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Please use this identifier to cite or link to this item: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/9578

Title: 精密傳動元件雷射處理技術研究---子計畫二:雷射表面退火處理阻擋疲勞裂縫成長 (III)
Ratardation of Fatigue Crack Growth by Laser Surface Annealing (III)
Authors: 蔡履文
Contributors: NTOU:Institute of Materials Engineering
國立臺灣海洋大學:材料工程研究所
Keywords: 疲勞裂縫成長;304不銹鋼;雷射表面退火;殘留應力;有限元素分析
Fatigue crack growth;304 stainless steel;Laser surface annealing;Residual stress;Finite element analysis (FEA)
Date: 2000
Issue Date: 2011-06-28T07:09:34Z
Publisher: 行政院國家科學委員會
Abstract: 本研究為探討大氣及氣態氫環境中,殘留應力對疲勞裂縫成長之影響,304不銹鋼板材進行雷射銲接及雷射熱處理,利用輸入熱能方式產生殘留應力。304不銹鋼平板經雷射熱處理其殘留應力量測結果顯示:熱處理中心區為殘留張應力區,而兩旁為殘留壓應力區,並且隨著距離的增加壓應力逐漸減小。量測缺口前端殘留應力場,缺口尖端距離熱處理中心線距離減小,缺口前端之殘留壓應力則增加,而熱處理中心區為張應力區。疲勞試驗結果顯示經雷射熱處理之Compact tension (CT)試片,熱處理區前方區域因殘留壓應力之影響,使疲勞裂縫成長速率具有減緩效果,改變CT試片缺口位置相對雷射熱處理中心線位置,試片缺口尖端愈接近熱處理中心線,原始高阻擋裂縫成長現象消失。裂縫成長在熱處理區以及疲勞裂縫成長通過熱處理區後,均顯示相當於母材之裂縫成長特性。雷射銲件疲勞裂縫成長實驗,結果大致與雷射熱處理試件相同。而在氣態氫環境中,經雷射熱處理試件,其疲勞裂縫成長起始區與大氣環境中相同均有減速的現象,即在脆化環境於低ΔK值範圍下,殘留應力仍具有阻擋疲勞裂縫成長的效應。
The fatigue crack growth behavior of the 304 austenitic stainless steel annealed by a CO/sub 2/ laser is investigated in this work. Metallographic observations indicate that distinct locations of a laser-treated specimen reveal the similar microstructures and microhardness, as a result of no substantial phase transformation occurs in the laser-heated region. The results of fatigue crack growth test demonstrate that the as-treated specimen has a higher resistance to fatigue crack growth in the region preceding the laser track. However, marked retardation of crack growth in the low .DELTA.K range disappears for the specimen stress-relieved at 850.degree.C for one hour. Similar result has been observed in the specimen with shorter notch tip to centerline of laser track distance. Residual stress measurements of the laser surface-annealed specimen indicate that there is a peak in stress distribution in the laser track and it changes from tensile into compressive stresses with increasing the distance away from the laser track. Also, it reveals that the width of the tensile stress field is far wider than that of laser track itself. The stress field ahead of laser track will be changed from tensile into compressive residual stresses after introducing a sharp notch. The presence of residual compressive stresses ahead of notch tip results in the reduced fatigue crack growth rate in the compact tension specimen.
Relation: NSC89-2216-E019-011
URI: http://ntour.ntou.edu.tw/ir/handle/987654321/9578
Appears in Collections:[材料工程研究所] 研究計畫

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