This paper discussed the des igning method of damage tolerance,studie d the life evaluation method of fatigue crack extension of long cracks and the d etermining method of dimension ao of ini tial crack.

• 论述了损伤容限设计方法 ,研究了长裂纹的疲劳裂纹扩展寿命估算方法和初始裂纹尺寸a0 的确定方法。