The effect of environment on fatigue and crack closure in aluminium alloys
The effect of environment on fatigue and crack closure in aluminium alloys
The role of fatigue crack closure in the corrosion fatigue of plate aluminium alloys has been investigated. Fatigue crack growth rates in alloys 7010 (Al-Zn-Mg-Cu), 2024 (Al-Cu-Mg) and 8090 (Al-Li-Cu-Mg) were compared to air and 3.5% salt water at R = 0.1 and R = 0.5 (frequency 1 Hz) and crack closure loads were measured. In air, the alloys showed a large (8090); moderate (7010); and small (2024) increase in growth rate at the higher R-ratio. Rates at R = 0.5 coincided with `effective' rates at R = 0.1 indicating that the R-ratio effect was due to crack closure at R = 0.1. In 8090, increasing the test frequency influenced a fracture mode transition from tensile to shear mode fracture, which was shown to be an environmental effect. The salt water environment was found to markedly increase the fatigue crack growth rates in 7010-T7651 and 8090-T8771 but had minimal effect on 2024-T351. Fatigue crack closure in 7010 and 2024 was not significantly changed in salt water compared to air and hence did not contribute to the corrosion fatigue effect. In 8090 by comparison, the extremely low fatigue rates observed in air were dominated by a high level of crack closure which was greatly reduced in salt water.
A comparison of the three alloys has identified different crack closure mechanisms. In 7010 and 8090 roughness-induced closure was dominant in air and salt water. In air, 8090 showed a large additional closure contribution due to oxide-induced closure. In 2024 the closure was due to plasticity-induced closure, and was not significantly influenced by the environment.
The fatigue crack growth rates have been compared in terms of the material mechanical properties and the fracture mechanism. In 7010 and 8090 the corrosion fatigue effect observed in salt water has been explained in terms of the change in fracture mechanism produced by a hydrogen-activated cross-slip mechanism.
University of Southampton
1992
Kemp, Ronald Martin John
(1992)
The effect of environment on fatigue and crack closure in aluminium alloys.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
The role of fatigue crack closure in the corrosion fatigue of plate aluminium alloys has been investigated. Fatigue crack growth rates in alloys 7010 (Al-Zn-Mg-Cu), 2024 (Al-Cu-Mg) and 8090 (Al-Li-Cu-Mg) were compared to air and 3.5% salt water at R = 0.1 and R = 0.5 (frequency 1 Hz) and crack closure loads were measured. In air, the alloys showed a large (8090); moderate (7010); and small (2024) increase in growth rate at the higher R-ratio. Rates at R = 0.5 coincided with `effective' rates at R = 0.1 indicating that the R-ratio effect was due to crack closure at R = 0.1. In 8090, increasing the test frequency influenced a fracture mode transition from tensile to shear mode fracture, which was shown to be an environmental effect. The salt water environment was found to markedly increase the fatigue crack growth rates in 7010-T7651 and 8090-T8771 but had minimal effect on 2024-T351. Fatigue crack closure in 7010 and 2024 was not significantly changed in salt water compared to air and hence did not contribute to the corrosion fatigue effect. In 8090 by comparison, the extremely low fatigue rates observed in air were dominated by a high level of crack closure which was greatly reduced in salt water.
A comparison of the three alloys has identified different crack closure mechanisms. In 7010 and 8090 roughness-induced closure was dominant in air and salt water. In air, 8090 showed a large additional closure contribution due to oxide-induced closure. In 2024 the closure was due to plasticity-induced closure, and was not significantly influenced by the environment.
The fatigue crack growth rates have been compared in terms of the material mechanical properties and the fracture mechanism. In 7010 and 8090 the corrosion fatigue effect observed in salt water has been explained in terms of the change in fracture mechanism produced by a hydrogen-activated cross-slip mechanism.
This record has no associated files available for download.
More information
Published date: 1992
Identifiers
Local EPrints ID: 461853
URI: http://eprints.soton.ac.uk/id/eprint/461853
PURE UUID: b479abb8-4502-4d98-81f9-2dd9c1dc0a69
Catalogue record
Date deposited: 04 Jul 2022 18:57
Last modified: 04 Jul 2022 18:57
Export record
Contributors
Author:
Ronald Martin John Kemp
Download statistics
Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.
View more statistics