In this paper,the work hardening and softening behavior of AZ31 magnesium alloy sheets by hard plate accumulative roll bonding(HP-ARB)process in a specific temperature range was studied for the first time,and the cycl...In this paper,the work hardening and softening behavior of AZ31 magnesium alloy sheets by hard plate accumulative roll bonding(HP-ARB)process in a specific temperature range was studied for the first time,and the cyclic stress relaxation test,EBSD,TEM and other characterization methods were used.When the rolling temperature is 350℃,the grain size of magnesium sheets is refined to 4.32(±0.36)μm on average,and it shows an excellent combination of strength and plasticity.The tensile strength reaches 307(±8.52)MPa and the elongation is 12.73(±0.84)%.At this time,the curve of work hardening rate decreases smoothly and the degree of hardening is the lowest,and the amplitude of stress drop △σ_(p) in work softening test is the smallest with the increase of cycle times,which shows that the well coordination between work hardening and softening behavior has been achieved.Research has found that the combined effect of grain boundary strengthening and fine grain strengthening enhances the yield and tensile strength of magnesium sheets after three passes HP-ARB process at 350℃.This is attributed to the high degree of dislocation slip opening in the pyramidal surfaceand<c+a>,which not only coordinates the c-axis strain of the entire grain,but also promotes the slip transfer of dislocations in the fine-grained region,significantly improving the elongation of the sheets.This study provides a new idea for the forming and manufacturing of high performance magnesium alloy sheets.展开更多
To obtain the Ti_(p)with different aspect ratios,the Ti_(p)/Mg-5Zn-0.3Ca composite prepared by semi-solid stir casting was subjected to extrusion at 220℃,180℃,and 140℃,respectively.Then,the effect of the Ti_(p)’s ...To obtain the Ti_(p)with different aspect ratios,the Ti_(p)/Mg-5Zn-0.3Ca composite prepared by semi-solid stir casting was subjected to extrusion at 220℃,180℃,and 140℃,respectively.Then,the effect of the Ti_(p)’s aspect ratio on the microstructure,mechanical properties,work hardening and softening behaviors of Ti_(p)/Mg-5Zn-0.3Ca composites was investigated.The results indicated that the Ti_(p)could be elongated obviously after low-temperature extrusion,and the aspect ratio of which would reach to 13.7:1 as the extrusion temperature deceased to 140℃.Then the“Ti/Mg”layer-like structure was formed in the Ti_(p)/Mg-5Zn-0.3Ca composite.Accompanied with the elongation of Ti_(p),the dynamic recrystallized grains and dynamic precipitates were both refined significantly,however,the dynamic recrystallization rate changed a little.The elongated Ti_(p)endowed the Ti_(p)/Mg-5Zn-0.3Ca composites with better matching of strength and toughness without the sacrifice of elongation and bending strain.Both the work hardening rate and softening rate of Ti_(p)/Mg-5Zn-0.3Ca composites increased with the increasing aspect ratio of Ti_(p).The formation of“Ti/Mg”layer-like structure contributed to the redistribution of strain from large aggregations to a network-like distribution,which effectively suppresses the initiation and propagation of micro-cracks,thus enhancing the plasticity of the Ti_(p)/Mg-5Zn-0.3Ca composites.展开更多
Existing creep constitutive models rarely incorporate studies on the coupling mechanism between creep damage and rock strain softening/hardening.This study analyzed the strain softening and hardening behaviors of argi...Existing creep constitutive models rarely incorporate studies on the coupling mechanism between creep damage and rock strain softening/hardening.This study analyzed the strain softening and hardening behaviors of argillaceous sandstone and sandy mudstone during load-induced failure based on the plastic increment theory.These behaviors were then coupled with an improved Burgers creep model to establish a coupled creep-damage and plastic softening/hardening model.Finally,the validity and engineering applicability of the proposed model were verified through FLAC~(3D)numerical simulations.The numerical simulation results of standard cylindrical specimens show that the established coupling model can effectively reflect the unloading creep deformation law and failure characteristics of argillaceous sandstone and sandy mudstone.Taking the diversion tunnel of a hydropower station in Northwest China as an example for engineering application,the coupled creep-damage and plastic softening/hardening model is introduced into FLAC~(3D)to carry out numerical simulation calculation of the tunnel under excavation and unsupported creep conditions.The results show that the uncoordinated deformation of the upper and lower walls of the surrounding rock of the tunnel is more prominent.When the buried depth of the tunnel increases to 80 m,the monitoring point C in the sandy mudstone area of the upper wall shows nonlinear accelerated deformation under unsupported creep conditions,and the maximum displacement in the horizontal direction reaches 44.5 mm,and the maximum displacement in the vertical direction reaches 53.5 mm.The coupled creep-damage and plastic softening/hardening model established in the research results can well describe the whole process of uncoordinated deformation and failure in the unloading creep process of soft-hard interbedded rock mass.展开更多
Multi-pass hot processing methods are commonly used in magnesium(Mg)alloys to overcome the poor workability due to limited slip systems,which generally involve complicated post-deformation softening and hardening beha...Multi-pass hot processing methods are commonly used in magnesium(Mg)alloys to overcome the poor workability due to limited slip systems,which generally involve complicated post-deformation softening and hardening behaviors.In this work,to reveal post-deformation softening and hardening mechanisms of a Mg-2Y-1Zn alloy,double-stage hot compression tests and microstructural observations were conducted.The results showed that the softening fraction of Mg-2Y-1Zn alloy showed a non-linear dependence on deformation conditions and could be general coupled by Z parameter.Due to the formation and cross-overlapping of twins and kinks,only static recovery(SRV)occurred during holding process at 300℃/0.001 s^(-1) which led to the least static softening:5.52% after 10 s of holding.For samples at 400℃/0.001s^(-1),the enhanced post-deformation softening,which is 11.93% after 10 s of holding,was attributed to static recrystallization(SRX)followed continuous dynamic recrystallization(CDRX)happened during first deformation stage as well as SRV influenced by the LPSO phases.Under deformation condition of 400℃/0.1 s^(-1),the coupled meta-dynamic recrystallization(MDRX)and SRX resulted in serious stress relaxation,which is 42.83% after 10 s of holding,and caused hardening phenomenon at reloading stage.The 18R-LPSO and 14H-LPSO phases synchronously worked on deformation behaviors and limited the growth of recrystallized grains.Further,a simplified static softening kinetics model was established based on Johnson-Mehl-Avrami-Kolmogorov equation and employed to rationalize experimental data.展开更多
