钛合金双态组织高温拉伸行为的晶体塑性有限元研究

创建一个包含多变体结构特征的双态组织几何模型,提出一种变形协调性的评估方法,采用以率相关滑移为主的晶体塑性有限元本构关系,研究了具有不同组织特征的Ti-6Al-4V合金双态组织的高温拉伸行为。结果表明：在多晶变形过程中,α_p相承载了更多的应变;在变形后的样品中,出现了大致对称分布于拉伸方向两侧的高应变交叉条带;存在于α_p与β_T之间的包围结构特征,可加剧局域应变分配的差异;随着α_p相体积分数的升高应变量降低,整体应变协调性先较快降低而后平稳;随着α_s片层厚度的增加高应变条带特征弱化,整体应变协调系数升高;含双变体α_s片层团簇结构的β_T组织,其应变协调性低于含单变体和三变体的组织。     

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．     

明渠断面流速与边壁切应力相关的试验研究

根据Ｐｒａｎｄｔｌ理论关于对数流速分布的假定,利用间接测量法测量了相同流量不同水深情况下明渠底部的切应力分布．结果显示,在明渠边壁糙率突然减少的两边流速分布和边壁切应力均有最大值．根据作者的试验结果,给出了槽底平均切应力τ０与明渠流弗汝德数Ｆｒ的相关关系,可供参考．     

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.     

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.     

Impact of ZnO gate interfacial layer on piezoelectric response of AlGaN/GaN C-HEMT based ring gate capacitor

We report on a piezoelectric response investigation of AlGaN/GaN circular high electron mobility transistor (C-HEMT) based ring gate capacitor as a new stress sensor device to be potentially applied for dynamic high-pressure sensing. A ring gate capacitor of C-HEMT with an additional ZnO gate interfacial layer was used to measure the changes in the piezoelectric charge induced directly by the variation of piezoelectric polarization of both gate piezoelectric layers (AlGaN, ZnO) for harmonic loading at different excitation frequences. Our experimental results show that about 10 nm thick piezoelectric ZnO layer grown on ring gate/AlGaN interface of C-HEMT can yield almost a 60% increase in the piezoelectric detection sensitivity of the device due to its higher piezoelectric coefficient. A three-dimensional CoventorWare simulation is carried out to confirm the increase in the measured piezoelectric response of ZnO based ring gate capacitor of C-HEMT.