銲接溫度與應力之分析實驗

Abstract

本研究目的主要在探討銲接溫度場與應力場之變化情形。為模擬分析銲接過程中溫度與應力之變化情形，本研究採用熱彈塑性理論，並配合熱-結構耦合元素及考慮非線性材料特性等來進行銲接平板之有限元素數值分析。在模擬分析過程中，主要可區分為熱學與力學模式兩種分析理論。在實驗上，實驗材料選用SUS 304沃斯田鐵型不□鋼，銲接方法則採用自生氣護鎢極電弧銲，並以鑽孔應變計法來量測銲件殘留應力值。本研究結果顯示使用54 %的GTAW電弧效率可準確模擬銲件溫度場的分佈狀況。在銲接過程中，由於銲接熱源的高溫作用將會導致銲道附近有較高的溫度梯度存在。且接近銲接熱源的區域因受到高溫而膨脹，但受到遠離銲接熱源周圍區域之束縛，因此會在銲接熱源附近產生較高的壓縮熱應力。隨著銲接熱源的消失，在靠近銲道附近的區域因受到冷卻而收縮，但受到遠離銲道周圍區域之束縛，因此會在銲道附近產生較高的拉伸殘留應力。本研究結果發現使用ANSYS數值分析軟體可準確模擬銲件殘留應力的大小與分佈情形。

This study was to investigate the fundamental characteristics of the temperature and stress fields in butt-welded plate during welding process. The thermo-elastic-plastic theory and the thermo-mechanical coupled elements were employed in this analytical model with temperature dependent material properties. A three-dimensional model using ANSYS finite element method was designed to estimate the magnitude and distribution of the temperatures, thermal stresses, and residual stresses in weldment. The theoretical considerations can be divided into the thermal and mechanical model. Type 304 stainless steels were used as test specimens, which were welded with an autogenous GTA welding. The welding residual stress was determined by using hole-drilling strain-gage method of ASTM standard E837. The analytical results were compared with the experimental data containing temperatures and residual stresses. The results of this study show that using the arc efficiency of 54 % in GTA welding can obtain the best correlation with the experimental results, and it was then used for the analytical models. Because of the heat source is concentrated locally, the temperature fields adjacent to the heat source are rather steep. The transient thermal stresses are in compressive state since the expansions of these regions are restrained by surrounding cold metal that is at lower temperatures. As the heat source had passed by, the fusion zones have been cooled and hence have a tendency of contraction. A great tensile residual stress was produced in solidified welds, and then rapidly decreased to zero over a distance several times the welded zone. There is a fairly good agreement between theoretical analysis and experimental results using the finite element method.