The current study performed a finite element analysis of the strain localization behavior of a voided ductile material using a non-local plasticity formulation in which the yield strength depends on both an equivalent...The current study performed a finite element analysis of the strain localization behavior of a voided ductile material using a non-local plasticity formulation in which the yield strength depends on both an equivalent plastic strain measurement (hardening parameter) and Laplacian equivalent. The introduction of gradient terms to the yield function was found to play an important role in simulating the strain localization behavior of the voided ductile material. The effect of the mesh size and characteristic length on the strain localization were also investigated. An FEM simulation based on the proposed non-local plasticity revealed that the load-strain curves of the voided ductile material subjected to plane strain tension converged to one curve, regardless of the mesh size. In addition, the results using non-local plasticity also exhibited that the dependence of the deformation behavior of the material on the mesh size was much less sensitive than that with classical local plasticity and could be successfully eliminated through the introduction of a large value for the characteristic length.展开更多
With increasing diameters of aluminum alloy thin-walled tubes(AATTs),the tube forming limits,i.e.the minimum bending factors,and their predictions under multi-index constraints including wrinkling,thinning and flatten...With increasing diameters of aluminum alloy thin-walled tubes(AATTs),the tube forming limits,i.e.the minimum bending factors,and their predictions under multi-index constraints including wrinkling,thinning and flattening have been being a key problem to be urgently solved for improving tube forming potential in numerical control(NC)bending processes of AATTs with large diameters.Thus in this paper,a search algorithm of the forming limits is put forward based on a 3D elastic-plastic finite element(FE)model and a wrinkling energy prediction model for the bending processes under axial compression loading(ACL)or not.This algorithm enables to be considered the effects of process parameter combinations including die,friction parameters on the multi-indices.Based on this algorithm,the forming limits of the different size tubes are obtained,and the roles of the process parameter combinations in enabling the limit bending processes are also revealed.The followings are found:the first,within the appropriate ranges of friction and clearances between the different dies and the tubes enabling the bending processes with smaller bending factors,the ACL enables the tube limit bending processes after a decrease of the mandrel ball thickness and diameters;then,without considering the effects of the tube geometry sizes on the tube constitutive equations,the forming limits will be decided by the limit thinning values for the tubes with diameters smaller than 80 mm,while the wrinkling for the tubes with diameters no less than 80 mm.The forming limits obtained from this algorithm are smaller than the analytical results,and reduced by 57.39%;the last,the roles of the process parameter combinations in enabling the limit bending processes are verified by experimental results.展开更多
The stretch forming and the deep-drawing processes were carried out at 300 and 673 K to determine the safe forming and fracture limits of IN625 alloy.The experimentally obtained strain-based fracture forming limit dia...The stretch forming and the deep-drawing processes were carried out at 300 and 673 K to determine the safe forming and fracture limits of IN625 alloy.The experimentally obtained strain-based fracture forming limit diagram(FFLD)was transformed into a stress-based(σ-FFLD)and effective plastic strain(EPS)vs triaxiality(η)plot to remove the excess dependency of fracture limits over the strains.For the prediction of fracture limits,seven different damage models were calibrated.The Oh model displayed the best ability to predict the fracture locus with the least absolute error.Though the experimentally obtained fracture limits have only been used for the numerical analysis,none of the considered damage models predicted the fracture strains over the entire considered range of stress triaxiality(0.33<η<0.66).The deep drawing process window helped to determine wrinkling,safe and fracture zones while drawing the cylindrical cups under different temperature and lubricating conditions.Further,the highest drawing ratio of 2 was achieved at 673 K under the lubricating condition.All the numerically predicted results of both stretch forming and deep drawing processes using the Hill 1948 anisotropic yielding function were found to be good within the acceptable range of error.展开更多
This article examines the influence of annealing temperature on fracture toughness and forming limit curves of dissimilar aluminum/silver sheets.In the cold roll bonding process,after brushing and acid washing,the pre...This article examines the influence of annealing temperature on fracture toughness and forming limit curves of dissimilar aluminum/silver sheets.In the cold roll bonding process,after brushing and acid washing,the prepared surfaces are placed on top of each other and by rolling with reduction more than 50%,the bonding between layers is established.In this research,the roll bonding process was done at room temperature,without the use of lubricants and with a 70%thickness reduction.Then,the final thickness of the Ag/Al bilayer sheet reached 350μm by several stages of cold rolling.Before cold rolling,it should be noted that to decrease the hardness created due to plastic deformation,the roll-bonded samples were subjected to annealing heat treatment at 400℃for 90 min.Thus,the final samples were annealed at 200,300 and 400℃for 90 min and cooled in a furnace to examine the annealing temperature effects.The uniaxial tensile and microhardness tests measured mechanical properties.Also,to investigate the fracture mechanism,the fractography of the cross-section was examined by scanning electron microscope(SEM).To evaluate the formability of Ag/Al bilayer sheets,forming limit curves were obtained experimentally through the Nakazima test.The resistance of composites to failure due to cracking was also investigated by fracture toughness.The results showed that annealing increases the elongation and formability of the Ag/Al bilayer sheet while reduces the ultimate tensile strength and fracture toughness.However,the changing trend is not the same at different temperatures,and according to the results,the most significant effect is obtained at 300℃and aluminum layers.It was also determined that by increasing annealing temperature,the fracture mechanism from shear ductile with small and shallow dimples becomes ductile with deep cavities.展开更多
