engleski

Numerical simulation of fatigue crack propagation in stiffened panels

In stiffened panels of aged aircraft and ship structures, under a variety of loading and environmental conditions, fatigue cracks may initiate at sites of stress concentration due to geometrical discontinuities. So-called multiple site damage (MSD) is generated when cracks initiate at several adjacent stiffeners. For damage tolerance design it is important to determine fatigue crack growth life of structural parts with damage cracks [1]. Fatigue crack propagation in stiffened panels has been investigated experimentally and by numerical simulation employing an introduced crack growth simulation procedure for multiple propagating cracks [2]. When stiffened panels undergo tensile loading, bending occurs due to the cut stiffeners. The influence of bending stresses on crack propagation life of stiffened panels under cyclic tensile loading has been investigated in this paper. An incremental crack growth simulation procedure based on integration of Paris' equation, which takes into account interaction of several propagating cracks, was introduced. Mode I stress intensity factors (SIF), KI, were calculated by a FEM program using shell elements and assuming plane stress conditions [3]. FE analysis for stiffened panel specimens showed high bending stresses in the intact ligament, which should be taken into account in the crack growth simulation. Therefore, the SIF values calculated from nodal displacements of singular shell elements in a post processing FE procedure were scaled by a factor which depends on the ratio of bending and membrane stress component in the crack tip region. Using the introduced simulation procedure crack propagation lives were simulated and compared with the results of fatigue tests on stiffened panel specimens with a single and with three collinear cracks.

Crack Growth Interaction; Fatigue; Multiple Cracks; Stiffened Panel

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