The effects of the deformation temperature and the strain rate on the hot deformation behavior of pure copper were investigated based on compression tests. The expressions of strain hardening rate, dynamic recrystalli...The effects of the deformation temperature and the strain rate on the hot deformation behavior of pure copper were investigated based on compression tests. The expressions of strain hardening rate, dynamic recrystallization critical stress, saturated stress, dynamic recovery volume fraction and dynamic recrystallization volume fraction were determined. According to the processing map, the instability regions occur in regions of 400?450 °C, 0.001?0.05 s?1 and 450?750 °C, 0.05?1 s?1. The deformation mechanism in the stability region is dynamic recrystallization. The flow stress was predicted. The results also show that the true stress–true strain curves predicted by the extracted model are in good agreement with the experimental results.展开更多
The deformation behavior of AZ61 Mg alloy during hot deformation has been investigated in wide temperature and strain rate range by a Gleeble simulator. Specimens are deformed in compression in the temperature range o...The deformation behavior of AZ61 Mg alloy during hot deformation has been investigated in wide temperature and strain rate range by a Gleeble simulator. Specimens are deformed in compression in the temperature range of 523-673 K and at strain rates of 0.001-1 s-1. It is found that the flow curves exhibit a peak and then decrease towards steady-state of classical DRX, which decrease with rising temperature and decreasing strain rate. The deformation behavior of the specimens can be attributed to the occurrence of strain hardening and softening. As stress decreases, the strain hardening rate declines at a fast rate when temperature rises or strain rate decreases. The shapes of θ-σ curves indicate some important features such as subgrain formation, the criticai stress, the peak stress and steady stress. The onset of DRX can be determined by the point of inflection on θ-σ or Inθ-σ curves.展开更多
The effects of microstructure and its evolution on the macroscopic superelastic stress-strain response of polycrystalline Shape Memory Alloy(SMA)are studied by a microstructure-based constitutive model developed in th...The effects of microstructure and its evolution on the macroscopic superelastic stress-strain response of polycrystalline Shape Memory Alloy(SMA)are studied by a microstructure-based constitutive model developed in this paper.The model is established on the following basis:(1)the transformation conditions of the unconstrained single crystal SMA microdomain(to be distinguished from the bulk single crystal),which serve as the local criterion for the derivation of overall transfor- mation yield conditions of the polycrystal;(2)the micro-to macro-transition scheme by which the connection between the polycrystal aggregates and the single crystal microdomain is established and the macroscopic transformation conditions of the polycrystal SMA are derived;(3)the quantitative incorporation of three microstruc- ture factors(i.e.,nucleation,growth and orientation distribution of martensite)into the modeling.These microstructural factors are intrinsic of specific polycrystal SMA systems and the role of each factor in the macroscopic constitutive response is quan- titatively modeled.It is demonstrated that the interplay of these factors will result in different macroscopic transformation kinematics and kinetics which are responsible for the observed macroscopic stress-strain hardening or softening response,the latter will lead to the localization and propagation of transformation bands in TiNi SMA.展开更多
This study proposed a new and more flexible S-shaped rock damage evolution model from a phenomenological perspective based on an improved Logistic function to describe the characteristics of the rock strain softening ...This study proposed a new and more flexible S-shaped rock damage evolution model from a phenomenological perspective based on an improved Logistic function to describe the characteristics of the rock strain softening and damage process.Simultaneously,it established a constitutive model capable of describing the entire process of rock pre-peak compaction and post-peak strain softening deformation,considering the nonlinear effects of the initial compaction stage of rocks,combined with damage mechanics theory and effective medium theory.In addition,this research verified the rationality of the constructed damage constitutive model using results from uniaxial and conventional triaxial compression tests on Miluo granite,yellow sandstone,mudstone,and glutenite.The results indicate that based on the improved Logistic function,the theoretical damage model accurately describes the entire evolution of damage characteristics during rock compression deformation,from maintenance through gradual onset,accelerated development to deceleration and termination,in a simple and unified expression.At the same time,the constructed constitutive model can accurately simulate the stress-strain process of different rock types under uniaxial and conventional triaxial compression,and the theoretical model curve closely aligns with experimental data.Compared to existing constitutive models,the proposed model has significant advantages.The damage model parameters a,r and β have clear physical meanings and interact competitively,where the three parameters collectively determine the shape of the theoretical stress−strain curve.展开更多
Based on the microstructure-based constitutive model established in Part Ⅰ,a detailed numerical investigation on the role of each microstructure pa- rameter in the kinematical and kinetic evolution of polycrystalline...Based on the microstructure-based constitutive model established in Part Ⅰ,a detailed numerical investigation on the role of each microstructure pa- rameter in the kinematical and kinetic evolution of polycrystalline SMA under ax- isymmetrical tension loading is performed.Some macroscopic constitutive features of stress-induced martensite transformation are discussed.展开更多
