SEDL / STP / STP948-EB / STP25632S

Fractographic Aspects of the Effect of Environment on the Fatigue Crack Propagation Mechanism in a High-Strength Aluminum Alloy

Ranganathan, N
Maître de conferences, E.N.S.M.A., Poitiers,

Bouchet, B
Ingenieur de recherche, E.N.S.M.A., Poitiers,

Petit, J
Directeur de recherche, E.N.S.M.A., Poitiers,

Pages: 23    Published: Jan 1987

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Abstract

Fatigue crack propagation tests were conducted in three different environments, air, vacuum, and high purity nitrogen (N²) [3 ppm water vapor (H²O) + 1 ppm oxygen (O²)], on a high-strength aluminum alloy, 2024-T351. From tests conducted at a load ratio of 0.5, a typical behavior in the N² environment is brought into light. At moderate ΔK-values, the crack growth behavior in N² is similar to that observed in vacuum. As ΔK decreases, the crack growth curve shifts towards the one obtained in air showing a progressive environmental effect occurring in the presence of traces of water vapor.

The fractographic observations for these tests show that the environmental effect observed in the crack growth curves is accompanied by changes in the fracture surface morphology.

The observed results are discussed considering an energy-based model and by taking into account a discontinuous crack growth mechanism at low growth rates.