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Title: | 異材銲道發生延遲裂紋之研究 Study on Delayed Cracking of a Dissimilar-Metal Weld |
Authors: | Hung-Ta Kuo 郭鴻達 |
Advisor: | 吳文方(Wen-Fang Wu) |
Co-Advisor: | 楊哲人(Jer-Ren Yang) |
Keyword: | 異材銲道,銲接延遲裂紋,殘餘氫含量,多道次銲接,銲接模擬, weld delayed cracking,residual hydrogen content,multi-passes weld,welding simulation, |
Publication Year : | 2009 |
Degree: | 博士 |
Abstract: | 本文以銲接模擬之方法,針對重型鋼結構之主要結構銲道,進行銲後發生延遲裂紋之可能性進行評估。研究過程中使用二維軸對稱模型作有限元素分析,除了對相異類別母材之多道次銲接進行結構與熱彈塑性之耦合分析外,亦在耦合計算過程中考慮了材料之相變態、殘餘相比例、結構拘束度與殘餘氫含量等影響因子。為分析可擴散氫之分佈模式,模擬「遮蔽金屬電弧銲接」之殘餘氫濃度被刻意的施加在第三道次之銲珠,並沿著該銲珠週圍的三個方向,共選定14個節點進行龜裂可能性分析。由分析數據中萃取出「銲後殘餘應力」、「殘餘可擴散氫」與「溫度梯度」等影響因素,並結合Alan Glover-Brian Graville模型以比對銲後發生龜裂之可能性。研究結果顯示,本論文所分析銲接結構選定的節點中,有6個節點被評估為會立即發生龜裂,龜裂率高達42.85%,其中4點歸咎於殘餘應力過高,另外2個節點可能肇因於位於熱影響區之粗晶區,在殘餘應力與殘氫量之共同作用下,以致在殘餘應力不高之情況下,在高溫冷卻過程中即發生龜裂。此一結果與台灣某工地發生鋼結構銲後龜裂之情形非常吻合。 In the present dissertation, simulation is carried out to study the likelihood of occurrence of delayed cracking in a load-carrying weld. In particular, a big weld joining together two separate heavy decks to construct a huge annular steel structure in a construction site is studied in detail. A two-dimensional axial symmetric model is built for finite element simulation. The multi-pass welding joining two base metals made of different materials, the iterated and coupled calculation between structural deformation and thermal-elasto-plastic process, the material phase transformations, the residual phase percentage after phase transformation, the structural constraint, and the residual hydrogen concentration are all taken into consideration in the simulation. A hydrogen concentration model resulted from a real shielded metal arc welding process is also considered in the third weld bead for analyzing the diffusible hydrogen distribution pattern. Fourteen nodes in three specific directions around the third weld bead are chosen for evaluating the likelihood of delayed cracking. From the simulation, variation histories of the residual stress, the residual hydrogen concentration, and the temperature gradient during cooling are obtained. They are used for evaluating the likelihood of occurrence of delayed cracks based on a so-called “Alan Glover-Brian Graville” model. The result indicates that, among the selected fourteen nodes, six will crack after welding processes are completed. Four of them are owing to that their residual stresses are higher than the ultimate strength; and the other two is attributed to the combined effect of residual stress and diffusible hydrogen concentration. For the latter case, cracks occurs during the cooling process even the residual stresses are not substantially high. The evaluation result is very similar to cracks found in a construction site in northern Taiwan. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/22895 |
Fulltext Rights: | 未授權 |
Appears in Collections: | 機械工程學系 |
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ntu-98-1.pdf Restricted Access | 5.57 MB | Adobe PDF |
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