Notch Size and Residual Stress Effects on Fatigue Strength of Metal Materials Subjected to Foreign Object Damage

To investigate the effects of notch size and residual stress on fatigue strength of different metal materials, based on the concept of fatigue notch coefficient, combined with the impact test data of different material specimens, the relationship between fatigue notch coefficient, fatigue strength and damage notch size, residual stress of different metal materials damaged specimens was studied by using Peterson's theoretical stress concentration coefficient calculation formula. The main conclusions are that fatigue strength will decrease due to the impact damage, and this decrease is mainly due to the size of the notch and the distribution of the residual stress near the notch. The ratio of notch depth to notch radius determines the reduction of fatigue strength. The larger the ratio is, the greater the degree of fatigue strength reduction is. The residual stress caused by foreign object damage in specimens of different materials may be tensile or compressive stresses. Whether it is tensile or compressive depends on the ratio of Young's moduli of the two impinging materials. The tensile stress is beneficial for the fatigue strength, while the compressive stress is detrimental. The conclusions can not only guide the design of anti-foreign damage of blades, but also have theoretical significance for the establishment of criteria for judging and repairing damaged blades.