To compensate for the shortcomings of quasi-static law in anti-fatigue analysis of foundry crane metal structures,the fatigue life evaluation method of foundry crane metal structure considering load dynamic response a...To compensate for the shortcomings of quasi-static law in anti-fatigue analysis of foundry crane metal structures,the fatigue life evaluation method of foundry crane metal structure considering load dynamic response and crack closure effect is proposed.In line with the theory of mechanical vibration,a dynamic model of crane structure during the working cycle is constructed,and dynamic coefficients under diverse actions are analysed.Calculation models of the internal force dynamic change process of dangerous cross-sections and a simulation model of first principal stress-time history are established by using the steel structure design criteria,which is utilised to extract the change of first principal stress of danger points over time.Then,the double-parameter stress spectrum is obtained by the rain flow counting method.The fatigue life calculation formula is corrected by introducing a crack closure parameter that can be calculated by the stress ratio and the effective stress ratio.Under the finite element model imported into Msc.Patran,crack propagation analysis is performed by the growth method in the fatigue integration module Msc.Fatigue.Taking the metal structure of a 100/40t-28.5m foundry crane with track offset as an example,the accuracy of calculation results and the feasibility and applicability of the proposed method are verified by theoretical calculation and finite element simulation,which provide a theoretical basis for improvement of the fatigue resistance design of foundry cranes.展开更多
The crack tip strain gauge method in the compliance technique was used to determine the opening load of notched crack of axle steel,and the nonlinear finite element ADINA program, to which the cyclic stress-strain cur...The crack tip strain gauge method in the compliance technique was used to determine the opening load of notched crack of axle steel,and the nonlinear finite element ADINA program, to which the cyclic stress-strain curve of axle steel was applied,was used to analyze the stress-strain field ahead of the crack tip and the opening load of notched crack.The results of both the compliance technique and the numerical method were in good agreement.In this pa- per,the concept of the sensitive point is proposed and the key to the determination of the crack opening load in the experiment is to place a strain gauge at sensitive point.It is certified by both experimental and numerical methods that the sensitive point has the best linear relation- ship character and the value of strain is much greater.展开更多
Threshold of fatigue for short through cracks for Al-Li alloy 8090 was evaluated to be lower than that of long cracks,and to decrease with the shortening of the crack length.The correla- tion among the threshold,crack...Threshold of fatigue for short through cracks for Al-Li alloy 8090 was evaluated to be lower than that of long cracks,and to decrease with the shortening of the crack length.The correla- tion among the threshold,crack wake,and crack tip shielding of the short fatigue cracks was discussed.The super demarcation length and lowest theoretical threshold of short through fa- tigue cracks were presented.展开更多
Fatigue crack growth rates of Al-Li alloy 8090 in air were found to be strongly dependent up- on the aging conditions.The naturally aged and underaged specimens showed the highest re- sistance to the fatigue crack pro...Fatigue crack growth rates of Al-Li alloy 8090 in air were found to be strongly dependent up- on the aging conditions.The naturally aged and underaged specimens showed the highest re- sistance to the fatigue crack propagation.The fatigue crack growth resistance of the overaged specimen is the lowest and that of the peakaged specimen in between.As compared to air, 3.5% NaCl solution does not change the effect of aging conditions on the fatigue crack growth,but causes a decrease of the resistance to the fatigue crack growth under the same ag- ing condition.Both short cracks from notch and physically short cracks showed much higher rates of fatigue crack propagation in comparison with long cracks under the same aging condi- tion and stress intensity level.The growth behavior of the short crack depends on its type.The growth rate of short crack from notch decreases first to a minimum and then increases with in- creasing △K.However,the physically short crack grows at a progressively increasing rate. The effects of aging conditions are explained in terms of the slip planarity of dislocations and the cyclic slip reversibility.The observed short crack behavior is considered to be dependent on the crack closure and the local plasticity near the crack tip.展开更多
