The use of ultra-high strength steels through sheet metal forming process offers a practical solution to the lightweight design of vehicles.However,sheet metal forming process not only produces desirable changes in ma...The use of ultra-high strength steels through sheet metal forming process offers a practical solution to the lightweight design of vehicles.However,sheet metal forming process not only produces desirable changes in material properties but also causes material damage that may adversely influence the service performance of the material formed.Thus,an investigation is conducted to experimentally quantify such influence for a commonly used steel（the 22MnB5 steel） based on the hot and cold forming processes.For each process,a number of samples are used to conduct a uniaxial tensile test to simulate the forming process.After that,some of the samples are trimmed into a standard shape and then uniaxially extended until fracture to simulate the service stage.Finally,a microstructure test is conducted to analyze the microdefects of the remaining samples.Based on the results of the first two tests,the effect of material damage on the service performance of 22MnB5 steel is analyzed.It is found that the material damages of both the hot and cold forming processes cause reductions in the service performance,such as the failure strain,the ultimate stress,the capacity of energy absorption and the ratio of residual strain.The reductions are generally lower and non-linear in the former process but higher and linear in the latter process.Additionally,it is found from the microstructure analysis that the difference in the reductions of the service performance of 22MnB5 by the two forming processes is driven by the difference in the micro damage mechanisms of the two processes.The findings of this research provide a useful reference in terms of the selection of sheet metal forming processes and the determination of forming parameters for 22MnB5.展开更多
The effects of forming damage are analyzed,which occur during hot stamping process,on the load-carrying capacity and failure mode of hot stamped beams.A damage-coupled pre-forming constitutive model was proposed,in wh...The effects of forming damage are analyzed,which occur during hot stamping process,on the load-carrying capacity and failure mode of hot stamped beams.A damage-coupled pre-forming constitutive model was proposed,in which the damage during hot stamping process was introduced into the service response.The constitutive model was applied into the three-point bending simulation of a hot stamped beam,and then the influences of forming damage on the load-carrying capacity and cracks propagation were investigated.The results show that the forming damage reduces the maximum load capacity of the hot stamped beam by 7.5%.It also causes the crack to occur earlier and promotes crack to propagate along the radial direction of the punch.展开更多
The aerodynamic safety of trains may be greatly threatened when encountering wind barrier s with unexpected damage under strong wind conditions.A validated numerical method was utilized to explore the aerodynamic impa...The aerodynamic safety of trains may be greatly threatened when encountering wind barrier s with unexpected damage under strong wind conditions.A validated numerical method was utilized to explore the aerodynamic impact of various forms of wind barrier damage on the aerodynamic performance of a travelling train.The relationships between the aerodynamic parameters and the varying damage forms and wind conditions were investigated.Results indicate that bilateral damage has a more pronounced aerodynamic impact on both the train and wind barrier compared to unilateral damage,posing a greater risk to the operational safety of the train.While the damage length has minimal impact on aerodynamic loads on the wind barrier,it significantly affects the train.Specifically,the maximum peaks and amplitudes of the side force and overturning moment of the train head exhibit an upward trend as the damage length increases,followed by a decrease once the damage length surpasses the length of the train,which was determined as the most unfavourable length of damage.Furthermore,the peaks and amplitudes of the train aerodynamic forces show a linear increase with the wind speed,while the maximum pressure peak and amplitude on the wind barrier also rise at an escalating rate.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.51375201)CSAE(Beijing)Automotive Lightweight Technology Research Institute Development Fund Project of China
文摘The use of ultra-high strength steels through sheet metal forming process offers a practical solution to the lightweight design of vehicles.However,sheet metal forming process not only produces desirable changes in material properties but also causes material damage that may adversely influence the service performance of the material formed.Thus,an investigation is conducted to experimentally quantify such influence for a commonly used steel（the 22MnB5 steel） based on the hot and cold forming processes.For each process,a number of samples are used to conduct a uniaxial tensile test to simulate the forming process.After that,some of the samples are trimmed into a standard shape and then uniaxially extended until fracture to simulate the service stage.Finally,a microstructure test is conducted to analyze the microdefects of the remaining samples.Based on the results of the first two tests,the effect of material damage on the service performance of 22MnB5 steel is analyzed.It is found that the material damages of both the hot and cold forming processes cause reductions in the service performance,such as the failure strain,the ultimate stress,the capacity of energy absorption and the ratio of residual strain.The reductions are generally lower and non-linear in the former process but higher and linear in the latter process.Additionally,it is found from the microstructure analysis that the difference in the reductions of the service performance of 22MnB5 by the two forming processes is driven by the difference in the micro damage mechanisms of the two processes.The findings of this research provide a useful reference in terms of the selection of sheet metal forming processes and the determination of forming parameters for 22MnB5.
基金Supported by the National Natural Science Foundation of China(5137520151775227)。
文摘The effects of forming damage are analyzed,which occur during hot stamping process,on the load-carrying capacity and failure mode of hot stamped beams.A damage-coupled pre-forming constitutive model was proposed,in which the damage during hot stamping process was introduced into the service response.The constitutive model was applied into the three-point bending simulation of a hot stamped beam,and then the influences of forming damage on the load-carrying capacity and cracks propagation were investigated.The results show that the forming damage reduces the maximum load capacity of the hot stamped beam by 7.5%.It also causes the crack to occur earlier and promotes crack to propagate along the radial direction of the punch.
基金supported by the National Science Foundation of Guangdong Province(Gr ant No.2022A1515010011)the Jiangmen Basic and Theoretical Science Research Project(2023)(Grant No.2023JC01020)the Hong Kong and Macao Joint Research and Development Fund of Wuyi University(Grant No.2019WGALH17)。
文摘The aerodynamic safety of trains may be greatly threatened when encountering wind barrier s with unexpected damage under strong wind conditions.A validated numerical method was utilized to explore the aerodynamic impact of various forms of wind barrier damage on the aerodynamic performance of a travelling train.The relationships between the aerodynamic parameters and the varying damage forms and wind conditions were investigated.Results indicate that bilateral damage has a more pronounced aerodynamic impact on both the train and wind barrier compared to unilateral damage,posing a greater risk to the operational safety of the train.While the damage length has minimal impact on aerodynamic loads on the wind barrier,it significantly affects the train.Specifically,the maximum peaks and amplitudes of the side force and overturning moment of the train head exhibit an upward trend as the damage length increases,followed by a decrease once the damage length surpasses the length of the train,which was determined as the most unfavourable length of damage.Furthermore,the peaks and amplitudes of the train aerodynamic forces show a linear increase with the wind speed,while the maximum pressure peak and amplitude on the wind barrier also rise at an escalating rate.
