摘要
本研究利用有限元素法建立一套應用於大型銲接件溫度與應力分佈計算之電腦輔助工程分析技術。殘留張應力是決定銲接件結構強度的關鍵因素，而本研究建立之分析技術將可預測最大的殘留張應力發生之位置。此外，本研究亦透過銲接實驗之溫度量測驗結果與模擬分析結果進行比對，以確認該有限元素模型之有效性。希望本研究建立之有限元素模型可以協助設計大型銲接件之製程參數並改善銲接件結構之強健性。
　　本研究使用雙橢圓熱源模型作為有限元素分析之熱源輸入方式。有限元素分析模型計算所求得之溫度場分佈與實驗量測結果比對，可以發現在各量測點，二者之溫度變化趨勢相近，特別是模擬結果與其中一組實驗結果相當吻合，因此確認此有限元素分析模型之有效性。在銲接與冷卻過程結束後，熔融區之等效應力值遠大於熱影響區外銲接件邊緣之等效應力值。模擬結果顯示最大殘留等效應力值發生於熔融區，其大小約為294 MPa，此殘留應力值大於降伏強度290 MPa，因此塑性變形可能發生於此高殘留應力區。銲接件內殘留應力值之大小隨著與熔融及熱影響區之距離增加而下降。對垂直於銲道方向之正向應力而言，較大的殘留應力集中在銲道起始與結束的區域，且為壓應力。對平行於銲道方向之正向應力，在銲道區有較大的殘留張應力，然而隨著距離銲道越遠，殘留張應力會逐漸變小，甚至在靠近銲接件邊緣地帶轉變為殘留壓應力。

ABSTRACT

The aim of this study is using finite element method (FEM) to develop a computer aided engineering (CAE) technique for calculating temperature and stress distributions in large-plate welding. From the stress distribution, the maximum tensile residual stress can be predicted which is the most critical parameter in determining the structural integrity of large-plate weldments. Experimental measurements of temperature are carried out to validate the FEM simulation. Hopefully, the developed CAE technique and validated FEM model could help plan a better welding process for large-plate welding and improve its structural robustness.
A double ellipsoidal volumetric heat source is employed in the FEM model to simulate large-plate welding. The simulated variation of temperature at selected positions is compared with experimental measurements to verify the effectiveness of the FEM modeling developed. The thermal history at selected positions shows a similar trend between simulations and experiments. In particular, simulation results of temperature variation concur with one of the three given experiments. At the melt pool area after the welding and cooling process, von-Mises equivalent stress is much larger than that at the edge of plate. The maximum residual stress (in von-Mises equivalent form) is located at the melt pool area and has a value of 294 MPa which is close to the yield strength (290 MPa). Therefore, plastic deformation is expected to take place around this highly stressed region. The magnitude of residual stress decreases with increasing distance from the melt pool area and heat affected zone. Higher compressive residual stress is concentrated at the starting and ending regions on the welding path, for the normal stress component (xx) in the direction perpendicular to the welding path. For the normal stress component (yy) in the direction parallel to the welding path, larger tensile residual stress is located at the melt pool area and it becomes compressive stress at the region away from the welding path.

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