in which the maximum first principal stress is taken as the objective function. After optimization, the stress concentration is evidently relieved; the maximum first principal stress and the maximum von Mises stress on the critical area are reduced by 30.39% and 25.34%respectively, showing that the uniaxial symmetry non-circular hole is capable of reducing the stress level of bolt clearance holes on the turbine disk.展开更多
This paper presents an incremental cutting method for evaluating the longitudinal residual stresses in a butt welded thin plate via combining the traditional residual stress measurement methods and the advanced optica...This paper presents an incremental cutting method for evaluating the longitudinal residual stresses in a butt welded thin plate via combining the traditional residual stress measurement methods and the advanced optical technique.The proposed approach,which can be called digital image correlation（DIC）-aided slitting technique,introduces a successive extension slot to a specimen and employs the DIC technique to measure the released displacement profiles of the cutting sections after each cutting increment.Then the displacement profiles are used to directly calculate the residual stress distributions up to the slot tip and hence,a stress distribution can be obtained after a cutting increment.Finally,all of the stress distributions are averaged to ultimately determine the original residual stress field.This method does not include any complex experimental operations or tedious derivation,and the resolution of stress variation is greatly improved by the continuous measurement of the released displacements.The presented method has been preliminarily verified by a specimen with residual stress introduced by a four-point bending test.The results show that residual stresses determined by the DIC-aided slitting technique agree well with those from finite element（FE） prediction.The residual stress in a friction stir welded aluminum specimen obtained by the presented technique is also consistent with the evaluations given by X-ray diffraction.Furthermore,the residual stresses obtained by the DIC-aided slitting technique demonstrate higher accuracy and stability than the evaluations derived by the DIC-aided contour method.展开更多
The strain monitoring and stress analysis of a new type of post-prestressed tunnel liner were carried out. The instrumentation block of the tunnel liner, with the dimensions of 12.06 m in length, 6 500 mm in diameter,...The strain monitoring and stress analysis of a new type of post-prestressed tunnel liner were carried out. The instrumentation block of the tunnel liner, with the dimensions of 12.06 m in length, 6 500 mm in diameter, and 650 mm in thickness, was post-prestressed with the unbonded tendons, each of which consists of 8 pieces of double-looped strands and the axial spacing of the tendons is 500 mm. Concrete strain meters, rebar meters, load cell and zero-stress meters were installed for the strain monitoring. The tensioning loads were applied incrementally in three cycles (50%, 77% and 100%) at the concrete age of 28 d and the tensioning work lasted for 187.1 h. Strain readings were taken before and after each cycle during tensioning period and at the specified time interval after tensioning period. It is found that concrete creep developed over tensioning period is 30% of total strain and 41.5% of elastic strain respectively. Prestress force in the unbonded tendon and concrete stress in the liner were evaluated according to the observed strain variations. Both of them are time-dependent, and about 5.3%, 8.3% and 9.0% of the prestress losses are observed at the age of 1 d, 30 d and 60 d respectively after stressing. The distribution of prestress in the liner is relatively uniform and meets the design requirement.展开更多
To evaluate the residual stress in TiAl based alloys by X ray diffraction, X ray elastic constants (REC) of a γ TiAl alloy were determined. From these results, the stress state of a given phase in a duplex TiAl based...To evaluate the residual stress in TiAl based alloys by X ray diffraction, X ray elastic constants (REC) of a γ TiAl alloy were determined. From these results, the stress state of a given phase in a duplex TiAl based alloy under a uniaxial tensile loading has been characterized by X ray diffraction. The results show that the X ray elastic constants and the microscopic stresses of the given phase are different from the apparent elastic constants and the macroscopic stresses of the alloy. The reason of the different distribution of the alloy was also discussed. [展开更多
Based on[1],the stress structures of the smooth region and shear lip of the specimens have been investigated in the paper.The characteristics of the stress structure in the smooth region have been found that the varia...Based on[1],the stress structures of the smooth region and shear lip of the specimens have been investigated in the paper.The characteristics of the stress structure in the smooth region have been found that the variable z can separated out;the stresses in the midsection can be obtained by the plane strain FEM results or HRR structure modified by the stress triaxiality.The effects of load level and thickness on the stress structure can be reflected by the distribution of CTOD along the thickness direction.The obtained expressions of the stresses are very simple and visualized.The analyses of the stress structure in the shear lip show that the stresses can be obtained by different methods of interpolation to a certain precise degree.A new degree parameter of the plane strain state has been put forward and studied.The parameter can reflect relatively well the variation of the kind and thickness of the specimen as well as the load level.The fracture parameter has also been investigated to be sure that it can be obtained by modified CTOD with the stress triaxiality.展开更多