The effect of strain hardening and strain softening behavior of flow stress changing with temperature on welding residual stress, plastic strain and welding distortion of ATN0 1-T4 aluminum alloy was studied by finite...The effect of strain hardening and strain softening behavior of flow stress changing with temperature on welding residual stress, plastic strain and welding distortion of ATN0 1-T4 aluminum alloy was studied by finite simulation method. The simulation results show that the weld seam undergoes strain hardening in the temperature range of 180-250 ℃, however, it exhibits strain softening at temperature above 250 ℃ during welding heating and cooling process. As a result, the strain hardening and strain softening effects counteract each other, introducing slightly influence on the welding residual stress, residual plastic strain and distortion. The welding longitudinal residual stress was determined by ultrasonic stress measurement method for the flat plates of A7N01-T4 aluminum alloy. The simulation results are well accordant with test ones.展开更多
Ab initio calculations are used to understand the fundamental mechanism of the solid solution softening/hardening of the Mo-binary system.The results reveal that the Mo-Ti,Mo-Ta,Mo-Nb,and Mo-W interactions are primari...Ab initio calculations are used to understand the fundamental mechanism of the solid solution softening/hardening of the Mo-binary system.The results reveal that the Mo-Ti,Mo-Ta,Mo-Nb,and Mo-W interactions are primarily attractive with negative heats of formation,while the interactions of Mo-Re,and Mo-Zr would be mainly repulsive with positive heats of formation.It is also shown that the addition of Re and Zr would cause the solid solution softening of Mo by the decrease of the unstable stacking fault energy and the increase of ductility.On the contrary,the elements of W,Ta,Ti,and Nb could bring about the solid-solution hardening of Mo through the impediment of the slip of the dislocation and the decrease of ductility.Electronic structures indicate that the weaker/stronger chemical bonding due to the alloying elements should fundamentally induce the solid solution softening/hardening of Mo.The results are discussed and compared with available evidence in literatures,which could deepen the fundamental understanding of the solid solution softening/hardening of the binary metallic system.展开更多
Toward accurately simulating both hardening and softening effects for metals up to failure,a new finite strain elastoplastic J2-flow model is proposed with the yield strength therein as a function of the plastic work ...Toward accurately simulating both hardening and softening effects for metals up to failure,a new finite strain elastoplastic J2-flow model is proposed with the yield strength therein as a function of the plastic work in the explicit form.With no need to identify any adjustable parameters,the uniaxial stress-strain response predicted from this new model is shown to automatically and accurately match any given data from monotonic uniaxial extension tests of bars.As such,the objectives in three respects are achieved for the first time,i.e.,(i)both the hardening and softening effects up to failure can be simulated in the sense of matching test data with no errors,(ii)the usual tedious implicit procedures toward identifying numerous unknown parameters need not be involved and can be totally bypassed,and(iii)the model applicability can be ensured in a broad sense for various metallic materials with markedly different transition effects from hardening to softening.With the new model,the complete response features of stretched bars and twisted tubes up to failure are studied,including the failure effects of bars under monotonic extension and tubes under monotonic torsion and,furthermore,the fatigue failure effects of bars under cyclic loading.The results show accurate agreement with the uniaxial data,and the results for both the shear stress and the normal stress at the finite torsion display realistic hardening-to-softening transition effects for the first time.展开更多
The Ti_(p)/ZX60 composites with different Ti_(p) contents were prepared by semi-solid stirring casting.After extrusion,the microstructure,work hardening and softening behavior of the Ti_(p)/ZX60 composites were analyz...The Ti_(p)/ZX60 composites with different Ti_(p) contents were prepared by semi-solid stirring casting.After extrusion,the microstructure,work hardening and softening behavior of the Ti_(p)/ZX60 composites were analyzed compared with the ZX60(Mg-6Zn-0.2Ca)alloy.The results showed that the addition of Ti_(p) could not only promote the nucleation of dynamic recrystallized(DRXed)grains,but also be propitious to the refinement of DRXed grains.With increasing Ti_(p) content,the size of DRXed grains decreased accompanied with increasing volume fraction of DRXed grains.As the Ti_(p) content increased to 15 vol.%,the average size and volume fraction of DRXed grains reached to~0.32μm and 93.2%,respectively.Besides,both the strength and elongation were improved by the addition of Ti_(p).With increasing content of Ti_(p),a substantial increase in the strength was achieved with little change in the elongation.However,the elongation decreased sharply when the Ti_(p) content further increased to 15 vol.%.The addition of Ti_(p) led to an increase in the work hardening rate,which gradually increased with increasing Ti_(p) content.However,the softening rate did not demonstrate the same tendency with increasing Ti_(p) content.Unlike the conventional ceramic particles,the Ti_(p) can be deformed in coordination with the matrix alloy,which imparted a higher softening rate to the matrix alloy.Even though the softening rate improved as the Ti_(p) content increased from 5 to 10 vol.%,it dropped deeply as the Ti_(p) content increased to 15 vol.%owing to the fracture of Ti_(p) during extrusion.展开更多
An approximate method for describing the plastic hardening-softening behaviour of circular pipes subjected to pure bending is presented. Theoretical estimation based on the uniform ovalization model and local collapse...An approximate method for describing the plastic hardening-softening behaviour of circular pipes subjected to pure bending is presented. Theoretical estimation based on the uniform ovalization model and local collapse model proposed in the paper is incorporated to give several simple formulations with reasonable accuracy for determining the relationship between bending moment (M) and curvature (kappa) in the purely bended pipes. Attention is focused on the critical curvature associated with maximum resistant moment and the maximum change in the original diameter before the end of uniform ovalization stage as well as the local collapse behaviour. Some comparisons between analytical results and experimental results are made in order to examine the theory.展开更多
