Mechanisms of Slow Fatigue Crack Growth in High Strength Aluminum Alloys: Role of Microstructure and Environment

Suresh, S.; Bretz, P. E.

doi:10.1007/bf02645122

Cited by 159 publications

(55 citation statements)

References 25 publications

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“…Increasing the dislocation glide resistance increases the proximity of the nucleated dislocations to the crack tip, and thus, causes the threshold stress intensity to increase. With this result being contrary to experimental observations, we suggest that it indicates the importance of features not included in the model, such as microcracking at large precipitates [36] and the spatial heterogeneity of the dislocation glide resistance [37,34]; thus, providing sound motivation for future work. Despite these short comings of the present model, we assert that this work represents a step towards the development of atomistic based fatigue crack growth laws in real materials, which could be used in mesoscale modeling for the generation of physics based crack growth laws in macroscopic simulation.…”

Section: Discussioncontrasting

confidence: 87%

“…Thus, it is possible that the enhanced fatigue crack growth in these regions, due to the increased mobility of dislocations, dominates the overall change in threshold fatigue crack growth rates. The idea of a decreasing fatigue threshold with increasing heterogeneity was also put forth by Suresh et al [34] to describe experimentally observed crack growth rates in aluminum alloy 7075. In that work, the threshold stress intensity range decreased as the spacing between precipitates increased as the alloy was aged.…”

Section: Crack Growth Per Cyclementioning

confidence: 96%

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An atomistic investigation into the nature of near threshold fatigue crack growth in aluminum alloys

Baker

Warner

2014

Engineering Fracture Mechanics

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a b s t r a c tDespite decades of study, the atomic-scale mechanisms of fatigue crack growth remain elusive. Here we use the coupled atomistic-discrete dislocation method, a multiscale simulation method, to examine the influence of dislocation glide resistance on near-threshold fatigue crack growth in an aluminum alloy. The simulations indicate that the threshold increases with an increase in dislocation glide resistance, and that a transition in the crack growth direction can occur when dislocation nucleation is inhibited by other nucleated dislocations. Three main mechanisms of fatigue crack propagation are observed: cleavage along the primary slip plane, crack extension by dislocation emission, and crack extension by opening along lattice defects.

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Section: Discussioncontrasting

confidence: 87%

Section: Crack Growth Per Cyclementioning

confidence: 96%

An atomistic investigation into the nature of near threshold fatigue crack growth in aluminum alloys

Baker

Warner

2014

Engineering Fracture Mechanics

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“…The corresponding K max initially increased slightly and then rose sharply. A similar observation has been reported for underaged, peak-aged, and overaged 7075 aluminum alloy in moist air of relative humidity 95% [1].…”

Section: Fig 6 -Data Showing Variation Of Alternating and Maximum Stsupporting

confidence: 66%

“…2 and 3. Similar behavior was reported for underaged, peak-aged, and overaged 7075 aluminum alloys tested in moist air of 95% relative humidity [1], 2024-T351 aluminum alloy in dry and wet argon [2], Al-3% Mg alloy in dry nitrogen at 298°K and in liquid nitrogen at 77°K [3], 7091 aluminum alloy in air of humidity greater than 90% [4], and 2024-T3 aluminum alloy in laboratory air at ambient temperature [5]. Such observations have also been made for low and medium carbon, medium carbon alloy, 2 l A Cr-1 Mo, rotor, 4340, JIS SB42, and AerMet 100 steels [6][7][8][9][10][11][12][13][14][15].…”

Section: Fatigue Crack Growth Ratesupporting

confidence: 58%

Environmentally Influenced Near-Threshold Fatigue Crack Growth in 7075-T651 Aluminum Alloy

