An atomistic investigation into the nature of near threshold fatigue crack growth in aluminum alloys

a b s t r a c tGaAs is brittle at room temperature at the macro-scale; however, ductility emerges when its characteristic dimension reduces to the nano-scale. Using molecular dynamics simulations, we reveal that there is a brittle-to-ductile transition in GaAs nano-rods due to the competition between generation of cracks and initiation of dislocations. Such a competition is sensitive to aspect ratios of nano-rods. These results well explain experimentally observed ductility of GaAs nano-rods and have important implications for the design of semiconductor materials with tailored mechanical properties.

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“…6). This is why partial dislocation-generated stacking faults are widely observed in FCC metals and alloys [39][40][41]. …”

Section: Discussionmentioning

confidence: 99%

Size-dependent brittle-to-ductile transition in GaAs nano-rods

Wang

Shen

Song

et al. 2015

Engineering Fracture Mechanics

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“…Machova and co‐workers examined various near‐tip plastic phenomena in body centered cubic iron. Warner and co‐workers proposed a coupled atomistic‐discrete dislocation framework where the cracktip was atomistic, while the surrounding medium was assumed as a continuum (via finite element methods). From these atomistic studies, new functional dependence of crack growth has emerged at the nanoscale for a number of materials of interest .…”

Section: Latest Developments – Atomistictsmentioning

confidence: 99%

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

Chowdhury

Şehitoğlu

2016

Fatigue Fract Eng Mat Struct

129

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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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“…Increasing computer power has led to a concomitant increase in atomistic studies of fracture covering many of the topics mentioned above. We point to a few representative references for intrinsic brittle/ductile behavior [7][8][9][10][11], grain boundary fracture [12][13][14][15], H and other chemical embrittlement [15][16][17][18][19][20], and crack/defect interactions [21][22][23][24][25]. In this wide range of literature, various simulation methods have been used to probe phenomena qualitatively or quantitatively.…”

Section: Introductionmentioning

confidence: 99%

Atomistic modeling of fracture

Andric,

Curtin

2018

Modelling Simul. Mater. Sci. Eng.

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Atomistic modeling of fracture is intended to illuminate the complex response of atoms in the very high stressed region just ahead of a sharp crack. Accurate modeling of the atomic scale fracture is crucial for describing the intrinsic nature of a material (intrinsic ductility/brittleness), chemical effects in the crack-tip vicinity, the crack interaction with different defects in solids such as grain boundaries, solutes, precipitates, dislocations, voids, etc. Here, different methods for atomistic modeling of fracture are compared in their ability to obtain quantitatively useful results that are in agreement with the basic principles of linear elastic fracture mechanics (LEFM). We demonstrate that the complicated atomic crack-tip behavior is precisely described in simulations of semi-infinite cracks, where the loading is uniquely controlled by the applied stress intensity factor K. Such ‘K-test’ simulations are shown to be equally applicable in crystalline and amorphous materials, and to be suitable for quantitative evaluation of various critical stress intensity factors, the overall material fracture toughness, and quantitative comparison with theories. We further demonstrate that the simulation of a nanoscale center-crack tension (CCT) specimen often leads to the results that do not satisfy the conditions for application of LEFM. The simulated intrinsic fracture toughness, one of the basic material properties, using CCT test geometry is shown to be dependent on the crack size and far-field loading. In general, this study resolves quantitative differences between several methods for atomistic modeling of fracture and recommends that application of simulations based on nanoscale finite size cracks not be pursued.

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An atomistic investigation into the nature of near threshold fatigue crack growth in aluminum alloys

Cited by 17 publications

References 37 publications

Size-dependent brittle-to-ductile transition in GaAs nano-rods

Size-dependent brittle-to-ductile transition in GaAs nano-rods

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

Atomistic modeling of fracture

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