Fastener holes in aircraft are common sites for initiation of fatigue crack growth. Cold expansion of the hole, typically by drawing an oversized mandrel through the hole, is a standard technique to improve fatigue life. When airframes are subjected to higher temperatures, in supersonic aircraft for example, there is concern that the beneficial residual stresses from cold expansion may relax due to creep. Methods of predicting and measuring residual stresses caused by the cold expansion process have been developed but the effects of creep relaxation have not been investigated. The paper describes experimental measurement and finite element prediction of cold expansion residual stresses and their redistribution after creep, with and without additional mechanical load. Exoerimental measurements of near-surface stresses used an X-ray diffraction method while average through-the-thickness stresses were measured using a new method based on Sachs' boring. This new method allowed non-axisymmetric residual stresses to be measured as was the case when creep relaxation occurred with mechanical load. Axisymetric and three-dimensional finite element analysis were used to predict the stress distribution through the thickness of the component showing good agreement with measurements. Creep relaxation of residual stress does indeed occur, but some benefit of the cold expansion remains, particularly when creep relaxation is combined with the application of mechanical load.
Creep relaxation of residual stresses around cold expanded holes
Transactions of the ASME, Journal of Engineering Materials and Technology ; 123 , 1 ; 125-131
2001
7 Seiten, 11 Bilder, 2 Tabellen, 20 Quellen
Article (Journal)
English
Flugzeug , Befestigungselement , Bohrung (Bohrloch) , Kaltumformen , Ermüdungsriss , Rissausbreitung , Eigenspannung , Spannungsrelaxation , Kriechen (Werkstoff) , Finite-Elemente-Methode , Spannungsverteilung , mechanische Beanspruchung , Aluminiumlegierung , Kriechfestigkeit , Zugeigenschaft , Röntgenbeugung
Residual Stress Distributions around Cold Expanded Holes
British Library Conference Proceedings | 1993
|