电站锅炉再热器带"三通"集箱静压分布的数值模拟及受热面热偏差计算

为解决再热器超温爆管问题,采用标准K-ε方程的湍流模型进行数值模拟,得到了有支管和无支管的再热器带"三通"集箱内的速度矢量和静压分布.在此基础上编写了较为通用的电站锅炉受热面热偏差计算程序,并应用该程序计算了2个不同结构再热器的屏间热偏差.结果表明:为了减少受热面因热偏差过大而发生超温爆管的情况,应在设计时尽量使管屏(子)避开集箱"三通"涡流区,或者将集箱"三通"避开烟温高峰区布置.此热偏差计算程序可以用于不同容量机组的多种结构和类型的受热面热偏差计算,适用于集箱轴向、径向引入引出的布置方式,可用于大型电站锅炉过热器及再热器的优化设计.     

碳纤维增强聚合物复合材料车身T型接头静态性能与失效机制

通过解析预测、有限元分析和试验手段对热塑性碳纤维增强聚合物复合材料（CFRP）T型接头的面外弯曲和弯扭耦合力学性能进行研究,分析了T型接头的结构失效形式与力-位移曲线的关系,并将解析模型、有限元仿真与试验结果进行对比。在弯曲刚度方面,解析模型、有限元分析结果相对试验结果的刚度误差分别为4.7%和0.5%。在弯扭耦合刚度方面,解析模型及有限元仿真的结果相对试验结果的弯扭耦合刚度误差分别为6.9%和9.6%。试验结果表明,CFRP层合板的渐进失效引起T型接头弯曲刚度的衰减,当力达到2 047 N时接头开始发生失效,失效形式包括纤维的断裂、缠绕、树脂的压碎及纤维和树脂的分层等。      

T形接头三丝高速焊接温度场的分析

根据焊接过程中的电弧形貌和热源的叠加原理推导出了三丝焊接的高斯热源计算公式,建立了合适的有限元数学模型,在充分考虑对流、辐射、熔池蒸发、液体流动以及相变潜热等边界条件的情况下,对T形接头的三丝高速焊接过程中温度场的瞬态变化进行了计算和分析.最后提取计算结果与试验结果进行对照.结果表明,计算所得的焊缝截面形状与实际试验相...     

Numerical analysis of the axial strength of CHS T-joints reinforced with external stiffeners

This study reinforced circular hollow section (CHS) T-joints with external stiffeners and analyzed the axial strength of both the unreinforced and reinforced T-joints. The SHELL181 element in ANSYS was used to establish FE models of the T-joints. A comparison between the experimental results indicated that the numerical method could be used to compute the strength for the unreinforced and reinforced CHS T-joints. To further investigate the reinforcement effect of the external stiffeners, a numerical parametric study was conducted. The study then evaluated the variations in strength of differently sized stiffeners. It was found that the joint strength increased significantly as the size of the stiffener increased. The reinforcement effect is more dependent on the stiffener length than on the stiffener height, but it is reasonable to adopt stiffeners with equal lengths and heights since this shape is commonly-used in engineering projects.     

Defects and tensile properties of 6013 aluminum alloy T-joints by friction stir welding

In this paper, 6013-T4 T-joints were successfully fabricated with different welding parameters by friction stir welding in two different combination modes of skins and stringers. The distribution features and formation mechanisms of defects in T-joints were observed and analyzed. The effect of defects and welding parameters on tensile properties of T-joints was investigated. The result shows that the T-joint without tunnel defect only can be obtained with the traverse speed of 100 mm/min in this experiment, and the welding parameters influence the features and sizes of kissing bond defects. The fracture of T-joints along the shin is attributed to the kissing bond defect and the tunnel defect is the main factor affecting the tensile properties along the stringer.     