Fiber Metal Laminates(FMLs),as high-performance composite materials,demonstrate exceptional potential in a wide range of applications,such as aeronautical and astronautical industries.However,the traditional cured FML...Fiber Metal Laminates(FMLs),as high-performance composite materials,demonstrate exceptional potential in a wide range of applications,such as aeronautical and astronautical industries.However,the traditional cured FMLs possess complex interlayer stresses and low forming limits,restricting further promotion and application of FMLs.Low-constraint FMLs exhibit a lower forming resistance and better formability due to no curing during the forming process;however,the formation mechanism and response are not clear.This paper presents the Forming Limit Diagram(FLD)of low-constraint GLARE(glass fiber reinforced aluminum laminates)based on the forming limit test,and compares it with the conventionally cured laminates to evaluate the differences in the forming limit.In addition,combined with the analysis of failure mechanism and micro-deformation mechanism of specimens,the influence of different temperatures(20–80℃)and forming states(width)on the deformation performance of laminates is further explored.The results reveal that the forming limit curve of low-constraint laminates shifts up with the increase of temperature,the forming limit initially increases with the increase of width,then followed by a gradual decrease,and the maximum principal strain of low-constraint laminates is increased by 29% at 80℃ compared to 20℃.The cured laminate has a principal strain range of 0–0.02,while the low-constraint laminates have a principal strain range of 0.03–0.14.Compared with cured laminates,low-constraint laminates possess a higher forming limit due to the improvement in deformable degree between layers by resin flow and fiber slippage,which enhances their formability.This study is expected to serve as a reference for establishing forming limit criteria and optimizing forming schemes for low-constraint laminates.展开更多
Repeated unidirectional bending （RUB） was carried out to improve the texture of commercial AZ31B magnesium alloy sheets. All specimens were prepared in the rolling direction. The forming limit diagrams （FLDs） of A...Repeated unidirectional bending （RUB） was carried out to improve the texture of commercial AZ31B magnesium alloy sheets. All specimens were prepared in the rolling direction. The forming limit diagrams （FLDs） of AZ31B magnesium alloy sheet were determined experimentally by conducting stretch-forming tests at room temperature, 100, 200 and 300 ℃ Compared with the as-received sheet, the lowest limited strain of AZ31B magnesium alloy sheet with tilted texture in the FLD increased by 79% at room temperature and 104% at 100 ℃. The texture also affected the extension of the forming limit curves （FLC） in the FLD. However, the FLCs of two kinds of sheets almost overlapped at temperature above 200 ℃. It can be concluded that the reduction of （0002） texture intensity is effective to the improvement of formability not only at room temperature but also at low-and-medium temperature. The effect of texture on FLDs becomes weak with increasing temperature.展开更多
A theoretical prediction on forming limit diagram（FLD） of AZ31 magnesium alloy sheet was developed at warm temperatures based on the M-K theory. Two different yield criteria of von Mises and Hill＇48 were applied in...A theoretical prediction on forming limit diagram（FLD） of AZ31 magnesium alloy sheet was developed at warm temperatures based on the M-K theory. Two different yield criteria of von Mises and Hill＇48 were applied in this model. Mechanical properties of AZ31 magnesium alloy used in the prediction were obtained by uniaxial tensile tests and the Fields-Backofen equation was incorporated in the analysis. In addition, experimental FLDs of AZ31 were acquired by conducting rigid die swell test at different temperatures to verify the prediction. It is demonstrated from a comparison between the predicted and the experimental FLDs at 473 K and 523 K that the predicted results are influenced by the type of yield criterion used in the calculation, especially at lower temperatures. Furthermore, a better agreement between the predicted results and experimental data for AZ31 magnesium alloy sheet at warm temperatures was obtained when Hill＇48 yield criterion was applied.展开更多
A modified Swift type flow stress—strain relation was presented in order to describe the uniaxial tension test curve reasonably. The FLD-strain （forming limit diagram made up of limit strain） of 5754O aluminum allo...A modified Swift type flow stress—strain relation was presented in order to describe the uniaxial tension test curve reasonably. The FLD-strain （forming limit diagram made up of limit strain） of 5754O aluminum alloy sheet was calculated based on the two flow stress—strain relations using Yld2000-2d yield function. By comparing the theoretical and experimental results, it is found that the calculated FLD-strain based on the modified Swift flow stress—strain relation can reasonably describe the experimental results. However, though the common Voce flow stress—strain relation can describe the deformation behavior during homogenous deformation phase accurately, the FLD-strain calculated based on it is obviously lower than the experimental result. It is concluded that the higher the hardening rate of sheet metal is, the higher the forming limit is. A method for determining the reasonable flow stress—strain relation is recommended for describing the material behavior during inhomogenous phase and the forming limit of sheet metal.展开更多
The conventional forming limit diagram （FLD） is described as a plot of major strain versus minor strain. However, FLD is dependent on forming history and strain path. In the present study, a forming limit stress-bas...The conventional forming limit diagram （FLD） is described as a plot of major strain versus minor strain. However, FLD is dependent on forming history and strain path. In the present study, a forming limit stress-based diagram （FLSD） has been adopted to predict the fracture limit of aluminum alloy （AA） 5052-O1 sheet. Nakazima test is simulated by plastic constitutive formula derived from the modified Gurson-Tvergaard-Needleman （GTN） model. An in situ tensile test with scanning electron microscope （SEM） is proposed to determine the parameters in GTN model. The damage evolution is observed and recorded, and the parameters of GTN model are identified through counting void fraction at three damage stages of AA5052-O 1. According to the experimental results, the original void volume fraction, the volume fraction of potential nucleated voids, the critical void volume fraction, the void volume fraction at the final failure of material are assigned as 0.002 918, 0.024 9, 0.030 103, 0.048 54, respectively. The stress and strain are obtained at the last loading step before crack. FLSD and FLD of AA5052-O 1 are plotted. Compared with the experimental Nakazima test and uniaxial tensile test, the predicted results show a good agreement. The parameters determined by in situ tensile test can be applied to the research of the forming limit for ductile metals.展开更多
High strength aluminum alloy plate has a low elongation at room temperature, which leads to the forming of its components need a high temperature. Liquid or gas is used as the pressure-transfer medium in the existing ...High strength aluminum alloy plate has a low elongation at room temperature, which leads to the forming of its components need a high temperature. Liquid or gas is used as the pressure-transfer medium in the existing flexible mould forming process, the heat resistance of the medium and pressurizing device makes the application of aluminum alloy plate thermoforming restricted. To solve this problem, the existing medium is replaced by the heat-resisting solid granules and the general pressure equipments are applied. Based on the pressure-transfer performance test of the solid granules medium, the feasibility that the assumption of the extended Drucker-Prager linear model can be used in the finite element analysis is proved. The constitutive equation, the yield function and the theoretical forming limit diagram（FLD） of AA7075 sheet are established. Through the finite element numerical simulation of hot granules medium pressure forming（HGMF） process, not only the influence laws of the process parameters, such as forming temperature, the blank-holder gap and the diameter of the slab, on sheet metal forming performance are discussed, but also the broken area of the forming process is analyzed and predicted, which are coincided with the technological test. The conical part whose half cone angle is 15° and relative height H/d0 is 0.57, is formed in one process at 250℃. The HGMF process solves the problems of loading and seal in the existing flexible mould forming process and provides a novel technology for thermoforming of light alloy plate, such as magnesium alloy, aluminium alloy and titanium alloy.展开更多