Fracture prediction is a technical issue in the field of petroleum exploration and production worldwide.Although there are many approaches to predict the distribution of cracks underground,these approaches have some l...Fracture prediction is a technical issue in the field of petroleum exploration and production worldwide.Although there are many approaches to predict the distribution of cracks underground,these approaches have some limitations.To resolve these issues,we ascertained the relation between numerical simulations of tectonic stress and the predicted distribution of fractures from the perspective of geologic genesis,based on the characteristics of the shale reservoir in the Longmaxi Formation in Dingshan;the features of fracture development in this reservoir were considered.3 D finite element method(FEM)was applied in combination with rock mechanical parameters derived from the acoustic emissions.The paleotectonic stress field of the crack formation period was simulated for the Longmaxi Formation in the Dingshan area.The splitting factor in the study area was calculated based on the rock breaking criterion.The coefficient of fracture development was selected as the quantitative prediction classification criteria for the cracks.The results show that a higher coefficient of fracture development indicates a greater degree of fracture development.On the basis of the fracture development coefficient classification,a favorable area was identified for the development of fracture prediction in the study area.The prediction results indicate that the south of the Dingshan area and the DY3 well of the central region are favorable zones for fracture development.展开更多
The concept of fault junction is proposed to describe the relationship between the two faults by the authors. The junction relationship between Ganjiang and Tanlu faults is analyzed in this paper, and this has been el...The concept of fault junction is proposed to describe the relationship between the two faults by the authors. The junction relationship between Ganjiang and Tanlu faults is analyzed in this paper, and this has been elucidated through numerical simulation about the tectonic stress field analysis. Numerical simulation of the tectonic stress field conducted for the major mineralization stage of the Jiujiang-Ruichang junction area reveals that the stress field of the junction structure at the major mineralization stage shows a relatively close relationship with the formation of the ore deposits (occurrences).展开更多
The influence of welding parameters of butt joints, made by three processes (MMA, MAG and T.I.M.E), on their geometric characteristics has been evaluated, which in turn caused a change of the fatigue strength. That fo...The influence of welding parameters of butt joints, made by three processes (MMA, MAG and T.I.M.E), on their geometric characteristics has been evaluated, which in turn caused a change of the fatigue strength. That fore the statistic analysis and FEM were used and a method developed in the Institute of Welding, which consist in a direct connection of parameters used during welding with the fatigue strength of joints welded by various processes. It has been proven, among others, which by using more advanced welding processes (T.I.M.E) the fatigue strength of welded joints can be increased in comparison to joints welded by MMA and MAG.展开更多
The excellent properties of SiC bring new challenges for the device packaging.In this study,the bonding strength,fracture behaviors and microstructural evolution of micron-porous Ag joint were elevated during thermal ...The excellent properties of SiC bring new challenges for the device packaging.In this study,the bonding strength,fracture behaviors and microstructural evolution of micron-porous Ag joint were elevated during thermal cycling(–50 ℃–250 ℃) in SiC/DBC(direct bonding copper) die attachment structure for different time.During harsh thermal shock test,the strength of sintered joint deceased gradually with the increase of cycling number,and the value just was half of the value of as-sintered after 1 000 cycles.Coarsening of Ag grains was observed in micron-porous joint with the structure inhomogeneity and defects increasing,which were the reasons of the strength decease.In addition,it was also found that the fracture behavior of sintered joints was changed from ductile deformation of Ag grain to brittle fracture of crack propagation after 1 000 cycles.This study will add the understanding in the mechanical properties of Ag sinter joining and its applications at high temperature.展开更多