The paper describes an energy-based constitutive model for sand, which is modified based on the modified plastic strain energy approach, represented by a unique relationship between the modified plastic strain energy ...The paper describes an energy-based constitutive model for sand, which is modified based on the modified plastic strain energy approach, represented by a unique relationship between the modified plastic strain energy and a stress parameter, independent of stress history. The modified plastic strain energy approach was developed based on results from a series of drained plastic strain compression tests along various stress paths on saturated dense Toyoura sand with accurate stress and strain measurements. The proposed model is coupled with an isotropically work-hardening and softening, non-associtated, elasto-plastic material description. The constitutive model concerns the inherent and stress system-induced cross-anisotropic elastic deformation properties of sand. It is capable of simulating the deformation characteristics of stress history and stress path, the effects of pressure level, anisotropic strength and void ratio, and the strain localization.展开更多
Confinement of rock bolts by the surrounding rock formation has long been recognized as a positive contributor to the pull-out behavior,yet only a few experimental works and analytical models have been reported,most o...Confinement of rock bolts by the surrounding rock formation has long been recognized as a positive contributor to the pull-out behavior,yet only a few experimental works and analytical models have been reported,most of which are based on the global rock bolt response evaluated in pull-out tests.This paper presents a laboratory experimental setup aiming to capture the rock formation effect,while using distributed fiber optic sensing to quantify the effect of the confinement and the reinforcement pull-out behavior on a more local level.It is shown that the behavior along the sample itself varies,with certain points exhibiting stress drops with crack formation.Some edge effects related to the kinematic freedom of the grout to dilate are also observed.Regardless,it was found that the mid-level response is quite similar to the average response along the sample.The ability to characterize the variation of the response along the sample is one of the many advantages high-resolution fiber optic sensing allows in such investigations.The paper also offers a plasticity-based hardening load transfer function,representing a"slice"of the anchor.The paper describes in detail the development of the model and the calibration/determination of its parameters.The suggested model captures well the coupled behavior in which the pull-out process leads to an increase in the confining stress due to dilative behavior.展开更多
A modified plastic strain energy as hardening state parameter for dense sand was proposed, based on the results front a series of drained plane strain tests on saturated dense Japanese Toyoura sand with precise stress...A modified plastic strain energy as hardening state parameter for dense sand was proposed, based on the results front a series of drained plane strain tests on saturated dense Japanese Toyoura sand with precise stress and strain measurements along many stress paths. In addition, a unique hardening function between the plastic strain energy and the instantaneous stress path was also presented, which was independent of stress history. The proposed state parameter and hardening function was directly verified by the simple numerical integration method. It is shown that the proposed hardening function is independent of stress history and stress path and is appropriate to be used as the hardening rule in constitutive modeling for dense sand, and it is also capable of simulating the effects on the de-formation characteristics of stress history and stress path for dense sand.展开更多
A shape hardening function is developed that improves the predictive capabilities of the generalized bounding surface model for cohesive soils, especially when applied to overconsolidated specimens. This improvement i...A shape hardening function is developed that improves the predictive capabilities of the generalized bounding surface model for cohesive soils, especially when applied to overconsolidated specimens. This improvement is realized without any changes to the simple elliptical shape of the bounding surface, and actually reduces the number of parameters associated with the model by one.展开更多
A set of analytical equations for the variation of the axial force along depth and the pile-top load-settle-ment curve were established, using tri-linear softening model to pile-side soil and bilinear hardening model ...A set of analytical equations for the variation of the axial force along depth and the pile-top load-settle-ment curve were established, using tri-linear softening model to pile-side soil and bilinear hardening model to pile-end soil . Influences of the pile-side and pile-end soil behavior on the load-settlement curve were discussed, indica-ting that the lowering reason for the variation step degree of the axial force along depth is the softening of the pile-side soil to result in the side friction lowering when the pile-top load is increased. To verify the reliability of thismethod, the parameters used in calculation are obtained from the test in Zhuzhou area. The obtained results are thencompared with the tested results. Contrast shows that the calculated results and the tested values are very close,which illustrates that the proposed method is reliable.展开更多
Aim To construct an analytic solution for the asymptotic field near a tensile cracktip of power-law hardening material under Plane stress condition. Methods Constructing funtion method was used. Results The exact as...Aim To construct an analytic solution for the asymptotic field near a tensile cracktip of power-law hardening material under Plane stress condition. Methods Constructing funtion method was used. Results The exact asymptotic field was found. Conclusion The exact analytic solution for the problem is available.展开更多
基金supported by the Natural Science Foundation of Heilongjiang Province(No.JQ2022E004).
