Different contents of Ni(0.3wt.%to 1.2wt.%)were added to the QT400-18L ductile iron to investigate the effect of Ni addition on the impact toughness of cast ductile irons at low temperatures.The impact toughnesses of ...Different contents of Ni(0.3wt.%to 1.2wt.%)were added to the QT400-18L ductile iron to investigate the effect of Ni addition on the impact toughness of cast ductile irons at low temperatures.The impact toughnesses of the samples at room and low temperatures were tested.The microstructures and fractographs were observed.Results show that with the increase of Ni addition there is a general trend of refinement of the ferrite matrix while the nodule density shows no obvious change.When the Ni content is 0.7wt.%,the matrix structure is the refined ferrite with a very small fraction(about 2%)of pearlite near the eutectic cell boundaries.When the Ni content is further increased,the fraction of pearlite increases significantly and reaches more than 5%when 1.2wt.%Ni is added.The impact toughness at room temperature increases as the content of Ni increases from 0.3 wt.%to 0.7 wt.%,but decreases as the Ni content further increases to 1.2wt.%due to the increase of pearlite fraction.The maximum value of the impact work is 18.5 J at room temperature with 0.7wt.%Ni addition.The average value of the impact work is still more than 13 J even at-30℃.In addition,the fracture mechanism changes from ductile manner to brittleness as the testing temperature decreases from 20℃to-60℃.展开更多
The Impact toughness and fracture toughness of Austempered Ductile Iron (ADI) are described. The notched and un-notched Charpy impact toughness of ADI at room temperature are somewhat lower than that of steel castings...The Impact toughness and fracture toughness of Austempered Ductile Iron (ADI) are described. The notched and un-notched Charpy impact toughness of ADI at room temperature are somewhat lower than that of steel castings or forged steel pieces, however, they are approximately three times higher than that of normal pearlitic ductile iron. The impact toughness of ADI decreases with decreasing temperature; but at-40℃ it still maintains about 70% of the value at room temperature. The properties of fracture toughness are important in safety design and failure analysis. In this study all fracture toughness data of ADI are higher than that of conventional ductile iron, and are equivalent to or better than that of steel castings or forged steel pieces with the tensile strength equivalent to ADI.展开更多
The impact fretting wear has largely occurred at nuclear power device induced by the flow-induced vibra- tion, and it will take potential hazards to the service of the equipment. However, the present study focuses on ...The impact fretting wear has largely occurred at nuclear power device induced by the flow-induced vibra- tion, and it will take potential hazards to the service of the equipment. However, the present study focuses on the tangential fretting wear of alloy 690 tubes. Research on impact fretting wear of alloy 690 tubes is limited and the related research is imminent. Therefore, impact fretting wear behavior of alloy 690 tubes against 304 stainless steels is investigated. Deionized water is used to simulate the flow environment of the equipment, and the dry envi- ronment is used for comparison. Varied analytical tech- niques are employed to characterize the wear and tribochemical behavior during impact fretting wear. Char- acterization results indicate that cracks occur at high impact load in both water and dry equipment; however, the water as a medium can significantly delay the cracking time. The crack propagation behavior shows a jagged shape in the water, but crack extended disorderly in dry equip- ment because the water changed the stress distribution and retarded the friction heat during the wear process. The SEM and XPS analysis shows that the main failure mechanisms of the tube under impact fretting are fatiguewear and friction oxidation. The effect of medium（water） on fretting wear is revealed, which plays a potential and promising role in the service of nuclear power device and other flow equipments.展开更多
Impact behavior of polymers has received considerable attention in recent years,and much work based on fracture mechanic approaches has been carried out.In this paper,fracture behavior in large deformation of a high d...Impact behavior of polymers has received considerable attention in recent years,and much work based on fracture mechanic approaches has been carried out.In this paper,fracture behavior in large deformation of a high density polyethylene(HDPE)materials was investigated through experimental impact testing on single edge notched specimen(SENB)and by using theoretical and analytical fracture criteria concepts.Moreover,a review of the main fracture criteria is given in order to characterize the toughness of this polymer in the both cases(static and dynamic).The fractured specimens obtained from the Charpy impact test were characterized with respect to their fracture surfaces.Characteristic zones of the fracture surface can be assigned to different stages and mechanisms of the fracture process.Finally,for a better understanding of fracture and damage mechanisms and to provide the best estimation of fracture toughness in impact,an experimental approach based on microscopic observations(SEM)was used.展开更多
