The Effect of the Laboratory Specimen on Fatigue Crack Growth Rate

Forth, Scott C.; Johnston, William M.; Seshadri, Banavara R.

doi:10.1007/1-4020-4972-2_226

Cited by 17 publications

(9 citation statements)

References 8 publications

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“…There is also an even smaller difference between the FCG rates measured in thin and thick specimens. A similar behavior was reported by Forth et al in FCG tests performed under constant load conditions, when they tested C(T), M(T), and ESE(T) specimens, using the same material as well as specimen width (w) and thickness (t) [23,24]. They concluded that the differences observed in FCG rates were probably caused by environmental effects and roughness of the crack faces, which could explain the variation reported in these results.…”

Section: Resultssupporting

confidence: 85%

Verification of the ΔKeff hypothesis along the fatigue crack path in thin and thick Al specimens

González

Castro

Gonzáles

et al. 2019

Frattura Ed Integrità Strutturale

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Elber assumed that the actual driving force for fatigue crack growth (FCG) is the effective stress intensity factor ΔK eff. To verify this hypothesis, both DC(T) and C(T) specimens are cut from a 6351-T6 Al alloy circular bar with two different thicknesses, 2 and 30mm, tested under fixed ΔK and Kmax to simulated plane stress and plane strain FCG conditions. A strain-gage bonded on the back face of the specimens is used to measure the crack length and a custom-made Labview program is used to control the applied load, maintaining ΔK and K max constant along the crack path. Moreover, the crack opening load is redundantly measured during the FCG tests, using far field strains from the back face gage and near field strains from a series of gages bonded along the crack path, as well as an independent digital image correlation system to measure displacement/strain fields on the face of the specimens. These tests show that the Al specimens reproduce the behavior previously observed in similar tests in 1020 steel: a significant decrease of the opening load as the cracks grow along the specimens, while maintaining a FCG rate essentially constant under the fixed {ΔK, Kmax} loading, a behavior that cannot be explained by the ΔKeff hypothesis. KEYWORDS. Fatigue crack growth driving forces; Crack opening force measurements; ΔK eff limitations.

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Section: Resultssupporting

confidence: 85%

Verification of the ΔKeff hypothesis along the fatigue crack path in thin and thick Al specimens

González

Castro

Gonzáles

et al. 2019

Frattura Ed Integrità Strutturale

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“…As a support of the theories against the similitude hypothesis, we mention the experimental results by Newman et al (2004), who observed that "in the threshold regime there is something missing in the (closure) model", and those by Forth et al (2006), revealing that similitude does not hold in Region I (the near-threshold region) and also in the lower portion of Region II. To solve this problem, Molent et al (2006) and Jones et al (2007) have recently proposed a generalized Frost and Dugdale (1958) crack growth law, assuming that the crack growth rate is proportional to the accumulated plastic strain, averaged over a characteristic length ahead of the crack tip:…”

Section: Comparison With the Generalized Frostmentioning

confidence: 81%

A unified fractal approach for the interpretation of the anomalous scaling laws in fatigue and comparison with existing models

Carpinteri

Paggi

2009

Int J Fract

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In this paper, a critical reexamination of the fractal models for the analysis of crack-size effects in fatigue is proposed. The enhanced ability to detect and measure very short cracks has in fact pointed out the so-called anomalous behavior of short cracks with respect to their longer counterparts. The cracksize dependencies of both the fatigue threshold and the Paris' constant C are only two notable examples of these anomalous scaling laws. In this context, a unified theoretical model seems to be missing and the behavior of short cracks can still be considered as an open problem. A new generalized theory based on fractal geometry is herein proposed, which permits to consistently interpret the short crack-related anomalous scaling laws within a unified theoretical framework. The proposed model is used to interpret relevant experimental data related to the crack-size dependence of the fatigue threshold in metals. As a main result, the model gives an explanation to the experimentally observed variability in the slope of the asymptote of the scaling law for the fatigue threshold in the short crack regime.

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“…Unlike monotonic properties, determination of cyclic attributes requires more rigorous tests, sophisticated measurements of local flow behaviour, crack lengths, etc. Moreover, the standardized experiments are very lengthy, expensive and by themselves do not absolutely address the inherent material response to the damage accurately . The persistent hurdle in establishing a uniform law is that the fatigue is a very strongly microstructure‐sensitive phenomenon.…”

Section: Motivation and Objectivementioning

confidence: 99%

Mechanisms of fatigue crack growth – a critical digest of theoretical developments

Chowdhury

Şehitoğlu

2016

Fatigue Fract Eng Mat Struct

136

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A B S T R A C T Recent advances in the processing technology are permitting the manufacture of novel metallic materials with superior fatigue properties via microstructure tailoring. In the light of these promising developments, there is a rising need for establishing a synergy between state-of-the-art experimental characterizations and physically based theoretical underpinnings. A revisit to the existing predictive literature is thus a timely requirement prior to furthering new design guidelines against cyclic damage. To that end, this paper recounts an overview of the key mechanistic and analytical theories on the fatigue crack growth mechanisms. Emphasis is placed on categorizing the proposed modelling endeavours based on their fundamental principles. In doing so, contributions and limitations thereof are carefully examined on the basis of most updated experimental revelations. The objective is to provide a perspective to the current generation of engineers and researchers alike. This concise yet critical narrative would essentially assist in formulating even more advanced microstructure-damage relationships in the modern context. A commentary is added at the end outlining the promising avenues for future research.CTOD, FCG = crack tip opening displacement, fatigue crack growth MD, DFT = molecular dynamics, density functional theory RVE = representative volume element LEFM, EPFM = linear elastic and elastic plastic fracture mechanics E, H = Young's modulus, plastic modulus GB = grain boundary K max , K min , K open , = maximum, minimum and opening stress-intensity factors K c = fracture toughness under mode I loading ΔK eff th , ΔK th = (effective) threshold stress intensity factor range da/dN = fatigue crack growth rate per cycle (a is the crack length and N is the number of cycles) L deflect , θ deflect = length and angle of a deflected crack respectively θ = angle between slip and crack paths σ yield , σ cyclic yield , σ fracture = monotonic, cyclic yields strengths and static fracture strength σ ′ f , ε ′ f = strength and ductility coefficient in Coffin-Manson-Basquin rule: Δε plastic ¼ 2ε ′ f 2N f ð Þ c σ eff , σ hydro = effective and hydrostatic stress ρ * = effective radius of a sharp crack ρ slip , _ ρ vacancy , ρ interface = dislocation density, vacancy generation rate and interface density P H 2 , P O 2 = partial pressures of hydrogen and oxygen m, C = Paris exponent, Paris proportionality constant m Schmid = Schmid factor τ friction , τ forward friction , τ reverse friction = friction (Peierls) stress for free (unobstructed), forward and reverse dislocation glide

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The Effect of the Laboratory Specimen on Fatigue Crack Growth Rate

Cited by 17 publications

References 8 publications

Verification of the ΔKeff hypothesis along the fatigue crack path in thin and thick Al specimens

Verification of the ΔKeff hypothesis along the fatigue crack path in thin and thick Al specimens

A unified fractal approach for the interpretation of the anomalous scaling laws in fatigue and comparison with existing models

Mechanisms of fatigue crack growth – a critical digest of theoretical developments

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