Experimental and numerical investigations of the compressive behavior of carbon fiber-reinforced polymer-strengthened tubular steel T-joints

A method for strengthening damaged tubular steel T-joints under axial compression by wrapping them with carbon fiber-reinforced polymer (CFRP) sheets was proposed and evaluated. The influence of the CFRP strengthening on the failure mode and load capacity of T-joints with different degrees of damage was investigated using experiments and finite element analyses. Five T-joints were physically tested: one bare joint to obtain the peak load and corresponding displacement (D_1m), two reinforced joints to provide a reference, and two pre-damaged then retrofitted joints to serve as the primary research objects. The ratio of the pre-loaded specimen chord displacement to the value of D_1m was considered to be the degree of damage of the two retrofitted joints, and was set to 0.80 and 1.20. The results demonstrate that the maximum capacity of the retrofitted specimen was increased by 0.83%–15.06% over the corresponding unreinforced specimens. However, the capacity of the retrofitted specimen was 2.51%–22.77% lesser compared with that of the directly reinforced specimens. Next, 111 numerical analysis models (0.63≤b≤0.76, 9.70≤g≤16.92) were established to parametrically evaluate the effects of different geometric and strengthening parameters on the load capacity of strengthened tubular T-joints under different degrees of damage. The numerical analysis results revealed that the development of equivalent plastic strain at the selected measuring points was moderated by strengthening with CFRP wrapping, and indicated the optimal CFRP strengthening thickness and wrapping orientation according to tubular T-joint parameters. Finally, reasonable equations for calculating the load capacity of CFRP-strengthened joints were proposed and demonstrated to provide accurate results. The findings of this study can be used to inform improved CFRP strengthening of damaged tubular steel structures.     

The stiffness of laser stake welded T-joints in web-core sandwich structures

The purpose of this paper is to describe experiments carried out on laser stake welded T-joints of web-core steel sandwich structures. A special test setup was developed to measure the shear-induced rotation at the T-joint. The ratio of the shear force to rotation angle gave the joint stiffness. This stiffness was measured for specimens with two different face-plate thicknesses. The influence of weld thickness, root gap and occurrence of contact were further investigated with finite element simulations. Finally, the shear stiffness of the sandwich structure transverse to the web plate direction was determined using the experimentally obtained average joint stiffness value. The validation of the shear stiffness was carried out by considering a beam in four-point bending. The agreement between calculated deflection and stress and experimental results was found to be good.     

窄问隙埋弧焊工艺在H型钢梁生产中的应用

以板厚为20mm的Q345-B钢材为对象,采用埋弧自动焊工艺,通过4组试件研究构件组装间隙和构件施焊时摆放倾角对T型接头熔深的影响。通过接头宏观金相观察和力学性能试验,得出结论：构件组装时预留合适的间隙,施焊时摆放较大的倾角均有利于增加接头的熔深值,且质量也可得到保障。     

Study on fire resistance of circular hollow section (CHS) T-joint stiffened with internal rings

This paper aims to study the fire resistant performance of circular hollow section (CHS) T-joint stiffened with internal rings under axial compression at elevated temperatures. Experimental study and finite element analysis are combined to carry out the investigation. Two full-scale tubular joints, one is un-stiffened and the other is stiffened with ring-stiffeners, are designed and tested. A constant axial loading is applied at brace end of the joints firstly, and then the joints are heated in accordance with ISO 834 standard heating curve uniformly in an electric heating furnace until failure. It is found that the internal rings enhance the fire resistant performance of CHS T-joint by decreasing the temperature of chord efficiently and prolonging the fire-resistant time. Sequentially, the corresponding finite element models of the two joints are built on basis of the experiments by employing sequentially coupled thermal-stress method. By comparing with the experimental data including temperatures of chord and brace and displacements of crown, saddle and brace end, the finite element models are verified to be accurate and reliable. And then numerical analysis is conducted to investigate the reinforcing efficiency of ring-stiffeners and impact of geometrical parameters (β and γ) on the fire resistant performance of the stiffened joints by adopting the verified modeling method. It is summarized that the failure mode converts with geometrical dimensions of ring-stiffener and geometrical parameters of tubular joint changing.     

