Abstract
The 7xxx series of aluminium alloys are sensitive to intergranular hydrogen environmentally assisted cracking (HEAC) in moist air environments. A new generation of 7xxx alloys used in aircraft components (including AA7449)
have been found to be more sensitive to HEAC. This investigation aims to quantify the HEAC crack growth rates of AA7449-T7651 in moist air at different temperatures. Double cantilever beam specimens were loaded at a constant
displacement and placed in moist air (80-85% relative humidity) at temperatures between 25-80ºC. Regular measurements of crack length permitted the determination of the crack growth rate as a function of the stress intensity factor
(KI) during stage I (high KI dependence of growth rate) and stage II (low KI dependence of growth rate). Increasing the temperature was found to increase the crack growth rate during stage II cracking, following Arrhenius kinetics.
The activation energy for the stage II crack growth rate at a stress intensity factor of 14.5 MPa m^0.5 was estimated as 84.7 kJ/mol. Additionally, the threshold stress intensity factor for HEAC was found to decrease with increasing
temperature. This was attributed to a higher hydrogen solubility at higher temperatures. The crack growth rate of AA7449-T7651 at room temperature was similar to that of overaged AA7050 and AA7075-T7651, ranging between
1.3-2.1*10-7 mm/s. It was inferred that the alloy temper has more influence than the composition during stage II cracking at room temperature.
have been found to be more sensitive to HEAC. This investigation aims to quantify the HEAC crack growth rates of AA7449-T7651 in moist air at different temperatures. Double cantilever beam specimens were loaded at a constant
displacement and placed in moist air (80-85% relative humidity) at temperatures between 25-80ºC. Regular measurements of crack length permitted the determination of the crack growth rate as a function of the stress intensity factor
(KI) during stage I (high KI dependence of growth rate) and stage II (low KI dependence of growth rate). Increasing the temperature was found to increase the crack growth rate during stage II cracking, following Arrhenius kinetics.
The activation energy for the stage II crack growth rate at a stress intensity factor of 14.5 MPa m^0.5 was estimated as 84.7 kJ/mol. Additionally, the threshold stress intensity factor for HEAC was found to decrease with increasing
temperature. This was attributed to a higher hydrogen solubility at higher temperatures. The crack growth rate of AA7449-T7651 at room temperature was similar to that of overaged AA7050 and AA7075-T7651, ranging between
1.3-2.1*10-7 mm/s. It was inferred that the alloy temper has more influence than the composition during stage II cracking at room temperature.
Original language | English |
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Article number | 109199 |
Number of pages | 9 |
Journal | Corrosion Science |
Volume | 180 |
Early online date | 19 Dec 2020 |
DOIs | |
Publication status | E-pub ahead of print - 19 Dec 2020 |
Keywords
- Fracture mechanics
- AA7449
- Hydrogen environmentally assisted cracking
- Double cantilever beam
- Moist air
- Aluminium alloys
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Dive into the research topics of 'The influence of temperature on hydrogen environmentally assisted cracking of AA7449-T7651 in moist air'. Together they form a unique fingerprint.Student theses
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Hydrogen environmentally assisted cracking of aerospace aluminium : An investigation on the increased susceptibility of novel aircraft alloys to cracking in moist air under static loads
De Francisco, U. (Author), Peel, M. J. (Supervisor) & Larrosa, N. O. (Supervisor), 25 Jan 2022Student thesis: Doctoral Thesis › Doctor of Philosophy (PhD)
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