A unified method of design for fatigue crack growth resistance in structural materials

Gavras, Anastasios G.; Donald, JK

doi:10.1016/j.ijfatigue.2012.07.009

Cited by 12 publications

(6 citation statements)

References 18 publications

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“…The final part of the tests was run at constant load (95% of the maximum load reached during the second part to the test) at a cyclic frequency of 5 Hz to obtain data in Region III of fast crack growth. The generated FCG data were analyzed, and fracture toughness values were obtained using Fracture Technology Associates' automated analysis software [37]. Closure evaluations were done using the adjusted compliance ratio (ACR) technique [38,39].…”

Section: Fatigue Crack Growth Testingmentioning

confidence: 99%

Fatigue crack growth mechanisms at the microstructure scale in as-fabricated and heat treated Ti-6Al-4V ELI manufactured by electron beam melting (EBM)

Galarraga

Warren

Lados

et al. 2017

Engineering Fracture Mechanics

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Electron beam melting (EBM) is a metal powder bed fusion additive manufacturing (AM) technology that fabricates parts by selectively scanning consecutive powder layers with an electron beam. Additive manufacturing technologies are increasing in importance for aerospace and medical applications, where the demand for a fundamental understanding and predictability of static and dynamic material properties are high. Ti-6Al-4V is the most widely used and studied alloy for this technology, and is the focus of this work in its Extra Low Interstitial (ELI) variation. The layered manufacturing of metallic components by EBM creates a unique directional microstructure, and consequently, anisotropic properties. Microstructure evolution, and its influence on mechanical properties of the alloy in the asfabricated condition, has been documented by various researchers. However, fatigue crack propagation and the effects of the directional structure have not been sufficiently studied, imposing a barrier for this technology's potential extension to high-integrity applications. In this study, fatigue crack growth (FCG) both parallel and perpendicular to the build directions was studied for different stress ratios and crack growth stages. The interaction between the directional as-fabricated EBM microstructure and FCG was investigated and compared to that of the equiaxed β annealed microstructure obtained by annealing above the β transus temperature. The FCG threshold, ΔK th , was analytically modeled for the two relative crack propagation directions at different stress ratios, and FCG microstructural mechanisms were established for all three regions of crack propagation.

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Section: Fatigue Crack Growth Testingmentioning

confidence: 99%

Fatigue crack growth mechanisms at the microstructure scale in as-fabricated and heat treated Ti-6Al-4V ELI manufactured by electron beam melting (EBM)

Galarraga

Warren

Lados

et al. 2017

Engineering Fracture Mechanics

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“…Cracks are categorised based on the relationship between their dimensions, as shown in Fig. 1, such as length (a) and width (w), length of shielding zone (l s ), characteristic microstructural size (m s ) and the plastic zone radius (r p ) [23,[28][29][30][31]. A physically small crack (hereafter referred as small crack) is defined as a crack of length in the range between 20 µm and 1 mm [24] and is generally smaller than the typical non-destructive testing (NDT) detection limit (< 1 mm) [29,[32][33][34].…”

Section: Small Crack Growth Behaviour and Modified Nasgro Equationmentioning

confidence: 99%

Simulation of fatigue small crack growth in additive manufactured Ti–6Al–4V material

Gupta

Sun

Bennett

2020

Continuum Mech. Thermodyn.

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Additive manufacturing (AM) offers design freedom and ability to fabricate parts of complex shapes which are not often possible with the conventional methods of manufacturing. In an AM part, even with optimum build parameters, a complete elimination of defects is not possible and this makes it hard to fully deploy the AM technology to build load bearing parts operating under cyclic loading conditions. Many of these defects are < 1 mm in size and are categorised as ‘small cracks’. Local interaction of cracks with microstructural features and closure effects at the wake of the crack tip are some of the factors which make the growth behaviour of small and long cracks different. A crack growth life prediction method, which effectively considers the small crack growth behaviour, has been discussed in this paper. This proposed method includes a detailed finite element-based crack growth simulation using the ANSYS SMART fracture technology. The lifing calculations utilise the modified NASGRO equation and small crack growth data which was obtained from the published long crack growth data, corrected for closure effects. The predicted stress versus number of cycles curves were compared against the fatigue test results for the AM specimens in Ti–6Al–4V material. A good correlation between the predictions and test results suggests that the proposed method can be used to assess the small crack growth life of AM parts where the fatigue effects of cyclic loading can be quite significant.

