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Stresses and Strains in a Cold-Worked Annulus

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Aircraft structures rept.

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The fatigue process in aircraft structure is very often associated with the presence of stress concentrations of one kind or another, and fastener holes represent by far the most numerous such feature in any mainly metallic structure. For some time new substantial attention has been given to methods for improving the fatigue behaviour of structures containing holes, one of the most successful of these methods being the cold-expansion process. In common with other mechanical means, hole cold-expansion achieves its quite dramatic effect life improvement factors typically of the order of two to five by modifying the local stress field to become benign so far as the fatigue process in concerned. In the cold-expansion process the hole is expanded by the passage of an oversize or interference-fit tapered mandrel through the hole, a sleeve or protective bush being used to prevent the possibility of scoring or galling. Analytically-derived plane strain stresses and strains in an annulus pressurised sufficiently to cause plastic flow are given. Unloading giving rise to reyielding around the bore is then examined, along with the effect of reaming. Cold-working is then included in the analysis in terms of interference between mandrel and hole. Finally, comparisons of stress and strain predictions are made with those from a finite element analysis. Australia.

Subject Categories:

  • Aircraft
  • Properties of Metals and Alloys
  • Mechanics

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