Close-distance coal seams are widely distributed over China,and the coal pillars left by the overlying coal seams afect the retracement channel of the underlying coal seam in the stopping stage.Based on the engineerin...Close-distance coal seams are widely distributed over China,and the coal pillars left by the overlying coal seams afect the retracement channel of the underlying coal seam in the stopping stage.Based on the engineering background of close-distance seam mining in a coal mine,the reasonable position of the underlying coal seam's stopping line and the support method of the large section roadway during stopping are investigated using feld measurements,similar simulation experiments,and numerical simulations.There are three types of location relationships between the stopping line of the underlying coal seam and the stopping line of the overlying coal seam:"externally staggered with the upper stopping line"(ESUL,stops mining under the overlying goaf),"overlapped with upper stopping line"(OUL),and"internally staggered with the upper stopping line"(ISUL,ISUL-SD for shorter internal staggered distances,ISUL-LD for longer ones).There are diferent stress arch structures in the overlying strata of the above three positions,and the stress arch evolution process exists in the process of ESUL→OUL→ISUL-SD→ISUL-LD:a front and rear double stress arch structure→the front arch gradually decreases→the front arch dies out,and the double arch synthesizes the single arch→the single-arch range expands→the nested double arch.The relationship between the stress arch structure and the position of the stopping line is evaluated as follows:(1)ESUL:the stress concentration in the roof plate of the retracement channel of the underlying coal seam is the highest,because the overburden block of the extensive collapse zone acts directly on the roof plate of the retracement channel,resulting in relative difculties in roof support.(2)OUL:although the retracement channel roof pressure is minimal,the overlying rock structure has the potential for rotation or slippage instability.(3)ISUL-SD:the pressure on the roof of the retracement channel is small and the overburden structure is stable,which is conducive to the safe retraction of the support and not limited by the width of the end-mining coal pillar.(4)ISUL-LD:it is basically the same as the condition of stopping under the non-goaf;however,it has a limitation on the width of the end-mining coal pillar.The location of the stopping line is selected as ISUL-SD,and the retraction process of the self-excavating retraction channel was adopted.A partition asymmetric support scheme which is proven by feld practice is proposed,through a comprehensive analysis of the pre-stress feld simulation of the support scheme,based on the diferent control requirements of the roof above the support and the roof of the retracement channel in the stopping area.This method realizes safe and smooth withdrawal of the support.展开更多
The structure and rheological properties of carbon-based particle suspensions, i.e., carbon black（CB）, multi-wall carbon nanotube（MWNT）, graphene and hollow carbon sphere（HCS） suspended in polydimethylsiloxane（...The structure and rheological properties of carbon-based particle suspensions, i.e., carbon black（CB）, multi-wall carbon nanotube（MWNT）, graphene and hollow carbon sphere（HCS） suspended in polydimethylsiloxane（PDMS）, are investigated. In order to study the effect of particle shape on the structure and rheological properties of suspensions, the content of surface oxygen-containing functional groups of carbon-based particles is controlled to be similar. Original spherical-like CB（fractal filler）, rod-like MWNT and sheet-like graphene form large agglomerates in PDMS, while spherical HCS particles disperse relatively well in PDMS. The dispersion state of carbon-based particles affects the critical concentration of forming a rheological percolation network. Under weak shear, negative normal stress differences（ΔN） are observed in CB, MWNT and graphene suspensions, while ΔN is nearly zero for HCS suspensions. It is concluded that the vorticity alignment of CB, MWNT and graphene agglomerates under shear results in the negative ΔN. However, no obvious structural change is observed in HCS suspension under weak shear, and accordingly, the ΔN is almost zero.展开更多
基金financially supported by the Director Fund of National Energy Deepwater Oil and Gas Engineering Technology Research and Development Center(Grant No.KJQZ-2024-2103)。
文摘The Steel Catenary Riser(SCR)is a vital component for transporting oil and gas from the seabed to the floating platform.The harsh environmental conditions and complex platform motion make the SCR’s girth-weld prone to fatigue failure.The structural stress fatigue theory and Master S-N curve method provide accurate predictions for the fatigue damage on the welded joints,which demonstrate significant potential and compatibility in multi-axial and random fatigue evaluation.Here,we propose a new frequency fatigue model subjected to welded joints of SCR under multiaxial stress,which fully integrates the mesh-insensitive structural stress and frequency domain random process and transforms the conventional welding fatigue technique of SCR into a spectrum analysis technique utilizing structural stress.Besides,a full-scale FE model of SCR with welds is established to obtain the modal structural stress of the girth weld and the frequency response function(FRF)of modal coordinate,and a biaxial fatigue evaluation about the girth weld of the SCR can be achieved by taking the effects of multi-load correlation and pipe-soil interaction into account.The research results indicate that the frequency-domain fatigue results are aligned with the time-domain results,meeting the fatigue evaluation requirements of the SCR.
