Correlation of Fatigue Crack Growth by Crack Tip Deformation Behaviour

Hammouda, M.M.I.; Ahmad, Seleem; Sallam, Hossam El-Din M.

doi:10.1111/j.1460-2695.1995.tb00144.x

Cited by 21 publications

(22 citation statements)

References 23 publications

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“…Owing to the difficulty of calculations of stresses (force parameters) in the vicinity of various concentrators in structural elements during their service, especially with regard for elastoplastic strains of material and the action of the environment (working medium), it is necessary to search for the most simple approaches to solution of the problem. To a certain extent, this can be realized by using the strain parameters, because strains can not only be calculated but measured directly on members as well.Local strains can be determined, for example, in terms of relative displacements of the lips of a notch [1-3] or a crack [6][7][8][9][10][11]. In particular, this was corroborated by numerous attempts (during the last 5-10 years) to use strain criteria on the basis of the characteristics of the relative displacement 8 in analysis of the kinetics of cracks in a deformable body.…”

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confidence: 99%

“…In particular, this was corroborated by numerous attempts (during the last 5-10 years) to use strain criteria on the basis of the characteristics of the relative displacement 8 in analysis of the kinetics of cracks in a deformable body. Among them, for example, the COD and CTOD [6,7], COA and CTOA [8], ASef f [9], and ~5 [I0] approaches as well as the method of marks [11] should be mentioned. Note that, contrary to the previously known methods regulated by BS (British Standards) [6], the estimation of the value of 8 immediately in the vicinity of the tip of a crack [10] or near the tip of a notch [4,5] is considered now as the main problem.…”

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confidence: 99%

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Unified model of nucleation and growth of fatigue macrocracks. Part 2. Application of deformational parameters of the fracture mechanics of materials in the stage of crack initiation

Ostash¹,

Panasyuk²,

Kostyk³

1998

Mater Sci

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We propose a new approach to the experimental estimation of local strains at the tip of a concentrator. The approach is based on the measurement of displacement of certain points in the vicinity of the tip of a notch, which is further associated with the effective radius of the notch. Various concentrators in structures are simulated within a wide range of variation in radii of notches (p = 0.1-6.5 mm ) and in the geometry of specimens. We establish the main dependences between the value of the range of local strains Ae* and the period N i prior to the nucleation of a fatigue macrocrack. Thus, by using the experimental quantity Ae*, we can estimate the period N i prior to the nucleation of a fatigue crack of length a i = ae for structural elements of a complicated geometry.As is known, the problem of fatigue fracture of materials is an actual problem of modern materials science and fracture mechanics of materials [ 1,2]. In solution of this problem, investigation of the nucleation of macrocracks near stress concentrators in structural elements plays an important role. For this purpose, the force (stress), strain, and energetic parameters of the stress-strain state of the material are mainly used. The force approach to solution of the problem was earlier considered in [2]. Owing to the difficulty of calculations of stresses (force parameters) in the vicinity of various concentrators in structural elements during their service, especially with regard for elastoplastic strains of material and the action of the environment (working medium), it is necessary to search for the most simple approaches to solution of the problem. To a certain extent, this can be realized by using the strain parameters, because strains can not only be calculated but measured directly on members as well.Local strains can be determined, for example, in terms of relative displacements of the lips of a notch [1-3] or a crack [6][7][8][9][10][11]. In particular, this was corroborated by numerous attempts (during the last 5-10 years) to use strain criteria on the basis of the characteristics of the relative displacement 8 in analysis of the kinetics of cracks in a deformable body. Among them, for example, the COD and CTOD [6,7], COA and CTOA [8], ASef f [9], and ~5 [I0] approaches as well as the method of marks [11] should be mentioned. Note that, contrary to the previously known methods regulated by BS (British Standards) [6], the estimation of the value of 8 immediately in the vicinity of the tip of a crack [10] or near the tip of a notch [4,5] is considered now as the main problem.In this work, we present the results of investigation of the possibility of use of strain criteria in determination of the period N i prior to the nucleation of fatigue macrocracks near stress concentrators in certain steels and aluminum alloys. In our investigations, we employ the concept [2] that the main parameters of the process of nucleation of a macrocrack are the range Ae* of local elastoplastic strains near the tip of a notch and the characteristic size a t* ...

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confidence: 99%

mentioning

confidence: 99%

Unified model of nucleation and growth of fatigue macrocracks. Part 2. Application of deformational parameters of the fracture mechanics of materials in the stage of crack initiation

Ostash¹,

Panasyuk²,

Kostyk³

1998

Mater Sci

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“…A two‐dimensional plane‐stress elastic–plastic finite element analysis (FEA) [ 2] was performed on half of a plate with a symmetrically located artificially advancing mode I long edge crack under constant amplitude axial loading, with and without a transient SOL cycle, and two SOL cycles successively applied (TOL). The loading patterns are listed in Tables 1 and 2.…”

Section: Finite Element Analysismentioning

confidence: 99%

“…A single overload (SOL) is the simplest situation which possibly involves both retardation and acceleration in FCG. The response to a SOL is well documented [ 1–3].…”

Section: Introductionmentioning

confidence: 99%

“…The FCG rate following the application of a SOL was satisfactorily correlated [ 2] with a previously developed crack tip deformation parameter [ 10]. Crack tip blunting is responsible for the immediate increase in FCG rate after the SOL application, whilst the following FCG retardation behaviour is due to the residual stress–strain fields generated around the crack tip resulting in both plasticity‐induced crack tip closure and strain hardening effects.…”

Section: Introductionmentioning

confidence: 99%

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Fatigue Crack Growth Due to Two Successive Single Overloads

Hammouda

Ahmad

Seleem

et al. 1998

Fatigue Fract Eng Mat Struct

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The behaviour of fatigue growth and cyclic tip deformation of long cracks due to two successive single overloads was investigated both experimentally and numerically. The results show the effect of the ratio of the second and first overloads, and the crack increment between the two overloads. The contributions of both crack tip blunting and residual stress fields were separated and accommodated in a previously developed crack tip deformation parameter, which was utilized to predict the resulting fatigue crack growth behaviour. The following trends were experimentally observed. Should the ratio of the second and first overloads not be less than one, fatigue crack growth rates followed the predictions based on the second overload. Otherwise, either of the following two situations resulted: (1) when the two overloads were closely applied, the second overload caused an initial acceleration in growth rates followed by a behaviour controlled by the first overload; (2) when the second overload was applied after the crack growth had reached its minimum rate due to the first overload, more retardation in growth rate was observed. Based on the model developed in the paper, it is possible to enhance the retardation effect of an overload if this overload is preceded by another overload. This enhancement depends on the ratio of the two overloads and the crack increment between them.

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