Analysis of cracks in aging aircraft structures, with and without composite-patch repairs
In this very interesting paper, the authors describe with many details a method of analysis of cracked panels in numerous complex situations, including the stress-intensity-factors (S.I.F.), namely: finite-sized stiffened panels with multiple cracks, stiffened cracked panels with broken stiffeners, flexible fasteners, panels with repaired cracks, cracks emanating from holes with or without fasteners, repaired or not, etc. ... The cases of two-dimensional or three-dimensional bodies are treated independently. The whole method, named finite element alternating method, was presented in earlier papers, but thoroughly developed and completed is here. Briefly described, the method comprises several stages: to calculate the stress-field of the uncracked panel, with its stiffeners or repairing patches, with the finite element method using a coarse grid; then to calculate the stresses on the crack boundaries, this stage gives undue residual stresses on the panel boundaries; to reverse the stresses on crack boundaries to create traction-free crack faces; to calculate the S.I.F. by appropriate methods under the present situations; to reverse the residual stresses and to calculate the new stressfield; then to iterate until the residual stresses cancel and the S.I.F. stabilized. The difficult point is to calculate the S.I.F. for the different cases which are examined. For instance, analytical solutions for crack tips in an infinite skin subjected to arbitrary tractions on the crack faces give the S.I.F. for coupled modes I and II. The applications show clear corrections compared to less accurate methods. For crack emanating from holes, an analytical solution gives the residual tractions on the crack faces, then Green functions allow to determine the \(k\)-factors, etc... The applications give evolutions of the crack size versus different parameters and show notable reductions of the S.I.F. thanks to the adhesive patch utilization of variable stiffnesses. The results are summarized in form of very useful charts of great interest, in particular in aeronautics, which fully justify this attractive method.
scientific article; zbMATH DE number 149455