Abstract: A laboratory study of multiple site damage (MSD) in aging airplanes was conducted. A net section stress criterion was found to be well correlated with the failure of MSD specimens. The tests also showed that in the presence of MSD, the residual strength of the structure, critical crack length and even crack propagation life are greatly reduced in comparison with the isolated cracks considered by the current damage tolerance requirements. On the other hand, based on the stress intensity factor solution using a compound method, the prediction of MSD crack propagaiton life is well fitted with test results.

Key words: multiple-site-damage, cracks stress intensity factor, crack propagation life