The influence of orientation on the creep properties of the nickel-base single crystal superalloy SRR99 was investigated at 760℃ and various levels of applied stress.It was found that the effect of anisotropy was str...The influence of orientation on the creep properties of the nickel-base single crystal superalloy SRR99 was investigated at 760℃ and various levels of applied stress.It was found that the effect of anisotropy was strikingly prominent at this temperature.Deformation mechanisms of single crystals with three principal orientations at 760℃/790 MPa were explained according to detailed observations of dislocation arrangements by means of transmission electron microscopy （TEM）.Liability to shearing γ＇ precipitates for [011] orientation and co-planar slip for [111] orientation resulted in poor creep strength and short stress rupture life.It was also found that the apparent primary creep strain could be measured when the applied stress was increased to 565 MPa.Modified power law equation was adopted and the concept of a threshold stress σ 0 which determines dislocation looping or shearing to be activated was then involved.Through detailed calculations,the threshold stress was obtained to further analyse the distribution of the applied stress and better rationalize the anisotropic creep behaviour in the stereographic triangle in combination with TEM observations.展开更多
为了提高建筑物变形监测中的预测精度,降低噪声对变形预测的影响,本文在局部均值分解(Local Mean Decomposition,LMD)方法的基础上,引入小波阈值去噪方法,提出一种新的LMD-小波阈值去噪方法。该方法实现信号去噪,步骤为:首先是通过LMD...为了提高建筑物变形监测中的预测精度,降低噪声对变形预测的影响,本文在局部均值分解(Local Mean Decomposition,LMD)方法的基础上,引入小波阈值去噪方法,提出一种新的LMD-小波阈值去噪方法。该方法实现信号去噪,步骤为:首先是通过LMD将信号分解为若干个乘积函数(Product Function,PF)以及余量,通过消除趋势波动分析方法计算H指数的方式得到PF分量中高频噪声分量与低频有用信号分量;其次是通过小波阈值去噪方法对高频分量进行进一步降噪,得到有用信息,并重构降噪后信号、低频分量以及余量得到降噪后信号;最后建立RBF神经网络模型对降噪后数据进行建模与预测。使用建筑物监测数据对本文提出方法进行验证,结果表明:本文方法较LMD方法、经验模态分解(Empirical Mode Decomposition,EMD)方法的降噪效果更好,降噪后数据预测精度更高,可在工程类监测项目中进一步应用。展开更多
The relationships between fatigue threshold △Kth and the initial yield .strength σ0 of normalized 1035 steel after various prestrain (at fist, second and third hardening stages respectively) were investigated throug...The relationships between fatigue threshold △Kth and the initial yield .strength σ0 of normalized 1035 steel after various prestrain (at fist, second and third hardening stages respectively) were investigated through the analysis of theσ-εcurves and transmission electron microscope (TEM). After prestraining at first or second hardening stage, there is a marked drop in the values of △Kth and σ0. This is in correspondence with the depinning of the solute atoms from the dislocation lines in the Cottrell atmosphere.At the third hardening stage of prestrain the fatigue threshold increases rapidly and △Kth is even 1.6 times as large as the original value. This is because at this stage no dislocation-cell free areas can be found and the refinement of the dislocation cells occurs with the increase in the prestrain level.展开更多
基金supported by "Hundreds of Talents Project"the National Basic Research Program (973 Program) of China under Grant No.2010CB631200 (2010CB631206)
文摘The influence of orientation on the creep properties of the nickel-base single crystal superalloy SRR99 was investigated at 760℃ and various levels of applied stress.It was found that the effect of anisotropy was strikingly prominent at this temperature.Deformation mechanisms of single crystals with three principal orientations at 760℃/790 MPa were explained according to detailed observations of dislocation arrangements by means of transmission electron microscopy （TEM）.Liability to shearing γ＇ precipitates for [011] orientation and co-planar slip for [111] orientation resulted in poor creep strength and short stress rupture life.It was also found that the apparent primary creep strain could be measured when the applied stress was increased to 565 MPa.Modified power law equation was adopted and the concept of a threshold stress σ 0 which determines dislocation looping or shearing to be activated was then involved.Through detailed calculations,the threshold stress was obtained to further analyse the distribution of the applied stress and better rationalize the anisotropic creep behaviour in the stereographic triangle in combination with TEM observations.
文摘The relationships between fatigue threshold △Kth and the initial yield .strength σ0 of normalized 1035 steel after various prestrain (at fist, second and third hardening stages respectively) were investigated through the analysis of theσ-εcurves and transmission electron microscope (TEM). After prestraining at first or second hardening stage, there is a marked drop in the values of △Kth and σ0. This is in correspondence with the depinning of the solute atoms from the dislocation lines in the Cottrell atmosphere.At the third hardening stage of prestrain the fatigue threshold increases rapidly and △Kth is even 1.6 times as large as the original value. This is because at this stage no dislocation-cell free areas can be found and the refinement of the dislocation cells occurs with the increase in the prestrain level.
