Study on analysis model for simulating hot cracking phenomenon at heat affected zone of weldment

本研究的目的是从动力学的角度，明确并获得焊件热影响区（HAZ）的热裂纹现象。特别地，主要目的是研究和提出高温和大非线性条件下焊接件的三维热弹塑性分析模型/方法。本研究的总结如下。提出并验证了新型的三维热弹塑性分析模型/方法，该模型/方法除适用于弧焊方法外，还适用于激光/电子束焊接方法。采用高温下材料常数的设定、熔融金属的处理、热源的设置等新型特殊方法，可以提出高精度的有限元分析方法。研究并提出了一种精确、动态测量靠近熔体的高温区温度和应变的新型方法。并利用该方法进行了实际测量。通过对分析结果与测量结果的详细对比，验证了所提出的新型分析方法的有效性。在此基础上，提出了基于等效塑性应变的焊件热影响区液化裂纹的新型评价/预测方法。

The object of this study is to make clear and obtain hot crack phenomenon at the heat affected zone (HAZ) of a weldedment from the view point of dynamics. Especially, the main object is to investigate and propose the three-dimensional thermal elastic-plastic analysis model/method for the weldment under the conditions of elevated temperature and large nonlinearity. The summary of this study is as following.The new-type of the three-dimensional thermal elastic-plastic analysis model/method was proposed and validated, which was able to apply for laser/electron-beam welding methods in addition to an arc welding method. The high-accuracy analysis with finite element method was able to be proposed by using the new-type special method of setting of a material constant at elevated temperature, of dealing of a molten metal, of setting of a heat source and so on.The new-type method for accurate and dynamic measurement of the temperature and strain at the elevated temperature zone very near the molten part was investigated and proposed. Moreover an actual measurement by using the proposed method was carried out. The proposed new-type analysis method was able to be validated by comparing the analysis result to the measurement result in detail.Furthermore, the new-type evaluating/prediction method for liquation cracking at HAZ of a weldedment was proposed based on the equivalent-plastic strain obtained from the above analysis method.