Deformation approach to the evaluation of the period of initiation and growth of fatigue macrocracks

Panasyuk, V. V.; Ostash, О. P.; Kostyk, E. M.; Chepil, R. V.

doi:10.1007/bf00558787

Cited by 7 publications

(12 citation statements)

References 17 publications

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“…It was taken that the period prior to the initial microcrack initiation N i was equal to the number of load cycles prior to the formation of a crack = d* * * with length a i [17]. Dependences ( AOy, Ni) and (d, Ni) were constructed by using the stress approach [17], and dependences (Ae*, Ni) and (d*, Ni) by using the strain approach [20,21]. The values of A~y and Ae* were used as the parameters of cyclic crack resistance at the stage of macrocrack initiation for N i = 3 9 105 and N i = 3 9 102 in the low-amplitude and high-amplitude regions of the diagrams, respectively (see Table 1).…”

Section: Experimental Techniquementioning

confidence: 99%

“…The length of a macrocrack was measured by a cathetometer KM-6 at 25• magnification at a load of as large as 70% of the maximal one. The displacement of points (opening displacement) near the tip of a notch or a crack was measured by a gage of linear displacements [20] in the range 0-300 pan with an accuracy of +0.5 [tm at the frequency of a load cycle of 0.1 Hz.…”

Section: Experimental Techniquementioning

confidence: 99%

“…The closure of a fatigue macrocrack and the value of AKef f were estimated by using the well-known technique [22]. Within the strain approach, diagrams of macrocrack growth (v, A e*) [20] were constructed. On their basis, the values of Ae* at v = 10-sin/cycle and v = 10-1~…”

Section: Experimental Techniquementioning

confidence: 99%

“…These parameters were determined within the frameworks of the stress [15,16] and strain [20,21] approaches. It was taken that the period prior to the initial microcrack initiation N i was equal to the number of load cycles prior to the formation of a crack = d* * * with length a i [17].…”

Section: Experimental Techniquementioning

confidence: 99%

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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: Experimental Techniquementioning

confidence: 99%

Section: Experimental Techniquementioning

confidence: 99%

Section: Experimental Techniquementioning

confidence: 99%

Section: Experimental Techniquementioning

confidence: 99%

See 2 more Smart Citations

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

Ostash¹,

Kostyk²,

Makoviichuk³

et al. 1999

Mater Sci

Self Cite

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“…The lengths and orientations of these lines are determined in the process of numerical solution of the problem by the method of singular integral equations. The values of the crack tip opening displacement are also determined.Disk specimens with notches or cracks are used in the investigation of the processes of initiation and development of cracks under static and cyclic loading [1][2][3][4]. The level of local strains near a concentrator characterized by the jump of normal displacements (opening displacement) at its tip 6 can be regarded as a parameter that controls these processes in elastoplastic materials.…”

mentioning

confidence: 99%

Tension of an elastoplastic disk. Part 1. Central crack

Panasyuk¹,

Savruk²,

Ivanyts'ka³

et al. 1999

Mater Sci

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539.375 Within the framework of the model of plasticity bands, we consider an elastoplastic problem of fracture mechanics of the development of plasticity bands near the tips of a central crack in a disk. We assume that, in the plane stressed state, plastic strains in the vicinity of the crack tip are localized along three plasticity bands (L I , L 2 , and L~ ) one of which is located on the continuation of the crack and the other two make nonzero angles with the direction of the crack and that, under the conditions of plane deformation, plastic strains are localized along two plasticity bands (L I and ~ ). The band (~) is modeled by a line of discontinuity of normal and tangential displacements and the bands (L l and L 2) are modeled by lines of discontinuity of tangential displacements. The lengths and orientations of these lines are determined in the process of numerical solution of the problem by the method of singular integral equations. The values of the crack tip opening displacement are also determined.Disk specimens with notches or cracks are used in the investigation of the processes of initiation and development of cracks under static and cyclic loading [1][2][3][4]. The level of local strains near a concentrator characterized by the jump of normal displacements (opening displacement) at its tip 6 can be regarded as a parameter that controls these processes in elastoplastic materials. To find this parameter, it is necessary to solve the problem of determination of the strain-stress state of the disk taking into account elastoplastic strains near the tip of the concentrator. For this purpose, we use the model of plasticity bands (see, e.g., [5-1 1]) according to which the plasticity zone is localized along narrow bands lying on the continuations of the crack. As follows from the experimental data presented in [5][6][7], this model reflects the actual process of deformation in the first stage of the development of plastic strains in thin plates. However, in many cases (in particular, in disks with central cracks [6]), under loads of certain types, we observe the appearance of new bands inclined to the line of continuation of the crack. Neglecting these inclined bands, we get underestimated values of the displacement ~ [12].In the present work, within the framework of the model of plasticity bands, we solve the problem of elastoplastic equilibrium of a disk with central crack and study the influence of inclined plasticity bands on the crack tip opening displacement. Plane Stressed StateA thin disk of radius R containing a central crack L 1 of length 2/1 is related to a Cartesian coordinates xOy. The disk is subjected to tension by two concentrated forces F applied at points Zo = + ih (Fig. 1). The material of the disk is perfectly elastoplastic.In the disk subjected to tension, near the crack tips, we first observe the appearance of plastic bands directed along the continuation of the crack. Further, as the load increases, we observe the appearance of two additional bands at each tip making nonzero an...

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Rectangular Specimens with Edge Notches

Savruk

Kazberuk

2016

Stress Concentration at Notches

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Deformation approach to the evaluation of the period of initiation and growth of fatigue macrocracks

Cited by 7 publications

References 17 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

Tension of an elastoplastic disk. Part 1. Central crack

Rectangular Specimens with Edge Notches

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