Crack growth simulation and residual strength prediction in thin shell structures

The dissertation mainly deals with self-similar and non-self-similar crack growth simulations in thin-shell metallic structures. An analysis methodology and a software program for predicting the structural integrity and residual strength of pressurized, thin-shell, built-up structures are developed.; The first part of the dissertation discusses the crack tip opening angle (CTOA) fracture criterion obtained and correlated from coupon tests to predict fracture behavior and residual strength of built-up aircraft fuselages. Geometrically nonlinear, elastic-plastic, thin shell finite element analyses are used to simulate stable crack growth and to predict residual strength. Both measured and predicted results of laboratory flat panel tests and full-scale fuselage panel tests show substantial reduction of residual strength due to the occurrence of multi-site damage (MSD). Detailed comparisons of stress distributions, stable crack growth history, and residual strength between the predicted and experimental results are used to assess the feasibility and validity of the analysis methodology.; The second part of the dissertation discusses issues related to crack trajectory prediction in thin shells; an evolving methodology uses the crack turning phenomenon to improve the structural integrity of aircraft structures. A directional criterion is developed based on the maximum tangential stress theory, but taking into account the effect of T-stress and fracture toughness orthotropy. Possible extensions of the current crack growth directional criterion to handle geometrically and materially nonlinear problems are discussed. The path independent contour integral method for T -stress evaluation is derived and its accuracy is assessed using a p- and hp-version adaptive finite element method. Curvilinear crack growth is simulated in coupon tests and in full-scale fuselage panel tests. Both T-stress and fracture toughness orthotropy are found to be essential to predict the observed crack paths.; The analysis methodology and software program developed herein will allow engineers to maintain aging aircraft economically while insuring continuous airworthiness. Consequently, it will improve the technology to support the safe operation of the current aircraft fleet as well as the design of more damage-tolerant aircraft for the next-generation fleet.