With the implementation of environmental protection, sustainable development and conservation-oriented policies, components and parts of thin-walled welded tubes have gained increasing application in the aircraft and ...With the implementation of environmental protection, sustainable development and conservation-oriented policies, components and parts of thin-walled welded tubes have gained increasing application in the aircraft and automotive industries because of their advantages： easily achieving forming and manufacturing process at low cost and in a short time. The current research on welded tube plastic forming is mainly concentrated on tube internal high-pressure forming, tube bending forming, and tube spinning forming. The focuses are on the material properties and char- acterization of welded tubes, finite element modeling for welded tube forming, and inhomogeneous deformation behavior and the mechanism and rules of deformation coordination in welded tube plastic forming. This paper summarizes the research progress in welded tube plastic forming from these aspects. Finally, with a focus on the urgent demand of the aviation, aerospace and automotive industries for high-strength and light-weight tubes, this paper discusses the development trends and challenges in the theory and technology of welded tube plastic forming in the future. Among them, laser tailor-welded technology will find application in the manufacture of high-strength steel tubes. Tube-end forming technology, such as tube flaring and flanging technology, will expand its appli- cation in welded tubes. Therefore, future studies will focus on the FE modeling regarding how to consider effects of welding on residual stresses, welding distortions and microstructure, the inhomo- geneous deformation and coordination mechanism of the plastic forming process of tailor-welded tubes, and some end-forming processes of welded tubes, and more comprehensive research on the formin~ mechanism and limit of welded tubes.展开更多
The process of automobile lightweight can be promoted by the application of tailor rolled blank（TRB）in the automobile industry.Therefore,research on the formability of TRB is of good practical significance and appli...The process of automobile lightweight can be promoted by the application of tailor rolled blank（TRB）in the automobile industry.Therefore,research on the formability of TRB is of good practical significance and application value because of the enormous potential of TRB in the aspect of automobile lightweight.Aiming at the present condition of lack of researches on the influence of characteristic parameters on TRB drawing process,the drawing formability of TRB was studied with a combination method of simulation and experiment by taking square box as the research object.Firstly,drawing simulation and experiment of TRB were carried out.Then,effects of thickness transition zone（TTZ）position and blank size on the drawing formability of TRB were analyzed.Forming limit and TTZ movement for TRB square box during the drawing process were respectively discussed,when transition zones of TRB were located at different positions and blanks were of different sizes.The results indicate that lubrication condition exerts greater influence on TRB forming limit in comparison with TTZ movement,and the smaller blank size and TTZ being located at the blank center or slightly offset to the thinner side are preferable for acquiring greater forming limit and smaller TTZ movement.展开更多
In order to effectively predict the fracture of AA7075-T6 sheet, the forming limit curves of AA7075-T6 high-strength sheet were drawn according to Morciniak Kuczyski (M K) model and Lou Huh criterion, respectively. Th...In order to effectively predict the fracture of AA7075-T6 sheet, the forming limit curves of AA7075-T6 high-strength sheet were drawn according to Morciniak Kuczyski (M K) model and Lou Huh criterion, respectively. The errors between the predicted values of the two theoretical prediction models and experimental values were calculated by error analysis. The forming limit curves were verified by the punch stretch test to evaluate the prediction accuracy of M K model and Lou Huh criterion. The error analysis results show that the mean error of Lou Huh criterion with the optimal parameters for all tensile specimens is 25.04%, while the mean error of M K model for all tensile specimens is 74.24%. The prediction accuracy of Lou Huh criterion in predicting the fracture of AA7075-T6 sheet is higher. The punch stretch test results show that the forming limit curve drawn by Lou Huh criterion can effectively predict the fracture of AA7075-T6 sheet, but the prediction accuracy of M K model is relatively poor.展开更多
The Forming Limit Curve （FLC） of the third generation aluminum-lithium （Al-Li） alloy 2198-T3 is measured by conducting a hemispherical dome test with specimens of different widths. The theoretical prediction of th...The Forming Limit Curve （FLC） of the third generation aluminum-lithium （Al-Li） alloy 2198-T3 is measured by conducting a hemispherical dome test with specimens of different widths. The theoretical prediction of the FLC of 2198-T3 is based on the M-K theory utilizing respectively the von Mises, Hill＇48, Hosford and Barlat 89 yield functions, and the different predicted curves due to different yield functions are compared with the experimentally measured FLC of 2198-T3. The results show that though there are differences among the four predicted curves, yet they all agree well with the experimentally measured curve. In the area near the planar strain state, the predicted curves and experimentally measured curve are very close. The predicted curve based on the Hosford yield function is more accurate under the tension-compression strain states described in the left part of the FLC, while the accuracy is better for the predicted curve based on Hill＇48 yield function under the tension-tension strain states shown in the right part.展开更多
The objective of this work is to study the cryogenic sheet metal forming behaviour of precipitation hardening AW-6016-T4.In this regard,the flow curves and forming limit curves were obtained by tension and Nakazima ex...The objective of this work is to study the cryogenic sheet metal forming behaviour of precipitation hardening AW-6016-T4.In this regard,the flow curves and forming limit curves were obtained by tension and Nakazima experimental testing methods in thetemperature ranges from-196to25°C.It was found that strength and elongation increase with decreasing temperature.Small butperceived differences between microstructure of the material deformed at the room and cryogenic temperatures respectively wereidentified by electron backscatter diffraction(EBSD)analysis.However,no significant difference in the precipitation kinetics duringcontinuous heating in the DSC has been observed.This study has demonstrated the potential of cryogenic forming by manufacturinga B-pillar part with8mm depth of side design element as compared to6mm at room temperature.展开更多
