【作者】 梁志芳；

【导师】 李午申； 薛振奎；

【作者基本信息】 天津大学 ， 材料加工工程， 2004， 博士

【摘要】 焊接是最常见也是最重要的材料连接方法,但是焊接加工形成的焊接接头经过了焊接过程的特殊热循环,该处的物理化学性能都是与母材有差异的。这种差异最终导致了焊接构件的焊接接头处在使用过程中产生断裂、疲劳、腐蚀等损伤。因此,该处对于焊接质量的控制就成为很重要的位置。金属磁记忆检测方法是由俄罗斯专家在1997年提出的一种无损检测方法。该方法利用铁磁性材料在地磁场中加工和使用过程中的应力和变形造成的磁畴组织定向不可逆的取向,形成的漏磁场来确定构件的应力应变集中部位。为了推动金属磁记忆检测方法在焊接质量检测中的应用,本文进行了对焊接接头质量影响最大的焊接裂纹的金属磁记忆特征的研究。首先,本文对TSC-1M-4型金属磁记忆检测设备用于焊接检测时采用的检测参数进行了研究,确定了Ho选择为ON、S选择为1mm、b选择为15mm是适合焊接质量检测最佳检测参数组合。其次,提出了裂纹、裂纹应力场、漏磁场三者之间的关系是研究的核心理论支柱。针对X70管线钢研究了该材料中的裂纹尖端的应力分布; 以及应力分布与漏磁磁场之间的关系; 应力与金属磁记忆检测信号之间的关系。之后,通过自行设计的实验进行了焊接裂纹金属磁记忆检测时空有效性研究,认为X70钢构件冷却到低于100℃后的任何时间进行检测的结果都是有效的; 在距离金属磁记忆特征信号70mm为半径的范围内是有效的焊接裂纹可疑区。再后,通过自行设计的拉伸试验以及二次正交旋转组合试验设计焊接管道裂纹标准样本库的检测,找到了焊接裂纹的四个金属磁记忆检测信号特征参数:Deta、△Hp/△Lx、△Hp和MMM检测信号傅立叶分析的相位突变点。提出焊接裂纹处MMM检测信号Deta、△Hp/△Lx、△Hp、以及傅立叶分析相位突变点等四个特征量的综合分析可以反映焊接裂纹的存在和几何形状。最后,得到了焊接裂纹的金属磁记忆信号特征量Deta、△Hp/△Lx、△Hp和焊接裂纹的几何描述量裂纹长度、裂纹角度、裂纹埋深之间的关系,建立了它们之间的回归关系模型。更多还原

【Abstract】 Weld is the most important and widely used material-connecting method. However, the weld joint produced by welding process experiences the extremely welding heat cycle, and is different from the body material in physical and chemic performance. Then, these differences incur that the weld components rupture, fatigue, and corrupt at the weld joint during used. Therefore, the weld joint is the most significant point in the weld-quality-controlling. Metal magnetic memory is a nondestructive testing method, which is invented by Russian expert in 1997. The method use the ferromagnetic leakage magnetic field to detect the stress concentration position because the leakage magnetic field is produced by the magnetic domain orient irreversible change due to operating strain and stress in earth magnetic field. In order to apply the metal magnetic memory method to test the welding quality, the metal magnetic memory characteristic of the welding crack is studied, which is the most badly factor tampering with the weld joint quality. Firstly, the detection parameter is studied when the TSC-1M-4 metal magnetic memory device is used in the weld detection. It is the best detection parameter group that Ho set as ON, S set as 1mm and b set as 15mm. Secondly, the main aspects of the research are thought as the three relationships of the crack, stress field of the crack and leakage field of the stress concentration. As the subject investigated, X70 line-pipe steel has been researched on the stress field around the crack tip, the relationship between the stress field and the leakage field, and the relationship between the stress and the metal magnetic memory signal. Thirdly, the time and space availability of weld crack’s metal magnetic memory testing is researched by the self-layout experiment. The detection result is available when the weld joint is cooled below 100℃, and the doubtful weld crack area include the positions from which the distance to the metal magnetic memory characteristic signal position is no more than 70mm. Fourthly, such self layout experiments has been carried out as tension, one-factor rotate weld pipeline standard sample cracks, and quadratic rotation-orthogonal combination design weld pipeline standard sample cracks, and these are detected by metal magnetic memory method. From the detection results, it is concluded that there are four metal magnetic memory signal characteristic of weld crack-Deta, △Hp/△Lx, △Hp and Fourier analysis phase saltation of metal magnetic memory signal. Comprehensive analysis of all the four signal characters above can reflect the existence and geometry shape of weld crack. Finally, the regression equations has arrived between such the signal characteristic variances as Deta, △Hp/△Lx and △Hp and such weld crack geometry shape parameter as length, angle and depth.更多还原