This paper was produced for the 2019 NAFEMS World Congress in Quebec Canada

Resource Abstract

Aircraft structural integrity assurance requires the demonstration of the airframe capability to sustain critical operational loads being the structure affected by the damages expected to be developed during the aircraft live. These damages are the result of the structure exposure to environmental conditions, cyclic loading or impacts that can lead to a wide set of damaging processes such as corrosion, fatigue or composite delamination. The capability of the structure to sustain the required loads while being affected by the damages susceptible to be developed during the aircraft service life is called Residual Strength. The determination of the Residual Strength of the airframe is a mandatory requirement for aircraft certification under the Federal Aviation Agency (FAA) and the European Aviation Safety Agency (EASA) regulations.



In the particular case of material fatigue causing damage to the airframe, cracks will be developed in the structure that may have a significant impact over the residual strength. The impact of these cracks can be evaluated by analytic approaches for conventional configurations such as typical airframe geometries and crack scenarios. If these cracks are the result of unconventional conditions, in the sense of cracks originated by material mechanisms such as stress corrosion cracking or material embrittlement instead of being originated by fatigue damage under cyclic loading, no analytic approaches are available for calculations and usually costly dedicated test campaigns are required to properly evaluate the effect of the damages over the residual strength.



A new virtual testing approach is being developed by the authors in Airbus able to produce accurate and reliable residual strength predictions under unconventional crack scenarios. These predictions can be used to generate the evidences required for airframe certification while avoiding or at least reducing to a minimum the requirement of dedicated test campaigns. This virtual testing approach is based on advanced numerical simulations using implicit and explicit FEM.



In the paper, the virtual testing approach has been applied to a riveted lap joint structure with unconventional cracking. A sensitivity study of the effect of design parameters and crack scenarios over the joint residual strength have been performed. Correlation between virtual and physical testing is shown.