The forming limit curve （FLC） can be obtained by means of curve fitting the limit strain points of different strain paths. The theory of percent regression analysis is applied to the curve fitting of forming limit e...The forming limit curve （FLC） can be obtained by means of curve fitting the limit strain points of different strain paths. The theory of percent regression analysis is applied to the curve fitting of forming limit experimental data.Forecast intervals of FLC percentiles can be calculated. Thus reliability and confidence level can be considered. The theoretical method to get the limits of limit strain points distributing region is presented, and the FLC position can be adjusted according to practical requirement. Method for establishing FLC with high reliability using small samples is presented at the same time. This method can make full use of the current experimental data and the previous data.Compared with the traditional method that can only use current experimental data, fewer specimens are required in the present method to obtain the same precision and the result is more accurate with the same number of specimens.展开更多
The influence of initial groove angle on strain rate inside and outside groove of Ti6Al4V alloy was investigated.Based on the evolution of strain rate inside and outside groove,the effect of strain rate difference on ...The influence of initial groove angle on strain rate inside and outside groove of Ti6Al4V alloy was investigated.Based on the evolution of strain rate inside and outside groove,the effect of strain rate difference on the evolution of normal stress and effective stress inside and outside groove was also analyzed.The results show that when linear loading path changes from uniaxial tension to equi-biaxial tension,the initial groove angle plays a weaker role in the evolution of strain rate in the M-K model.Due to the constraint of force equilibrium between inside and outside groove,the strain rate difference makes the normal stress inside groove firstly decrease and then increase during calculation,which makes the prediction algorithm of forming limit convergent at elevated temperature.The decrease of normal stress inside groove is mainly caused by high temperature softening effect and the rotation of groove,while the increase of normal stress inside groove is mainly due to strain rate hardening effect.展开更多
The effects of annealing treatments(ATs)on the microstructure of Zr-Sn-Nb alloy strips were studied.Based on the characteristics of strips for nuclear fuel assemblies,punching experiments were carried out and the form...The effects of annealing treatments(ATs)on the microstructure of Zr-Sn-Nb alloy strips were studied.Based on the characteristics of strips for nuclear fuel assemblies,punching experiments were carried out and the formability of zirconium alloy strips was quantitatively evaluated.The results indicate that the proportions of small-angle grain boundaries of the zirconium alloy under conditions of annealing treatment at 580°C(ATⅠ)and annealing treatment at 620°C(ATⅡ)are 14.3%and 23.2%,respectively,while that of the as-received material is 12.4%.And the forming limit margin fields of the zirconium alloy under ATⅠcan reach 0.43%,while the values of the as-received material and the ATⅡare-0.35%and-2.8%,respectively.The annealing process affects the evolution process of the strip recrystallization texture and the grain size.Moreover,the total texture and pole density are closely related to the degree of anisotropy of the strip.Besides,the small-angle grain boundary affects the strain path and crack expansion of the necking unit during the strip punching process,while the grain size affects the hardening exponent of the material.展开更多
Forming limit diagram (FLD) is an important performance index to describe the maximum limit of principal strains that can be sustained by sheet metals till to the onset of localized necking. It offers a convenient and...Forming limit diagram (FLD) is an important performance index to describe the maximum limit of principal strains that can be sustained by sheet metals till to the onset of localized necking. It offers a convenient and useful tool to predict the forming limit in the sheet metal forming processes. In the present study, FLD has been determined experimentally for Ti?6Al?4V alloy at 400 °C by conducting a Nakazima test with specimens of different widths. Additionally, for theoretical FLD prediction, various anisotropic yield criteria (Barlat 1989, Barlat 1996, Hill 1993) and different hardening models viz., Hollomon power law (HPL), Johnson?Cook (JC), modified Zerilli–Armstrong (m-ZA), modified Arrhenius (m-Arr) models have been developed. Theoretical FLDs have been determined using Marciniak and Kuczynski (M?K) theory incorporating the developed yield criteria and constitutive models. It has been observed that the effect of yield model is more pronounced than the effect of constitutive model for theoretical FLDs prediction. However, the value of thickness imperfection factor (f0) is solely dependent on hardening model. Hill (1993) yield criterion is best suited for FLD prediction in the right hand side region. Moreover, Barlat (1989) yield criterion is best suited for FLD prediction in left hand side region. Therefore, the proposed hybrid FLD in combination with Barlat (1989) and Hill (1993) yield models with m-Arr hardening model is in the best agreement with experimental FLD.展开更多
Commercially pure titanium（CP Ti） has been actively used in the plate heat exchanger due to its light weight, high specific strength, and excellent corrosion resistance. However, researches for the plastic deformati...Commercially pure titanium（CP Ti） has been actively used in the plate heat exchanger due to its light weight, high specific strength, and excellent corrosion resistance. However, researches for the plastic deformation characteristics and press formability of the CP Ti sheet are not much in comparison with automotive steels and aluminum alloys. The mechanical properties and hardening behavior evaluated in stress-strain relation of the CP Ti sheet are clarified in relation with press formability. The flow curve denoting true stress-true strain relation for CP Ti sheet is fitted well by the Kim-Tuan hardening equation rather than Voce and Swift models. The forming limit curve（FLC） of CP Ti sheet as a criterion for press formability was experimentally evaluated by punch stretching test and analytically predicted via Hora＇s modified maximum force criterion. The predicted FLC by adopting Kim-Tuan hardening model and appropriate yield function shows good correlation with the experimental results of punch stretching test.展开更多
文摘The current study performed a finite element analysis of the strain localization behavior of a voided ductile material using a non-local plasticity formulation in which the yield strength depends on both an equivalent plastic strain measurement (hardening parameter) and Laplacian equivalent. The introduction of gradient terms to the yield function was found to play an important role in simulating the strain localization behavior of the voided ductile material. The effect of the mesh size and characteristic length on the strain localization were also investigated. An FEM simulation based on the proposed non-local plasticity revealed that the load-strain curves of the voided ductile material subjected to plane strain tension converged to one curve, regardless of the mesh size. In addition, the results using non-local plasticity also exhibited that the dependence of the deformation behavior of the material on the mesh size was much less sensitive than that with classical local plasticity and could be successfully eliminated through the introduction of a large value for the characteristic length.
