The low-cycle fatigue （LCF） behavior of a nickel-based single crystal superalloy with [001] orientation was studied at an intermediate temperature of T0℃ and a higher temperature of To ＋ 250℃ under a constant low...The low-cycle fatigue （LCF） behavior of a nickel-based single crystal superalloy with [001] orientation was studied at an intermediate temperature of T0℃ and a higher temperature of To ＋ 250℃ under a constant low strain rate of 10^-3 s^-1 in ambient atmosphere. The superalloy exhibited cyclic tension-compression asymmetry which is dependent on the temperature and applied strain amplitude. Analysis on the fracture surfaces showed that the surface and subsurface casting micropores were the major crack initiation sites. Interior Ta-rich carbides were frequently observed in all specimens. Two distinct types of fracture were suggested by fractogaphy. One type was characterized by Mode-I cracking with a microscopically rough surface at To ＋ 250℃. Whereas the other type at lower temperature T0℃ favored either one or several of the octahedral {111} planes, in contrast to the normal Mode-I growth mode typically observed at low loading frequencies （several Hz）. The failure mechanisms for two cracking modes are shearing of γ＇ precipitates together with the matrix at T0℃ and cracking confined in the matrix and the γ/γ＇interface at To - 250℃.展开更多
In this paper fretting fatigue crack behavior in 1045 steel is studied by in-situ observation and finite element analysis.in-situ fretting fatigue experiments are conducted to capture real-time fretting fatigue crack ...In this paper fretting fatigue crack behavior in 1045 steel is studied by in-situ observation and finite element analysis.in-situ fretting fatigue experiments are conducted to capture real-time fretting fatigue crack formation and propagation process.The fretting fatigue tests under different load conditions are carried out,then the lifetime and fracture surface are obtained.The crack propagation rates under different loading conditions are measured by in-situ observations.With in-situ observation,crack initiation location and direction are analyzed.Finite element model is used to calculate J-integral which then is applied to fitting with experimental crack growth rate,and establishing crack growth rate model.From fitted S-N curve,it turns out that smaller load ratio leads to higher lifetime.Crack initiates slightly below the point equivalent to line contact of the contact surface in different test conditions,and crack direction shows no obvious relationship with load parameters.The established crack growth rate model well agrees with the test results.展开更多
At elevated temperature, creep failures of polycrystalline metals after long-term constant loading are often caused by the nucleation, growth and coalescence of creep voids on the grain boundaries. Void h＇action is a...At elevated temperature, creep failures of polycrystalline metals after long-term constant loading are often caused by the nucleation, growth and coalescence of creep voids on the grain boundaries. Void h＇action is an important parameter for the evaluation of creep damage level of structural materials operating at high temperature. In this paper, a 2-D numerical simulation method was developed for analyzing the void fraction evolution during the process of creep, based on some hypothesis from experiments. The model was implemented and then was used to predict the evolution of void fraction in the 2.25Cr-1Mo steel of uniaxial creep experiment at 570 ℃, in which the simulation results showed good agreement with the experimental results.展开更多
基金supported by the National Natural Science Foundation of China(No.50371042).
文摘The low-cycle fatigue （LCF） behavior of a nickel-based single crystal superalloy with [001] orientation was studied at an intermediate temperature of T0℃ and a higher temperature of To ＋ 250℃ under a constant low strain rate of 10^-3 s^-1 in ambient atmosphere. The superalloy exhibited cyclic tension-compression asymmetry which is dependent on the temperature and applied strain amplitude. Analysis on the fracture surfaces showed that the surface and subsurface casting micropores were the major crack initiation sites. Interior Ta-rich carbides were frequently observed in all specimens. Two distinct types of fracture were suggested by fractogaphy. One type was characterized by Mode-I cracking with a microscopically rough surface at To ＋ 250℃. Whereas the other type at lower temperature T0℃ favored either one or several of the octahedral {111} planes, in contrast to the normal Mode-I growth mode typically observed at low loading frequencies （several Hz）. The failure mechanisms for two cracking modes are shearing of γ＇ precipitates together with the matrix at T0℃ and cracking confined in the matrix and the γ/γ＇interface at To - 250℃.
基金financially supported by the National Natural Science Foundation of China(Nos.91860101,11632010,11902370 and 11572171)National Major Science and Technology Projects of China(No.2017-VI-0003-0073)。
文摘In this paper fretting fatigue crack behavior in 1045 steel is studied by in-situ observation and finite element analysis.in-situ fretting fatigue experiments are conducted to capture real-time fretting fatigue crack formation and propagation process.The fretting fatigue tests under different load conditions are carried out,then the lifetime and fracture surface are obtained.The crack propagation rates under different loading conditions are measured by in-situ observations.With in-situ observation,crack initiation location and direction are analyzed.Finite element model is used to calculate J-integral which then is applied to fitting with experimental crack growth rate,and establishing crack growth rate model.From fitted S-N curve,it turns out that smaller load ratio leads to higher lifetime.Crack initiates slightly below the point equivalent to line contact of the contact surface in different test conditions,and crack direction shows no obvious relationship with load parameters.The established crack growth rate model well agrees with the test results.
基金supported by National Natural Science Foundation of China(No.51071094) and the IHI-Tsinghua Joint Research Center
文摘At elevated temperature, creep failures of polycrystalline metals after long-term constant loading are often caused by the nucleation, growth and coalescence of creep voids on the grain boundaries. Void h＇action is an important parameter for the evaluation of creep damage level of structural materials operating at high temperature. In this paper, a 2-D numerical simulation method was developed for analyzing the void fraction evolution during the process of creep, based on some hypothesis from experiments. The model was implemented and then was used to predict the evolution of void fraction in the 2.25Cr-1Mo steel of uniaxial creep experiment at 570 ℃, in which the simulation results showed good agreement with the experimental results.
