FOD缺口型损伤对TC4疲劳极限强度的影响

针对TC4钛合金风扇/压气机叶片前缘常遭受的外物损伤(FOD)缺口型损伤,进行了不同冲击角度下高速弹道冲击试验研究、损伤特征与应力集中分析,开展了冲击后不处理和冲击后去残余应力退火试样的高循环疲劳试验和疲劳极限强度预测。结果表明:随着冲击角度的增大入射侧损伤尺寸和应力集中系数基本保持不变,出射侧缺口损伤深度和损伤长度减小。损伤深度范围为0.6~1.5mm,应力集中系数范围为2.6~3.4。缺口型损伤试样的疲劳极限强度下降为光滑试样的27%~53%,与应力集中系数并不是呈反比关系。退火试样的高循环疲劳(HCF)性能或略微下降或基本不变,表明残余应力影响较小,残余应力对疲劳极限强度的影响程度不足光滑试样的10%。缺口型损伤试样的HCF性能与损伤底部半径的相关性不明显,随着最大损伤深度和损伤长度的增加而下降,表明制定维修手册时应着重考虑缺口型损伤的最大深度和损伤长度。Peterson经验公式对HCF性能的预测精度不理想,误差最大为45%,需要发展高精度的FOD缺口型损伤构件HCF性能预测方法。 

Effect of FOD notch-type damage on fatigue limit strength of TC4

To deal with foreign object damage (FOD) notch-type damages which the leading edge of TC4 titanium alloy fan/compressor blades suffered, test study on high-speed ballistic impacts, and analysis of damage characteristics and stress concentrations were carried out under different impact angles, while high cycle fatigue tests and fatigue limit strength prediction of as-impacted and residual stress relief annealed specimens were conducted. Conclusions were made below: with the increase of impact angles, damage sizes at incident side and stress concentrating coefficients remained constant, and the notched damage depth and length decreased. The range of the damage depth was 0.6－1.5mm, and the range of stress concentrating coefficients was 2.6－3.4. The fatigue limit strength of notch-type damaged specimens reduced to 27%－35% of smooth specimens, and was not inverse to stress concentrating coefficients. The high cycle fatigue (HCF） behavior of annealed specimens declined slightly or remained basically unchanged, indicating that the effect of the residual stress was slight. Influence of the residual stress on the fatigue limit strength was less than 10% of the smooth specimen. The HCF behavior of notch-type damaged specimens had no obvious correlation with the damage root radius, but declined with the increase of the maximum damage depth and damage length, indicating that special consideration must be given when preparing the maintenance manual. Prediction accuracy of HCF behavior by Peterson formula was unsatisfactory, of which the maximum error was 45%. It required to develop high precision prediction method for HCF behavior of FOD notch-type damaged components.