Citation: Barragán, E.R.; Ambriz,
R.R.; Frutos, J.A.; García, C.J.;
Gómora, C.M.; Jaramillo, D. Fatigue
Crack Arrest Induced by Localized
Compressive Deformation. Materials
2022, 15, 4553. https://doi.org/
10.3390/ma15134553
Academic Editor:
Francesco Iacoviello
Received: 28 May 2022
Accepted: 25 June 2022
Published: 28 June 2022
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Article
Fatigue Crack Arrest Induced by Localized
Compressive Deformation
Edú R. Barragán, Ricardo R. Ambriz * , José A. Frutos, Christian J. García, César M. Gómora and David Jaramillo
Instituto Politécnico Nacional CIITEC-IPN, Cerrada de Cecati S/N Col. Sta. Catarina, Azcapotzalco,
Mexico City 02250, Mexico; ebarragang1800@alumno.ipn.mx (E.R.B.); jfrutosmtz@gmail.com (J.A.F.);
cjgarcia@ipn.mx (C.J.G.); cmendozago@ipn.mx (C.M.G.); djvigu@gmail.com (D.J.)
* Correspondence: rrambriz@ipn.mx
Abstract:
The localized compressive deformation (LCD) effect generated by an indentation process at
the crack tip on the fatigue crack growth of the 7075-T651 aluminum alloy is reported. Eccentrically
loaded single-edge crack tension specimens (ESE(T)) were pre-cracked at a crack length of about
20 mm by applying a constant amplitude fatigue loading. Subsequently, the LCD process was
performed by using a semi-spherical indenter with a radius of 16 mm to compress the crack tip zone
at different forces (5.0, 7.0, 12.5, 13.5, 15.5 kN), applied on the opposite surfaces of the specimens. The
fatigue cracking process was continued on the compressed samples until an overall crack length of
about 30 mm was obtained. The compressive load and the number of delayed cycles is discussed in
terms of crack length and crack tip opening displacement (CTOD). A direct relationship between the
compressive force induced by the LCD process and the delay of the crack propagation due to the crack
arrest was observed. This effect became evident at a compressive force of 5.0 kN, where the crack
propagation was arrested for about 9000 cycles in comparison with the non-LCD sample. However,
when the force increased, the crack arrest also increased. The crack was considered to be completely
arrested at a compressive load of 15.5 kN, since the crack did not grow after the application of more
than 3 × 10
6
cycles.
Keywords:
fatigue crack arrest; localized compressive deformation; crack tip; 7075-T651 aluminum
alloy
1. Introduction
The 7075-T651 aluminum alloy is widely used for aircraft structural components
that require superior strengths. Aluminum alloys used in civil aircraft remain the top
engineering material, because the majority of aircraft are made with at least 70% aluminum
alloys [
1
]. Most of these components are subjected to cyclic loading, which can produce the
nucleation and propagation of fatigue cracks leading to catastrophic failures. Tajabadi [
2
]
analyzed the failure of a structural component made of 7075-T651 aluminum alloy used
to strengthen the center box for the wing connection in an Airbus A-300 aircraft subjected
to more than 19,000 flight cycles. He reported several stress concentrator sources for the
failure, such as corrosion flaws, scratches produced by careless maintenance and geometry
changes, which combined to cause the fatigue cracks’ failure. Several factors influence
the fatigue crack growth process, but actual engineering analysis is largely dependent
upon a stress intensity factor range. Thus, the level of the cyclic load applied (constant or
variable amplitude), as well as the geometry of the component, are the most important.
It is worth considering that even if the crack’s propagation stage can be represented by
a power law behavior, some characteristics of the materials may retard its growth. For
example, Ritchie et al. [
3
] summarize some mechanisms (crack tip shielding) which can
retard or even arrest the propagation of a crack; for example, the beneficial residual stress
fields. For instance, work-hardening processes can retard fatigue crack growth depending
Materials 2022, 15, 4553. https://doi.org/10.3390/ma15134553 https://www.mdpi.com/journal/materials
