Anelasticity and grain boundary sliding

Lee, L. C.; Morris, Stephen

doi:10.1098/rspa.2009.0624

Cited by 20 publications

(25 citation statements)

References 15 publications

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“…In the curve for M = 10 −8 , all the features summarized in figure 3 are present: for u 1, the mechanical loss L varies as u −1 ; for 1 u 10 5 , L follows the power-law asymptote discussed above; the local maximum caused by elastically accommodated grain-boundary sliding is found at u ∼ 10 −8 ; thereafter, L varies as u −1 , as shown in figure 3. At the local maximum L 0.05, approximately equal to the value found in Lee & Morris (2010, fig. 9) for the same values of the control parameters.…”

Section: Comparison With Numerical Solutionsmentioning

confidence: 54%

“…Although the precise magnitude of the background loss due to diffusion depends on the details described above, our assumption t D t h means that this local maximum occurs at such large frequencies that the diffusive loss is then negligibly small in any case. Consequently, as discussed in the context of figure 6, the results of Lee & Morris (2010) concerning the local maximum apply directly.…”

Section: Resultsmentioning

confidence: 99%

“…• coincides with the principal axes of stress for simple shear (Lee & Morris 2010). As a result, at the high frequencies at which the simplified boundary conditions apply, grains can deform under simple shear.…”

Section: Asymptotes To the Loss Spectrummentioning

confidence: 99%

“…According to Morris & Jackson (2009b) and Lee & Morris (2010), for the bicrystal system shown in figure 1, the external power supplied at the sample boundaries is either dissipated at the grain interface S I or stored as strain energy within the perfectly elastic grains, i.e.…”

Section: Asymptotes To the Loss Spectrummentioning

confidence: 99%

“…Schematic of the mechanical loss spectrum; for the asymptote for uM 1 (refer to Lee & Morris (2010)). …”

Section: Asymptotes To the Loss Spectrummentioning

confidence: 99%

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Stress concentrations, diffusionally accommodated grain boundary sliding and the viscoelasticity of polycrystals

2010

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Using analytical and numerical methods, we analyse the Raj-Ashby bicrystal model of diffusionally accommodated grain-boundary sliding for finite interface slopes. Two perfectly elastic layers of finite thickness are separated by a given fixed spatially periodic interface. Dissipation occurs by time-periodic shearing of the viscous interfacial region, and by time-periodic grain-boundary diffusion. Although two time scales govern these processes, of particular interest is the characteristic time t D for grain-boundary diffusion to occur over distances of order of the grain size. For seismic frequencies ut D 1, we find that the spectrum of mechanical loss Q -1 is controlled by the local stress field near corners. For a simple piecewise linear interface having identical corners, this localization leads to a simple asymptotic form for the loss spectrum: for ut D 1, Q −1 ∼ const.u −a . The positive exponent a is determined by the structure of the stress field near the corners, but depends both on the angle subtended by the corner and on the orientation of the interface; the value of a for a sawtooth interface having 120• angles differs from that for a truncated sawtooth interface whose corners subtend the same 120• angle. When corners on an interface are not all identical, the behaviour is even more complex. Our analysis suggests that the loss spectrum of a finely grained solid results from volume averaging of the dissipation occurring in the neighbourhood of a randomly oriented three-dimensional network of grain boundaries and edges.

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Section: Comparison With Numerical Solutionsmentioning

confidence: 54%

Section: Resultsmentioning

confidence: 99%

Section: Asymptotes To the Loss Spectrummentioning

confidence: 99%

Section: Asymptotes To the Loss Spectrummentioning

confidence: 99%

“…Schematic of the mechanical loss spectrum; for the asymptote for uM 1 (refer to Lee & Morris (2010)). …”

Section: Asymptotes To the Loss Spectrummentioning

confidence: 99%

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Stress concentrations, diffusionally accommodated grain boundary sliding and the viscoelasticity of polycrystals

2010

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Grain size‐sensitive viscoelastic relaxation and seismic properties of polycrystalline MgO

et al. 2016

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Torsional forced‐oscillation experiments on a suite of synthetic MgO polycrystals, of high‐purity and average grain sizes of 1–100 µm, reveal strongly viscoelastic behavior at temperatures of 800–1300°C and periods between 1 and 1000 s. The measured shear modulus and associated strain energy dissipation both display monotonic variations with oscillation period, temperature, and grain size. The data for the specimens of intermediate grain size have been fitted to a generalized Burgers creep function model that is also broadly consistent with the results for the most coarse‐grained specimen. The mild grain size sensitivity for the relaxation time τL, defining the lower end of the anelastic absorption band, is consistent with the onset of elastically accommodated grain boundary sliding. The upper end of the anelastic absorption band, evident in the highest‐temperature data for one specimen only, is associated with the Maxwell relaxation time τM marking the transition toward viscous behavior, conventionally ascribed a stronger grain size sensitivity. Similarly pronounced viscoelastic behavior was observed in complementary torsional microcreep tests, which confirm that the nonelastic strains are mainly recoverable, i.e., anelastic. With an estimated activation volume for the viscoelastic relaxation, the experimentally constrained Burgers model has been extrapolated to the conditions of pressure and temperature prevailing in the Earth's uppermost lower mantle. For a plausible grain size of 10 mm, the predicted dissipation Q−1 ranges from ~10−3 to ~10−2 for periods of 3–3000 s. Broad consistency with seismological observations suggests that the lower mantle ferropericlase phase might account for much of its observed attenuation.

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Structures of the oceanic lithosphere‐asthenosphere boundary: Mineral‐physics modeling and seismological signatures

Olugboji

Karato

Park

2013

Geochem Geophys Geosyst

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We explore possible models for the seismological signature of the oceanic lithosphere‐asthenosphere boundary (LAB) using the latest mineral‐physics observations. The key features that need to be explained by any viable model include (1) a sharp (<20 km width) and a large (5–10%) velocity drop, (2) LAB depth at ~70 km in the old oceanic upper mantle, and (3) an age‐dependent LAB depth in the young oceanic upper mantle. We examine the plausibility of both partial melt and sub‐solidus models. Because many of the LAB observations in the old oceanic regions are located in areas where temperature is ~1000–1200°K, significant partial melting is difficult. We examine a layered model and a melt‐accumulation model (at the LAB) and show that both models are difficult to reconcile with seismological observations. A sub‐solidus model assuming absorption‐band (AB) physical dispersion is inconsistent with the large velocity drop at the LAB. We explore a new sub‐solidus model, originally proposed by Karato [2012], that depends on grain‐boundary sliding. In contrast to the previous model where only the AB behavior was assumed, the new model predicts an age‐dependent LAB structure including the age‐dependent LAB depth and its sharpness. Strategies to test these models are presented.

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Anelasticity and grain boundary sliding

Cited by 20 publications

References 15 publications

Stress concentrations, diffusionally accommodated grain boundary sliding and the viscoelasticity of polycrystals

Stress concentrations, diffusionally accommodated grain boundary sliding and the viscoelasticity of polycrystals

Grain size‐sensitive viscoelastic relaxation and seismic properties of polycrystalline MgO

Structures of the oceanic lithosphere‐asthenosphere boundary: Mineral‐physics modeling and seismological signatures

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