Statistical Fatigue and Residual Strength Analysis of New/Aging Aircraft Structure

The paper describes an ongoing work with populating the world´s largest stress intensity factor data base with 92.4 million new solutions and separate work consisting of large-scale residual strength analysis of the C-130 center-wing-box (CWB) considering numerous different multiple-crack crack configurations. A computationally efficient and reliable procedure is used for calculating stress intensity factor solutions K(y) to be stored in the data base. An extended technique is used in predicting the residual strength of the C-130 CWB for multiple crack configurations. The proposed method requires a method/solver that can solve the very complex nonlinear contact problems between rivets and the skin/stiffeners, failure of rivets with a very low computational cost per crack configuration. The splitting scheme described in the paper is the basic tool used to obtain this objective. All mathematical equations are solved with high accuracy with respect to the exact mathematical solution of the problem and with control of the point-wise error (less than 1%) in all stress intensity functions K(y). For residual strength analysis of the CWB, the software used scales very well on computer hardware like SGI Altix (ASC/Eagle/Hawk) and IBM P5 (NAVO/Babbage/Kraken). Several three-dimensional analyses representative of the size and complexity of the C-130 center wing box have been completed. An example of such an analysis explicitly modeled the wing skins, spar caps, spar webs, and stringers which resulted in 90 million nodes and 14 million finite elements. Depending on the polynomial order, p, used in the solution, the total degrees of freedom ranges from 243-742 million for polynomial orders p = 2 - 4; respectively. For a more accurate solution polynomial order, 5 is needed which results in a problem with 1.2 billions of degrees-of freedom.