Lee¹,

Sanders²,

George³

et al. 1996

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Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, SPONSOR/MONITOR'S ACRONYM(S) SPONSOR/MONITOR'S REPORT NUMBER(S)Approved for public release; distribution is unlimited. SUPPLEMENTARY NOTES ABSTRACTThe near-threshold fatigue crack growth behavior of a 7075-T651 aluminum alloy was studied in laboratory air, vacuum, and an aqueous 3.5% NaCl solution. Results obtained indicate that raising the stress ratio R enhanced the near-threshold fatigue crack growth with a greater crack growth rate da/dN and smaller threshold stress intensity range AK" in laboratory air and an aqueous 3.5% NaCl solution. However, the reverse was observed in vacuum. The near-threshold fatigue crack growth was most sluggish with the smallest da/dN and greatest AK^, values in vacuum, intermediate with an intermediate da/dN and AK^, in the aqueous 3.5% NaCl solution, and fastest with the greatest da/dN and smallest AK," values in laboratory air. In laboratory air and aqueous 3.5% NaCl solution AK", initially decreased with increasing R until a value of 0.5 was reached, and then leveled off or decreased slightly. The AK ft values for these two environments appear to converge at a higher R. On the other hand, in vacuum, the AKth increased linearly with increasing R. In addition, at lower R, a greater resistance to nearthreshold fatigue crack growth was detected in the aqueous 3.5% NaCl solution than in laboratory air. This is attributable to crack closure, induced by corrosion product at the crack tip. 15. SUBJECT TERMS fatigue, near-threshold fatigue crack growth, stress ratio, vacuum, laboratory air, 3.5% NaCl solution, threshold stress intensity range, maximum stress intensity 16. Abstract:The near-threshold fatigue crack growth behavior of a 7075-T651 aluminum alloy was studied in laboratory air, vacuum, and an aqueous 3.5% NaCl solution. Results obtained indicate that raising the stress ratio R enhanced the near-threshold fatigue crack growth with a greater crack growth rate da/dN and smaller threshold stress intensity range AK t h in laboratory air and an aqueous 3.5% NaCl solution. However, the reverse was observed in vacuum. The near-threshold fatigue crack growth was most sluggish with the smallest da/dN and greatest AK t h values in vacuum, intermediate with an intermediate da/dN and AK t h in the aqueous 3.5% NaCl solution, and fastest with the greatest da/dN and smallest AK t h values in laboratory air. In laboratory air and aqueous 3.5% NaCl solution AK t h initially decreased with increasing R until a value of 0.5 was reached, and then leveled off or decreased slightly. The AK t h values for these two environments appear to converge at a higher R. On the...

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“…Most of experimental observations have indicated that the threshold increases in proportion to a square root of the characteristic microstructural dimension such as packet size and grain size. [3][4][5][6][7][8] Therefore, the fine grain structure is advantageous in the suppression to fatigue crack initiation, while the coarse grain size is superior in the resistance of fatigue crack growth. 9,10) Continuous cyclic bending (CCB) 11) has been proposed as a straining technique that can produce high strain in the surface layers and low strain in the central part of the metal sheet.…”

Section: Introductionmentioning

confidence: 99%

Improvement of Fatigue Properties by Means of Continuous Cyclic Bending and Annealing in an Al-Mg-Mn Alloy Sheet

et al. 2004

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The fatigue properties in the Al-Mg-Mn alloy sheet subjected by the continuous cyclic bending (CCB) and annealing have been investigated. By the CCB and subsequent annealing, the gradient microstructure with coarse-grained surface layers and fine-grained central layer is produced in the sheet. The fatigue life of the CCBent and annealed sheet is 2-4 times longer than that of the as-received one. The existence of the coarse-grained surface layers makes the crack propagation rate lower by a factor of 1/2 to 1/3. The fatigue crack growth in the sheet consisting of such different microstructure layers is characterized by the fractography. Further, factors improving the fatigue properties are discussed.

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Mechanisms of Slow Fatigue Crack Growth in High Strength Aluminum Alloys: Role of Microstructure and Environment

Cited by 159 publications

References 25 publications

An atomistic investigation into the nature of near threshold fatigue crack growth in aluminum alloys

An atomistic investigation into the nature of near threshold fatigue crack growth in aluminum alloys

Environmentally Influenced Near-Threshold Fatigue Crack Growth in 7075-T651 Aluminum Alloy

Improvement of Fatigue Properties by Means of Continuous Cyclic Bending and Annealing in an Al-Mg-Mn Alloy Sheet

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