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Fatigue crack propagation tests with cyclic stress of constant amplitude and
frequency were carried out on stiffened panel specimens damaged with a single
crack or an array of collinear cracks, until fracture occurred. A numerical
simulation procedure for multiple propagating cracks which takes account of
crack interaction was introduced. The Mode I stress intensity factors, KI, were
calculated from finite element nodal displacements results. A bending effect due
to the cut stiffeners has been taken into account in the stress intensity factor
calculation. The experiment and numerical simulation showed a higher crack
growth rate in the case of the stiffened panel with three cracks, which is due to cut
cross sectional area and crack interaction.