The corrosion fatigue propagation behaviour of high strength low alloy Cr-Ni and Si-Mn steels has been investigated in 3.5 %NaCl solution spryly at the frequencies of 0.1 and 5.5 Hz. It was shown that the fatigue crac...The corrosion fatigue propagation behaviour of high strength low alloy Cr-Ni and Si-Mn steels has been investigated in 3.5 %NaCl solution spryly at the frequencies of 0.1 and 5.5 Hz. It was shown that the fatigue crack initiation resistances of the two steels are significantly re- duced in salt spray;the fatigue crack growth rates of steels increase with the decrease of fre- quency and are much higher in salt spray than in air within low ΔK range.A critical stress in- tensity factor was observed for each steel and the crack growth stoppage will occur if the ΔK values are lower than it.It was found that the active dissolution makes great contribution to the fatigue crack growth within low ΔK range.展开更多
The growth behavior of fatigue cracks for alurninum-lithium alloy 2090 and traditional aluminum alloy2024 was investisated. Specific einphasis was placed on explorins the correlation among crack closure effect,intrins...The growth behavior of fatigue cracks for alurninum-lithium alloy 2090 and traditional aluminum alloy2024 was investisated. Specific einphasis was placed on explorins the correlation among crack closure effect,intrinsic growth resistance and fractographic features. A comparing to alloy 7075 , alloy 2090 shows the excel-lent nominal growth resistance of fatigue cracks, inferior intrinsic growth resistance in the near-threshold zoneand superior one in the Ⅲ zone. The mechanism of extrinsic toughness effect in the near-threshold zone iscrack closure effect. The excellect norninal and intrinsic growth resistance of fatigue cracks in the Ⅲ zone is at-tributed to the delamination toughness effect. A certain level of crack closure effect and the near-delaminationtoughness effect ean be achieved in the Paris zone.展开更多
Pronounced changes of nuclear charge radii provide a stringent benchmark on the theoretical models and play a vital role in recognizing various nuclear phenomena.In this work,the systematic evolutions of nuclear charg...Pronounced changes of nuclear charge radii provide a stringent benchmark on the theoretical models and play a vital role in recognizing various nuclear phenomena.In this work,the systematic evolutions of nuclear charge radii along even Z=84-120 isotopic chains are first investigated by the recently developed new ansatz under the covariant density functional.The calculated results show that the shell closure effects of nuclear charge radii appear remarkably at the neutron numbers N=126 and 184.Interestingly,the arch-like shapes of charge radii between these two strong neutron-closed shells are naturally observed.Across the N=184 shell closure,the abrupt increase in charge radii is still evidently emerged.In addition,the rapid raise of nuclear charge radii from the neutron numbers N=138 to N=144 is disclosed clearly in superheavy regions due to the enhanced shape deformation.展开更多
A highly linear correlation exists between the differences in charge radii of mirror-pair nuclei and the slope parameter of symmetry energy,as reported in literature.This study investigates the impact of neutron-proto...A highly linear correlation exists between the differences in charge radii of mirror-pair nuclei and the slope parameter of symmetry energy,as reported in literature.This study investigates the impact of neutron-proton correlations,deduced from neutron-and proton-pair condensation near the Fermi surface,on determining the symmetry energy slope parameter using Skyrme density functionals.Differential charge radii of Ni isotopes are employed to assess the validity of the proposed model.Results suggest that the modified model can reproduce the shell quenching of charge radii at the neutron number N=28 along the Ni isotopic chain.The shell closure effect of the charge radii can also be predicted at the neutron number N=50.Correlations between the differences in charge radii of the mirror pair nuclei ^(32)Ar-^(32)Si and ^(54)Ni-^(54)Fe and the slope parameter of symmetry energy are also analyzed.Notably,the range of the symmetry energy slope is influenced by the neutron-pair condensation near the Fermi surface.Moreover,a relatively stiff equation of state can be inferred from the mirror pairs ^(32)Ar-^(32)Si and ^(54)Ni-^(54)Fe when the effect of the neutron-pair condensation is considered.展开更多
A general model of fatigue crack growth(FCG) in ductile alloys under variable amplitude loading is proposed based on the passivation-lancet theory and the crack closure concept.The model can capture the interactions o...A general model of fatigue crack growth(FCG) in ductile alloys under variable amplitude loading is proposed based on the passivation-lancet theory and the crack closure concept.The model can capture the interactions of single cycle overloading and underloading,sequential loading and spectrum loading effectively.Moreover,the retardation effect due to overloads and the acceleration effect due to underloading can be described quantitatively by a transition function of crack opening stress.The fatigue test data in 2024-T351,2024-T3 and 7075-T6 aluminum alloys under different types of variable amplitude loading and spectrum loading are used to validate the general model and the predictions by the general model are in good agreement with the test data.Furthermore,the predictions are also compared with the existing models,including FASTRAN,AFGROW and the state-space model,and the comparison results show that the general model predicts the FCG process more accurately.展开更多
基金the National Science-technology Support Projects for the 13th Five-year Plan(2017YFC0805703-4).