基金Supported by National Natural Science Foundation of China(Grant Nos.U1534209,51675446)Independent Subject of State Key Laboratory of Traction Power(Grant No.2019TPL-T13).
文摘ΔF-N curves are usually used to predict the fatigue life of spot welding in engineering,but they are time-consuming and laborious and not universal.For the purpose of predicting the fatigue life of spot welding accurately and efficiently,tensile-shear fatigue tests were conducted to obtain the fatigue life of spot-welded specimens with different sheet thicknesses combinations.These specimens were simulated by using the finite element method,and the structural stress was theoretically calculated.In the double logarithmic coordinate system,the structural stress-fatigue life(S-N)curve of spot welding was fitted by the least-squares method,based on the quasi-Newton method.The square of the correlation coefficient of the S-N curve was taken as the optimization objective,with the correction coefficients of force,bending moment,spot welding diameter,and sheet thickness as the variables.During the optimization process,three different ways were utilized to get three optimized spot welding S-N curves,which are suitable for different situations.The results show that the fitting effect of the S-N curve is improved,the data points are more compact,and the optimization effect is significant.These S-N curves can be used to predict the fatigue life,which provide the basis for practical engineering application.
基金supported by the Fund of State Key Laboratory of Ocean Engineering(No.1507)
文摘Most existing studies on the vibration analysis of cylindrical shells with structural stress are limited to uniform stress distribution. However, non-uniform stress distributions are encountered in many engineering applications. In this study, a unified solution for the vibration analysis of cylindrical shells with a general stress distribution is presented using the Fliigge shell theory and modal orthogonality simplification. The obtained analytical solution can be applied to a structure with arbitrary distributed stress, thus it has a wider range of applications than previous methods. The accuracy and advantage of the proposed method are validated by comparing with the finite element method results.
文摘Based on the study about the geological background of Beiya Gold Deposit, numerical simulation was conducted about the three-dimensional structural stress field for Beiya Gold Deposit by applying finite element theory and by employing a linear elasticity model. Results of the simulation indicate that the Beiya syncline is a faulted basin, and a hidden fracture occurs in the west wing of the syncline.Under the action of the EW-trending compressive force, four nearly NS-trending fractures (groups) were generated in the stress stretching areas of the two wings of the syncline, and these fractures constitute favorable tectonic positions for the upward intrusion of porphyry magma and the occurrence of Au-Pb-Zn polymetallic deposits.
基金Partially funded by the National Natural Science Foundation of China(No.51065012)。
文摘The constant amplitude loading fatigue tests were carried out on the 6061/7075 aluminum alloy TIG fillet welded lap specimens in this study,and the weld seam cross-section hardness was measured.The experimental results show that most specimens mainly failed at the 7075 side weld toes even though the base material tensile strength of 7075 is higher than that of 6061.The maximum stress-strain concentration in the two finite element models is located at the 7075 side weld toe,which is basically consistent with the actual fracture location.The weld zone on the 7075 side experiences severe material softening,with a large gradient.However,the Vickers hardness value on the 6061 side negligibly changes and fluctuates around 70 HV.No obvious defects are found on the fatigue fracture,but a large number of secondary cracks appear.Cracks germinate from the weld toe and propagate in the direction of the plate thickness.Weld reinforcement has a serious impact on fatigue life.Fatigue life will decrease exponentially as the weld reinforcement increases under low stress.It is found that the notch stress method can give a better fatigue life prediction for TIG weldments,and the errors of the predicted results are within the range of two factors,while the prediction accuracy decreases under low stress.The equivalent structural stress method can also be used for fatigue life prediction of TIG weldments,but the errors of prediction results are within the range of three factors,and the accuracy decreases under high stress.
