TC4-DT钛合金小裂纹扩展行为研究
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摘要
为了研究TC4-DT钛合金自然萌生小裂纹的扩展行为,针对单边缺口拉伸试样开展了室温下同一应力比R=0.06不同应力水平的小裂纹扩展实验,采用复型法对小裂纹的萌生和扩展行为进行观测。结果表明:同一应力比下,应力水平越低,小裂纹的萌生寿命越高,疲劳全寿命越长。应力水平对TC4-DT钛合金小裂纹扩展速率没有明显影响。裂纹扩展早期速率受微观组织的影响大,分散性较高。疲劳小裂纹萌生和扩展寿命占全寿命的70%-80%。TC4-DT钛合金疲劳小裂纹起源于试样缺口表面靠近中间位置和边缘部分,疲劳断口分析发现裂纹以近似椭圆形向试件内部扩展,在裂纹稳定扩展区可以明显的观察到疲劳辉纹。
The growth behavior of naturally-initiated small cracks in single edge notched tensile specimens of TC4-DT titanium alloy was studied. Fatigue experiments were conducted under constant stress rations R of 0. 06 with stress amplitudes of 380 MPa and 370 MPa at room temperature. Small cracks were monitored by replica method during fatigue testing. Results show that higher small crack initiation life and total life can be obtained under lower stress level. The stress level has little effect on small crack growth rate,while microstructure plays an important role on small crack growth rate,and leads to high dispersion of life data. Fatigue small crack initiation and growth life accounts for 70%-80% of the total life. Most small cracks of TC4-DT titanium alloy originate from the surface of the notch near the middle position and the edge of the sample. From SEM fracture analysis it can be found that cracks propagate inside the specimen with an approximate ellipse manner in the stable crack propagation region and the fatigue striations can be observed obviously.
The growth behavior of naturally-initiated small cracks in single edge notched tensile specimens of TC4-DT titanium alloy was studied. Fatigue experiments were conducted under constant stress rations R of 0. 06 with stress amplitudes of 380 MPa and 370 MPa at room temperature. Small cracks were monitored by replica method during fatigue testing. Results show that higher small crack initiation life and total life can be obtained under lower stress level. The stress level has little effect on small crack growth rate,while microstructure plays an important role on small crack growth rate,and leads to high dispersion of life data. Fatigue small crack initiation and growth life accounts for 70%-80% of the total life. Most small cracks of TC4-DT titanium alloy originate from the surface of the notch near the middle position and the edge of the sample. From SEM fracture analysis it can be found that cracks propagate inside the specimen with an approximate ellipse manner in the stable crack propagation region and the fatigue striations can be observed obviously.
引文
[1]朱知寿.新型航空高性能钛合金材料技术研究与发展[M].北京:航空工业出版社,2013.12
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[4]陈勃,高玉魁,吴学仁,马少俊.喷丸强化7475-T7351铝合金的小裂纹行为和寿命预测[J].航空学报,2010,(31)3:519-525.
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[14]Suh CM,Suh MS,Hwang NS.Growth behaviour of small surface fatigue cracks in AISI 304 stainless steel.Fatigue Fract Eng Mater Struct 2011;35:22-9.
[15]Suh CM,Lee JJ,Kang YG.Fatigue microcracks in type304 stainless steel at elevated temperature.Fatigue Fract Eng Mater Struct 1990;13(5):487-96.
[16]张丽,吴学仁,黄新跃.GH4169合金自然萌生小裂纹扩展行为的试验研究[J].航空学报,2015,36(3):840-847.
[17]Connolley T,Reed PAS,Starink MJ.Short crack initiation and growth at 600°C in notched specimens of Inconel 718.Mater Sci Eng A 2003;340:139-54.
[18]Caton MJ.Predicting fatigue properties of cast aluminum by characterizing small-crack propagation behavior,Ph D dissertation.University of Michigan.Ann Arbor,MI;2001.
[2]Newman J J,Philips E P,Swain M H.Fatigue-life prediction methodology using small-crack theory[J].International Journal of Fatigue,1999,21:109-119.
[3]Li W F,Zhang X P.Investigation of initiation and growth behavior of short fatigue cracks emanating from a single edge notch specimen using in-situ SEM[J].Materials Science and Engineering,2001,318:129-136.
[4]陈勃,高玉魁,吴学仁,马少俊.喷丸强化7475-T7351铝合金的小裂纹行为和寿命预测[J].航空学报,2010,(31)3:519-525.
[5]Chen Bo,Gao Yu Kui,Wu XueRen,et al.Small crack behavior and fatigue life prediction for shot peening aluminum alloy 7475-T7351.Acta Aeronautica et Astronautica Sinica,2010,(31)3:519-525.(in Chinese)
[6]Miller K J.The behaviour of short fatigue cracks and their initiation Part II-a general summary[J].Fatigue and Fracture of Engineering Materials and Structures,1987,10:93-113.
[7]郭瑞平,刘官厅,范天佑,等.冲击载荷下含表明裂纹圆柱壳体的动态断裂[J].应用动力学学报.2006,23(1):53-56
[8]S.Pearson Initiation of Fatigue Cracks in Commercial Aluminum Alloys and the Subsequent Propagation of Very Short Cracks.Eng.Fract.Mech.1975,7(1):235-247
[9]Kitagawa H Takahashi S.Mechanical Behaviour of Material[C].Boston:1976.627-631
[10]Okazaki M,Yada T,Endoh T.Surface small crack growth behavior in low-cycle fatigue at elevated temperature and application limit of macroscopic crack growth law[J].Nuclear engineering and design,1988,110:9-16
[11]胡本润,吴学仁.Ti-A6I-4V钛合金小裂纹扩展行为与寿命预测[D].1999.12.30
[12]Wu XueRen,Newman J C,Zhao W.Special issue on NASA CAE fatigue and fracture mechanics cooperative program.Beijing:Aviation Press,1994
[13]Wu XueRen,Newman J C,Zhao W,et al.Smallcrackgrowth and fatigue life[redictions for highstrength aluminum alloys:PartⅠ—and fracture mechanics analysis[J].Fatigue and Fracture of Enigneering Material and Structures,1998,21(11):1289-1306.
[14]Suh CM,Suh MS,Hwang NS.Growth behaviour of small surface fatigue cracks in AISI 304 stainless steel.Fatigue Fract Eng Mater Struct 2011;35:22-9.
[15]Suh CM,Lee JJ,Kang YG.Fatigue microcracks in type304 stainless steel at elevated temperature.Fatigue Fract Eng Mater Struct 1990;13(5):487-96.
[16]张丽,吴学仁,黄新跃.GH4169合金自然萌生小裂纹扩展行为的试验研究[J].航空学报,2015,36(3):840-847.
[17]Connolley T,Reed PAS,Starink MJ.Short crack initiation and growth at 600°C in notched specimens of Inconel 718.Mater Sci Eng A 2003;340:139-54.
[18]Caton MJ.Predicting fatigue properties of cast aluminum by characterizing small-crack propagation behavior,Ph D dissertation.University of Michigan.Ann Arbor,MI;2001.