Formation of nanometer coherent structures during spinodal decomposition and ordering coexistence phase transformation in Fe-24Al alloys

The nanometer coherent structure evolution of spinodal decomposition and ordering coexistence phase transformation in Fe-24Al alloys is investigated by the microscopic phase field kinetic model. The results show that the concentration and long-range order parameters all continuously change towards to their equilibrium values during phase transformation. With the increase of elastic interaction energy, the anisotropy along [01] or [10] elastic soft direction is more obvious and the time reaching equilibrium state is also shortened. According to the results, the formation of nanometer coherent structures during phase transformation is composed of the initial decreasing stage of order degree stage, the incubation stage, the continuous increasing stage of concentration order parameter and long-range order parameter, and the later stable stage. The spinodal decomposition and ordering is interaction; the initial ordering stage is a necessary condition of the coexistence phase transformation. The nanometer coherent structures are not found to grow during the whole phase transformation. The simulation results are in accordance with the results in experiment obtained by the aging treatment in Fe-24Al alloys.     

基于真实铁路振动环境的车载印制电路板可靠性分析

以我国西北地区铁路运输环境真实振动数据为基础,利用不同频率、幅值与相位的谐波叠加方法生成随机振动信号。采用理论分析方法,建立谐波相位影响随机振动的功率谱密度、峭度和偏离度的数学模型,进而根据该模型,编制Matlab程序对真实非高斯振动环境的时域信号进行数字模拟。利用ANSYS软件建立车载印制电路板（PCB ）的3D有限元模型,通过静力分析、模态分析验证有限元模型的正确性、合理性,同时根据结果对比,对有限元模型进行修正,保证获得较为准确的PCB有限元模型。最后,根据非高斯随机振动模拟结果和车载 PCB有限元模型,分析PCB的响应,根据材料的S‐N曲线、雨流计数法和Palmgren‐Miner准则,通过FE‐SAFE软件预测车载PCB在真实非高斯随机振动条件下的疲劳寿命。     

不同数值积分方式对海洋结构物疲劳裂纹扩展模拟结果的影响

海洋结构物的疲劳寿命预报是当前的研究热点,文章根据第二作者率领的课题组提出的海洋结构物疲劳寿命预报统一方法比较了疲劳裂纹扩展模拟的三种数值积分方法：逐周数值积分法、△N积分法和△a积分法,并分析了每种方法的适用条件。随后,以中心表面裂纹承受单向交变拉伸载荷的平板为例,分别运用三种方法计算了裂纹扩展寿命和最终裂纹尺寸。同时,研究了△N和△a取值不同对结果的影响。最后,综合考虑计算耗时和计算结果精度,给出了△N积分法和△a积分法的建议值,即△N/N≤1.0%,△a≤0.1 mm。     

基于临界面理论的焊接结构多轴疲劳寿命评估方法

目前多轴疲劳理论难以用于实际工程中焊接结构的疲劳寿命评估.文章将等效热点应力法与双参数临界面理论相结合,提出了一种能够应用于复杂焊接结构的多轴疲劳寿命评估方法.分别阐述了双参数临界面法的损伤参数、控制方程以及等效热点应力的定义,给出了焊接结构多轴疲劳寿命的评估过程,并应用有限元数值模拟验证了该方法的可行性.     

Fabrication and Interfacial Structure of Ni-YSZ-LSM Porous Scaffold for Solid Oxide Fuel Cells

A novel process route using tape casting and stacking for fabricating porous scaffold of solid oxide fuel cells (SOFC) was demonstrated. The linear shrinkages of anode (Ni-YSZ, YSZ stands for 3% Y_2O_3(mole fraction) stabilized ZrO_2) and cathode (LSM-YSZ, LSM stands for La_(0.8)Sr_(0.2)Mn0_3) were optimized to be uniform with that of electrolyte during sintering, by controlling the content of pore former. The micromorphology and interface microstructure of the cross-section of the porous scaffold were observed by optical microscope and scanning electron microscope, respectively. The element distribution and phase composition were analyzed by energy dispersive spectrometer and X-ray diffraction, respectively. The results showed that the porous scaffold with regular pore shape and high specific surface area was obtained after sintering at 1 350℃. The fabricated porous scaffold had defect free interfacial structures due to the uniform shrinkage of anode, cathode and electrolyte layers. In addition, it was shown that diffusions of Zr, Ni and La caused a progressive boundary between YSZ, Ni-YSZ and LSM-YSZ layers. The interface between anode and electrolyte (Ni-YSZ/YSZ) was mainly composed of Ni, YSZ and a small amount of NiO, and the interface between cathode and electrolyte (LSM-YSZ/YSZ) was mainly composed of YSZ, LSM and a small amount of La_2Zr_2O_7.     