基金funded by the National Key Research&Development Program of China(No.2021YFC2900100)the Guangxi Natural Science Foundation(No.2022GXNSFFA035025)+3 种基金the Chinese National Natural Science Foundation(No.42372099)the China Geological Survey(No.DD20190379)the Science&Technology Fundamental Resources Investigation Program(No.2022FY101800)the Major Talent Program of Guangxi Zhuang Autonomous Region,and the Innovation Project of Guangxi Graduate Education(No.YCSW2023345)。
文摘Quartz vein-type tungsten deposits are a common W deposit type.Their ore vein distribution was previously considered to be controlled by regional horizontal tectonic stress.In this paper,14 tungsten deposits with fan-shaped mineralization in SE China are summarized,and the relations between their ore veins and granite and the ore-forming structural stress field are analyzed.These deposits have a post-magmatic hydrothermal genesis and involve the formation of two sets of veins with similar strike and opposite dips at the top of the ore-causative granite bodies,forming a vertical fan-shaped profile.Their ore veins were coeval with the underlying granite bodies,and generally extend along the long axis of the granite.In such fan-shaped ore formation,the stress is highly focused at the top of the granite and gradually weakens outward.The maximum principal stress(σ1)is perpendicular to the granite contact surface,and radiates outward from the pluton.Meanwhile,the minimum principal stress(σ3)forms an arc-shaped band parallel to the contact surface.Our findings,together with published numerical modeling indicate that the emplacement dynamics of granitic magma(rather than regional horizontal tectonic stress)are essential controls on the distribution of ore veins in quartz vein-type tungsten deposits.
基金supported by the project PRIN_2022PNRR_P2022Y3PBY_001“MADLEINE,CUP:J53D23015830001”.Project funded under the National Recovery and Resilience Plan(NRRP),Mission 4 Component C2 Investment 1.1 by the European Union-NextGenerationEU.
文摘Experimental tests are essential for evaluating S-N curves and assessing the fatigue life of welded joints.However,in the case of complex geometries,experimental tests often cannot provide the necessary stress-strain data for specific materials and welded joints.Therefore,finite element(FE)analyses are frequently utilized to assess fatigue behavior in complex geometries and address the discontinuities induced by welding processes.In this study,the fatigue properties of titanium welded joints,produced using an innovative laser source and welded without the use of filler materials,were analyzed through numerical methods.Two different FEmethodswere applied to T-specimens fabricated from Ti6Al4V sheets:the hot-spot stress and notch-stress approach.The FE fatigue life predictions were validated using experimental fatigue test results.The Hot-Spot Stress method yielded a fatigue limit slightly below 100 MPa,demonstrating a consistent slope in the S-N response.Conversely,the Notch Stress method,using a 1 mm fictitious notch radius,indicated a higher fatigue strength corresponding to a range between 225 and 250MPa,providing amore conservative and localized fatigue estimate.Fatigue resistance in welded joints of steel and aluminum is commonly assessed using specific fatigue classes called“Fatigue Strength Classes(FAT)curves”and their associated S-N curves as recommended by the International Institute of Welding(IIW).However,no such FAT class assignments currently exist for titanium alloys.To address this gap,strain-based FAT curves were proposed by normalizing steel FAT curves using titanium’s elastic properties.This strain-based framework enables direct comparison across materials and provides a foundation for fatigue evaluation of titanium weldments.The author proposed a procedure to normalize steel FAT curves considering the different elastic material properties,enabling a comparison with Ti6Al4V data in terms of hot spot strain or notch strain.This approach facilitates the development of a universal framework for strain-based fatigue evaluation across different materials.
基金This paper is supported by the National Natural Science Foundation of China （Grant Nos. 40572063 and 40272051）；the Fostering Plan Fund for Trans-Century Excellent Talents and the Project 111 （No. B07011）.
文摘The Shangzhuang altered-rock type gold ore deposit is located in the middle segment of and controlled by the Wang＇ershan fault zone in the northwestern part of the Jiaodong gold province, China. The deformation evolution, the structure of strain and stress fields and its ore-controlling effect in the Shangzhuang deposit are discussed in this paper. It is revealed that the deformation evolution has mainly undergone four phases： the early ductile deformation, the second NE-striking horizontal simple shear, the third NE-striking compression-shear and the final NW-striking compression. The mineralization happened during the third stage in which the maximum principal stress gradually transited from NE to NW. The 3-D numerical simulations of the stress field show that, on the condition that the maximum principal stress is NE-striking, the fracture development in the fault zone is favored, while when the maximum principal stress is NW-striking, the fault zone is relatively extensional and it is suitable for the influx and emplacement of ore-forming fluids. The compression-shear strain field during the mineralization is characterized by the λ-type structure, the positive flower structure, etc. Orebodies are mostly equidistantly located in the dilatational spaces, which are distributed in the integral compressional circumstances. And the dilatational spaces are developed where the fault attitude changes or shear joint systems develop. In the overall compression-shear stress field, the strain field bears self-similarity at multiple scales, including the orebody, ore deposit and orefield. The selfsimilarity of the structure comprises the subequidistant distribution of fractures at the same scale and the similar shape of the fractures at various scales. Yet, due to the special geological structure, the orebodies are mostly located in the hanging wall in the Shangzhuang deposit, which is different from most deposits in the Jiaodong gold province. Analyses of the ore-controlling stress and strain fields in the deposit provide an important basis for deposit seeking.
