钢结构对接斜焊缝的计算

本文分析讨论了钢结构设计规范中关于“斜对接焊缝强度计算”的规定的来源,指出现行规范关于斜对接焊缝不需进行强度验算的倾角值是偏于保守的。     

钢结构厚板及其对接焊缝Z向性能试验

为了研究钢结构厚板及其对接焊缝Z向的拉伸性能和冲击韧性,对4种不同厚度的钢厚板,采用V形缺口对接连接,沿钢板母材、焊缝及热影响区的X向和Z向分别进行取样,进行单轴拉伸和冲击试验。试验表明,随着板厚的增加,材料的拉伸性能和冲击韧性变差;热影响区的拉伸及冲击性能比母材要差;焊缝金属的脆性比母材X向的明显。所以,在钢结构厚板的工程实践中,应特别注意厚板由于对接焊缝引起的Z向性能不足。     

金属磁记忆技术的机理与试验研究

在外应力作用下铁磁晶体应力能会增加,其相应的总自由能也会增加,而改变铁磁晶体的磁化状态会消耗能量,并趋向于自由能最低.通过对45号调质钢和非调质钢试件分组进行三点弯曲疲劳裂纹扩展试验和金相显微镜在位显微观测,并利用TSC-1M-4检测磁场信号,发现调质钢试件的磁记忆信号明显低于非调质钢试件的磁记忆信号,在对试件调质消除内应力后,不同的应力状态对试件的磁场特征信号具有显著的影响.     

钢结构对接焊缝数值模拟及参数分析

基于ANSYS有限元软件采用了双椭球热源模型、CO₂气体保护焊的焊接工艺,通过生死单元法模拟热源移动,建立了桥梁钢结构的焊接有限元模型,进行了对接焊缝的数值模拟分析,并与实验结果进行对比验证了模拟的可靠性。在此基础上研究了对接焊缝在坡口形状、X型坡口多层焊的焊接顺序、焊接速度、焊件厚度、焊接坡口角度、焊枪的施焊方向等不同因素下残余应力的变化情况。结果表明：相比于其他坡口的焊接,X型坡口焊接残余应力较小,多层焊情况时,X型坡口采用对称焊更有利;板厚、焊速的增加,坡口角度的减少及采用分中对称焊方法都能减少焊接残余应力的产生。     

斜对接焊缝连接的强度计算与设计

本文对现行《钢结构设计规范》中的第7.1.1条注的来源进行了说明,并讨论了三级质量的斜对接焊缝的强度计算问题,指出现行规范关于不需进行强度验算的斜时接焊缝的倾角值是偏于安全的。     

拉伸实验中的金属磁记忆信号总体特征研究

为了确定构件承载应力与金属磁记忆信号之间关系,以推进金属磁记忆法在构件检测中的应用,制备了不同尺寸和结构的拉伸试件,在试件承受不同拉伸载荷的情况下,进行了金属磁记忆检测,分析了金属磁记忆信号的总体特征Deta.研究表明:Deta作为金属磁记忆检测信号的特征量可以描述构件承载水平的高低;随着构件承载增加,Deta将逐渐减小,在达到材料屈服极限后,Deta保持在一定水平波动;对应材料X70屈服极限的Deta值是79.27A/m,高于该值时,X70构件是安全的.     

钢结构厚板对接焊缝的低温断裂韧性试验

随着钢板厚度的增加,焊接难度加大,且存在焊接裂纹缺陷的可能性也增大.为防止钢结构厚板焊接接头的脆性断裂,采用三点弯曲试样,以裂纹尖端张开位移(CTOD)为指标,对厚度为150mm的Q345B钢板对接焊缝低温下的断裂韧性进行试验研究. 分析了焊缝金属和热影响区断裂韧性CTOD值δm随温度的变化关系,并用Boltzmann函数对断裂韧性-温度曲线进行拟合,结合试样断口的扫描电镜图分析了断裂的微观机理. 试验结果表明:焊缝金属和热影响区的CTOD值δm随温度的降低而降低,从20 ℃~-60 ℃,降幅分别达78％和91％;热影响区CTOD值δm比焊缝金属和母材均要小. 试验积累了厚板对接焊缝的断裂韧性数据,为低温地区钢结构厚板对接焊缝脆性断裂的预防提供了技术基础.     