文摘In this paper,the work hardening and softening behavior of AZ31 magnesium alloy sheets by hard plate accumulative roll bonding(HP-ARB)process in a specific temperature range was studied for the first time,and the cyclic stress relaxation test,EBSD,TEM and other characterization methods were used.When the rolling temperature is 350℃,the grain size of magnesium sheets is refined to 4.32(±0.36)μm on average,and it shows an excellent combination of strength and plasticity.The tensile strength reaches 307(±8.52)MPa and the elongation is 12.73(±0.84)%.At this time,the curve of work hardening rate decreases smoothly and the degree of hardening is the lowest,and the amplitude of stress drop △σ_(p) in work softening test is the smallest with the increase of cycle times,which shows that the well coordination between work hardening and softening behavior has been achieved.Research has found that the combined effect of grain boundary strengthening and fine grain strengthening enhances the yield and tensile strength of magnesium sheets after three passes HP-ARB process at 350℃.This is attributed to the high degree of dislocation slip opening in the pyramidal surfaceand<c+a>,which not only coordinates the c-axis strain of the entire grain,but also promotes the slip transfer of dislocations in the fine-grained region,significantly improving the elongation of the sheets.This study provides a new idea for the forming and manufacturing of high performance magnesium alloy sheets.
基金supported by the“National Natural Science Foundation of China”(Grants.52271109 and 52001223)Support from the“National Key Research and Development Program for Young Scientists”(Grant.2021YFB3703300)+1 种基金the Major Special Plan for Science and Technology in Shanxi Province(202201050201012)the Special Fund Project for Guiding Local Science and Technology Development by the Central Government(Grant.YDZJSX2021B019)。
文摘To obtain the Ti_(p)with different aspect ratios,the Ti_(p)/Mg-5Zn-0.3Ca composite prepared by semi-solid stir casting was subjected to extrusion at 220℃,180℃,and 140℃,respectively.Then,the effect of the Ti_(p)’s aspect ratio on the microstructure,mechanical properties,work hardening and softening behaviors of Ti_(p)/Mg-5Zn-0.3Ca composites was investigated.The results indicated that the Ti_(p)could be elongated obviously after low-temperature extrusion,and the aspect ratio of which would reach to 13.7:1 as the extrusion temperature deceased to 140℃.Then the“Ti/Mg”layer-like structure was formed in the Ti_(p)/Mg-5Zn-0.3Ca composite.Accompanied with the elongation of Ti_(p),the dynamic recrystallized grains and dynamic precipitates were both refined significantly,however,the dynamic recrystallization rate changed a little.The elongated Ti_(p)endowed the Ti_(p)/Mg-5Zn-0.3Ca composites with better matching of strength and toughness without the sacrifice of elongation and bending strain.Both the work hardening rate and softening rate of Ti_(p)/Mg-5Zn-0.3Ca composites increased with the increasing aspect ratio of Ti_(p).The formation of“Ti/Mg”layer-like structure contributed to the redistribution of strain from large aggregations to a network-like distribution,which effectively suppresses the initiation and propagation of micro-cracks,thus enhancing the plasticity of the Ti_(p)/Mg-5Zn-0.3Ca composites.
基金funded by the Natural Science Foundation of China(Grant No.U22A20600)。
文摘Existing creep constitutive models rarely incorporate studies on the coupling mechanism between creep damage and rock strain softening/hardening.This study analyzed the strain softening and hardening behaviors of argillaceous sandstone and sandy mudstone during load-induced failure based on the plastic increment theory.These behaviors were then coupled with an improved Burgers creep model to establish a coupled creep-damage and plastic softening/hardening model.Finally,the validity and engineering applicability of the proposed model were verified through FLAC~(3D)numerical simulations.The numerical simulation results of standard cylindrical specimens show that the established coupling model can effectively reflect the unloading creep deformation law and failure characteristics of argillaceous sandstone and sandy mudstone.Taking the diversion tunnel of a hydropower station in Northwest China as an example for engineering application,the coupled creep-damage and plastic softening/hardening model is introduced into FLAC~(3D)to carry out numerical simulation calculation of the tunnel under excavation and unsupported creep conditions.The results show that the uncoordinated deformation of the upper and lower walls of the surrounding rock of the tunnel is more prominent.When the buried depth of the tunnel increases to 80 m,the monitoring point C in the sandy mudstone area of the upper wall shows nonlinear accelerated deformation under unsupported creep conditions,and the maximum displacement in the horizontal direction reaches 44.5 mm,and the maximum displacement in the vertical direction reaches 53.5 mm.The coupled creep-damage and plastic softening/hardening model established in the research results can well describe the whole process of uncoordinated deformation and failure in the unloading creep process of soft-hard interbedded rock mass.