文摘The measurement on radial profile of electrostatic Reynolds stress, plasma poloidal rotations, radial and poloidal electric field have been performed in the plasma boundary region of the HL-IM Tokamak using a multi-array of Mach/Langmuir probes. In the experiments of Lower Hybrid Current Drive (LHCD), Supersonic Molecular Beam injection (SMBI), Multi-shot Pellet Injection (MPI) and Neutral Beam injection (NBI), the correlation between the Reynolds stress and poloidal flow in the edge plasma is presented. The results indicate that a sheared poloidal flow can be generated in Tokamak plasma due to radially varying Reynolds stress.
基金co-supported by Aeronautical Science Foundation of China (No. 2012ZB52028)the Fundamental Research Funds for the Central Universities of China (No. NZ2012105)
文摘This study proposes a parameterized model of a uniaxial symmetry non-circular hole, to improve conventional circular bolt clearance holes on turbine disks. The profile of the model consists of eight smoothly connected arcs, the radiuses of which are determined by 5 design variables.By changing the design variables, the profile of the non-circular hole can be transformed to accommodate different load ratios, thereby improving the stress concentration of the area near the hole and that of the turbine disk. The uniaxial symmetry non-circular hole is optimized based on finite element method（FEM）, in which the maximum first principal stress is taken as the objective function. After optimization, the stress concentration is evidently relieved; the maximum first principal stress and the maximum von Mises stress on the critical area are reduced by 30.39% and 25.34%respectively, showing that the uniaxial symmetry non-circular hole is capable of reducing the stress level of bolt clearance holes on the turbine disk.
基金supported by the National Natural Science Foundation of China(No.11272029)
文摘This paper presents an incremental cutting method for evaluating the longitudinal residual stresses in a butt welded thin plate via combining the traditional residual stress measurement methods and the advanced optical technique.The proposed approach,which can be called digital image correlation（DIC）-aided slitting technique,introduces a successive extension slot to a specimen and employs the DIC technique to measure the released displacement profiles of the cutting sections after each cutting increment.Then the displacement profiles are used to directly calculate the residual stress distributions up to the slot tip and hence,a stress distribution can be obtained after a cutting increment.Finally,all of the stress distributions are averaged to ultimately determine the original residual stress field.This method does not include any complex experimental operations or tedious derivation,and the resolution of stress variation is greatly improved by the continuous measurement of the released displacements.The presented method has been preliminarily verified by a specimen with residual stress introduced by a four-point bending test.The results show that residual stresses determined by the DIC-aided slitting technique agree well with those from finite element（FE） prediction.The residual stress in a friction stir welded aluminum specimen obtained by the presented technique is also consistent with the evaluations given by X-ray diffraction.Furthermore,the residual stresses obtained by the DIC-aided slitting technique demonstrate higher accuracy and stability than the evaluations derived by the DIC-aided contour method.
基金Supported by National Natural Science Foundation of China (No. 50578110) .
文摘The strain monitoring and stress analysis of a new type of post-prestressed tunnel liner were carried out. The instrumentation block of the tunnel liner, with the dimensions of 12.06 m in length, 6 500 mm in diameter, and 650 mm in thickness, was post-prestressed with the unbonded tendons, each of which consists of 8 pieces of double-looped strands and the axial spacing of the tendons is 500 mm. Concrete strain meters, rebar meters, load cell and zero-stress meters were installed for the strain monitoring. The tensioning loads were applied incrementally in three cycles (50%, 77% and 100%) at the concrete age of 28 d and the tensioning work lasted for 187.1 h. Strain readings were taken before and after each cycle during tensioning period and at the specified time interval after tensioning period. It is found that concrete creep developed over tensioning period is 30% of total strain and 41.5% of elastic strain respectively. Prestress force in the unbonded tendon and concrete stress in the liner were evaluated according to the observed strain variations. Both of them are time-dependent, and about 5.3%, 8.3% and 9.0% of the prestress losses are observed at the age of 1 d, 30 d and 60 d respectively after stressing. The distribution of prestress in the liner is relatively uniform and meets the design requirement.
