Stress dependence of the creep behaviors and mechanisms of a third-generation Ni-based single crystal superalloy

Elevated temperature creep behaviors at 1100℃ over a wide stress regime of 120–174 MPa of a thirdgeneration Ni-based single crystal superalloy were studied. With a reduced stress from 174 to 120 MPa,the creep life increased by a factor of 10.5, from 87 h to 907 h, presenting a strong stress dependence.A splitting phenomenon of the close-(about 100 nm) and sparse-(above 120 nm) spaced dislocation networks became more obvious with increasing stress. Simultaneously, a_0010 superdislocations with low mobilities were frequently observed under a lower stress to pass through γ'precipitates by a combined slip and climb of two a_0110 superpartials or pure climb. However, a_0110 superdislocations with higher mobility were widely found under a higher stress, which directly sheared into γ'precipitates.Based on the calculated critical resolved shear stresses for various creep mechanisms, the favorable creep mechanism was systematically analyzed. Furthermore, combined with the microstructural evolutions during different creep stages, the dominant creep mechanism changed from the dislocation climbing to Orowan looping and precipitates shearing under a stress regime of 137–174 MPa, while the dislocation climbing mechanism was operative throughout the whole creep stage under a stress of 120 MPa, resulting a superior creep performance.     

三峡水电站坝内埋管非线性有限元分析

结合三峡工程实际,对坝内埋管结构进行了非线性有限元分析,着重研究了不同管顶混凝土厚度和配筋对管道结构应力和强度的影响．计算结果表明,增大管顶混凝土厚度,可以明显提高坝内埋管的抗裂安全,确保混凝土大坝的整体稳定性,但是配筋多少对管周混凝土的抗裂能力影响较小．     

等值应力法及其在架空电线力学计算中的应用

在解析法的基础上,利用应力与温度、比载和挡距的函数关系,求解架空送电线路导线力学计算的有效临界档距和判断控制气象条件,对其原理、应用作了分析介绍．这种方法简明、直观,在架空线路设计中有实用价值．     

工艺因素对过热器/再热器异种钢焊接接头残余应力的影响

工况下运行的异种钢接头易沿焊缝界面开裂而发生早期失效．本文对小直径钢１０２／Ｉｎｃｏｎｅｌ８２／ＴＰ３４７Ｈ异种钢管、不同坡口角度与不同热处理制度下接头中的焊接残余应力进行了实测,结果表明对适用于现场焊接且可延长接头寿命的改进型坡口并不会增大焊接应力,提出在工况温度下接头中的焊接应力并不能很快衰减、焊后热处理可显著地降低该种异种钢接头中焊接应力的观点．     

Finite element analysis of creep fracture initiation in a model superalloy material

Detailed finite element analyses were performed for a single edge-cracked specimen geometry under both plane stress and plane strain constraint for a superalloy material that obeys a power-law creep relationship. The objectives of these analyses were to elucidate the stationary creep crack-tip fields and to provide guidance for the experimental measurement of crack-tip deformations. New results demonstrate that, for both plane stress and plane strain, the angular variations in the creep strain fields do not agree with HRR-type predictions, although the radial variations are in agreement with HRR-type creep strain field predictions in a zone very near the crack tip. Thus, the use of experimental measurement of surface displacement and/or strain data for the location of HRR-type fields may not be possible, unless modifications to the existing HRR-type theory are made. It is also noted that the size of the stress-based HRR-dominance zone is only a fraction of the creep zone size in plane stress, and is very small (especially along =0°) compared to the creep zone size in plane strain. Furthermore, the dominance of the singular strain fields are at least two orders of magnitude smaller than the corresponding stress dominance zones. As such, unless the microstructural features of the material are smaller than the dimensions of the dominance zones, the basis for using stress or strain-based fracture parameters derived from the HRR-type fields for prediction of creep fracture initiation is unclear.     

Model-based Predictive Control for Spatially-distributed Systems Using Dimensional Reduction Models

In this paper, a low-dimensional multiple-input and multiple-output (MIMO) model predictive control (MPC) configuration is presented for partial differential equation (PDE) unknown spatially-distributed systems (SDSs). First, the dimension reduction with principal component analysis (PCA) is used to transform the high-dimensional spatio-temporal data into a low-dimensional time domain. The MPC strategy is proposed based on the online correction low-dimensional models, where the state of the system at a previous time is used to correct the output of low-dimensional models. Sufficient conditions for closed-loop stability are presented and proven. Simulations demonstrate the accuracy and efficiency of the proposed methodologies.     

人脸遮挡区域检测与重建

提出一种基于模糊主分量分析技术(FPCA)的人脸遮挡检测与去除方法.首先,有遮挡人脸被投影到特征脸空间并通过特征脸的线性组合得到一个重建人脸.计算重建图与原图的差图像,加权滤波后并归一化作为被遮挡的概率,以此概率为权重由原图和重建图合成新的人脸.在后续迭代中,根据遮挡概率使用模糊主分量分析进行分析重建,并使用累积误差进行遮挡检测.实验结果表明,算法可精确定位人脸遮挡区域,得到平滑自然的重建人脸图像,优于经典的迭代PCA方法.     

基于二维复判别分析的人脸识别研究

为了提高人脸正确识别率和效率,在行列方向的二维线性判别分析((2D)2LDA)基础之上,提出了一种二维复判别分析(2DCCDA)的人脸识别方法.该方法通过(2D)2LDA并行提取到的行和列特征矩阵,利用复二维鉴别式分析(C2DLDA)将行和列特征融合成复数特征矩阵,从复数特征矩阵中提取出最具分类能力的系数组成特征向量.相比较二维线性判别分析(2DLDA)和(2D)2LDA方法,2DCCDA需要更少的特征系数来表征一幅图像,并且正确识别率也相应提高.     

Perceived stress,sensation seeking,and college students’ abuse of the Internet

College students (n = 140) were examined to test whether sensation seeking and perceived stress would predict abuse of the Internet. Previous studies have found that disinhibition, boredom susceptibility, and total sensation seeking scores were related to Internet abuse ( 9 and 30). Because stress has been documented to have a negative effect on students ( Pierceall & Keim, 2007), and may be linked to Internet use ( Lavoie & Pychyl, 2001), it was tested as a possible predictor of Internet abuse. This study also analyzed abuse of the Internet for sexual purposes, because sexuality is prevalent online, and college students are in an age of sexual exploration. Results of stepwise regression analyses revealed that disinhibition and total perceived stress were predictive of Internet abuse for sexual purposes, and perceived hopelessness and boredom susceptibility were predictive of Internet abuse for non-sexual purposes. Implications for students and Internet abuse are discussed.