臺灣博碩士論文加值系統

有限元素法是眾多數值分析方法的一種，能被運用在工程上各種問題的求解。在各種應用中，無論是穩態、暫穩態、線性的、非線性的、熱傳方面、流體力學方面、甚至於電磁學方面，皆可應用有限元素法求解。隨著電腦科技的進步，CAD/CAM/CAE已經可以完全結合在一起。在CAD 軟體上設計材料或結構，藉著檔案的轉換（如：.DXF、.IGES、.STEP…），可以輕易地在CAE的軟體上開啟CAD完成的2D或3D設計圖，對設計的元件作結構外型、材料特性及尺寸方面作模擬的分析。使用高功率CO2雷射進行局部熱處理時，由於熱能的輸入使304不�袗�材內產生溫度梯度的變化，而造成體積的改變，因此造成在熱處理區及其鄰近區域產生殘留熱應力。本研究即是利用有限元素之分析軟體ABAQUS，分析304不�袗�於雷射熱處理後，殘留熱應力距雷射熱處理中心線的應力分佈狀態；並對試片垂直於雷射熱處理中心線作裂縫開槽、試片沿著雷射熱處理中心線作裂縫開槽，比較兩者裂縫成長之模式。模擬結果中發現當裂縫垂直雷射熱處理中心，雷射熱處理所造成的熱處理區主要為張應力，當遠離熱處理區時此張應力將會發生反轉而轉變成為壓應力。裂縫尖端會存在一個最大壓應力，當裂縫於熱處理區外成長時，裂縫前端之S11壓應力將會因為此疲勞裂縫之成長而引發更大之壓應力，故於實驗中可以觀察到此時裂縫之成長速率將明顯減緩。因此，在無相變態發生之鋼材中，使用雷射表面處理之技術，將可以因此壓應力的存在而有效避免疲勞裂縫於熱處理區域外圍之成核與成長。當裂縫沿著雷射熱處理中心，其裂縫尖端之表面層皆為張應力，且其S33張應力之值非常相近，而裂縫尖端之中心層皆為壓應力，且其S33壓應力之值亦非常相近。由於應力互相抵銷作用，因此，在實驗中未觀察到疲勞裂縫成長速率加快的情況。

The finite element method（FEM）is one of many numerical analysis used to obtain solutions in some engineering problems including steady state, unsteady state, linear, nonlinear, heat transfer, fluid mechanics, and electromagnetism…etc. With the rapid advancement of computer technology, CAD/CAM/CAE are integrated completely. To design the structure using a CAD software, CAD files of 2D/3D designed drawing （e.g. DXF, IGES, STEP…） can be easily loaded into CAE software by file transformation. It can simulate the form of structure, characteristic of materials and dimensions of the designed member. The residual thermal stresses are primarily resulted from volume change as variation of temperature gradient in 304 stainless steel by localized high power CO2 laser heat-treating. In this study, the stress redistribution of the residual thermal stress along the centerline of laser track was analyzed by ABAQUS, and the result was also compared with the stress distribution perpendicular to the crack propagation direction. It is found that the laser heat-treated area at crack propagation direction perpendicular to laser track is mainly comprised of tensile stress, and the tensile stress will be gradually converted into compressive stress as the distance increased from the laser-treated area. Further increase the distance from heat treatment area will result in decreasing the magnitude of compressive stress. The compressive S11 stress ahead of the crack tip will be increased as the crack tip grows outside the laser-treated area. Therefore, it is observed that the growth rate of crack tip outside the laser-treated area is decreased in the experiment. Thus, the application of laser surface treating technique can effectively prohibit the nucleation and growth of fatigue crack outside the heat-treated area if there is no phase transformation in the steel. When the crack propagation direction along the centerline of laser track, the surface layers of laser-treated area is dominated by tensile stress, and the central layers of laser-treated area is primaryly compressive stress. The stress ahead of the crack tip are compensated each other. Consequently, it is observed that the growth rate of the crack tip is not changed in the experiment.

目錄
頁數
目錄…………………………………………………………………..…….і
圖目錄……………………………………………………………………..iii
表目錄……………………………………………………………………..ix
第一章、緒論………………………………………………………..….1~3
1.1研究背景與動機………………….…………………………….…1
1.2研究目的……..………………………….………………………...3

第二章、文獻回顧……………………………………………………...4~14
2.1沃斯田鐵系不�袗�…………….…………………………………4
2.2沃斯田鐵系不�袗�的腐蝕…….…………………………………4
2.3疲勞裂縫成長………….…………………………………………7
2.3.1疲勞破壞簡介 …………………………….……………….…7
2.3.2疲勞裂縫成長率………………………………………………9
2.3.3殘留應力與疲勞裂縫成長率（da/dN）之關係…………….11
2.4有限元素法…….………………………………………………..12

第三章、有限元素法理論基礎及熱傳理論…………….……………15~27
3.1 ABAQUS 之理論簡介…………………………………….……15
3.2平衡方程式與虛功原理………………………………….……..17
3.3基本有限元素方程式…………………………………….……..20
3.4 ABAQUS驗証分析的技巧…………………………….……….21
3.5熱傳理論…………………………………………………….…..24
第四章、試片及有限元素模型建立……………………………….…28~41
4-1模擬試片（裂縫垂直雷射熱處理中心）………………………...28
4.2 模擬試片（裂縫沿雷射熱處理中心）…………………………30
4.3 有限元素模型之建立…………………………………………..33

第五章、ABAQUS模擬殘留熱應力對304不�袗�疲勞裂縫成長之研究……...……………………………………………………42~78
5.1 殘留熱應力對304不�袗�疲勞裂縫（裂縫垂直雷射熱處理中心）成長之影響…………………..……………………………42
5.1.1有限元素分析過程……………………..…………………..45
5.2 殘留熱應力對304不�袗�疲勞裂縫（裂縫沿雷射熱處理中心）成長之影響……………………...…..……………...…………50
5.2.1有限元素分析過程……………………………...…..………50
第六章、結論……………………………………………..……82~83
附表（一）………………………………………………………………..84
參考資料……………...………………………………………………85~87

參考資料
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