文摘To evaluate the residual stress in TiAl based alloys by X ray diffraction, X ray elastic constants (REC) of a γ TiAl alloy were determined. From these results, the stress state of a given phase in a duplex TiAl based alloy under a uniaxial tensile loading has been characterized by X ray diffraction. The results show that the X ray elastic constants and the microscopic stresses of the given phase are different from the apparent elastic constants and the macroscopic stresses of the alloy. The reason of the different distribution of the alloy was also discussed. [
文摘Based on[1],the stress structures of the smooth region and shear lip of the specimens have been investigated in the paper.The characteristics of the stress structure in the smooth region have been found that the variable z can separated out;the stresses in the midsection can be obtained by the plane strain FEM results or HRR structure modified by the stress triaxiality.The effects of load level and thickness on the stress structure can be reflected by the distribution of CTOD along the thickness direction.The obtained expressions of the stresses are very simple and visualized.The analyses of the stress structure in the shear lip show that the stresses can be obtained by different methods of interpolation to a certain precise degree.A new degree parameter of the plane strain state has been put forward and studied.The parameter can reflect relatively well the variation of the kind and thickness of the specimen as well as the load level.The fracture parameter has also been investigated to be sure that it can be obtained by modified CTOD with the stress triaxiality.
基金supported by the Open Fund (PLN 201718) of State Key Laboratory of Oil and Gas Reservoir Geology and ExploitationSouthwest Petroleum University and the Open Fund (SEC-2018-04) of Collaborative Innovation Center of Shale Gas Resources and EnvironmentSouthwest Petroleum University and the National Science and Technology Major Project of China (2017ZX05036003-003)
文摘Fracture prediction is a technical issue in the field of petroleum exploration and production worldwide.Although there are many approaches to predict the distribution of cracks underground,these approaches have some limitations.To resolve these issues,we ascertained the relation between numerical simulations of tectonic stress and the predicted distribution of fractures from the perspective of geologic genesis,based on the characteristics of the shale reservoir in the Longmaxi Formation in Dingshan;the features of fracture development in this reservoir were considered.3 D finite element method(FEM)was applied in combination with rock mechanical parameters derived from the acoustic emissions.The paleotectonic stress field of the crack formation period was simulated for the Longmaxi Formation in the Dingshan area.The splitting factor in the study area was calculated based on the rock breaking criterion.The coefficient of fracture development was selected as the quantitative prediction classification criteria for the cracks.The results show that a higher coefficient of fracture development indicates a greater degree of fracture development.On the basis of the fracture development coefficient classification,a favorable area was identified for the development of fracture prediction in the study area.The prediction results indicate that the south of the Dingshan area and the DY3 well of the central region are favorable zones for fracture development.
文摘The concept of fault junction is proposed to describe the relationship between the two faults by the authors. The junction relationship between Ganjiang and Tanlu faults is analyzed in this paper, and this has been elucidated through numerical simulation about the tectonic stress field analysis. Numerical simulation of the tectonic stress field conducted for the major mineralization stage of the Jiujiang-Ruichang junction area reveals that the stress field of the junction structure at the major mineralization stage shows a relatively close relationship with the formation of the ore deposits (occurrences).
文摘The influence of welding parameters of butt joints, made by three processes (MMA, MAG and T.I.M.E), on their geometric characteristics has been evaluated, which in turn caused a change of the fatigue strength. That fore the statistic analysis and FEM were used and a method developed in the Institute of Welding, which consist in a direct connection of parameters used during welding with the fatigue strength of joints welded by various processes. It has been proven, among others, which by using more advanced welding processes (T.I.M.E) the fatigue strength of welded joints can be increased in comparison to joints welded by MMA and MAG.
