A comparison of fatigue crack growth performance of two aerospace grade aluminium alloys reinforced with bonded crack retarders

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Abstract

To improve the fail-safety performance of integral metallic structures, the bonded crack retarder concept has been developed in recent years. This paper presents an experimental investigation on the effectiveness of bonded crack retarder on fatigue crack growth life in two aerospace aluminium alloys: 2624-T351 and 7085-T7651. M(T) specimens bonded with a pair of straps made of GLARE fibre-metal laminate were tested under the constant amplitude load. Although the bonded crack retarders increased the crack growth life in both alloys, the magnitude of life improvement is very different between them. Compared to unreinforced specimens, application of crack retarders has resulted in 90% increase in fatigue life in AA7085, but only 27% increase in AA2624. The significant difference in fatigue life improvement is owing to the material’s intrinsic fatigue crack growth rate property, i.e. the Paris law constants C and n. Value of n for AA7085 is 1.8 times higher than that for AA2624. Therefore, AA7085 is much more sensitive to reductions in the effective stress intensity factor brought by the crack retarders; hence better life improvement.
LanguageEnglish
Pages1237-1242
JournalFatigue and Fracture of Engineering Materials and Structures
Volume41
Issue number5
Early online date1 Dec 2017
DOIs
StatePublished - May 2018

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Fatigue crack propagation
Aluminum alloys
Cracks
Fatigue of materials
Stress intensity factors
Laminates
Crack propagation
Metals
Fibers

Keywords

  • Aluminium alloys
  • Bonded crack retarders
  • Fatigue crack growth rate
  • Paris Law
  • Stress intensity factor

Cite this

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title = "A comparison of fatigue crack growth performance of two aerospace grade aluminium alloys reinforced with bonded crack retarders",
abstract = "To improve the fail-safety performance of integral metallic structures, the bonded crack retarder concept has been developed in recent years. This paper presents an experimental investigation on the effectiveness of bonded crack retarder on fatigue crack growth life in two aerospace aluminium alloys: 2624-T351 and 7085-T7651. M(T) specimens bonded with a pair of straps made of GLARE fibre-metal laminate were tested under the constant amplitude load. Although the bonded crack retarders increased the crack growth life in both alloys, the magnitude of life improvement is very different between them. Compared to unreinforced specimens, application of crack retarders has resulted in 90{\%} increase in fatigue life in AA7085, but only 27{\%} increase in AA2624. The significant difference in fatigue life improvement is owing to the material’s intrinsic fatigue crack growth rate property, i.e. the Paris law constants C and n. Value of n for AA7085 is 1.8 times higher than that for AA2624. Therefore, AA7085 is much more sensitive to reductions in the effective stress intensity factor brought by the crack retarders; hence better life improvement.",
keywords = "Aluminium alloys, Bonded crack retarders, Fatigue crack growth rate, Paris Law, Stress intensity factor",
author = "Abdul Syed and Xiang Zhang and Michael Fitzpatrick",
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language = "English",
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AU - Zhang,Xiang

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N2 - To improve the fail-safety performance of integral metallic structures, the bonded crack retarder concept has been developed in recent years. This paper presents an experimental investigation on the effectiveness of bonded crack retarder on fatigue crack growth life in two aerospace aluminium alloys: 2624-T351 and 7085-T7651. M(T) specimens bonded with a pair of straps made of GLARE fibre-metal laminate were tested under the constant amplitude load. Although the bonded crack retarders increased the crack growth life in both alloys, the magnitude of life improvement is very different between them. Compared to unreinforced specimens, application of crack retarders has resulted in 90% increase in fatigue life in AA7085, but only 27% increase in AA2624. The significant difference in fatigue life improvement is owing to the material’s intrinsic fatigue crack growth rate property, i.e. the Paris law constants C and n. Value of n for AA7085 is 1.8 times higher than that for AA2624. Therefore, AA7085 is much more sensitive to reductions in the effective stress intensity factor brought by the crack retarders; hence better life improvement.

AB - To improve the fail-safety performance of integral metallic structures, the bonded crack retarder concept has been developed in recent years. This paper presents an experimental investigation on the effectiveness of bonded crack retarder on fatigue crack growth life in two aerospace aluminium alloys: 2624-T351 and 7085-T7651. M(T) specimens bonded with a pair of straps made of GLARE fibre-metal laminate were tested under the constant amplitude load. Although the bonded crack retarders increased the crack growth life in both alloys, the magnitude of life improvement is very different between them. Compared to unreinforced specimens, application of crack retarders has resulted in 90% increase in fatigue life in AA7085, but only 27% increase in AA2624. The significant difference in fatigue life improvement is owing to the material’s intrinsic fatigue crack growth rate property, i.e. the Paris law constants C and n. Value of n for AA7085 is 1.8 times higher than that for AA2624. Therefore, AA7085 is much more sensitive to reductions in the effective stress intensity factor brought by the crack retarders; hence better life improvement.

KW - Aluminium alloys

KW - Bonded crack retarders

KW - Fatigue crack growth rate

KW - Paris Law

KW - Stress intensity factor

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