Probabilistic analysis of multi-site damage in aircraft fuselages

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 computation of the failure probability is developed. The MSD problem of a PSE is considered, where the uncertainties in crack initiation and crack growth as well as yield stress and fracture toughness are described by random variables. For the crack growth calculations the finite element alternating method [1], which avoids a remeshing of the finite element problem, is used. After specifying link up and failure criteria, importance sampling is employed to obtain the probability of failure of the PSE due to MSD.