建筑钢结构熔透对接焊缝缺陷对焊缝抗拉承载力影响的研究

超声波探伤计算建筑钢结构熔透对接焊缝的缺陷率,对含有不同位置缺陷及缺陷率的焊缝进行拉力试验,用缺陷率-焊缝强度关系图分析焊缝抗拉承载力达到:母材强度,GB50017-2003一、二、三级熔透对接焊缝设计值,母材屈服强度标准值时,建筑钢结构熔透对接焊缝可允许存在的体积性缺陷率限值.研究结果表明:存在于熔透对接焊缝中部的缺...     

铸钢节点对接焊缝有效缺口应力分析

为了研究铸钢节点对接焊缝的疲劳性能和寿命评估方法,对一种常用的铸钢热轧钢对接焊缝试件进行了疲劳试验研究,得到了刚度、位移与疲劳寿命阶段之间的关系。根据疲劳试验现象和断面的电镜扫描结果,提出了该类试件的疲劳失效机理。此外,采用有效缺口应力法预测了铸钢节点对接焊缝的疲劳寿命,并在考虑了平均应力和焊接残余应力的前提下,提出了改进的有效缺口应力法,分别将预测结果与实测疲劳寿命进行了对比。研究结果表明：铸钢节点对接焊缝的疲劳过程可分为稳定阶段和断裂阶段。稳定阶段占总寿命比例≥80%,断裂阶段≤20%。有效缺口应力法能在一定程度预测疲劳寿命的变化趋势,但结果偏危险,改进的有效缺口应力法能提供较安全的预测结果。     

Fatigue damage evaluation by metal magnetic memory testing简

Tension-compression fatigue test was performed on 0.45% C steel specimens. Normal and tangential components of magnetic memory testing signals, Hp（y） and Hp（x） signals, with their characteristics, K of Hp（y） and Hp（x）M of Hp（x）, throughout the fatigue process were presented and analyzed. Abnormal peaks of Hp（y） and peak of Hp（x） reversed after loading; Hp（y） curves rotated clockwise and Hp（x） curves elevated significantly with the increase of fatigue cycle number at the first a few fatigue cycles, both Hp（y） and Hp（x） curves were stable after that, the amplitude of abnormal peaks of Hp（y） and peak value of Hp（x） increased more quickly after fatigue crack initiation. Abnormal peaks of Hp（y） and peak of Hp（x） at the notch reversed again after failure. The characteristics were found to exhibit consistent tendency in the whole fatigue life and behave differently in different stages of fatigue. In initial and crack developing stages, the characteristics increased significantly due to dislocations increase and crack propagation, respectively. In stable stage, the characteristics remained constant as a result of dislocation blocking, K value ranged from 20 to 30 A/（m·mm）-1, and Hp（x）M ranged from 270 to 300 A/m under the test parameters in this work. After failure, both abnormal peaks of Hp（y） and peak of Hp（x） reversed, K value was 133 A/（m·mm）-1 and Hp（x）M was -640 A/m. The results indicate that the characteristics of Hp（y） and Hp（x） signals were related to the accumulation of fatigue, so it is feasible and applicable to monitor fatigue damage of ferromagnetic components using metal magnetic memory testing （MMMT）.     

振动时效用于降低异种钢对接焊缝残余应力的试验研究

通过对异种钢圆筒对接焊缝试件进行振动时效处理,并用盲孔法测量试件振前和振后的残余应力表明,振动时效处理可以大大降低异种钢圆筒对接焊缝的残余应力,最大值可从振前的540MPa下降到振后的119 MPa;残余应力1σ,σ2消除率分别达到61%和48.7%,远大于标准规定的焊接件应力消除率应大于30%的要求;均化程度由振前的421 MPa,428 MPa均化到振后的241MPa,316 MPa,达到了标准规定的“振后的计算值应小于振前的计算值”的要求.     