冲击荷载下钢筋混凝土结构动力性能研究进展

钢筋混凝土结构广泛运用于结构中的承重结构,在役期间可能遭受意外撞击。钢筋混凝土结构在冲击荷载下的动力性能与静载下的力学性能有很大不同。该文在国内外相关文献研究基础上,总结了近三十年来冲击荷载下钢筋混凝土结构在试验研究、理论研究和有限元数值分析方面取得的研究进展,并指出了尚待进一步研究的内容。     

基于信噪峭度比的水下目标动态谱增强算法研究

根据非高斯噪声环境中水下运动目标辐射线谱信号的四阶累积量对角切片特征,定义了信噪峭度比的概念,导出了其理论计算公式.理论分析表明,在一定条件下,信噪峭度比总是大于用自相关函数定义的信噪比,提出了基于信噪峭度比分析法的水下运动目标辐射线谱信号的四阶累积量对角切片谱特征增强新算法.用水下某目标辐射线谱的实测数据,对该算法的性能进行了仿真研究.结果表明,该算法具有良好的抑制非高斯噪声能力,且不必对噪声分布作高斯性假设.因此,该算法具有重要的工程应用价值.     

深圳地铁地震反应分析

根据深圳地铁抗震设计需要,对深圳地铁的3种典型断面,采用释放荷载方法进行了平面有限元静力计算,确定初始应力场,采用子空间迭代法进行了振型计算,确定合理的积分步长。在此基础上,运用Newmark隐式时间积分法对地铁的3种典型断面进行了地震反应分析,确定了在地震荷载作用下衬砌结构的薄弱部位及其相互的位移和应力,计算结果为深圳地铁的抗震设计提供了依据。     

Vibration-assisted decommissioning of a slip joint: Application to an offshore wind turbine

An alternative option to the traditional grouted joint for wind turbines is a direct steel-to-steel connection, also known as slip joint. In a recently published work, a proof of concept of a vibration-assisted installation and decommissioning technique of a slip joint was illustrated. Leveraging on the obtained results, the current study shows for the first time a decommissioning campaign carried out using a vibration-assisted technique applied on a prototype hydraulic wind turbine tower located in the North Sea, and connected to the monopile through a slip joint. The key aspect of the dismounting procedure is a priori knowledge of the resonance frequency clusters corresponding to the slip joint’s cross-sectional modes. Therefore, field hammer tests and experimental modal analysis were carried out inside the wind turbine tower. The identified frequencies and mode shapes were then compared with numerical ones estimated by a finite element model of the investigated structure. The comparison showed that a set of frequency clusters can be directly selected from a detailed numerical model. The preparatory work of the slip joint decommissioning was then executed by installing electric shaker devices, based on the dynamic identification results, and hydraulic jacks mounted inside the wind turbine tower. A first decommissioning trial was carried out in May 2019, while the final decommissioning was performed in August 2019. After analysing the measurements of the hydraulic pressures, displacements and excitation frequencies during the decommissioning campaigns, the results showed that it is possible to disconnect the slip joint if, in combination to a vertical static force, one of the identified cross-sectional mode shapes is excited. The vibration-assisted decommissioning proved to be a successful technique to dismount the connection in a controlled and straightforward manner.     

Radio Fiber Fine Structure During the Solar Flare on July 14，2000

Introduction　　AmongthefinestructuressuperposedonthecontinuumemissionofsolartypeIVradiobursts,oneofthemostfrequentlyobservedisfiber .Fibers,orintermediatedriftbursts ,werefirstobservedinsolartypeIVcontinuabyYoungetalin 196 1[1] .Thefiberstructuresinmetri…