Fatigue crack initiation and propagation in aileron lever using successive-initiation modeling approach

initiation and propagation due to cyclic mechanical fatigue damage in the T-38 aileron lever is modeled using a continuum damage modeling approach in conjunction with a "successive-initiation" technique. Successive initiation is a continuum-based damage-propagation methodology that is based on updating the state of damage in material and accumulating damage in individual elements according to their stress-life history. The elements are eliminated from the structure if they exceed the defined damage threshold. In contrast to available fracturemechanics approaches, this method does not require an initial crack and is capable of determining the initiation site. The model is used to predict the number of cycles to crack initiation and propagation to critical size. This approach successfully predicts the location of crack initiation, propagation path and propagation rate. Field data and experimental observations of the cracks correlated very well with finite element results. Probability design approach using a Monte Carlo simulation is used to determine the sensitivity of fatigue-life response to variation in load and mechanical-property inputs. As expected, the most important parameter was found to be the damage exponent. A sensitivity study was conducted without damage parameters as input variables. The results of this study show that load variations are more important than material-property variations.