The width and spacing of adiabatic shear bands (ASBs) in the serrated chips generated during high speed orthogonal cutting of 30CrNi3MoV structurai steel were measured by opticai microscopy (OM), the temperature rise ...The width and spacing of adiabatic shear bands (ASBs) in the serrated chips generated during high speed orthogonal cutting of 30CrNi3MoV structurai steel were measured by opticai microscopy (OM), the temperature rise in the shear band was estimated. The microstructures of the ASBs were also characterized by SEM and TEM. The results show that the width and spacing of ASBs decrease with the increase of the cutting speed. The further observations show that the microstructure between the matrix and the center of the ASB gradually changes, and that the martensitic phase transformation, carbide precipitation and recrystallization may occur in the ASB.展开更多
Wind turbine gearbox bearings fail with the service life is much shorter than the designed life.Gearbox bearings are subjected to rolling contact fatigue(RCF)and they are observed to fail due to axial cracking,surface...Wind turbine gearbox bearings fail with the service life is much shorter than the designed life.Gearbox bearings are subjected to rolling contact fatigue(RCF)and they are observed to fail due to axial cracking,surface flaking,and the formation of white etching areas(WEAs).The current study reviewed these three typical failure modes.The underlying dominant mechanisms were discussed with emphasis on the formation mechanism of WEAs.Although numerous studies have been carried out,the formation of WEAs remains unclear.The prevailing mechanism of the rubbing of crack faces that generates WEAs was questioned by the authors.WEAs were compared with adiabatic shear bands(ASBs)generated in the high strain rate deformation in terms of microstructural compositions,grain refinement,and formation mechanism.Results indicate that a number of similarities exist between them.However,substantial evidence is required to verify whether or not WEAs and ASBs are the same matters.展开更多
High-strength bainitic steels have created a lot of interest in recent times because of their excellent combination of strength,ductility,toughness,and high ballistic mass efficiency.Bainitic steels have great potenti...High-strength bainitic steels have created a lot of interest in recent times because of their excellent combination of strength,ductility,toughness,and high ballistic mass efficiency.Bainitic steels have great potential in the fabrication of steel armor plates.Although various approaches and methods have been conducted to utilize the retained austenite(RA)in the bainitic matrix to control mechanical properties,very few attempts have been conducted to improve ballistic performance utilizing transformationinduced plasticity(TRIP)mechanism.In this study,high-strength bainitic steels were designed by controlling the time of austempering process to have various volume fractions and stability of RA while maintaining high hardness.The dynamic compressive and ballistic impact tests were conducted,and the relation between the effects of TRIP on ballistic performance and the adiabatic shear band(ASB)formation was analyzed.Our results show for the first time that an active TRIP mechanism achieved from a large quantity of metastable RA can significantly enhance the ballistic performance of high-strength bainitic steels because of the improved resistance to ASB formation.Thus,the ballistic performance can be effectively improved by a very short austempering time,which suggests that the utilization of active TRIP behavior via tuning RA acts as a primary mechanism for significantly enhancing the ballistic performance of high-strength bainitic steels.展开更多
文摘The width and spacing of adiabatic shear bands (ASBs) in the serrated chips generated during high speed orthogonal cutting of 30CrNi3MoV structurai steel were measured by opticai microscopy (OM), the temperature rise in the shear band was estimated. The microstructures of the ASBs were also characterized by SEM and TEM. The results show that the width and spacing of ASBs decrease with the increase of the cutting speed. The further observations show that the microstructure between the matrix and the center of the ASB gradually changes, and that the martensitic phase transformation, carbide precipitation and recrystallization may occur in the ASB.
基金This work was financially supported by the National Natural Science Foundation of China(Grant No.51275225).
文摘Wind turbine gearbox bearings fail with the service life is much shorter than the designed life.Gearbox bearings are subjected to rolling contact fatigue(RCF)and they are observed to fail due to axial cracking,surface flaking,and the formation of white etching areas(WEAs).The current study reviewed these three typical failure modes.The underlying dominant mechanisms were discussed with emphasis on the formation mechanism of WEAs.Although numerous studies have been carried out,the formation of WEAs remains unclear.The prevailing mechanism of the rubbing of crack faces that generates WEAs was questioned by the authors.WEAs were compared with adiabatic shear bands(ASBs)generated in the high strain rate deformation in terms of microstructural compositions,grain refinement,and formation mechanism.Results indicate that a number of similarities exist between them.However,substantial evidence is required to verify whether or not WEAs and ASBs are the same matters.
基金supported by the Agency for Defense Development(grant No.UE161030GD)the Korea University Grant for Dr.S.S.Sohnthe BK21 Plus Project for Center for Creative Industrial Materials。
文摘High-strength bainitic steels have created a lot of interest in recent times because of their excellent combination of strength,ductility,toughness,and high ballistic mass efficiency.Bainitic steels have great potential in the fabrication of steel armor plates.Although various approaches and methods have been conducted to utilize the retained austenite(RA)in the bainitic matrix to control mechanical properties,very few attempts have been conducted to improve ballistic performance utilizing transformationinduced plasticity(TRIP)mechanism.In this study,high-strength bainitic steels were designed by controlling the time of austempering process to have various volume fractions and stability of RA while maintaining high hardness.The dynamic compressive and ballistic impact tests were conducted,and the relation between the effects of TRIP on ballistic performance and the adiabatic shear band(ASB)formation was analyzed.Our results show for the first time that an active TRIP mechanism achieved from a large quantity of metastable RA can significantly enhance the ballistic performance of high-strength bainitic steels because of the improved resistance to ASB formation.Thus,the ballistic performance can be effectively improved by a very short austempering time,which suggests that the utilization of active TRIP behavior via tuning RA acts as a primary mechanism for significantly enhancing the ballistic performance of high-strength bainitic steels.