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“…An effective one -different from the original and modified plasticity induced crack closure formulation (e.g. Donald and Paris 1999;Cui et al 2011;Gavras et al 2013) -can be determined taking the log-relative contributions into account: ΔK e = (ΔK)…”

Section: Crack Tip Stress Intensity Criterionmentioning

confidence: 99%

Fatigue damage criteria classification, modelling developments and trends for welded joints in marine structures

Besten

2018

Ships and Offshore Structures

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Fatigue is typically a governing limit state for marine structures. Welded joints are the weakest links in that respect. Physics involve several resistance dimensions, a range of scales and distinct contributions in different stages of the accumulative damage process. Fatigue damage criteria developed over time have been classified with respect to type of information, geometry, parameter and process zone including plane and life region annotations. The criteria are evaluated regarding model (in)capabilities, showing up to what extent (governing) physics are taken into account. Modelling developments and trends towards complete strength, multi-scale and total life criteria have been identified. Incorporating all four (interacting) fatigue resistance dimensions: material, geometry, loading & response and environment translates into a complete strength fatigue damage criterion. Considering macro-, meso-and micro-scale information provides a multi-scale fatigue damage criterion. Correlation of crack initiation and growth requires matching intact and cracked geometry parameters, revealing a total life fatigue damage criterion. HIGHLIGHTS• Classification of fatigue damage criteria with respect to type of information, geometry, parameter and process zone including plane and life region annotations.• Identification of modelling developments and trends towards complete strength, multi-scale and total life fatigue damage criteria for welded joints in marine structures. NomenclatureA notch strain energy density process zone area C crack growth or fatigue resistance curve intercept (endurance coefficient) D fatigue damage E normal strain at macro-scale E Young's modulus J crack tip energy density J 1 hydrostatic stress or strain component J 2 deviatoric stress or strain component K σ crack tip stress intensity factor K ɛ crack tip strain intensity factor K' work hardening coefficient K N notch stress intensity factor K N I mode-I notch stress intensity factor K N III mode-III notch stress intensity factor K I mode-I stress intensity factor K I T total mode-I stress intensity factor K I r residual mode-I stress intensity factor K III mode-III stress intensity factor K * FE dimensionless FE based notch stress intensity factor N (total) number of cycles until failure N i number of cycles corresponding to initiation N g number of cycles corresponding to growth R notch strain energy density process zone radius S stress based fatigue damage criterion S B Battelle structural normal stress range S e effective notch stress range S eq (equivalent) Von Mises stress range S n nominal stress range S s hot spot structural stress range S T total stress range T temperature T B Battelle structural shear stress range T σS strength scatter band index W energy based fatigue damage criterion W N notch strain energy W N A notch strain energy density Y n notch factor Y f far field factor a crack size (i.e. length) a 0 critical defect size a d long-term corrosion pit size (i.e. depth) a i (real) defect or initial crack size a n (root) not...

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A unified method of design for fatigue crack growth resistance in structural materials

Cited by 12 publications

References 18 publications

Fatigue crack growth mechanisms at the microstructure scale in as-fabricated and heat treated Ti-6Al-4V ELI manufactured by electron beam melting (EBM)

Fatigue crack growth mechanisms at the microstructure scale in as-fabricated and heat treated Ti-6Al-4V ELI manufactured by electron beam melting (EBM)

Simulation of fatigue small crack growth in additive manufactured Ti–6Al–4V material

Fatigue damage criteria classification, modelling developments and trends for welded joints in marine structures

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