基金supported by the National Natural Science Foundation of China(Grant Nos.59975076,50175092,50905144)the National Science Found of China for Distinguished Young Scholars(Grant No.50225518)
文摘With increasing diameters of aluminum alloy thin-walled tubes(AATTs),the tube forming limits,i.e.the minimum bending factors,and their predictions under multi-index constraints including wrinkling,thinning and flattening have been being a key problem to be urgently solved for improving tube forming potential in numerical control(NC)bending processes of AATTs with large diameters.Thus in this paper,a search algorithm of the forming limits is put forward based on a 3D elastic-plastic finite element(FE)model and a wrinkling energy prediction model for the bending processes under axial compression loading(ACL)or not.This algorithm enables to be considered the effects of process parameter combinations including die,friction parameters on the multi-indices.Based on this algorithm,the forming limits of the different size tubes are obtained,and the roles of the process parameter combinations in enabling the limit bending processes are also revealed.The followings are found:the first,within the appropriate ranges of friction and clearances between the different dies and the tubes enabling the bending processes with smaller bending factors,the ACL enables the tube limit bending processes after a decrease of the mandrel ball thickness and diameters;then,without considering the effects of the tube geometry sizes on the tube constitutive equations,the forming limits will be decided by the limit thinning values for the tubes with diameters smaller than 80 mm,while the wrinkling for the tubes with diameters no less than 80 mm.The forming limits obtained from this algorithm are smaller than the analytical results,and reduced by 57.39%;the last,the roles of the process parameter combinations in enabling the limit bending processes are verified by experimental results.
基金Science and Engineering Research Board,Government of India(ECR/2016/001402)BITS-Pilani,Hyderabad Campus。
文摘The stretch forming and the deep-drawing processes were carried out at 300 and 673 K to determine the safe forming and fracture limits of IN625 alloy.The experimentally obtained strain-based fracture forming limit diagram(FFLD)was transformed into a stress-based(σ-FFLD)and effective plastic strain(EPS)vs triaxiality(η)plot to remove the excess dependency of fracture limits over the strains.For the prediction of fracture limits,seven different damage models were calibrated.The Oh model displayed the best ability to predict the fracture locus with the least absolute error.Though the experimentally obtained fracture limits have only been used for the numerical analysis,none of the considered damage models predicted the fracture strains over the entire considered range of stress triaxiality(0.33<η<0.66).The deep drawing process window helped to determine wrinkling,safe and fracture zones while drawing the cylindrical cups under different temperature and lubricating conditions.Further,the highest drawing ratio of 2 was achieved at 673 K under the lubricating condition.All the numerically predicted results of both stretch forming and deep drawing processes using the Hill 1948 anisotropic yielding function were found to be good within the acceptable range of error.
基金Project(4013311)supported by the National Science Foundation of Iran(INSF)。
文摘This article examines the influence of annealing temperature on fracture toughness and forming limit curves of dissimilar aluminum/silver sheets.In the cold roll bonding process,after brushing and acid washing,the prepared surfaces are placed on top of each other and by rolling with reduction more than 50%,the bonding between layers is established.In this research,the roll bonding process was done at room temperature,without the use of lubricants and with a 70%thickness reduction.Then,the final thickness of the Ag/Al bilayer sheet reached 350μm by several stages of cold rolling.Before cold rolling,it should be noted that to decrease the hardness created due to plastic deformation,the roll-bonded samples were subjected to annealing heat treatment at 400℃for 90 min.Thus,the final samples were annealed at 200,300 and 400℃for 90 min and cooled in a furnace to examine the annealing temperature effects.The uniaxial tensile and microhardness tests measured mechanical properties.Also,to investigate the fracture mechanism,the fractography of the cross-section was examined by scanning electron microscope(SEM).To evaluate the formability of Ag/Al bilayer sheets,forming limit curves were obtained experimentally through the Nakazima test.The resistance of composites to failure due to cracking was also investigated by fracture toughness.The results showed that annealing increases the elongation and formability of the Ag/Al bilayer sheet while reduces the ultimate tensile strength and fracture toughness.However,the changing trend is not the same at different temperatures,and according to the results,the most significant effect is obtained at 300℃and aluminum layers.It was also determined that by increasing annealing temperature,the fracture mechanism from shear ductile with small and shallow dimples becomes ductile with deep cavities.
基金supported by the National Natural Science Fund of China(Nos.52005153,12227801,32300666,12072005,U23A2607)the Tianjin"Project+Team"Key Training Program,China(No.XC202052)+4 种基金the Key Program of Research and Development of Hebei Province,China(Nos.202030507040009,23311812D)the Natural Science Foundation of Hebei Province,China(No.E2023202183)the Project of High-Level Team Construction Introduction of Hebei Province,China(No.244A7620D)the Research Cooperation Project of Universities Stationed in Hebei Province and Shijiazhuang City,China(No.241080114A)Hebei Province Military-Civilian Integration Science and Technology Innovation Project,China(No.SJMYF2022X15)。
文摘Fiber Metal Laminates(FMLs),as high-performance composite materials,demonstrate exceptional potential in a wide range of applications,such as aeronautical and astronautical industries.However,the traditional cured FMLs possess complex interlayer stresses and low forming limits,restricting further promotion and application of FMLs.Low-constraint FMLs exhibit a lower forming resistance and better formability due to no curing during the forming process;however,the formation mechanism and response are not clear.This paper presents the Forming Limit Diagram(FLD)of low-constraint GLARE(glass fiber reinforced aluminum laminates)based on the forming limit test,and compares it with the conventionally cured laminates to evaluate the differences in the forming limit.In addition,combined with the analysis of failure mechanism and micro-deformation mechanism of specimens,the influence of different temperatures(20–80℃)and forming states(width)on the deformation performance of laminates is further explored.The results reveal that the forming limit curve of low-constraint laminates shifts up with the increase of temperature,the forming limit initially increases with the increase of width,then followed by a gradual decrease,and the maximum principal strain of low-constraint laminates is increased by 29% at 80℃ compared to 20℃.The cured laminate has a principal strain range of 0–0.02,while the low-constraint laminates have a principal strain range of 0.03–0.14.Compared with cured laminates,low-constraint laminates possess a higher forming limit due to the improvement in deformable degree between layers by resin flow and fiber slippage,which enhances their formability.This study is expected to serve as a reference for establishing forming limit criteria and optimizing forming schemes for low-constraint laminates.
