Analytical methodology for predicting fatigue life distribution of fuselage splices

Methodologies to predict fatigue life distribution of fuselage splices, measured as the number of cycles to visible cracks, were developed in this work. Modeling procedures using three dimensional nonlinear finite element (FE) analysis were developed to obtain the stress state at the rivet hole. Contact surfaces, which include friction effects, were used to simulate the rivet to hole and skin to skin interactions. The squeezing force (SF) resulting from the riveting process and the coefficient of friction (CF) used for the contact surfaces were taken as random variables. Analytical expressions for local stress as a function of the squeezing force and coefficient of friction were developed using a response surface technique along with limited FE analyses. Based on the calculated local stresses, a strain-life approach was employed to predict fretting fatigue crack nucleation at the rivet hole. A Monte Carlo simulation was developed, which integrated the two random variables into the models, to determine the fatigue life distribution to visible cracks. Results from the simulation showed that the predicted fatigue life distribution correlated very well with the existing test data. Further sensitivity studies indicated that the squeezing force has a stronger influence on the life distribution than the coefficient of friction.