文摘To compensate for the shortcomings of quasi-static law in anti-fatigue analysis of foundry crane metal structures,the fatigue life evaluation method of foundry crane metal structure considering load dynamic response and crack closure effect is proposed.In line with the theory of mechanical vibration,a dynamic model of crane structure during the working cycle is constructed,and dynamic coefficients under diverse actions are analysed.Calculation models of the internal force dynamic change process of dangerous cross-sections and a simulation model of first principal stress-time history are established by using the steel structure design criteria,which is utilised to extract the change of first principal stress of danger points over time.Then,the double-parameter stress spectrum is obtained by the rain flow counting method.The fatigue life calculation formula is corrected by introducing a crack closure parameter that can be calculated by the stress ratio and the effective stress ratio.Under the finite element model imported into Msc.Patran,crack propagation analysis is performed by the growth method in the fatigue integration module Msc.Fatigue.Taking the metal structure of a 100/40t-28.5m foundry crane with track offset as an example,the accuracy of calculation results and the feasibility and applicability of the proposed method are verified by theoretical calculation and finite element simulation,which provide a theoretical basis for improvement of the fatigue resistance design of foundry cranes.
文摘The crack tip strain gauge method in the compliance technique was used to determine the opening load of notched crack of axle steel,and the nonlinear finite element ADINA program, to which the cyclic stress-strain curve of axle steel was applied,was used to analyze the stress-strain field ahead of the crack tip and the opening load of notched crack.The results of both the compliance technique and the numerical method were in good agreement.In this pa- per,the concept of the sensitive point is proposed and the key to the determination of the crack opening load in the experiment is to place a strain gauge at sensitive point.It is certified by both experimental and numerical methods that the sensitive point has the best linear relation- ship character and the value of strain is much greater.
文摘Threshold of fatigue for short through cracks for Al-Li alloy 8090 was evaluated to be lower than that of long cracks,and to decrease with the shortening of the crack length.The correla- tion among the threshold,crack wake,and crack tip shielding of the short fatigue cracks was discussed.The super demarcation length and lowest theoretical threshold of short through fa- tigue cracks were presented.
文摘Fatigue crack growth rates of Al-Li alloy 8090 in air were found to be strongly dependent up- on the aging conditions.The naturally aged and underaged specimens showed the highest re- sistance to the fatigue crack propagation.The fatigue crack growth resistance of the overaged specimen is the lowest and that of the peakaged specimen in between.As compared to air, 3.5% NaCl solution does not change the effect of aging conditions on the fatigue crack growth,but causes a decrease of the resistance to the fatigue crack growth under the same ag- ing condition.Both short cracks from notch and physically short cracks showed much higher rates of fatigue crack propagation in comparison with long cracks under the same aging condi- tion and stress intensity level.The growth behavior of the short crack depends on its type.The growth rate of short crack from notch decreases first to a minimum and then increases with in- creasing △K.However,the physically short crack grows at a progressively increasing rate. The effects of aging conditions are explained in terms of the slip planarity of dislocations and the cyclic slip reversibility.The observed short crack behavior is considered to be dependent on the crack closure and the local plasticity near the crack tip.
文摘The corrosion fatigue propagation behaviour of high strength low alloy Cr-Ni and Si-Mn steels has been investigated in 3.5 %NaCl solution spryly at the frequencies of 0.1 and 5.5 Hz. It was shown that the fatigue crack initiation resistances of the two steels are significantly re- duced in salt spray;the fatigue crack growth rates of steels increase with the decrease of fre- quency and are much higher in salt spray than in air within low ΔK range.A critical stress in- tensity factor was observed for each steel and the crack growth stoppage will occur if the ΔK values are lower than it.It was found that the active dissolution makes great contribution to the fatigue crack growth within low ΔK range.
