Analysis of crack tip plasticity for microstructurally small cracks using crystal plasticity theory

Crack tip plastic zone sizes and crack tip opening displacements (CTOD) for stationary microstructurally small cracks are calculated using the finite element method. To simulate the plastic deformation occurring at the crack tip, a two-dimensional small strain constitutive relationship from single crystal plasticity theory is implemented in the finite element code ANSYS as a user-defined plasticity subroutine. Small cracks are modeled in both single grains and multiple grains, and different crystallographic conditions are considered. The computed plastic zone sizes and CTOD are compared with those found using conventional isotropic plasticity theory, and significant differences are observed.     

Surface modification of starch nanocrystals through ring‐opening polymerization of ε‐caprolactone and investigation of their microstructures

Bionanoparticles of starch obtained by submitting native potato starch granules to acid hydrolysis conditions. The resulted starch nanoparticles were used as core or macro initiator for polymerization of ε‐caprolactone (CL). Starch nanoparticle‐g‐polycaprolactone was synthesized through ring‐opening polymerization (ROP) of CL in the presence of Sn(Oct)₂ as initiator. The detailed microstructure of the resulted copolymer was characterized with NMR spectroscopy. Thermal characteristic of the copolymer was investigated using DSC and TGA. By introducing PCL, the range of melting temperature for starch was increased and degradation of copolymer occurred in a broader region. X‐ray diffraction and TEM micrographs confirmed that there was no alteration of starch crystalline structure and morphology of nanoparticles, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Kinetics study of Ti[O(CH2)4OCHCH2]4 initiated ring‐opening polymerization of ε‐caprolactone by differential scanning calorimetry

Chemical shrinkage was used for the in situ measurement of the progressing chemical stabilization reactions and the influence of ozone during the stabilization of polyacrylonitrile. A method for evaluating the activation energy through the sensitivity temperature is presented. The calculated results show that the activation energies were 161.57 kJ/mol in air and 181.23 kJ/mol in ozone-enriched air. Therefore, the chemical reactions were postponed during stabilization in ozone-enriched air. Ozone seemed to act in three ways: first, ozone promoted the formation of the serious skin–core structure. Second, ozone accelerated the chemical reactions and shortened the stabilization time at lower heating rates. Third, ozone postponed the chemical reactions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

重庆嘉华大坪隧道变断面衬砌台车设计

本文介绍变断面衬砌台车设计,用以解决重庆嘉华大坪隧道变断面大跨度衬砌施工。     

改进的BP神经网络在大坝安全监控中的应用

针对经典BP神经网络运行中存在的缺陷，提出了改进的BP神经网络，不仅解决了经典BP网络易陷入局部最小的弊端，而且应用的0.618分割选取法能使网络快速找到较优隐含层节点数，初始权值的自相关修正进一步提高了网络的稳定性。实际应用证明，改进的BP神经网络有效提高了网络质量，适合大型网络的构建与训练。     

连续箱梁桥中跨合龙段劲性骨架优化设计

结合某连续箱梁桥悬臂施工实践,对中跨合龙段劲性骨架设置和受力进行了分析,推导了劲性骨架设计的理论计算公式,并分析了劲性骨架刚度大小对桥梁整体结构的影响。     

Data requirements for neutron activation: Part I: Cross sections

Existing neutron cross section libraries such as EAF-2003 contain a large number of reactions. Of these only a small proportion are significant in the production of the nuclides that dominate activation quantities such as activity or γ-dose rate at various decay times. These reactions were identified in a recent extensive set of calculations on all the elements and reported in the ‘Activation Handbook’. These 1340 reactions are considered here and the set of reactions with no differential or integral data are listed and prioritised. A set of 339 reactions with very limited possibility of measurement are given; these require further study by theoretical calculations. A set of 100 reactions with either discrepant or no data, that might be measurable are listed and are recommended to be the subject of future experimental work.     

三峡水库安坪库岸段斜坡破坏机制及稳定性评价

基于斜坡的工程地质测绘和实验室分析,总结了研究地段区域滑坡规律,引入粘弹性基础板的弯曲破坏原理,对该地段斜坡破坏机制进行分析。从岩体本身的质量和岩体在地球内外营力作用下所表现的自稳性两方面考虑,采用两级模糊综合评判理论对测区进行斜坡稳定性工程地质单元划分,并利用刚体平衡理论验证模糊评判结果。     

东津水电站引水隧洞进口不良地质段施工

东津水电站引水隧洞进口段工程地质条件恶劣，施工干扰大，渡汛工期紧。采用喷锚支护洞脸边坡，洞口明挖３ｍ浇筑钢筋混凝土明拱和Ｌ形护坡墙；洞身段采用新奥法施工，先打通上导洞；进口４０ｍ分段开挖，分段衬砌；进水塔压板混凝土模板采用门字框架钢支撑；排除了施工干扰，防止了洞口滑塌，进口段塌方的恶性事故发生，保证了引水隧洞工程的顺利施工。     

具有厚大断面的大型球墨铸铁铸件的生产

首先通过电炉—LF精炼炉—VD精炼炉—包内球化的工艺路线获得了足够的优质铁液,然后通过选取合适的分型面、设置合理的浇注系统、设计专用的冷铁、安放足够大的保温冒口和上表面加大加工余量来去除夹渣等措施,成功生产了具有厚大断面的大型球墨铸铁铸件。