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Fatigue life of aircraft structure fastener holes are enhanced through cold expansion
process, which creates an annular zone of compressive residual stresses around the hole.
Durability and damage tolerance analysis of structures containing cold expanded adjacent holes
require quantification of cold expansion-induced compressive residual stresses. Threedimensional
non-linear FE simulation of sequential cold expansion of two closely spaced
adjacent holes in Al 7075-T651 plate is carried out to predict the beneficial residual stresses
completely. Further, an experimental investigation on sequential cold expansion of adjacent holes
is carried out using cold expansion tooling system developed in-house and the retained expansion
levels are measured. Comparison of FE simulation results and results of experimental
investigations indicate that developed simplified FE simulation approach is capable of adequately
predicting cold expansion-induced beneficial residual stresses around the hole, including through
thickness variations.
Keywords: fatigue life; adjacent fastener holes; cold expansion; compressive residual stress. |
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