Hysteretic behaviour of tubular T-joints reinforced with doubler plates after fire exposure

The hysteretic behaviour of tubular T-joints reinforced with doubler plates was experimentally and numerically investigated in this study. Two specimens were tested to failure under cyclic axial load at the brace end, one under ambient temperature and the other after fire exposure. Specimens with identical material and geometric properties were compared. The failure modes of the specimens were cracking along the weld toe at the intersection of the plate and brace. The results indicated that the hysteretic behaviour and energy dissipation of the joint after fire exposure were smaller than those at ambient temperature. The finite element package ABAQUS was then used to simulate the joint specimens. In a comparison of the hysteretic curve, skeleton curve, energy dissipation and failure location, the simulation and experimental results were in good agreement. The finite element method was subsequently used to carry out a parametric study. Parameters τ and ε had little influence on the post-fire hysteretic behaviour of the joint, but joints with a large γ or small α, β, or ξ values had a low capacity for hysteretic behaviour after fire exposure.     

薄板T型接头TIG焊温度场的研究

运用大型有限元分析软件ABAQUS,建立了适当的模型对薄板T型TIG焊接接头的温度场进行了数值模拟。模拟中考虑了随温度变化的材料性能,考虑了模型的对流和辐射换热以及潜热的影响。采用热电偶测量了典型位置的温度场以验证模拟结果,结果表明,建立的模型能较准确地模拟薄板TIG焊的温度场。     

A fracture mechanics approach to estimate the fatigue endurance of welded t-joints including residual stress effects

Residual stresses and weld defects play a major role in the fatigue behaviour of welded structures, so these effects need to be accounted for in a theoretical analysis. A simplified engineering procedure based on linear‐elastic fracture mechanics is applied to estimate the fatigue behaviour, particularly the limit of endurance. Local geometrical irregularities and pre‐existing flaws, which are typical for this kind of weld, are covered by an overall notch intensity factor instead of a specific stress intensity factor, so the initial flaw size is not needed explicitly in the analysis. The effect of residual stresses can be easily included. The cut‐compliance method was applied to measure the residual stress distribution on the cross‐section of the weld. A welded T‐joint was used as a benchmark. Unexpectedly, compressive residual stresses were found to prevail in the root region. According to the analysis, they contribute to the endurance limit of the considered joint by about 50%. This result was confirmed by fatigue tests where a significant decrease in the fatigue strength after a post‐weld stress relieving heat treatment was observed.     

焊接顺序对T型接头角焊缝残余变形的影响

为研究焊接顺序对T型接头角焊缝残余变形的影响,对平对接接头的焊接过程进行数值模拟和焊接实验,验证焊接模拟的合理性;建立T型接头双面角焊缝的有限元模型,采用生死单元技术和热结构耦合的方法对T型接头焊接过程中的温度场和应力场进行数值模拟,分析4种焊接顺序对其残余变形的影响。结果表明,模拟结果与残余应力测试结果吻合良好,说明焊接模拟过程合理有效。T型接头在焊后发生了挠曲变形,焊接顺序2的残余变形最小,变形量为0.61 mm,采用从两侧向中间的焊接顺序能够减小T型接头的残余变形。     

Numerical analysis and experiment of composite sandwich T-joints subjected to pulling load

This paper presents an investigation into the failure mechanism and alternative design of composite sandwich T-joints subjected to pulling load. Based on a conventional design of sandwich T-joint as the baseline, numerical modeling and analysis using finite element (FE) method was performed to assess the strength against pulling load. The effect of a cutout in the web panel near the joint has been considered. To validate the models, sandwich T-joint samples were manufactured and tested. Detailed FE analysis and inspection of the experimental results indicated that the failure was mainly due to the excessive stress in the adhesive between the cleat flange and the T-joint base panel. The manufacture defects, which reduced the strength of the T-joint test samples had also been investigated. This has been further demonstrated by experimental results of repaired T-joint samples. A very good correlation between the test data and FE results were obtained. An unconventional design of T-joint for simpler manufacture process was proposed. Based on the design, T-joint samples were modeled, manufactured and tested to demonstrate the manufacture process and evaluate the improved strength.