The Behaviour of Short Fatigue Cracks and Their Initiation Part Ii‐a General Summary

Miller, K. J.

doi:10.1111/j.1460-2695.1987.tb01153.x

Cited by 281 publications

(112 citation statements)

References 17 publications

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“…For crystalline metals, fatigue lifetimes are largely dominated by the loading cycles required to initiate damage as opposed to propagating a ''fatal'' crack. The term initiation, however, is often a misnomer, because the rate-limiting process is generally not crack initiation but rather early propagation of small (often preexisting) f laws through a dominant microstructural barrier, e.g., a grain boundary or hard second-phase particle (38,39). The lower fatigue limits of amorphous alloys can be attributed to the lack of a microstructure that provides local arrest points for newly initiated or preexisting cracks (16,20,21).…”

Section: Fig 2 Stress-life Fatigue Data (S-n)mentioning

confidence: 99%

Solution to the problem of the poor cyclic fatigue resistance of bulk metallic glasses

Launey

Hofmann

Johnson

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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The recent development of metallic glass-matrix composites represents a particular milestone in engineering materials for structural applications owing to their remarkable combination of strength and toughness. However, metallic glasses are highly susceptible to cyclic fatigue damage, and previous attempts to solve this problem have been largely disappointing. Here, we propose and demonstrate a microstructural design strategy to overcome this limitation by matching the microstructural length scales (of the second phase) to mechanical crack-length scales. Specifically, semisolid processing is used to optimize the volume fraction, morphology, and size of second-phase dendrites to confine any initial deformation (shear banding) to the glassy regions separating dendrite arms having length scales of Ϸ2 m, i.e., to less than the critical crack size for failure. Confinement of the damage to such interdendritic regions results in enhancement of fatigue lifetimes and increases the fatigue limit by an order of magnitude, making these ''designed'' composites as resistant to fatigue damage as high-strength steels and aluminum alloys. These design strategies can be universally applied to any other metallic glass systems.composites ͉ damage confinement ͉ endurance limit ͉ semisolid processing M onolithic bulk metallic glasses (BMGs) have emerged over the past 15 years as a class of materials with unique and unusual properties that make them potential candidates for many structural applications (1). These properties include their near theoretical strengths combined with high formability, low damping, large elastic strain limits, and the ability to be thermoplastically formed into precision net shape parts in complex geometries (2, 3), all of which are generally distinct from, or superior to, corresponding crystalline metals and alloys. However, monolithic BMGs can also display less desirable properties that have severely restricted their structural use. In particular, properties limited by the extension of cracks, such as ductility, toughness, and fatigue, can be compromised in BMGs by inhomogeneous plastic deformation at ambient temperatures where plastic flow is confined in highly localized shear bands (4, 5). Such severe strain localization with the propagation of the shear bands is especially problematic under tensile stress states where catastrophic failure can ensue along a single shear plane with essentially zero macroscopic ductility (6, 7). Consequently, resulting plane-strain K Ic fracture toughnesses in monolithic BMGs are often low (Ϸ15-20 MPa ͌ m), as compared with most crystalline metallic materials, although they are an order of magnitude larger than those for (ceramic) oxide glasses (8, 9). If such strain localization is suppressed such that plastic flow is allowed to be extensive, for example, by blunting the crack tip, then damage would be distributed over larger dimensions with toughness values increasing to Ϸ50 MPa ͌ m or more (8, 10). Whereas some metallic glasses appear to be intrinsically brittle in thei...