文摘The growth behavior of fatigue cracks for alurninum-lithium alloy 2090 and traditional aluminum alloy2024 was investisated. Specific einphasis was placed on explorins the correlation among crack closure effect,intrinsic growth resistance and fractographic features. A comparing to alloy 7075 , alloy 2090 shows the excel-lent nominal growth resistance of fatigue cracks, inferior intrinsic growth resistance in the near-threshold zoneand superior one in the Ⅲ zone. The mechanism of extrinsic toughness effect in the near-threshold zone iscrack closure effect. The excellect norninal and intrinsic growth resistance of fatigue cracks in the Ⅲ zone is at-tributed to the delamination toughness effect. A certain level of crack closure effect and the near-delaminationtoughness effect ean be achieved in the Paris zone.
基金funded by the Key Laboratory of High Precision Nuclear Spectroscopy,Institute of Modern Physics,Chinese Academy of Sciencessupported partly by the National Natural Science Foundation of China under Grants No.12135004,No.11635003,No.11961141004 and No.12047513+1 种基金the support of the National Natural Science Foundation of China under Grants No.11975096the Fundamental Research Funds for the Central Universities(2020NTST06)。
文摘Pronounced changes of nuclear charge radii provide a stringent benchmark on the theoretical models and play a vital role in recognizing various nuclear phenomena.In this work,the systematic evolutions of nuclear charge radii along even Z=84-120 isotopic chains are first investigated by the recently developed new ansatz under the covariant density functional.The calculated results show that the shell closure effects of nuclear charge radii appear remarkably at the neutron numbers N=126 and 184.Interestingly,the arch-like shapes of charge radii between these two strong neutron-closed shells are naturally observed.Across the N=184 shell closure,the abrupt increase in charge radii is still evidently emerged.In addition,the rapid raise of nuclear charge radii from the neutron numbers N=138 to N=144 is disclosed clearly in superheavy regions due to the enhanced shape deformation.
基金Supported by the Open Project of Guangxi Key Laboratory of Nuclear Physics and Nuclear Technology(NLK2023-05)the Central Government Guidance Funds for Local Scientific and Technological Development,China(Guike ZY22096024)+5 种基金the Natural Science Foundation of Ningxia Province,China(2024AAC03015)the Key Laboratory of Beam Technology of Ministry of Education,China(BEAM2024G04)supported by the National Natural Science Foundation of China(11705118,12175151)the Major Project of the GuangDong Basic and Applied Basic Research Foundation(2021B0301030006)supported by the key research and development project of Ningxia(2024BEH04090)the Key Laboratory of Beam Technology of Ministry of Education,China(BEAM2024G05)。
文摘A highly linear correlation exists between the differences in charge radii of mirror-pair nuclei and the slope parameter of symmetry energy,as reported in literature.This study investigates the impact of neutron-proton correlations,deduced from neutron-and proton-pair condensation near the Fermi surface,on determining the symmetry energy slope parameter using Skyrme density functionals.Differential charge radii of Ni isotopes are employed to assess the validity of the proposed model.Results suggest that the modified model can reproduce the shell quenching of charge radii at the neutron number N=28 along the Ni isotopic chain.The shell closure effect of the charge radii can also be predicted at the neutron number N=50.Correlations between the differences in charge radii of the mirror pair nuclei ^(32)Ar-^(32)Si and ^(54)Ni-^(54)Fe and the slope parameter of symmetry energy are also analyzed.Notably,the range of the symmetry energy slope is influenced by the neutron-pair condensation near the Fermi surface.Moreover,a relatively stiff equation of state can be inferred from the mirror pairs ^(32)Ar-^(32)Si and ^(54)Ni-^(54)Fe when the effect of the neutron-pair condensation is considered.
基金supported by the Gas Turbine Establishment of China (Grant No. GTE022006084)
文摘A general model of fatigue crack growth(FCG) in ductile alloys under variable amplitude loading is proposed based on the passivation-lancet theory and the crack closure concept.The model can capture the interactions of single cycle overloading and underloading,sequential loading and spectrum loading effectively.Moreover,the retardation effect due to overloads and the acceleration effect due to underloading can be described quantitatively by a transition function of crack opening stress.The fatigue test data in 2024-T351,2024-T3 and 7075-T6 aluminum alloys under different types of variable amplitude loading and spectrum loading are used to validate the general model and the predictions by the general model are in good agreement with the test data.Furthermore,the predictions are also compared with the existing models,including FASTRAN,AFGROW and the state-space model,and the comparison results show that the general model predicts the FCG process more accurately.