基金Project(CSTC2010AA4035)supported by Scientific and Technological Project of Chongqing Science and Technology Commission,ChinaProject(50504019)supported by the National Natural Science Foundation of China+1 种基金Project(CDJZR11130008)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(CDJXS10130001)supported by the Chongqing University Postgraduates'Science and Innovation Fund,China
文摘Repeated unidirectional bending （RUB） was carried out to improve the texture of commercial AZ31B magnesium alloy sheets. All specimens were prepared in the rolling direction. The forming limit diagrams （FLDs） of AZ31B magnesium alloy sheet were determined experimentally by conducting stretch-forming tests at room temperature, 100, 200 and 300 ℃ Compared with the as-received sheet, the lowest limited strain of AZ31B magnesium alloy sheet with tilted texture in the FLD increased by 79% at room temperature and 104% at 100 ℃. The texture also affected the extension of the forming limit curves （FLC） in the FLD. However, the FLCs of two kinds of sheets almost overlapped at temperature above 200 ℃. It can be concluded that the reduction of （0002） texture intensity is effective to the improvement of formability not only at room temperature but also at low-and-medium temperature. The effect of texture on FLDs becomes weak with increasing temperature.
基金Project(51375328)supported by the National Natural Science Foundation of ChinaProject(20143009)supported by Graduates Innovation Project of Shanxi Province,ChinaProject(2015-036)supported by Shanxi Scholarship Council of China
文摘A theoretical prediction on forming limit diagram（FLD） of AZ31 magnesium alloy sheet was developed at warm temperatures based on the M-K theory. Two different yield criteria of von Mises and Hill＇48 were applied in this model. Mechanical properties of AZ31 magnesium alloy used in the prediction were obtained by uniaxial tensile tests and the Fields-Backofen equation was incorporated in the analysis. In addition, experimental FLDs of AZ31 were acquired by conducting rigid die swell test at different temperatures to verify the prediction. It is demonstrated from a comparison between the predicted and the experimental FLDs at 473 K and 523 K that the predicted results are influenced by the type of yield criterion used in the calculation, especially at lower temperatures. Furthermore, a better agreement between the predicted results and experimental data for AZ31 magnesium alloy sheet at warm temperatures was obtained when Hill＇48 yield criterion was applied.
基金Project(51005010)supported by the National Natural Science Foundation of China
文摘A modified Swift type flow stress—strain relation was presented in order to describe the uniaxial tension test curve reasonably. The FLD-strain （forming limit diagram made up of limit strain） of 5754O aluminum alloy sheet was calculated based on the two flow stress—strain relations using Yld2000-2d yield function. By comparing the theoretical and experimental results, it is found that the calculated FLD-strain based on the modified Swift flow stress—strain relation can reasonably describe the experimental results. However, though the common Voce flow stress—strain relation can describe the deformation behavior during homogenous deformation phase accurately, the FLD-strain calculated based on it is obviously lower than the experimental result. It is concluded that the higher the hardening rate of sheet metal is, the higher the forming limit is. A method for determining the reasonable flow stress—strain relation is recommended for describing the material behavior during inhomogenous phase and the forming limit of sheet metal.
基金Aeronautical Science Foundation of China （03H53048）
文摘The conventional forming limit diagram （FLD） is described as a plot of major strain versus minor strain. However, FLD is dependent on forming history and strain path. In the present study, a forming limit stress-based diagram （FLSD） has been adopted to predict the fracture limit of aluminum alloy （AA） 5052-O1 sheet. Nakazima test is simulated by plastic constitutive formula derived from the modified Gurson-Tvergaard-Needleman （GTN） model. An in situ tensile test with scanning electron microscope （SEM） is proposed to determine the parameters in GTN model. The damage evolution is observed and recorded, and the parameters of GTN model are identified through counting void fraction at three damage stages of AA5052-O 1. According to the experimental results, the original void volume fraction, the volume fraction of potential nucleated voids, the critical void volume fraction, the void volume fraction at the final failure of material are assigned as 0.002 918, 0.024 9, 0.030 103, 0.048 54, respectively. The stress and strain are obtained at the last loading step before crack. FLSD and FLD of AA5052-O 1 are plotted. Compared with the experimental Nakazima test and uniaxial tensile test, the predicted results show a good agreement. The parameters determined by in situ tensile test can be applied to the research of the forming limit for ductile metals.
