Abstract:

To develop the severe spectrum, a method for determining the exceedance envelope of a severe spectrum is proposed based on the analysis of the exceedance curves of a fleet of Fokker 27 airplanes. First, the exceedance curves of 59 airplanes with similar service methods are selected, and the damage per flight of the fleet is calculated on the basis of the accumulated linear damage theory. Assuming the damage per flight of the Fokker 27 fleet follows the log-normal distribution, the damage degree of the severe spectrum is obtained according to the reliability requirement on the safe life of a fleet. Next, a log-normal distribution is used to depict the scatter of exceedance under a specified acceleration. Thus, an exceedance envelope of the severe spectrum is obtained by the extrapolation of the exceedance curve. The analysis shows that the exceedance of the severe spectrum should be increased with 1.177 times of its standard deviation.

Key words: fatigue, life, severe spectrum, load spectrum, exceedance