Influence of the crack morphology on the fatigue crack growth rate: A continuously-kinked crack model based on fractals

The characterisation of the stress fields in proximity of crack tips is a fundamental task in fracture mechanics, providing means for the assessment of the fracture resistance or the crack growth rate. Among several methods available for the computation of the crack‐tip stress intensity factor, an extremely efficient and flexible solution strategy is obtained using the distributed dislocation technique. This method has been successfully applied to several remote loading conditions and cracked geometries and can also take into account the effect of surface friction and roughness through the inclusion of an appropriate interface model. In this paper, we make use of a non‐linear algorithm, which uses dislocations distributed along the crack, to compute the crack‐tip stress intensity factors under remote mixed‐mode stress fields. It is shown that the algorithm can be effectively applied to different geometries, notably to cases where the mode mixity originates from geometrical features, such as in the presence of notches or re‐entrant corners. In particular, the effect of dilatancy is correctly captured with the adopted method, and its consequences are discussed with regard to the onset of unstable crack propagation under monotonic loading.

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“…Other authors adopted a fractal description of the interface, eg, derived from a digitalisation of the fracture surface profiles. ()…”

Section: Description Of the Modelmentioning

confidence: 99%

Near‐tip stress fields of rough and frictional cracks under mixed‐mode loading

Spagnoli

Carpinteri

Terzano

2018

Fatigue Fract Eng Mat Struct

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“…Crack path is influenced by the crack morphology and irregularities that affect the growth rate and induce combinations of mode I and mode II, typically decreasing the propagation rate for the same stress level, due to the surface interference effects …”

Section: Introductionmentioning

confidence: 99%

Mixed mode fatigue and fracture in planar geometries: Observations onK_eqand crack path modelling

Tavares

Reis

Freitas

et al. 2019

Fatigue Fract Eng Mat Struct

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The mixed mode I‐II fatigue and fracture is briefly reviewed, addressing experimental and numerical modelling aspects, and focusing on planar specimens. One major challenge concerns the determination of equivalent stress intensity factor (Keq) in mixed mode situations. Several approaches were compared through the determination of Keq/KI over a wide range of values of KI/KII or KII/KI. Whereas all different approaches converge to the same value as KI/KII increases, the same does not happen for large KII/KI, where differences between values of Keq persist. In the regions of 0 < KI/KII < 2 and 0 < KII/KI < 2, no stable trend of results can be defined. Experimental fatigue crack growth results are presented for Al alloy AA6082‐T6. Compact tension specimens, modified with holes, and four‐point bending specimens under asymmetrical loading promoting mixed mode situations, were subjected to fatigue crack growth tests, where crack path and crack growth rate were measured. The presentation of the fatigue crack growth data was made using a Paris law based upon Keq. Differences in the Paris law constants were found for the different Keq criteria. Recent developments in numerical techniques, as the implementation of the extended finite element method (XFEM) in finite element software packages allows to determine accurately crack paths in mixed mode fracture. This article highlights concepts for mixed‐mode fatigue and fracture and supporting data, identifying challenges still to be overcome.

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“…9 Successful applications of the fractal geometry to size effect-related fatigue problems have been proposed by the present authors in the past few years. [10][11][12] Alternatively, a simple and effective way to take into account the effects of the material microstructure on the crack behaviour at small scale consists in using the non-uniform stress field arising in a uniformly loaded non-homogeneous material due to the embedded inohomogeneities: as a matter of fact, even for a structural component under a uniform remote stress, an oscillating stress field might develop at the microscale. In this paper, a theoretical model of a periodically kinked crack is developed to describe the influence of the deflection degree on the fatigue behaviour.…”

Section: Introductionmentioning

confidence: 99%

Interpreting some experimental evidences of fatigue crack size effects through a kinked crack model

Spagnoli

Vantadori

2014

Fatigue Fract Eng Mat Struct

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Threshold condition and rate of fatigue crack growth in both short and long crack regime appear to be significantly affected by the degree of crack deflection. In the present paper, a theoretical model of a periodically kinked crack is proposed to describe the influence of the crack deflection degree on the fatigue behaviour. The kinking of the crack is due to a periodic self‐balanced microstress field having length scale d. By correlating the parameter d with a characteristic material length (e.g. average grain size in metals, maximum aggregate size in concrete), the present model is applied to interpret some experimental findings related to crack size effects in fatigue of materials. Well‐known experimental results concerning three different situations (fatigue threshold, fatigue short crack growth and fatigue crack growth in the Paris regime) are analysed.

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Influence of the crack morphology on the fatigue crack growth rate: A continuously-kinked crack model based on fractals

Cited by 43 publications

References 16 publications

Near‐tip stress fields of rough and frictional cracks under mixed‐mode loading

Near‐tip stress fields of rough and frictional cracks under mixed‐mode loading

Mixed mode fatigue and fracture in planar geometries: Observations onK_eqand crack path modelling

Interpreting some experimental evidences of fatigue crack size effects through a kinked crack model

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Influence of the crack morphology on the fatigue crack growth rate: A continuously-kinked crack model based on fractals

Cited by 43 publications

References 16 publications

Near‐tip stress fields of rough and frictional cracks under mixed‐mode loading

Near‐tip stress fields of rough and frictional cracks under mixed‐mode loading

Mixed mode fatigue and fracture in planar geometries: Observations onKeqand crack path modelling

Interpreting some experimental evidences of fatigue crack size effects through a kinked crack model

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Product

Resources

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Mixed mode fatigue and fracture in planar geometries: Observations onK_eqand crack path modelling