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
The influence of the MnS plastic inclusion on the accumulation of internal damage was considered, and the Gurson– Tvergaard–Needleman (GTN) model was calibrated based on the finite element inverse method and image a...The influence of the MnS plastic inclusion on the accumulation of internal damage was considered, and the Gurson– Tvergaard–Needleman (GTN) model was calibrated based on the finite element inverse method and image analysis method using ABAQUS and GTN models. The modified GTN damage model was used to simulate the initiation and propagation of cracks in an as-cast 304 stainless steel with MnS inclusions at 900 C. The simulation results agreed well with the experimental results, indicating that the model can be effectively applied to examine the high-temperature fracture behavior of MnS inclusions. The simulation and high-temperature tensile test results revealed that MnS inclusions increased the number of holes initiation and the probability of hole polymerization, reduced the crack propagation resistance, accelerated the occurrence of material fracture behavior, and were closely related to the stress state at high temperatures. When the stress triaxiality was low, the plastic strain in the metal matrix was high, and the MnS plastic inclusions accelerated the polymerization of the pores, making metal fracture failure more likely. On the other hand, when the stress triaxiality was high, the stress state in the metal matrix was biased to the tensile state, the plastic strain in the metal matrix was low, and the influence of MnS plastic inclusions on the fracture behavior was not evident.展开更多
A modified Gurson-Tvergaard-Needleman(GTN)model that accounts for the mixed(isotropic and kinematic)hardening of cast steel GS-20Mn5V was developed and implemented in the finite dement program ABAQUS/Standard via a us...A modified Gurson-Tvergaard-Needleman(GTN)model that accounts for the mixed(isotropic and kinematic)hardening of cast steel GS-20Mn5V was developed and implemented in the finite dement program ABAQUS/Standard via a user-defined material subroutine UMAT.This model couples the stress state and damage evolution(pore volume fraction increase)by a classic method that assumes that the total void volume fraction is divided into a nucleation and a growth part.A parametric study was conducted to assess the effect of modified GTN model parameters on mechanical properties such as the nucleation,growth and coalescence of voids and to obtain the optimal parameter combination by the orthogonal test method.The predicted load-displacement curves of notched specimens with the optimal parameters are favorably compared to the experimental curves.Therefore,the modified GTN model can be used to predict the damage evaluation and fracture behavior of GS-20Mn5V.展开更多
Based on the Gurson-Tvergaard-Needleman(GTN)damage model considering the defect damage evolution,the influence of void defects caused by the casting process on cast steel nodes mechanical properties was studied.Firstl...Based on the Gurson-Tvergaard-Needleman(GTN)damage model considering the defect damage evolution,the influence of void defects caused by the casting process on cast steel nodes mechanical properties was studied.Firstly,based on the GTN damage model,the model s parameter combination of G20Mn5N cast steel was given.Then,the mechanical properties of cast steel nodes were evaluated using the GTN damage model in ABAQUS software,and the influence of model parameters on the failure results was investigated.The results show that the cast steel node considering the GTN damage model fails under 1.93 times of the load.The bearing capacity is lower than that of the bilinear model,and the failure speed is faster.Changes in model parameters will cause a shift in the failure critical point.Meanwhile,the plastic strain index affects the void volume fractions,which shows different variation laws under uniaxial tensile and cyclic loads.Therefore,the GTN damage model establishes the relationship between the micro-defects and macro-mechanical properties of materials,which can better simulate the failure results of structures.展开更多
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This research was supported by the National Natural Science Foundation of China (Grant Nos. 51575475 and 51675465).
文摘The influence of the MnS plastic inclusion on the accumulation of internal damage was considered, and the Gurson– Tvergaard–Needleman (GTN) model was calibrated based on the finite element inverse method and image analysis method using ABAQUS and GTN models. The modified GTN damage model was used to simulate the initiation and propagation of cracks in an as-cast 304 stainless steel with MnS inclusions at 900 C. The simulation results agreed well with the experimental results, indicating that the model can be effectively applied to examine the high-temperature fracture behavior of MnS inclusions. The simulation and high-temperature tensile test results revealed that MnS inclusions increased the number of holes initiation and the probability of hole polymerization, reduced the crack propagation resistance, accelerated the occurrence of material fracture behavior, and were closely related to the stress state at high temperatures. When the stress triaxiality was low, the plastic strain in the metal matrix was high, and the MnS plastic inclusions accelerated the polymerization of the pores, making metal fracture failure more likely. On the other hand, when the stress triaxiality was high, the stress state in the metal matrix was biased to the tensile state, the plastic strain in the metal matrix was low, and the influence of MnS plastic inclusions on the fracture behavior was not evident.
基金The National Key Research and Development Program of China(No.2017YFC0805103)the National Natural Science Foundation of China(No.51578137,51438002,51108075)the Open Research Fund Program of Jiangsu Key Laboratory of Engineering Mechanics
文摘A modified Gurson-Tvergaard-Needleman(GTN)model that accounts for the mixed(isotropic and kinematic)hardening of cast steel GS-20Mn5V was developed and implemented in the finite dement program ABAQUS/Standard via a user-defined material subroutine UMAT.This model couples the stress state and damage evolution(pore volume fraction increase)by a classic method that assumes that the total void volume fraction is divided into a nucleation and a growth part.A parametric study was conducted to assess the effect of modified GTN model parameters on mechanical properties such as the nucleation,growth and coalescence of voids and to obtain the optimal parameter combination by the orthogonal test method.The predicted load-displacement curves of notched specimens with the optimal parameters are favorably compared to the experimental curves.Therefore,the modified GTN model can be used to predict the damage evaluation and fracture behavior of GS-20Mn5V.
基金The National Key Research and Development Program of China(No.2017YFC0805100)the National Natural Science Foundation of China(No.51578137)the Priority Academic Program Development of Jiangsu Higher Education Institutions,the Open Research Fund Program of Jiangsu Key Laboratory of Engineering Mechanics.
文摘Based on the Gurson-Tvergaard-Needleman(GTN)damage model considering the defect damage evolution,the influence of void defects caused by the casting process on cast steel nodes mechanical properties was studied.Firstly,based on the GTN damage model,the model s parameter combination of G20Mn5N cast steel was given.Then,the mechanical properties of cast steel nodes were evaluated using the GTN damage model in ABAQUS software,and the influence of model parameters on the failure results was investigated.The results show that the cast steel node considering the GTN damage model fails under 1.93 times of the load.The bearing capacity is lower than that of the bilinear model,and the failure speed is faster.Changes in model parameters will cause a shift in the failure critical point.Meanwhile,the plastic strain index affects the void volume fractions,which shows different variation laws under uniaxial tensile and cyclic loads.Therefore,the GTN damage model establishes the relationship between the micro-defects and macro-mechanical properties of materials,which can better simulate the failure results of structures.
