Estimation of Aircraft Structural Fatigue Life Using the Crack Severity Index Methodology

摘要

In thiswork, fatigue test results under different randomspectra have been used to validate the crack severity indexnmethodology inwhich only the normal load factor and aircraft grossweightwere considered as the load.The originalncrack severity index methodology was developed to quantify the relative severity in terms of crack growth potentialnusing the stress spectra recorded at the wing root. The crack severity index values have been used to determine thenflight mission severity through interpolation between known flaw growth curves of reference usages. Thisninterpolated flaw growth curve enables aircraft users to predict the cumulative fatigue crack growth damage basednon individual aircraft activity and provides a useful guide for scheduling future inspection and maintenancenactivities. To validate the crack severity index methodology based on normal load factor and aircraft gross weightndata instead of stress spectra, experimental fatigue lives were obtained for the stresses represented by normal loadnfactor and aircraft gross weight spectra of different random loads. Then, the differences in fatigue life as severitynmeasurements were compared with the crack severity index values. A good correlation was obtained, whichnvalidated the crack severity index methodology. The test results were also used to tune a simulation equation forncrack growth. The good correlation between the crack severity index values and fatigue test or crackngrowth simulation results suggests a simple way of predicting the structural fatigue life from crack severity indexnvalues.