2A70铝合金搅拌摩擦焊接头抗拉强度测定结果的不确定度评定

依照GB/T 2651—2008《焊接接头拉伸试验方法》对2A70铝合金搅拌摩擦焊T型接头的抗拉强度进行了测定,并对抗拉强度测定结果的不确定度进行了评定。结果表明:当置信度取95%,包含因子取2,该接头抗拉强度测定结果的扩展不确定度为14Mpa,相对扩展不确定度为3.8%;不确定报告可表示为R_m=(370±14)MPa,v=81,k=2。     

基于等效结构应力法的 T 型焊接接头剩余寿命分析

针对已服役结构的剩余寿命问题,利用美国 ASME 标准中的等效结构应力法,对含初始裂纹缺陷的 T 型接头进行剩余寿命评估,利用试验数据对等效应力法求解剩余寿命进行了验证,对比了不同初始缺陷尺寸对焊接接头剩余寿命的影响.同时,基于英国 BS７９１０ 标准中的剩余寿命计算方法,得到了一阶Paris 曲线及修正后的二阶 Paris 曲线下 T 型接头的疲劳剩余寿命,将 ２ 个标准所得结果进行对比.结果表明:含有初始裂纹对 T 型接头寿命结果影响很大;基于结构应力法求解疲劳寿命时,所得结果值接近试验结果及基于 BS７９１０ 标准中得到的结果,证明该方法具有高度准确性.     

震后火灾下内置单环加强T形圆管节点受火性能分析

为了分析火灾作用下考虑震损的内置单环加强T形相贯节点的抗火性能,开展了基于试验验证内置单环加强T形相贯节点计算模型的有限元分析。根据实际工程应用情况,考察参数支管与主管壁厚比、支管与主管的直径比、主管直径与两倍壁厚比及加强环厚度与主管壁厚比对节点抗火性能的影响,合理确定参数取值范围,利用Pushover分析法考虑地震引起的损伤,引入损伤变量,然后采用ANSYS中重启动分析方法,将地震引起的残余应力和残余变形全部传递到节点的抗火性能分析中,对不同损伤变量及不同参数下单环加强T形相贯节点的临界温度、耐火性能和失效机理进行分析。结果表明：损伤变量对内置单环加强T形圆管节点的抗火性能影响较大,节点临界温度随损伤变量的增大而大幅减小;支管与主管壁厚比对内置单环加强T形圆管节点的抗火性能影响效果不明显;随着支管与主管的直径比和加强环厚度与主管壁厚比的增大,内置单环加强T形圆管节点的临界温度呈下降趋势;随着主管直径与两倍壁厚比的增大,内置单环加强T形圆管节点的临界温度有较明显的上升趋势。     

T型接头TOFD检测时缺陷深度的定位计算与评判

讨论了在T型接头TOFD检测时如何建立模拟等腰三角形,以适应仪器内置的深度定位计算程序。介绍了显示深度与实际深度的修正计算方法,并通过计算显示深度测量值与计算值的误差,验证了上述计算方法的准确性。最后,通过对T型接头试块检测结果的分析,探讨了T型接头翼板未熔合、腹板未熔合及角焊缝内缺陷的评判规律。     

基于多点柔性支撑的钛合金激光焊接变形控制

钛合金带筋壁板类T形结构常见于航空制造领域,其激光焊接工艺已经比较成熟. 但是即便在激光高速焊接过程热输入已经很低,仍然会存在一定的焊后角变形. 由于航空制造的高精度要求,需要施加额外的主动控制以最大限度减小此类角变形. 文中提出并验证了基于可编程多点柔性支撑的主动变形控制方法. 针对传统刚性装夹、预置应力不适应于弱刚性带筋壁板结构的问题,设计了一套以STM32单片机为主控,直线电动推杆为执行机构的多点柔性支撑装置. 结果表明,可在焊接过程实时监测当前支撑位置的受力状态,并进行动态调节,从而达到有效抑制焊接角变形的效果.