基金Supported by National Natural Science Foundation of China(Grant Nos.51305386,51305385)Hebei Provincial Natural Science Foundation of China(Grant No.E2013203093)
文摘High strength aluminum alloy plate has a low elongation at room temperature, which leads to the forming of its components need a high temperature. Liquid or gas is used as the pressure-transfer medium in the existing flexible mould forming process, the heat resistance of the medium and pressurizing device makes the application of aluminum alloy plate thermoforming restricted. To solve this problem, the existing medium is replaced by the heat-resisting solid granules and the general pressure equipments are applied. Based on the pressure-transfer performance test of the solid granules medium, the feasibility that the assumption of the extended Drucker-Prager linear model can be used in the finite element analysis is proved. The constitutive equation, the yield function and the theoretical forming limit diagram（FLD） of AA7075 sheet are established. Through the finite element numerical simulation of hot granules medium pressure forming（HGMF） process, not only the influence laws of the process parameters, such as forming temperature, the blank-holder gap and the diameter of the slab, on sheet metal forming performance are discussed, but also the broken area of the forming process is analyzed and predicted, which are coincided with the technological test. The conical part whose half cone angle is 15° and relative height H/d0 is 0.57, is formed in one process at 250℃. The HGMF process solves the problems of loading and seal in the existing flexible mould forming process and provides a novel technology for thermoforming of light alloy plate, such as magnesium alloy, aluminium alloy and titanium alloy.
基金support from the National Science Fund for Excellent Young Scholars of China(No.51222509)the National Natural Science Foundation of China(No.51175429)+1 种基金the Research Fund of the State Key Laboratory of Solidification Processing(No.97-QZ-2014 and 90-QP-2013)of Chinathe Marie Curie International Research Staff Exchange Scheme(IRSES,Mat Pro Future,No.318968)within the 7th EC Framework Programme(FP7)
文摘With the implementation of environmental protection, sustainable development and conservation-oriented policies, components and parts of thin-walled welded tubes have gained increasing application in the aircraft and automotive industries because of their advantages： easily achieving forming and manufacturing process at low cost and in a short time. The current research on welded tube plastic forming is mainly concentrated on tube internal high-pressure forming, tube bending forming, and tube spinning forming. The focuses are on the material properties and char- acterization of welded tubes, finite element modeling for welded tube forming, and inhomogeneous deformation behavior and the mechanism and rules of deformation coordination in welded tube plastic forming. This paper summarizes the research progress in welded tube plastic forming from these aspects. Finally, with a focus on the urgent demand of the aviation, aerospace and automotive industries for high-strength and light-weight tubes, this paper discusses the development trends and challenges in the theory and technology of welded tube plastic forming in the future. Among them, laser tailor-welded technology will find application in the manufacture of high-strength steel tubes. Tube-end forming technology, such as tube flaring and flanging technology, will expand its appli- cation in welded tubes. Therefore, future studies will focus on the FE modeling regarding how to consider effects of welding on residual stresses, welding distortions and microstructure, the inhomo- geneous deformation and coordination mechanism of the plastic forming process of tailor-welded tubes, and some end-forming processes of welded tubes, and more comprehensive research on the formin~ mechanism and limit of welded tubes.
基金Item Sponsored by National Natural Science Foundation of China(51105068,51475086)Fundamental Research Funds for the Central Universities of China(N130323003,XNB201413)Science and Technology Research Project for Higher School of Hebei Province of China(Z2013068)
文摘The process of automobile lightweight can be promoted by the application of tailor rolled blank（TRB）in the automobile industry.Therefore,research on the formability of TRB is of good practical significance and application value because of the enormous potential of TRB in the aspect of automobile lightweight.Aiming at the present condition of lack of researches on the influence of characteristic parameters on TRB drawing process,the drawing formability of TRB was studied with a combination method of simulation and experiment by taking square box as the research object.Firstly,drawing simulation and experiment of TRB were carried out.Then,effects of thickness transition zone（TTZ）position and blank size on the drawing formability of TRB were analyzed.Forming limit and TTZ movement for TRB square box during the drawing process were respectively discussed,when transition zones of TRB were located at different positions and blanks were of different sizes.The results indicate that lubrication condition exerts greater influence on TRB forming limit in comparison with TTZ movement,and the smaller blank size and TTZ being located at the blank center or slightly offset to the thinner side are preferable for acquiring greater forming limit and smaller TTZ movement.
基金Project (51775481) supported by the National Natural Science Foundation of ChinaProject (E2019203418) supported by the Natural Science Foundation of Hebei Province, ChinaProject (ZD2017078) supported by the Science and Technology Plan of Hebei Higher School of Education Department, China。
文摘In order to effectively predict the fracture of AA7075-T6 sheet, the forming limit curves of AA7075-T6 high-strength sheet were drawn according to Morciniak Kuczyski (M K) model and Lou Huh criterion, respectively. The errors between the predicted values of the two theoretical prediction models and experimental values were calculated by error analysis. The forming limit curves were verified by the punch stretch test to evaluate the prediction accuracy of M K model and Lou Huh criterion. The error analysis results show that the mean error of Lou Huh criterion with the optimal parameters for all tensile specimens is 25.04%, while the mean error of M K model for all tensile specimens is 74.24%. The prediction accuracy of Lou Huh criterion in predicting the fracture of AA7075-T6 sheet is higher. The punch stretch test results show that the forming limit curve drawn by Lou Huh criterion can effectively predict the fracture of AA7075-T6 sheet, but the prediction accuracy of M K model is relatively poor.
基金co-supported by National Natural Science Foundation of China (No.50905008)Fund of National Engineering and Research Center for Commercial Aircraft Manufacturing (No.SAMC12-JS-15-008)
文摘The Forming Limit Curve （FLC） of the third generation aluminum-lithium （Al-Li） alloy 2198-T3 is measured by conducting a hemispherical dome test with specimens of different widths. The theoretical prediction of the FLC of 2198-T3 is based on the M-K theory utilizing respectively the von Mises, Hill＇48, Hosford and Barlat 89 yield functions, and the different predicted curves due to different yield functions are compared with the experimentally measured FLC of 2198-T3. The results show that though there are differences among the four predicted curves, yet they all agree well with the experimentally measured curve. In the area near the planar strain state, the predicted curves and experimentally measured curve are very close. The predicted curve based on the Hosford yield function is more accurate under the tension-compression strain states described in the left part of the FLC, while the accuracy is better for the predicted curve based on Hill＇48 yield function under the tension-tension strain states shown in the right part.
