TC17合金超高周疲勞裂紋萌生機(jī)理

TC17合金超高周疲勞裂紋萌生機(jī)理Very High Cycle Fatigue Failure Mechanism of TC17 Alloy

通過實驗研究了2種頻率(110Hz和20kHz)循環(huán)載荷作用下航空發(fā)動機(jī)葉片材料TC17合金的超高周疲勞失效行為，分析了不同失效形式下的裂紋萌生機(jī)理。結(jié)果表明，TC17合金在2種實驗載荷頻率下均存在表面和內(nèi)部萌生裂紋誘發(fā)疲勞失效2種失效形式，表面萌生裂紋誘發(fā)的疲勞失效主要是由加工缺陷和循環(huán)載荷作用下試樣表面滑移處應(yīng)力集中引起的橫向裂紋所致，內(nèi)部萌生裂紋誘發(fā)的疲勞失效是由循環(huán)載荷作用下材料初生α相的滑移斷裂所致。失效機(jī)理的不同使得材料的應(yīng)力-疲勞壽命(S-N)曲線呈雙線性，載荷頻率對TC17合金的裂紋萌生形式和萌生機(jī)理的影響不顯著。建立了基于薄弱取向晶粒區(qū)域尺寸的疲勞強(qiáng)度預(yù)測模型，模型預(yù)測值與實驗值吻合較好。

Titanium alloys have been widely used in bearing force components in aeronautical structures, such as blades and beams to withstand the high frequency dynamic loads, which requires an outstanding fatigue resistance performance in very high cycle regime during their service life. Very high cycle fatigue failure property of TC17 alloy used as aircraft engine blade material was studied by ultrasonic fatigue test machine and electromagnetic resonance fatigue test machine under 20 kHz and 110 Hz sinusoidal load, and crack initiation mechanism of different failure mode was analyzed. The results showed that, fatigue failure modes of TC17 alloy could be divided into surface induced failure and interior induced failure. Surface induced failure was caused by the machine defect and surface slide trace that triggered by the asymmetric loading. Interior induced failure was caused by slid fracture of primary α phase under asymmetric loading. Fatigue resistance of TC17 alloy was influenced by the fatigue crack initiation mechanism but concerned little about the loading frequency. The variation of the fatigue failure mechanism resulting in the S-N curves presenting bilinear. A fatigue strength predicted model is established based on the parameter of the weak crystal orientation area, which is in good agreement to the fatigue test result.

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