Airframe metal fatigue revisited

Molent, L.; Dixon, B.

doi:10.1016/j.ijfatigue.2019.105323

Cited by 17 publications

(9 citation statements)

References 28 publications

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“…Therefore, corrosion is considered a time-dependent nucleation source. All else being the same (spectrum, material, stress), the equivalent crack-like sizes of discontinuities are the major source of variability in the fatigue life of a component [30,31].…”

Section: Corrosion and Fatigue Of Airframe Alloys: Practical Considerationsmentioning

confidence: 99%

“…For pitting-induced fatigue cracks, it has been observed that the effective cracklike pit depth (EPS = equivalent pre-crack size) is a defining fatigue crack growth metric [6,[13][14][15][29][30][31][32][33][34][35][36][37][38][39]. Coupling this result with a well-proven crack growth model, such as that used in the lead crack framework [40], could enable predicting the impact with time of service-detected corrosion pitting on airframe or individual component structural integrities.…”

Section: Corrosion and Fatigue Of Airframe Alloys: Practical Considerationsmentioning

confidence: 99%

“…1. An Assessment Methodology for Fatigue Cracking from Corrosion Pits, Exemplified by Figure 17 Fatigue cracks from production-quality initial discontinuities begin to grow almost immediately after an aircraft enters service [31,35,36,40,[51][52][53][54][55]. Corrosion is likely to occur once the corrosion protection systems fail during service.…”

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confidence: 99%

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Management of Airframe In-Service Pitting Corrosion by Decoupling Fatigue and Environment

Molent¹,

Wanhill²

2021

CMD

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Corrosion-induced maintenance is a significant cost driver and availability degrader for aircraft structures. Although well-established analyses enable assessing the corrosion impact on structural integrity, this is not the case for fatigue nucleation and crack growth. This forces fleet managers to directly address detected corrosion to maintain flight safety. Corrosion damage occurs despite protection systems, which inevitably degrade. In particular, pitting corrosion is a common potential source of fatigue. Corrosion pits are discontinuities whose metrics can be used to predict the impact on the fatigue lives of structural components. However, a damage tolerance (DT) approach would be more useful and flexible. A potential hindrance to DT has been the assumption that corrosion-induced fatigue nucleation transitions to corrosion fatigue, about which little is known for service environments. Fortunately, several sources indicate that corrosion fatigue is rare for aircraft, and corrosion is largely confined to ground situations because aircraft generally fly at altitudes with low temperature and humidity Thus, it is reasonable to propose the decoupling of corrosion from the in-flight dynamic (fatigue) loading. This paper presents information to support this proposition, and provides an example of how a DT approach can allow deferring corrosion maintenance to a more opportune time.

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Section: Corrosion and Fatigue Of Airframe Alloys: Practical Considerationsmentioning

confidence: 99%

Section: Corrosion and Fatigue Of Airframe Alloys: Practical Considerationsmentioning

confidence: 99%

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Management of Airframe In-Service Pitting Corrosion by Decoupling Fatigue and Environment

Molent¹,

Wanhill²

2021

CMD

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“…Though this paper initially concentrated on the growth of long, artificially induced cracks, it should be recalled that the airworthiness certification of AM replacement parts requires a durability analysis [4] and that the EIDS that is required for the associated durability analysis is generally sub mm [4]. Indeed, as first shown by Lincoln and Melliere [78] as part of the USAF F-15 program and subsequently highlighted in [3,6,[79][80][81][82], a durability analysis necessitates the use of the associated small crack da/dN versus ∆K curve (a similar statement is contained in Appendix A3 of the ASTM fatigue test standard E647-13a [83]). In this context, as noted in [6], the experimental data revealed that the R ratio effect associated with the growth of small, naturally occurring cracks is often quite small.…”

Section: Residual Stresses: Am Replacement Parts and Cold Spraymentioning

confidence: 99%

Review of Requirements for the Durability and Damage Tolerance Certification of Additively Manufactured Aircraft Structural Parts and AM Repairs

et al. 2020

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The USAF requirements for the durability and damage tolerance certification for additively manufactured (AM) aircraft structural parts, which are detailed in Structures Bulletin EZ-19-01, raise a number of new and, as yet, unanswered questions. The present paper attempts to address three questions: How to perform a fracture mechanics-based analysis of crack growth in an AM part so as to account for the residual stresses, how to perform a fracture mechanics-based durability analysis of a cold spray repair so as to account for both the induced residual stresses and the presence of multiple co-located cracks, and how to perform a fracture mechanics-based durability analysis of an AM part so as to account for the presence of multiple collocated surface braking cracks. In this context, the present paper reveals the potential of the Hartman–Schijve variant of the NASGRO crack growth equation to accurately predict the growth of each of the individual (collocated) cracks that arose in a cold spray-repaired specimen and in a specimen from a crack that nucleated and grew from a rough surface.

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“…The current paper presents a series of experimental studies that reveals the importance of this phenomena, i.e., failure due to cracking that nucleates from material discontinuities in the substrate at the interface between the cold spray and the substrate. At this stage, it should be noted that the growth of small naturally occurring lead cracks, i.e., the cracks that determine the operational life of a component [31][32][33], which see the environment often grow in a near exponential fashion [26,[31][32][33][34][35][36][37] and follow a da/dN versus ∆K curve that is essentially a Paris-like crack growth equation with a small fatigue threshold. Furthermore, for small cracks growing in laboratory air, there are minimal R ratio effects [26,30,[37][38][39][40][41][42].…”

Section: Introductionmentioning

confidence: 99%

Experimental Studies into the Analysis Required for the Durability Assessment of 7075 and 6061 Cold Spray Repairs to Military Aircraft

Jones

Matthews²,

Peng

et al. 2020

Aerospace

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This paper presents an experimental study into the analysis required for the durability assessment of 7075 and 6061 cold spray repairs to military aircraft. To this end, it is first shown that provided the bulk stress in a 7075 cold spray coating can be kept beneath approximately 150 MPa, then the coating should not crack. A range of examples are presented in which the interface between the coating and the substrate only fails subsequent to crack growth in the substrate. We also show that failure of cold spray repaired/coated panels can also be due to the nucleation and growth of cracks in the substructure immediately adjacent to the coated/repaired region. As such, when performing a durability analysis for a cold spray repair, the growth of such small naturally occurring cracks, both at the interface and immediately adjacent to the ends of the coating, need to be accounted for.

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Airframe metal fatigue revisited

Cited by 17 publications

References 28 publications

Management of Airframe In-Service Pitting Corrosion by Decoupling Fatigue and Environment

Management of Airframe In-Service Pitting Corrosion by Decoupling Fatigue and Environment

Review of Requirements for the Durability and Damage Tolerance Certification of Additively Manufactured Aircraft Structural Parts and AM Repairs

Experimental Studies into the Analysis Required for the Durability Assessment of 7075 and 6061 Cold Spray Repairs to Military Aircraft

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