基金supported by the National Natural Science Foundation of China(52174361,52074114)Science and Technology Innovation Program of Hunan Province(2023RC3106)+2 种基金Open Fund of the China Spallation Neutron Source Songshan Lake Science City(KFKT2023B13)Graduate Training and Innovation Practice Base of Hunan Province,China Scholarship Council(202106130051)Postgraduate Scientific Research Innovation Project of Hunan Province(QL20220100,QL20230094).
文摘Multi-pass hot processing methods are commonly used in magnesium(Mg)alloys to overcome the poor workability due to limited slip systems,which generally involve complicated post-deformation softening and hardening behaviors.In this work,to reveal post-deformation softening and hardening mechanisms of a Mg-2Y-1Zn alloy,double-stage hot compression tests and microstructural observations were conducted.The results showed that the softening fraction of Mg-2Y-1Zn alloy showed a non-linear dependence on deformation conditions and could be general coupled by Z parameter.Due to the formation and cross-overlapping of twins and kinks,only static recovery(SRV)occurred during holding process at 300℃/0.001 s^(-1) which led to the least static softening:5.52% after 10 s of holding.For samples at 400℃/0.001s^(-1),the enhanced post-deformation softening,which is 11.93% after 10 s of holding,was attributed to static recrystallization(SRX)followed continuous dynamic recrystallization(CDRX)happened during first deformation stage as well as SRV influenced by the LPSO phases.Under deformation condition of 400℃/0.1 s^(-1),the coupled meta-dynamic recrystallization(MDRX)and SRX resulted in serious stress relaxation,which is 42.83% after 10 s of holding,and caused hardening phenomenon at reloading stage.The 18R-LPSO and 14H-LPSO phases synchronously worked on deformation behaviors and limited the growth of recrystallized grains.Further,a simplified static softening kinetics model was established based on Johnson-Mehl-Avrami-Kolmogorov equation and employed to rationalize experimental data.
基金Project(cstc2015jcyj BX0115)supported by the Chongqing Research Program of Basic Research and Frontier Technology,China
文摘The effects of the deformation temperature and the strain rate on the hot deformation behavior of pure copper were investigated based on compression tests. The expressions of strain hardening rate, dynamic recrystallization critical stress, saturated stress, dynamic recovery volume fraction and dynamic recrystallization volume fraction were determined. According to the processing map, the instability regions occur in regions of 400?450 °C, 0.001?0.05 s?1 and 450?750 °C, 0.05?1 s?1. The deformation mechanism in the stability region is dynamic recrystallization. The flow stress was predicted. The results also show that the true stress–true strain curves predicted by the extracted model are in good agreement with the experimental results.
文摘The deformation behavior of AZ61 Mg alloy during hot deformation has been investigated in wide temperature and strain rate range by a Gleeble simulator. Specimens are deformed in compression in the temperature range of 523-673 K and at strain rates of 0.001-1 s-1. It is found that the flow curves exhibit a peak and then decrease towards steady-state of classical DRX, which decrease with rising temperature and decreasing strain rate. The deformation behavior of the specimens can be attributed to the occurrence of strain hardening and softening. As stress decreases, the strain hardening rate declines at a fast rate when temperature rises or strain rate decreases. The shapes of θ-σ curves indicate some important features such as subgrain formation, the criticai stress, the peak stress and steady stress. The onset of DRX can be determined by the point of inflection on θ-σ or Inθ-σ curves.
基金The project supported by the Research Grant Committee(RGC)of Hong Kong SARthe National Natural Science Foundation of China and the Provincial Natural Foundation of Jiangxi Province of China
文摘The effects of microstructure and its evolution on the macroscopic superelastic stress-strain response of polycrystalline Shape Memory Alloy(SMA)are studied by a microstructure-based constitutive model developed in this paper.The model is established on the following basis:(1)the transformation conditions of the unconstrained single crystal SMA microdomain(to be distinguished from the bulk single crystal),which serve as the local criterion for the derivation of overall transfor- mation yield conditions of the polycrystal;(2)the micro-to macro-transition scheme by which the connection between the polycrystal aggregates and the single crystal microdomain is established and the macroscopic transformation conditions of the polycrystal SMA are derived;(3)the quantitative incorporation of three microstruc- ture factors(i.e.,nucleation,growth and orientation distribution of martensite)into the modeling.These microstructural factors are intrinsic of specific polycrystal SMA systems and the role of each factor in the macroscopic constitutive response is quan- titatively modeled.It is demonstrated that the interplay of these factors will result in different macroscopic transformation kinematics and kinetics which are responsible for the observed macroscopic stress-strain hardening or softening response,the latter will lead to the localization and propagation of transformation bands in TiNi SMA.
