A probabilistic estimation method of multiple site damage occurrence for aircraft structures

Abstract

A method for estimating the probability of the occurrence of multiple site damage (MSD) is presented. MSD is considered to occur when more than two cracks initiate in a structural component which contains multiple similar structural details. Crack initiation life of a single detail is assumed to follow the logarithmic normal distribution. The probability of multiple details initiating MSD is calculated based on the P-S-N curve of a single structural detail. The method is applied to an estimation example of three details to demonstrate the procedure. The estimation is validated by experiments. To obtain the basic fatigue properties of the material, tests with the single detail specimens are also conducted and reported. The effects of the number of details and stress levels are discussed, which indicates that for a specified fatigue life, the probability of MSD occurrence increases with the increase of the number of the details and the increase of the stress levels; for a given reliability, fatigue life corresponding to the occurrence of MSD decreases with the increase of the number of the details and the increase of stress levels.