Cyclic crack resistance of aluminum alloys in the crack origin and growth stages

Panasyuk, V. V.; Ostash, О. P.; Kostyk, E. M.; Kudryashov, V. G.; Neshpor, G. S.

doi:10.1007/bf01148672

Cited by 6 publications

(10 citation statements)

References 2 publications

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“…1 a, c, e). The length of the initial microcracks does not depend on the notch radius p and is equal to 30-50 p.m, which is in accordance with the structural parameter of the alloy [23]. Further, microcracks grow according to the mechanism of normal separation.…”

Section: Results Of Testsmentioning

confidence: 74%

Initiation and growth of corrosion-fatigue cracks near stress concentrators in V95pchT2 aluminum alloy

Ostash¹,

Kostyk²,

Makoviichuk³

et al. 1999

Mater Sci

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We investigate the kinetics of small fatigue cracks starting from notches in samples of V95pchT2 aluminum alloy in air and in a 3.5% NaCI solution. The influence of salt water is manifested in the initiation of pits on the notch surface and subsequent accelerated growth of small cracks (2-3 times faster than in the laboratory air). The size of an initial macrocrack a i does not depend on the level of stress or strain, notch radius, or environment and is equal to the characteristic distance d* = 100 ~m of the prefailure zone which is a material constant. The effect of crack closure in the presence of a corrosive medium is observed at the crack length a > 100 ~m. Within the frameworks of the approach proposed earlier for the study of initiation of a macrocrack near a notch, the basic dependences of values of local stresses or strains on the duration of the period of initiation of a macrocrack with length a i = d* are established, and the standard diagrams of cyclic crack resistance are constructed for V95pchT2 aluminum alloy at the stage of macrocrack growth in air and in a 3.5% NaCI solution.A corrosive environment substantially accelerates fatigue processes in the vicinity of stress concentrators in the form of clinched openings, fillets, notches, etc. Such a fatigue failure is often observed in the long-term operation of structural parts, made of high-strength aluminum alloys, of aircrafts and ships. It was established that surface pits appear as a result of the action of the corrosive environment [1,2]. These pits serve as nuclei of microcracks and cause their further development. Moreover, in aluminum alloys, pits appear near inclusions of the secondary phases rich with iron and silicon [ 1 ]. The degree of corrosion damage depends on the acting stresses and type of corrosion [2]. According to the Rebinder effect, the adsorption action of the corrosive environment, in particular of C1-ions, promotes an increase of plastic deformation in the surface layer which is manifested in an increase in dislocation density [3]. It is obvious that a decrease of the macroplasticity parameters ~g and ~5 of aluminum alloys by 10-20% reflects the absorption influence of the corrosive environment [4]. In the neighborhood of micro-and macrocracks, the action of the environment is even more substantial. This effect is characterized by the mechanism of enhancement of the local microplasticity in the presence of hydrogen known as the HELP mechanism [5,6]. This mechanism is inherent to high-strength aluminum alloys.The corrosive environment intensifies the development of fatigue cracks. Investigations of the growth of long cracks (macrocracks) in the corrosive environment were performed for high-strength aluminum alloys [7][8][9][10][11][12]. The corrosive environment was modelled by a 3.5% NaC1 solution. It was established that this environment accelerates the growth of both fatigue macrocracks ( 2-3 times in comparison with the growth in air) and fatigue cracks which are short from the microstructural point of view and physically ...

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Section: Results Of Testsmentioning

confidence: 74%

Initiation and growth of corrosion-fatigue cracks near stress concentrators in V95pchT2 aluminum alloy

Ostash¹,

Kostyk²,

Makoviichuk³

et al. 1999

Mater Sci

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“…12). This agreement is typical of many high-strength aluminum alloys [5] this agreement is absent [3]. According to the analysis given in [3], the different behavior of high-strength aluminum alloys and plastic steels must be caused by the fact that in aluminum alloys the characteristic quantity d* is the same for notched and smooth specimens, whereas in steels it is greater for smooth specimens than for notched ones.…”

Section: Determination Of Characteristics Of Resistance Of the Materimentioning

confidence: 86%

“…For cyclically hardened steel, d* is also independent of p (for O. 1 < p < 4.0 mm), but its value can be somewhat different for notched and smooth specimens [5]. The value of d* is considerably (by an order) greater than the original structural parameters of the material [5,7], for example, the grain size and the distance between inclusions of the secondary phase.…”