拉应力对不同厚度Q345钢磁记忆信号的影响

为明确磁记忆信号与拉应力之间的对应关系和几何尺寸对试件表面磁场的影响,对Q345低合金钢不同厚度板状试件进行静载拉伸实验.利用TSC-1M-4型磁检测仪,研究3种厚度的光滑试件表面磁记忆信号在不同拉应力下的变化规律.结果表明:弹性阶段磁记忆信号与拉应力之间有较好的相关性,塑性阶段两者相关性较弱;切向磁记忆信号对试件局部屈服的表征比法向磁记忆信号更敏感,利用切向磁场的畸变性可预判试件的早期塑性变形和应力集中区;同一应力水平下,试件表面磁场强度随厚度增加而减小,但不影响其变化规律.     

Characteristics of magnetic memory signals for medium carbon steel under static tensile conditions

To test the magnetic signals leaked from the surface of specimens during loading, the experiments of the static tensile of medium carbon 45^# steel were carried out. The results show that the magnetic field strength values rapidly vary when the load began, and the curves of the magnetic field strength change from irregularity to regularity with the increase of the load. Furthermore, by comparing with the state of on-line testing, it is found that the magnetic signals of out-of-line testing has more practicability. In the course of loading, though the dots of passing zero of the magnetic field strength continually changed their positions and quantities, the last rupture places were always approached by the dots of passing zero since the elastic loading phase. Some certain relations should exist between external stress and changing of magnetic signals inside the material, and correlative explanation is made based on dislocation theory and the mechanism of magnetic domain action, which provides the basis for further research of magnetic memory. Foundation item: Project(50235030) supported by the National Natural Science Foundation of China     

用磁声法MAE检测钢结构构件应力的机理和应用

分析了磁声发射的产生与接收、磁声发射与磁致伸缩、磁声发射的应力检测机理，应力对磁声发射的影响，磁声发射的检测系统等几个方面．从这些方面说明了用磁声发射来实施应力检测是可行的．证明磁声发射的强度既受外磁场变化影响，又受应力变化影响，并且磁声发射的变化幅度与所受应力大小有一定的关系，据此可为磁声发射检测铁磁材料的应力状态提供依据．但由于磁声发射的强度和施加于构件上应力状态的关系比较复杂，所以结合磁声发射和巴克素森BN两种方法各自优点的应力检测更比看好．     

环境磁场对磁记忆检测信号的影响

通过对一铁磁性试件进行磁记忆检测实验,选择手机信号作为干扰源,研究不同环境磁场下试件磁记忆检测信号的变化情况.同时,对试验过程中的环境磁场对磁场强度变化的影响进行了机理分析.研究结果表明:对不同程度的环境磁场干扰,检测得到的试件磁记忆信号差别显著;周围有放置手机但不通话时,环境磁场的干扰程度不大;随着周围环境的通话手机数量逐渐增多,环境磁场的干扰程度不断加大直至足以影响检测精度.     

Metal magnetic memory signals from surface of low-carbon steel and low-carbon alloyed steel

In order to investigate the regularity of metal magnetic signals of ferromagnetic materials under the effect of applied load, the static tensile test of Q235 steel and 18CrNiWA steel plate specimens were conducted and metal magnetic memory signals of specimens were measured during the test process. The influencing factors of metal magnetic memory signals and the relationship between axial applied load and signals were analyzed. The fracture and microstructure of the specimens were observed. The results show that the magnetic signals corresponding to the measured points change linearly approximately with increasing axial load. The microstructure of Q235 steel is ferrite and perlite, whereas that of 18CrNiWA steel is bainite and low-carbon martensite. The fracture of these two kinds of specimens is ductile rupture; carbon content of specimen materials and dislocation glide give much contribution to the characteristics of magnetic curves.