基金the Austrian Research Promotion Agency (FFG)the Federal Ministry for Transport, Innovation and Technology (bmvit) for sponsoring the project Kryo Alu in the framework of Kooperative F&E-Projekte-Industrielle Forschung, Experimentelle Entwicklung
文摘The objective of this work is to study the cryogenic sheet metal forming behaviour of precipitation hardening AW-6016-T4.In this regard,the flow curves and forming limit curves were obtained by tension and Nakazima experimental testing methods in thetemperature ranges from-196to25°C.It was found that strength and elongation increase with decreasing temperature.Small butperceived differences between microstructure of the material deformed at the room and cryogenic temperatures respectively wereidentified by electron backscatter diffraction(EBSD)analysis.However,no significant difference in the precipitation kinetics duringcontinuous heating in the DSC has been observed.This study has demonstrated the potential of cryogenic forming by manufacturinga B-pillar part with8mm depth of side design element as compared to6mm at room temperature.
文摘The forming limit curve （FLC） can be obtained by means of curve fitting the limit strain points of different strain paths. The theory of percent regression analysis is applied to the curve fitting of forming limit experimental data.Forecast intervals of FLC percentiles can be calculated. Thus reliability and confidence level can be considered. The theoretical method to get the limits of limit strain points distributing region is presented, and the FLC position can be adjusted according to practical requirement. Method for establishing FLC with high reliability using small samples is presented at the same time. This method can make full use of the current experimental data and the previous data.Compared with the traditional method that can only use current experimental data, fewer specimens are required in the present method to obtain the same precision and the result is more accurate with the same number of specimens.
基金Project(51775023)supported by the National Natural Science Foundation of ChinaProject(YWF-18-BJ-J-75)supported by the Fundamental Research Funds for the Central Universities,China
文摘The influence of initial groove angle on strain rate inside and outside groove of Ti6Al4V alloy was investigated.Based on the evolution of strain rate inside and outside groove,the effect of strain rate difference on the evolution of normal stress and effective stress inside and outside groove was also analyzed.The results show that when linear loading path changes from uniaxial tension to equi-biaxial tension,the initial groove angle plays a weaker role in the evolution of strain rate in the M-K model.Due to the constraint of force equilibrium between inside and outside groove,the strain rate difference makes the normal stress inside groove firstly decrease and then increase during calculation,which makes the prediction algorithm of forming limit convergent at elevated temperature.The decrease of normal stress inside groove is mainly caused by high temperature softening effect and the rotation of groove,while the increase of normal stress inside groove is mainly due to strain rate hardening effect.
文摘The effects of annealing treatments(ATs)on the microstructure of Zr-Sn-Nb alloy strips were studied.Based on the characteristics of strips for nuclear fuel assemblies,punching experiments were carried out and the formability of zirconium alloy strips was quantitatively evaluated.The results indicate that the proportions of small-angle grain boundaries of the zirconium alloy under conditions of annealing treatment at 580°C(ATⅠ)and annealing treatment at 620°C(ATⅡ)are 14.3%and 23.2%,respectively,while that of the as-received material is 12.4%.And the forming limit margin fields of the zirconium alloy under ATⅠcan reach 0.43%,while the values of the as-received material and the ATⅡare-0.35%and-2.8%,respectively.The annealing process affects the evolution process of the strip recrystallization texture and the grain size.Moreover,the total texture and pole density are closely related to the degree of anisotropy of the strip.Besides,the small-angle grain boundary affects the strain path and crack expansion of the necking unit during the strip punching process,while the grain size affects the hardening exponent of the material.
基金The financial support received for this research work from Department of Science and Technology (DST), Government of India, SERB-DST, SR/FTP/ETA0056/2011
文摘Forming limit diagram (FLD) is an important performance index to describe the maximum limit of principal strains that can be sustained by sheet metals till to the onset of localized necking. It offers a convenient and useful tool to predict the forming limit in the sheet metal forming processes. In the present study, FLD has been determined experimentally for Ti?6Al?4V alloy at 400 °C by conducting a Nakazima test with specimens of different widths. Additionally, for theoretical FLD prediction, various anisotropic yield criteria (Barlat 1989, Barlat 1996, Hill 1993) and different hardening models viz., Hollomon power law (HPL), Johnson?Cook (JC), modified Zerilli–Armstrong (m-ZA), modified Arrhenius (m-Arr) models have been developed. Theoretical FLDs have been determined using Marciniak and Kuczynski (M?K) theory incorporating the developed yield criteria and constitutive models. It has been observed that the effect of yield model is more pronounced than the effect of constitutive model for theoretical FLDs prediction. However, the value of thickness imperfection factor (f0) is solely dependent on hardening model. Hill (1993) yield criterion is best suited for FLD prediction in the right hand side region. Moreover, Barlat (1989) yield criterion is best suited for FLD prediction in left hand side region. Therefore, the proposed hybrid FLD in combination with Barlat (1989) and Hill (1993) yield models with m-Arr hardening model is in the best agreement with experimental FLD.
基金supported by the National Research Foundation of Korea (NRF) granted by the Korea government [2014R1A2A2A01005903]Priority Research Centers Program (2010-0020089)support from a grant [R0003356] (Tuning Professional Support Center in Daegu Metropolitan City) funded by the Ministry of Trade, Industry and Energy (MOTIE, Korea)
文摘Commercially pure titanium（CP Ti） has been actively used in the plate heat exchanger due to its light weight, high specific strength, and excellent corrosion resistance. However, researches for the plastic deformation characteristics and press formability of the CP Ti sheet are not much in comparison with automotive steels and aluminum alloys. The mechanical properties and hardening behavior evaluated in stress-strain relation of the CP Ti sheet are clarified in relation with press formability. The flow curve denoting true stress-true strain relation for CP Ti sheet is fitted well by the Kim-Tuan hardening equation rather than Voce and Swift models. The forming limit curve（FLC） of CP Ti sheet as a criterion for press formability was experimentally evaluated by punch stretching test and analytically predicted via Hora＇s modified maximum force criterion. The predicted FLC by adopting Kim-Tuan hardening model and appropriate yield function shows good correlation with the experimental results of punch stretching test.
