Evaluation of the Effectiveness of the Three-dimensional Residual Stresses Method Based on the Eigenstrain Methodology via X-ray Measurements
Evaluation of the Effectiveness of the Three-dimensional Residual Stresses Method Based on the Eigenstrain Methodology via X-ray Measurements
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DOI：
10.2472/jsms.64.932
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
M. Ogawa;T. Ishii;S. Furusako
中科院分区：
文献类型：
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作者：
M. Ogawa;T. Ishii;S. Furusako
为了防止焊接结构中疲劳或应力腐蚀裂纹引起的断裂，重要的是预测在服役检查期间观察到的裂纹的裂纹扩展。然而，三维焊接残余应力的非破坏性评估是困难的。今天，可以通过X射线衍射测量表面上的残余应力。利用中子衍射技术，即使在厚度方向上也可以无损测量焊接残余应力，但只能在特殊的辐照设备中使用。因此，不可能使用中子衍射作为现场测量技术。焊缝齐平法是一种基于特征应变法的三维焊接残余应力无损检测方法。在该方法中，三维焊接残余应力通过弹性FEM（有限元法）分析从本征应变分布来计算，本征应变分布通过逆分析从在去除焊接加强件时由应变计释放的应变来估计。在此，过量金属的去除有助于抑制裂纹的产生。因此，微珠冲洗法本质上是一种无损检测技术。然而，这种方法的估计精度变得相对较差时，加工应变被添加到加工表面上。第一作者已经开发了珠冲洗方法，以免受加工菌株的影响。在该方法中，本征应变不是由释放应变估算的，而是由X射线衍射表面残余应变估算的。在这项研究中，焊接残余应力的底面在实际焊接板估计从弹性应变测量上表面使用这种方法。为了评估估计的准确性，估计的底部表面上的残余应力与通过X射线衍射测量的残余应力进行比较。这里，本征应变分布不仅在焊接方向上，而且在厚度方向上被认为是提高估计精度。
In order to prevent fractures caused by fatigue or stress corrosion cracking in welded structures, it is important to predict crack propagation for cracks observed during in-service inspections. However, it is difficult to evaluate three-dimensional welding residual stresses non-destructively. Today, it is possible to measure residual stresses just on surface by X-ray diffraction. Neutron diffraction makes it possible to measure welding residual stresses non-destructively even in the thickness direction but it is only available in special irradiation facilities. Therefore, it is impossible to use neutron diffraction as an on-site measurement technique. As non-destructive method of three-dimensional welding residual stresses based on the eigenstrain methodology, the bead flush method has been proposed. In this method, three-dimensional welding residual stresses are calculated by an elastic FEM (Finite Element Method) analysis from eigenstrain distributions which are estimated by an inverse analysis from released strains by strain gauges in the removal of the weld reinforcement. Here, the removal of the excess metal contributes inhibition of crack initiation. Therefore, the bead flush method is a non-destructive technique essentially. However, estimation accuracy of this method becomes relatively poor when processing strains are added on the machined surface. The first author has been developed the bead flush method to be free from the influence of the processing strains. In this method, eigenstrains are estimated not from released strains but from residual strains on surface by X-ray diffraction. In this study, welding residual stresses on the bottom surface in an actual welded plate are estimated from elastic strains measured on the top surface using this method. To evaluate estimation accuracy, estimated residual stresses on the bottom surface are compared with residual stresses measured by X-ray diffraction. Here, eigenstrain distributions not only in the welding direction but also in the thickness direction are considered to improve the estimation accuracy.