Effect of a strengthening patch on safe life of an aircraft in a fleet

The effect of a strengthening patch applied at a fatigue critical area during service on the safe life of an aircraft in a fleet is studied.13; 13; The safe life defined as the life corresponding to a failure probability of 0.OO1 is obtained from the probability density function of fatigue life. This probabilistic description is derived by randomizing a S-N type relation valid for an aircraft under service loading.13; 13; Major sources of variability contributing to scatter in fatigue life are included in the analysis. They appear as13; parameters in the expression for fatigue life. The contributions of these sources to the variability in fatigue life are analysed.13; 13; Application of a strengthening patch at a critical area13; during service enhances fatigue life by reducing the local13; area stress, variability in the effectiveness of the patch in reducing the local area stress has a significant effect on the enhancement in safe life that can be achieved. The13; stage in service life at which the strengthening patch is13; applied is also an important factor affecting the safe fatigue life. The influences of these factors are analysed