基金Project(52074299)supported by the National Natural Science Foundation of ChinaProjects(2023JCCXSB02,BBJ2024083)supported by the Fundamental Research Funds for the Central Universities,China。
文摘This study proposed a new and more flexible S-shaped rock damage evolution model from a phenomenological perspective based on an improved Logistic function to describe the characteristics of the rock strain softening and damage process.Simultaneously,it established a constitutive model capable of describing the entire process of rock pre-peak compaction and post-peak strain softening deformation,considering the nonlinear effects of the initial compaction stage of rocks,combined with damage mechanics theory and effective medium theory.In addition,this research verified the rationality of the constructed damage constitutive model using results from uniaxial and conventional triaxial compression tests on Miluo granite,yellow sandstone,mudstone,and glutenite.The results indicate that based on the improved Logistic function,the theoretical damage model accurately describes the entire evolution of damage characteristics during rock compression deformation,from maintenance through gradual onset,accelerated development to deceleration and termination,in a simple and unified expression.At the same time,the constructed constitutive model can accurately simulate the stress-strain process of different rock types under uniaxial and conventional triaxial compression,and the theoretical model curve closely aligns with experimental data.Compared to existing constitutive models,the proposed model has significant advantages.The damage model parameters a,r and β have clear physical meanings and interact competitively,where the three parameters collectively determine the shape of the theoretical stress−strain curve.
基金The subject supported by the Research Grant Committee(RGC)of Hong Kong SARthe National Natural Science Foundation of China and the Provincial Natural Science Foundation of Jiangxi Province of China
文摘Based on the microstructure-based constitutive model established in Part Ⅰ,a detailed numerical investigation on the role of each microstructure pa- rameter in the kinematical and kinetic evolution of polycrystalline SMA under ax- isymmetrical tension loading is performed.Some macroscopic constitutive features of stress-induced martensite transformation are discussed.
基金Project(2007DFR70070) supported by China-Russia Government-to-Government Scientific and Technical Cooperation Foundation
文摘The effect of strain hardening and strain softening behavior of flow stress changing with temperature on welding residual stress, plastic strain and welding distortion of ATN0 1-T4 aluminum alloy was studied by finite simulation method. The simulation results show that the weld seam undergoes strain hardening in the temperature range of 180-250 ℃, however, it exhibits strain softening at temperature above 250 ℃ during welding heating and cooling process. As a result, the strain hardening and strain softening effects counteract each other, introducing slightly influence on the welding residual stress, residual plastic strain and distortion. The welding longitudinal residual stress was determined by ultrasonic stress measurement method for the flat plates of A7N01-T4 aluminum alloy. The simulation results are well accordant with test ones.
基金Project(51801129)supported by the National Natural Science Foundation of ChinaProject supported by the State Key Laboratory of Powder Metallurgy,China。
文摘Ab initio calculations are used to understand the fundamental mechanism of the solid solution softening/hardening of the Mo-binary system.The results reveal that the Mo-Ti,Mo-Ta,Mo-Nb,and Mo-W interactions are primarily attractive with negative heats of formation,while the interactions of Mo-Re,and Mo-Zr would be mainly repulsive with positive heats of formation.It is also shown that the addition of Re and Zr would cause the solid solution softening of Mo by the decrease of the unstable stacking fault energy and the increase of ductility.On the contrary,the elements of W,Ta,Ti,and Nb could bring about the solid-solution hardening of Mo through the impediment of the slip of the dislocation and the decrease of ductility.Electronic structures indicate that the weaker/stronger chemical bonding due to the alloying elements should fundamentally induce the solid solution softening/hardening of Mo.The results are discussed and compared with available evidence in literatures,which could deepen the fundamental understanding of the solid solution softening/hardening of the binary metallic system.
基金the National Natural Science Foundation of China(Nos.12172149 and12172151)the Start-up Fund from Jinan University of China。
文摘Toward accurately simulating both hardening and softening effects for metals up to failure,a new finite strain elastoplastic J2-flow model is proposed with the yield strength therein as a function of the plastic work in the explicit form.With no need to identify any adjustable parameters,the uniaxial stress-strain response predicted from this new model is shown to automatically and accurately match any given data from monotonic uniaxial extension tests of bars.As such,the objectives in three respects are achieved for the first time,i.e.,(i)both the hardening and softening effects up to failure can be simulated in the sense of matching test data with no errors,(ii)the usual tedious implicit procedures toward identifying numerous unknown parameters need not be involved and can be totally bypassed,and(iii)the model applicability can be ensured in a broad sense for various metallic materials with markedly different transition effects from hardening to softening.With the new model,the complete response features of stretched bars and twisted tubes up to failure are studied,including the failure effects of bars under monotonic extension and tubes under monotonic torsion and,furthermore,the fatigue failure effects of bars under cyclic loading.The results show accurate agreement with the uniaxial data,and the results for both the shear stress and the normal stress at the finite torsion display realistic hardening-to-softening transition effects for the first time.
基金supported financially by the National Natural Science Foundation of China (Nos.52271109 and 52001223)the authors also thank the Support from the"the National Key Research and Development Program for Young Scientists" (No.2021YFB3703300)the Special Fund Project for Guiding Local Science and Technology Development by the Central Government (No.YDZJSX2021B019).