基金partly supported by the Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for Scientific Research (Grant No. 19121587)supported by the Natural Science Foundation of Shaanxi Province (No.2021KW-25)。
文摘The excellent properties of SiC bring new challenges for the device packaging.In this study,the bonding strength,fracture behaviors and microstructural evolution of micron-porous Ag joint were elevated during thermal cycling(–50 ℃–250 ℃) in SiC/DBC(direct bonding copper) die attachment structure for different time.During harsh thermal shock test,the strength of sintered joint deceased gradually with the increase of cycling number,and the value just was half of the value of as-sintered after 1 000 cycles.Coarsening of Ag grains was observed in micron-porous joint with the structure inhomogeneity and defects increasing,which were the reasons of the strength decease.In addition,it was also found that the fracture behavior of sintered joints was changed from ductile deformation of Ag grain to brittle fracture of crack propagation after 1 000 cycles.This study will add the understanding in the mechanical properties of Ag sinter joining and its applications at high temperature.
基金supported by the National Natural Science Foundation of China(52004286)the Fundamental Research Funds for the Central Universities(2022XJNY02)+3 种基金the National Natural Science Foundation of China(51974317,52074296)the China Postdoctoral Science Foundation(2020T130701,2019M650895)the Fundamental Research Funds for the Central Universities(2022YJSNY18,2022YJSNY09)all of which were gratefully acknowledged.
文摘Close-distance coal seams are widely distributed over China,and the coal pillars left by the overlying coal seams afect the retracement channel of the underlying coal seam in the stopping stage.Based on the engineering background of close-distance seam mining in a coal mine,the reasonable position of the underlying coal seam's stopping line and the support method of the large section roadway during stopping are investigated using feld measurements,similar simulation experiments,and numerical simulations.There are three types of location relationships between the stopping line of the underlying coal seam and the stopping line of the overlying coal seam:"externally staggered with the upper stopping line"(ESUL,stops mining under the overlying goaf),"overlapped with upper stopping line"(OUL),and"internally staggered with the upper stopping line"(ISUL,ISUL-SD for shorter internal staggered distances,ISUL-LD for longer ones).There are diferent stress arch structures in the overlying strata of the above three positions,and the stress arch evolution process exists in the process of ESUL→OUL→ISUL-SD→ISUL-LD:a front and rear double stress arch structure→the front arch gradually decreases→the front arch dies out,and the double arch synthesizes the single arch→the single-arch range expands→the nested double arch.The relationship between the stress arch structure and the position of the stopping line is evaluated as follows:(1)ESUL:the stress concentration in the roof plate of the retracement channel of the underlying coal seam is the highest,because the overburden block of the extensive collapse zone acts directly on the roof plate of the retracement channel,resulting in relative difculties in roof support.(2)OUL:although the retracement channel roof pressure is minimal,the overlying rock structure has the potential for rotation or slippage instability.(3)ISUL-SD:the pressure on the roof of the retracement channel is small and the overburden structure is stable,which is conducive to the safe retraction of the support and not limited by the width of the end-mining coal pillar.(4)ISUL-LD:it is basically the same as the condition of stopping under the non-goaf;however,it has a limitation on the width of the end-mining coal pillar.The location of the stopping line is selected as ISUL-SD,and the retraction process of the self-excavating retraction channel was adopted.A partition asymmetric support scheme which is proven by feld practice is proposed,through a comprehensive analysis of the pre-stress feld simulation of the support scheme,based on the diferent control requirements of the roof above the support and the roof of the retracement channel in the stopping area.This method realizes safe and smooth withdrawal of the support.
基金financially supported by the National Natural Science Foundation of China(Nos.21474111,21222407 and 21274152)subsidized by the National Basic Research Program of China(973 Program,2012CB821500)
文摘The structure and rheological properties of carbon-based particle suspensions, i.e., carbon black（CB）, multi-wall carbon nanotube（MWNT）, graphene and hollow carbon sphere（HCS） suspended in polydimethylsiloxane（PDMS）, are investigated. In order to study the effect of particle shape on the structure and rheological properties of suspensions, the content of surface oxygen-containing functional groups of carbon-based particles is controlled to be similar. Original spherical-like CB（fractal filler）, rod-like MWNT and sheet-like graphene form large agglomerates in PDMS, while spherical HCS particles disperse relatively well in PDMS. The dispersion state of carbon-based particles affects the critical concentration of forming a rheological percolation network. Under weak shear, negative normal stress differences（ΔN） are observed in CB, MWNT and graphene suspensions, while ΔN is nearly zero for HCS suspensions. It is concluded that the vorticity alignment of CB, MWNT and graphene agglomerates under shear results in the negative ΔN. However, no obvious structural change is observed in HCS suspension under weak shear, and accordingly, the ΔN is almost zero.
