Chair of Engineering Mechanics Ifm-publication 2-333

Most aircraft fleets nowadays are operating under the concept of damage tolerance, which requires an aircraft to have sufficient residual strength in the presence of damage in one of its principal structural elements (PSE) during the interval of service inspections. The residual strength however is significantly reduced due to multi site damage (MSD). In the present paper, a probabilistic framework for the calculation of the failure probability is set up. The MSD problem of a PSE is considered, where crack initiation and crack growth as well as yield stress and fracture toughness are described by random variables. The crack growth calculations are carried out by means of the finite element alternating method (Park and Atluri 1998), which avoids a remeshing of the finite element problem. After specifying link up and failure criteria, importance sampling is employed to obtain the probability of failure of the PSE due to MSD.