文摘The Ti_(p)/ZX60 composites with different Ti_(p) contents were prepared by semi-solid stirring casting.After extrusion,the microstructure,work hardening and softening behavior of the Ti_(p)/ZX60 composites were analyzed compared with the ZX60(Mg-6Zn-0.2Ca)alloy.The results showed that the addition of Ti_(p) could not only promote the nucleation of dynamic recrystallized(DRXed)grains,but also be propitious to the refinement of DRXed grains.With increasing Ti_(p) content,the size of DRXed grains decreased accompanied with increasing volume fraction of DRXed grains.As the Ti_(p) content increased to 15 vol.%,the average size and volume fraction of DRXed grains reached to~0.32μm and 93.2%,respectively.Besides,both the strength and elongation were improved by the addition of Ti_(p).With increasing content of Ti_(p),a substantial increase in the strength was achieved with little change in the elongation.However,the elongation decreased sharply when the Ti_(p) content further increased to 15 vol.%.The addition of Ti_(p) led to an increase in the work hardening rate,which gradually increased with increasing Ti_(p) content.However,the softening rate did not demonstrate the same tendency with increasing Ti_(p) content.Unlike the conventional ceramic particles,the Ti_(p) can be deformed in coordination with the matrix alloy,which imparted a higher softening rate to the matrix alloy.Even though the softening rate improved as the Ti_(p) content increased from 5 to 10 vol.%,it dropped deeply as the Ti_(p) content increased to 15 vol.%owing to the fracture of Ti_(p) during extrusion.
文摘An approximate method for describing the plastic hardening-softening behaviour of circular pipes subjected to pure bending is presented. Theoretical estimation based on the uniform ovalization model and local collapse model proposed in the paper is incorporated to give several simple formulations with reasonable accuracy for determining the relationship between bending moment (M) and curvature (kappa) in the purely bended pipes. Attention is focused on the critical curvature associated with maximum resistant moment and the maximum change in the original diameter before the end of uniform ovalization stage as well as the local collapse behaviour. Some comparisons between analytical results and experimental results are made in order to examine the theory.
基金The project supported by the Association of International Education of Japan
文摘The paper describes an energy-based constitutive model for sand, which is modified based on the modified plastic strain energy approach, represented by a unique relationship between the modified plastic strain energy and a stress parameter, independent of stress history. The modified plastic strain energy approach was developed based on results from a series of drained plastic strain compression tests along various stress paths on saturated dense Toyoura sand with accurate stress and strain measurements. The proposed model is coupled with an isotropically work-hardening and softening, non-associtated, elasto-plastic material description. The constitutive model concerns the inherent and stress system-induced cross-anisotropic elastic deformation properties of sand. It is capable of simulating the deformation characteristics of stress history and stress path, the effects of pressure level, anisotropic strength and void ratio, and the strain localization.
基金funding support from the Israeli Ministry of Housing and Construction(Grant No.2028286).
文摘Confinement of rock bolts by the surrounding rock formation has long been recognized as a positive contributor to the pull-out behavior,yet only a few experimental works and analytical models have been reported,most of which are based on the global rock bolt response evaluated in pull-out tests.This paper presents a laboratory experimental setup aiming to capture the rock formation effect,while using distributed fiber optic sensing to quantify the effect of the confinement and the reinforcement pull-out behavior on a more local level.It is shown that the behavior along the sample itself varies,with certain points exhibiting stress drops with crack formation.Some edge effects related to the kinematic freedom of the grout to dilate are also observed.Regardless,it was found that the mid-level response is quite similar to the average response along the sample.The ability to characterize the variation of the response along the sample is one of the many advantages high-resolution fiber optic sensing allows in such investigations.The paper also offers a plasticity-based hardening load transfer function,representing a"slice"of the anchor.The paper describes in detail the development of the model and the calibration/determination of its parameters.The suggested model captures well the coupled behavior in which the pull-out process leads to an increase in the confining stress due to dilative behavior.
文摘A modified plastic strain energy as hardening state parameter for dense sand was proposed, based on the results front a series of drained plane strain tests on saturated dense Japanese Toyoura sand with precise stress and strain measurements along many stress paths. In addition, a unique hardening function between the plastic strain energy and the instantaneous stress path was also presented, which was independent of stress history. The proposed state parameter and hardening function was directly verified by the simple numerical integration method. It is shown that the proposed hardening function is independent of stress history and stress path and is appropriate to be used as the hardening rule in constitutive modeling for dense sand, and it is also capable of simulating the effects on the de-formation characteristics of stress history and stress path for dense sand.
基金supported by the Fulbright Colombia-Colciencias Scholarship and Universidad Militar Nueva Granada
文摘A shape hardening function is developed that improves the predictive capabilities of the generalized bounding surface model for cohesive soils, especially when applied to overconsolidated specimens. This improvement is realized without any changes to the simple elliptical shape of the bounding surface, and actually reduces the number of parameters associated with the model by one.
基金Project (01B028) supported by Department of Education of Hunan Province
文摘A set of analytical equations for the variation of the axial force along depth and the pile-top load-settle-ment curve were established, using tri-linear softening model to pile-side soil and bilinear hardening model to pile-end soil . Influences of the pile-side and pile-end soil behavior on the load-settlement curve were discussed, indica-ting that the lowering reason for the variation step degree of the axial force along depth is the softening of the pile-side soil to result in the side friction lowering when the pile-top load is increased. To verify the reliability of thismethod, the parameters used in calculation are obtained from the test in Zhuzhou area. The obtained results are thencompared with the tested results. Contrast shows that the calculated results and the tested values are very close,which illustrates that the proposed method is reliable.
文摘Aim To construct an analytic solution for the asymptotic field near a tensile cracktip of power-law hardening material under Plane stress condition. Methods Constructing funtion method was used. Results The exact asymptotic field was found. Conclusion The exact analytic solution for the problem is available.