Section: Phenomenological Model Of Nucleation Of a Fatigue Macrocrackmentioning

confidence: 97%

“…1 < p < 4.0 mm), but its value can be somewhat different for notched and smooth specimens [5]. The value of d* is considerably (by an order) greater than the original structural parameters of the material [5,7], for example, the grain size and the distance between inclusions of the secondary phase. At the same time, for quasibrittle materials (or plastic materials at low temperatures), they can coincide [3].…”

Section: Phenomenological Model Of Nucleation Of a Fatigue Macrocrackmentioning

confidence: 98%

“…For example, there exist qualitatively opposite dependences of the fatigue limit t~ R of a smooth specimen and the fatigue threshold Kth of a cracked specimen on the grain size for the same material [3]. It is also known [4] that for a given loading amplitude, the growth rate of microstructuraily short and physically small cracks is greater than that of macrocracks and only in the case where the size of the former is greater (sometimes, by a factor of several times) than the size of the grain, the distance between inclusions, etc., they have the same growth rates [5]. In addition, as the length of physically small cracks increases, their growth rate drops and some of them can stop growing.…”

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confidence: 98%

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Unified model of nucleation and growth of fatigue cracks. Part 1. Use of force parameters of fracture mechanics of materials in the stage of crack nucleation

Ostash¹,

Panasyuk²,

Kostyk³

1998

Mater Sci

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According to the phenomenological model of nucleation of a fatigue macrocrack, the process is considered as a two-parameter process. The process is described by the local stress or strain range and a certain linear parameter of the material. We propose the corresponding parameters, namely, the local stress range At~. and the characteristic size d" of the prefracture zone. The formation of this zone is caused by the anomaly of the yield strength of the material in subsurface layers, the microstructure, the loading amplitude, the cyclic strain hardening, and the environment. The quantity d* is a constant of the material, which is independent of the geometry of notch and specimen. The boundary of the prefracture zone is considered as a macrobarrier that determines the growth of microstructuraliy short and physically small cracks. The moment when a physically small crack oversteps the boundary of the prefracture zone is defined by the quantitative criterion (ao= d* ) of the initial size a 0 of a macrocrack in the material. The proposed dependences of ( A~., At,.) and (d*, Ni) can be regarded as a basis for the determination of characteristics of resistance of the material to the nucleation of a fatigue macrocrack.Due to the rapid development of fracture mechanics, especially structural fracture mechanics, in the past ten years considerable progress has been made in understanding the phenomena of fatigue of metals. A detailed analysis of successes and failures concerning the solution of this problem is given in [1,2]. By summing our own data and literature data, we propose to consider fatigue of materials as a process that consists of the following main stages: 1) nucleation and growth of microstructurally short cracks, 2) growth of physically small cracks and formation of a macrocrack, and 3) growth of the macrocrack up to total fracture of the body.Within the framework of this approach, the endurance limit of the material is estimated by the maximum stresses for which a crack in the material does not grow, i.e., the crack is retarded by certain physical barriers (crack resistance of the material). These barriers are caused by the microstructure of the material (boundaries of grains and twins, sizes of pearlitic colonies and martensitic packs, etc.). Thus, the endurance limit is, to a great extent, connected with a certain linear parameter of the structure of the material, in particular, with the distance between structural barriers [2]. At the same time, it is necessary to take into account the following fact: if the microstructural barrier of the material is considered as the main factor for its endurance limit, then it is impossible to explain some experimental data. For example, there exist qualitatively opposite dependences of the fatigue limit t~ R of a smooth specimen and the fatigue threshold Kth of a cracked specimen on the grain size for the same material [3]. It is also known [4] that for a given loading amplitude, the growth rate of microstructuraily short and physically small cracks is greater than that ...

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Effect of substructure on crack formation and total failure of industrial alloys of the aluminium-copper-magnesium system under low-cycle fatigue conditions

Teleshov¹,

Kuzginov²,

Sirotkina³

et al. 1990

Strength Mater

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Cyclic crack resistance of aluminum alloys in the crack origin and growth stages

Cited by 6 publications

References 2 publications

Initiation and growth of corrosion-fatigue cracks near stress concentrators in V95pchT2 aluminum alloy

Initiation and growth of corrosion-fatigue cracks near stress concentrators in V95pchT2 aluminum alloy

Unified model of nucleation and growth of fatigue cracks. Part 1. Use of force parameters of fracture mechanics of materials in the stage of crack nucleation

Effect of substructure on crack formation and total failure of industrial alloys of the aluminium-copper-magnesium system under low-cycle fatigue conditions

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