凹坑型硬物损伤对TC4材料疲劳强度的影响

针对风扇/压气机叶片中叶盆/叶背遭受的硬物损伤(FOD)凹坑型损伤,进行了不同冲击角度下模拟FOD试验、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研究和疲劳强度的预测。结果表明:损伤深度和应力集中系数均随着冲击角度的增加而变大,损伤深度范围为0.1~0.5mm,应力集中系数范围为1.3~1.7。不同冲击角度条件下,凹坑型损伤试样疲劳强度相对光滑试样下降程度在50%~70%范围内,与应力集中系数并不是呈单调下降关系,最危险冲击角为60°。去残余应力退火后凹坑型损伤试样的高循环疲劳（HCF）性能有所提高,表明残余应力的影响程度不容忽略。去残余应力试样的HCF性能并不是随应力集中系数的增大而下降,验证了微结构损伤的影响,说明损伤深度作为制定可用极限或维修极限的唯一参量具有一定的局限性。对凹坑型损伤试样的疲劳强度的预测误差在±20%以内。 

Effect of dent-type foreign object damage on fatigue strength of TC4 material

For the dent-type foreign object damage (FOD) suffered by the concave side/convex side of fan/compressor blades, experimental study on FOD simulation, analysis of damage characteristics and stress concentration were carried out under different impact angles, while high cycle fatigue tests and fatigue strength prediction of as-impacted and residual stress relief annealed specimens were conducted. Conclusions were drawn as follows: damage depths and stress concentration factors increased with the increase of the impact angle. The range of the damage depth was 0.1-0.5mm, and the range of the stress concentration factors was 1.3-1.7. Under the condition of different impact angles, the fatigue strength of the dent-type damage declined relative to smooth specimens within the range of 50%-70%, and didnt show a monotonic decreasing relationship with stress concentration factors. The worst angle was 60°. The high cycles fatigue(HCF) behavior of residual stress relief annealed specimens was improved, which indicated that effect of residual stress could not be ignored. The HCF behavior of residual stress relief annealed specimens did not decrease with the increase of stress concentration factors, which validated the effect of microstructure damage. It showed that the damage depth as the single parameter to build allowable limits and repair limits had some limitations. Prediction accuracy of fatigue strength for dent-type damaged specimens was within ±20%.