TA11鈦合金超高周疲勞行為

TA11鈦合金超高周疲勞行為Very High Cycle Fatigue Behavior of TA11 Titanium Alloy

利用常規(guī)疲勞試驗(yàn)方法獲得TA11合金在不同溫度，不同應(yīng)力比下的3×107及1×108超高周疲勞極限，并采用三參數(shù)冪函數(shù)法獲得合金超高周疲勞中值S-N曲線及其描述方程。研究發(fā)現(xiàn)：與傳統(tǒng)1×107疲勞極限相比，TA11合金的超高周（3×107及1×108）疲勞強(qiáng)度表現(xiàn)出繼續(xù)降低的趨勢(shì)，這一趨勢(shì)在負(fù)應(yīng)力比（R=-1）下不太明顯，在正應(yīng)力比（R=0.1，0.5）下十分顯著，并且室溫下的降低幅度大于高溫下的降低幅度；斷口分析表明，室溫下TA11合金試樣的超高周疲勞裂紋均萌生于表面，高溫下TA11合金試樣的超高周疲勞裂紋萌生方式與應(yīng)力比有關(guān)，R=-1和0.1時(shí)疲勞裂紋萌生于表面，R=0.5時(shí)疲勞裂紋萌生于內(nèi)部；TA11合金試樣的表面狀態(tài)是導(dǎo)致其疲勞壽命分散的主要原因。

The conventional fatigue test method was used to obtain the very high cycle fatigue (VHCF) limits of 3×107 and 1×108 cycles for TA11 titanium alloy in different temperatures and stress ratios. Three parameter power function method was used to obtain the VHCF median S-N curves and equations. The results show that the VHCF strength of 3×107 and 1×108 cycles presented a continue reducing trend compared with the traditional 1 x 107 fatigue limit. This trend is not obvious in negative stress ratio (R=-1), but significant in normal stress ratio (R=0.1 and 0.5), and the reduction amplitude of room temperature tests was greater than that of elevated temperature tests. The fracture morphologies showed that the VHCF cracks initiat at the specimen surface of TA11 alloy in room temperature tests, and the VHCF cracks initiation ways in elevated temperature tests relate to the stress ratio. The cracks initiate at the specimen surface when R=0.1 and 0.5 but in the internal when R=0.5; The surface state of TA11 alloy specimens is the main cause of its fatigue life dispersion.

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