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Section: Fig 2 Stress-life Fatigue Data (S-n)mentioning

confidence: 99%

Solution to the problem of the poor cyclic fatigue resistance of bulk metallic glasses

Launey

Hofmann

Johnson

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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“…The different parts of the figures correspond to snapshots taken from the three space directions. Referring to the classical A and B facets [1], illustrated in figure 17, experimental studies showed that uniaxial cyclic loadings lead to mixed A/B facets and biaxial loadings cause mostly B facets which are more damaging for the material. Figure 18b, referring to uniaxial-x case, shows localization bands oriented at 45 • with respect to loading direction, in snapshots taken from the top (y direction) and from the front (z direction) which is the free surface direction.…”

Section: Strain Localization In the Bulkmentioning

confidence: 99%

“…Since the micropropagation is affected by the local grain microstructure, this is the main source of the scatter that is classically found in this domain. The so called "Microstructurally Short Cracks (MSCs)" and the different stages of initiation and micropropagation have been described in a well known paper [1]. Microstructural features such as grain boundaries and crystallographic orientations play an important role in this process.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigations of the free surface effect in three-dimensional polycrystalline aggregates

Guilhem

Basseville

Curtit³

et al. 2013

Computational Materials Science

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The aim of the present paper is to investigate the consequences of the loading on the free surface response in polycrystalline aggregates. The study is made on a 316L stainless steel. Finite element computations using a crystal plasticity model are performed to simulate a polycrystalline aggregate submitted to different cyclic loadings. A statistical analysis of the results is carried out to extract information concerning the local stress and local strain fields at the free surface. The analysis of plastic strain localization on surface maps and inside the bulk through transparent volumetric views allows to exhibit the effects of the grain orientation and of the loading on local mechanical fields. The computation of an indicator characterizing extrusion/intrusion steps give some information on the initiation sites.

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“…Crack initiation phase can be divided into micro-structurally short crack initiation and subsequent micro-structurally short crack propagation, both of which are strongly influenced by local micro-structural features, such as crystallographic orientations, inclusions, voids, grain boundaries and material phases [23][24][25]. For crack propagation phase, different size and crystallographic orientation of the grains may also increase, decrease or arrest the crack growth [26][27][28][29].…”

Section: Introductionmentioning

confidence: 99%

A crystal plasticity study of cyclic constitutive behaviour, crack-tip deformation and crack-growth path for a polycrystalline nickel-based superalloy

Lin

Tong

2011

Engineering Fracture Mechanics

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Crystal plasticity has been applied to model the cyclic constitutive behaviour of a polycrystalline nickel-based superalloy at elevated temperature using finite element analyses.A representative volume element, consisting of randomly oriented grains, was considered for the finite element analyses under periodic boundary constraints. Strain-controlled cyclic test data at 650°C were used to determine the model parameters from a fitting process, where three loading rates were considered. Model simulations are in good agreement with the experimental results for stress-strain loops, cyclic hardening behaviour and stress relaxation behaviour. Stress and strain distributions within the representative volume element are of heterogeneous nature due to the orientation mismatch between neighboring grains. Stress concentrations tend to occur within "hard" grains while strain concentrations tend to locate within "soft" grains, depending on the orientation of grains with respect to the loading direction. The model was further applied to study the near-tip deformation of a transgranular crack in a compact tension specimen using a submodelling technique. Grain microstructure is shown to have an influence on the von Mises stress distribution near the crack tip, and the gain texture heterogeneity disturbs the well-known butterfly shape obtained from the viscoplasticity analysis at continuum level. The stress-strain response near the crack tip, as well as the accumulated shear deformation along slip system, is influenced by the orientation of the grain at the crack tip, which might dictate the subsequent crack growth through grains.Individual slip systems near the crack tip tend to have different amounts of accumulated shear deformation, which was utilised as a criterion to predict the crack growth path.

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The Behaviour of Short Fatigue Cracks and Their Initiation Part Ii‐a General Summary

Cited by 281 publications

References 17 publications

Solution to the problem of the poor cyclic fatigue resistance of bulk metallic glasses

Solution to the problem of the poor cyclic fatigue resistance of bulk metallic glasses

Numerical investigations of the free surface effect in three-dimensional polycrystalline aggregates

A crystal plasticity study of cyclic constitutive behaviour, crack-tip deformation and crack-growth path for a polycrystalline nickel-based superalloy

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