The non-uniform flow of polycrystals by grain-boundary sliding accommodated by power-law creep

Crossman, F. W.; Ashby, Michael F.

doi:10.1016/0001-6160(75)90082-6

Cited by 239 publications

(86 citation statements)

References 11 publications

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“…As before, we can obtain asymptotic solutions This confirms results obtained by several others workers (26,27), that both in the low strain rate limit when boundaries are fully relaxed and the stress distribution is inhomogeneous, and in the high strain rate limit when boundaries are unrelaxed and the stress is homogeneous, the strain rate of the polycrystal has the same stress dependence as the grain matrix. At an intermediate but narrow range of the stress when the grain boundaries slide effectively with equal ease as the grains deform (i.e., p gb), the strain rate sensitivity of the flow stress goes gu gb 58.…”

supporting

confidence: 91%

“…Crossman and Ashby (27), and more recently, Ghahremani (28), employed finite element analysis to obtain the solution for idealized polycrystals containing hexagons with sliding interfaces in material with a power-law type constitutive behavior. Their results showed qualitative agreement with Hart's model, namely that, at both high and low strain rates, the polycrystal flows according to the power-law creep of the grains, while the flow at low strain rates is somewhat accelerated by a grain boundary sliding.…”

Section: Grain Boundary Sliding and Internal Stressesmentioning

confidence: 99%

“…Instead of considering a strain rate enhancement, we may find it more satisfactory to refer to a stress enhancement factor f that produces the same increase in strain rate in a reference material without any boundaries (27). This factor f is defined as E = F (fo) m (for a-+0) (4.14)…”

Section: Strain Rate Enhancement and Stress Enhancementmentioning

confidence: 99%

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Creep cavitation in 304 stainless steel

Chen¹,

Argon²

1981

Acta Metallurgica

181

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A micromechanical analysis of deformation and fracture in creeping alloys is presented based on a mechanistic approach using continuum mechanics. The analysis was first carried out on a coarse microscopic level in which the self-consistent theory of Hill was employed to treat the steady state creep of heterogeneous alloys with coarse microstructures allowing for grain boundary sliding. Processes operating on a finer scale than the grain size such as grain boundary diffusion and surface diffusion were subsequently included in the analysis. It was found that the high stresses required for cavity nucleation occur at intergranular particles only in transients of grain boundary sliding, and that two modes of cavity growth result corresponding to rate control by each of the abovementioned diffusional processes.Creep cavitation in 304 stainless steel in the neighborhood of 0.5 Tm was studied experimentally to test these theoretical models. Our results suggest that a broad spectrum of interfacial energy may exist and that microstructural changes such as those caused by twins can alter cavitation behavior drastically. Cavities grow in most cases by grain boundary diffusion coupled with matrix creep, somewhat restricted by surface diffusion. However, the grain boundary sliding can be a dominant mode of cavity growth at high stresses and for large cavities.

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confidence: 91%

Section: Grain Boundary Sliding and Internal Stressesmentioning

confidence: 99%

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Creep cavitation in 304 stainless steel

Chen¹,

Argon²

1981

Acta Metallurgica

181

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“…For a periodic stepped boundary the viscosity (2 .4b) is increased by a factor (hld) 2 , when h is the height of the steps, and a dispersion of particles or precipitates in the grain boundary raises the value of ri B in a similar manner [ 18,19] . Plane strain model studies have been carried out by Crossman and Ashby [19] and Ghahremani [20] for polycrystalline aggregates with linearly viscous sliding at the grain boundaries and power law creep of the grains (see also discussion in [15]) . These studies show that at high stresses sliding has a negligible influence on the overall creep rate, whereas at low stresses sliding is essentially free ('c = 0), with higher overall creep strain-rates .…”

Section: Problem Formulationmentioning

confidence: 99%

A creep rupture model accounting for cavitation at sliding grain boundaries

Giessen

Tvergaard

1991

Int J Fract

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Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Giessen, E. V. D., & Tvergaard, V. (1991). A creep rupture model accounting for cavitation at sliding grain boundaries. International Journal of Fracture, 48(3). DOI: 10.1007/BF00036629 Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Abstract. An axisymmetric cell model analysis is used to study creep failure by grain boundary cavitation at facets normal to the maximum principal tensile stress, taking into account the influence of cavitation and sliding at adjacent inclined grain boundaries . It is found that the interaction between the failure processes on these two types of adjacent facets reduces the failure time significantly when cavitation is creep constrained . In all cases the time to cavity coalescence on transverse facets appears to be a useful lower bound measure of the material life-time . Sliding at the boundaries of the central grain of the cell model is accurately represented ; but in some computations a stress enhancement factor is used to incorporate also the effect of sliding between surrounding grains . The influence of grain boundary viscosity is included in the model and it is found that even in the absence of sliding, cavitation on inclined boundaries may significantly reduce the failure time .

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“…In those cases, the creep can be considered as extrinsic grain boundary sliding (EGBS) elaborated by Crossman and Ashby. 27) The EGBS is that the grain boundary sliding is inhibited by the secondary phase, particles, grain boundary intersection and grain boundary ledge, and grain boundary sliding must be accommodated by grain-interior deformation. However, The EGBS in this study is different with generally EGBS because the activation energy is Q 3 ¼ 25 kJ/mol that can compare with the value, Q 3 ¼ 32 kJ/mol at n $ 5 for 5 N Al.…”

Section: Effect Of Impurity Concentrationmentioning

confidence: 99%

Low-Temperature Creep at Ultra-Low Strain Rates in Pure Aluminum Studied by a Helicoid Spring Specimen Technique

et al. 2011

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The creep behavior in pure aluminum has been investigated by helicoid spring creep tests at strain rates, _ " ", lower than 10 À10 s À1 and low temperature ranging from 0:32T m to 0:43T m . It was found that the creep behavior in this region depends strongly on grain sizes and impurity concentrations. For high-purity aluminum (5 N Al) with an average grain size, d g > 1600 mm, nearly the wire diameter of the spring sample, where the role of grain boundary during creep deformation can be negligible, the stress exponent was n $ 5 and the activation energy was Q c ¼ 32 kJ/mol. Microstructural observation showed the formation of large dislocation cells ($10 mm) and tangled dislocations at the cell walls. For high-purity aluminum (5 N Al) with d g ¼ 24 mm, the stress exponent was n $ 1 and the activation energy was Q c ¼ 15 kJ/mol. On the other hand, for commercial low-purity aluminum (2 N Al) with d g ¼ 25 mm, the stress exponent was n ¼ 2 and the activation energy was Q c ¼ 25 kJ/mol. Microstructural observations revealed dislocations emitted from grain boundaries, those dislocations interacting with intragranular dislocations and the formation of dislocation cells in the grains. Based on those experimental results, the low-temperature creep mechanisms in pure aluminum at _ " " < 10 À10 s À1 have been discussed.

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The non-uniform flow of polycrystals by grain-boundary sliding accommodated by power-law creep

Cited by 239 publications

References 11 publications

Creep cavitation in 304 stainless steel

Creep cavitation in 304 stainless steel

A creep rupture model accounting for cavitation at sliding grain boundaries

Low-Temperature Creep at Ultra-Low Strain Rates in Pure Aluminum Studied by a Helicoid Spring Specimen Technique

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