基金financially supported by the National Natural Science Foundation of China(No.51274142)the Science&Technology Project of Liaoning Province(No.2009221005)the Science&Technology Project of Shenyang City(Nos.F10-035-2-00 and F11-069-2-00)
文摘Different contents of Ni(0.3wt.%to 1.2wt.%)were added to the QT400-18L ductile iron to investigate the effect of Ni addition on the impact toughness of cast ductile irons at low temperatures.The impact toughnesses of the samples at room and low temperatures were tested.The microstructures and fractographs were observed.Results show that with the increase of Ni addition there is a general trend of refinement of the ferrite matrix while the nodule density shows no obvious change.When the Ni content is 0.7wt.%,the matrix structure is the refined ferrite with a very small fraction(about 2%)of pearlite near the eutectic cell boundaries.When the Ni content is further increased,the fraction of pearlite increases significantly and reaches more than 5%when 1.2wt.%Ni is added.The impact toughness at room temperature increases as the content of Ni increases from 0.3 wt.%to 0.7 wt.%,but decreases as the Ni content further increases to 1.2wt.%due to the increase of pearlite fraction.The maximum value of the impact work is 18.5 J at room temperature with 0.7wt.%Ni addition.The average value of the impact work is still more than 13 J even at-30℃.In addition,the fracture mechanism changes from ductile manner to brittleness as the testing temperature decreases from 20℃to-60℃.
文摘The Impact toughness and fracture toughness of Austempered Ductile Iron (ADI) are described. The notched and un-notched Charpy impact toughness of ADI at room temperature are somewhat lower than that of steel castings or forged steel pieces, however, they are approximately three times higher than that of normal pearlitic ductile iron. The impact toughness of ADI decreases with decreasing temperature; but at-40℃ it still maintains about 70% of the value at room temperature. The properties of fracture toughness are important in safety design and failure analysis. In this study all fracture toughness data of ADI are higher than that of conventional ductile iron, and are equivalent to or better than that of steel castings or forged steel pieces with the tensile strength equivalent to ADI.
基金Supported by National Natural Science Foundation of China(Grant Nos.51375407,U1530136,51627806)Shanghai Municipal Science and Technology Talent Program of China(Grant No.14R21421500)Young Scientific Innovation Team of Science and Technology of Sichuan(Grant No.2017TD0017)
文摘The impact fretting wear has largely occurred at nuclear power device induced by the flow-induced vibra- tion, and it will take potential hazards to the service of the equipment. However, the present study focuses on the tangential fretting wear of alloy 690 tubes. Research on impact fretting wear of alloy 690 tubes is limited and the related research is imminent. Therefore, impact fretting wear behavior of alloy 690 tubes against 304 stainless steels is investigated. Deionized water is used to simulate the flow environment of the equipment, and the dry envi- ronment is used for comparison. Varied analytical tech- niques are employed to characterize the wear and tribochemical behavior during impact fretting wear. Char- acterization results indicate that cracks occur at high impact load in both water and dry equipment; however, the water as a medium can significantly delay the cracking time. The crack propagation behavior shows a jagged shape in the water, but crack extended disorderly in dry equip- ment because the water changed the stress distribution and retarded the friction heat during the wear process. The SEM and XPS analysis shows that the main failure mechanisms of the tube under impact fretting are fatiguewear and friction oxidation. The effect of medium（water） on fretting wear is revealed, which plays a potential and promising role in the service of nuclear power device and other flow equipments.
文摘Impact behavior of polymers has received considerable attention in recent years,and much work based on fracture mechanic approaches has been carried out.In this paper,fracture behavior in large deformation of a high density polyethylene(HDPE)materials was investigated through experimental impact testing on single edge notched specimen(SENB)and by using theoretical and analytical fracture criteria concepts.Moreover,a review of the main fracture criteria is given in order to characterize the toughness of this polymer in the both cases(static and dynamic).The fractured specimens obtained from the Charpy impact test were characterized with respect to their fracture surfaces.Characteristic zones of the fracture surface can be assigned to different stages and mechanisms of the fracture process.Finally,for a better understanding of fracture and damage mechanisms and to provide the best estimation of fracture toughness in impact,an experimental approach based on microscopic observations(SEM)was used.
