Structural relaxation in silicate melts and non-Newtonian melt rheology in geologic processes

Dingwell, Donald B.; Webb, Sharon L.

doi:10.1007/bf00197020

Cited by 330 publications

(190 citation statements)

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“…[41] It is common [Dingwell and Webb, 1989;Papale, 1999] to use the value of the normalized strain rate D′ rr /G 0 to characterize the transition between brittle and ductile fracture of magma. Figure 5a plots the values of D′ rr /G 0 as a function of time for the solutions in Figure 2.…”

Section: Simplified Equations For a Spherical Shell Modelmentioning

confidence: 99%

“…[2] Quantifying the explosiveness of a volcanic eruption requires an understanding of the transition from fluid-like response to solid-like response of flowing magma during the failure process [Heiken and Wohletz, 1985;Taddeucci and Wohletz, 2001;Dingwell and Webb, 1989;Zimanowski et al, 2003]. Failure criteria for materials typically depend on the state of stress, strain rate (here the term strain rate and rate of deformation are used interchangeably; see the comment related to (A6)), and temperature.…”

Section: Introductionmentioning

confidence: 99%

“…For example, Dingwell [1996Dingwell [ , p. 1054 wrote that "…a quantification of the conditions thought to be necessary for the generation of a brittle response of silicate melts was proposed [Dingwell and Webb, 1989]. The essence of that argument was that the strain rates of deformation of the magma must be sufficiently high to drive the melt phase into a non-Newtonian, shear-thinning phase that is terminated by brittle failure.…”

Section: Introductionmentioning

confidence: 99%

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Brittleness of fracture in flowing magma

Ichihara

Rubin

2010

J. Geophys. Res.

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[1] Understanding the transition to brittle fracture of flowing magma is essential for estimating the explosiveness of a volcanic eruption. In order to quantify brittleness of flowing magma, a new parameter b is introduced, which is a function of the ratio of the rate of change of the strain energy due to elastic distortional deformation to the mechanical power due to total distortional deformation rate. From the perspective of b, dependence of brittle fracture of magma on stress, decompression rate, strain rate, and shear-thinning effects are reviewed. The experimental data of Kameda et al. (2008) for rapid decompression of simulants of bubbly magma have also been reexamined. The results show that b exhibits a strong transition that correlates well with the observed transition between ductile expansion to brittle fragmentation. Moreover, b is useful in considering the effects of shear-thinning and steady-creep conditions on brittle fracture. Statements in the literature that suggest that materials behave in a brittle manner at sufficiently high strain rate are correct. However, these statements do not precisely quantify the notion of high strain rate so they are easy to misinterpret when considering the effect of shear thinning. Although shear thinning tends to increase the absolute magnitude of the total strain rate, it does not necessarily increase brittleness. Also, in principle, it is unlikely for brittle fracture to occur at steady creep. Cracking observed in steady-creep experiments of magma (Lavallee et al., 2007 may be attributed to small fluctuations with sufficiently high frequencies to satisfy the conditions for brittle fracture.

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Section: Simplified Equations For a Spherical Shell Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Brittleness of fracture in flowing magma

Ichihara

Rubin

2010

J. Geophys. Res.

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“…Given the relative invariance of the value of Goc in liquids in general and Silicate melts in particular (for further discussion, see Angell and Torreil [1983] and Dingwell and Webb [1989]), the relaxation time r (and relaxation strain rate y = T" 1 ) is proportional to the relaxed (Newtonian) shear viscosity of the melt. The Maxwell relationship applies for a Single relaxation time.…”

Section: Ding Well and Webbmentioning

confidence: 99%

Non‐Newtonian rheology of igneous melts at high stresses and strain rates: Experimental results for rhyolite, andesite, basalt, and nephelinite

Webb¹,

Dingwell²

1990

J. Geophys. Res.

268

182

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The stress‐strain rate relationships of four silicate melt compositions (high‐silica rhyolite, andesite, tholeiitic basalt, and nephelinite) have been studied using the fiber elongation method. Measurements were conducted in a stress range of 10–400 MPa and a strain rate range of 10−6 to 10−3 s−1. The stress‐strain rate relationships for all the melts exhibit Newtonian behavior at low strain rates, but non‐Newtonian (nonlinear stress‐strain rate) behavior at higher strain rates, with strain rate increasing faster than the applied stress. The decrease in calculated shear viscosity with increasing strain rate precedes brittle failure of the fiber as the applied stress approaches the tensile strength of the melt. The decrease in viscosity observed at the high strain rates of the present study ranges from 0.25 to 2.54 log10 Pa s. The shear relaxation times τ of these melts have been estimated from the low strain rate, Newtonian, shear viscosity, using the Maxwell relationship τ = ηs/G∞. Non‐Newtonian shear viscosity is observed at strain rates ( trueε˙=time−1 ) equivalent to time scales that lie 3 log10 units of time above the calculated relaxation time. Brittle failure of the fibers occurs 2 log10 units of time above the relaxation time. This study illustrates that the occurrence of non‐Newtonian viscous flow in geological melts can be predicted to within a log10 unit of strain rate. High‐silica rhyolite melts involved in ash flow eruptions are expected to undergo a non‐Newtonian phase of deformation immediately prior to brittle failure.

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“…(2) is the heat capacity of the melt taken over the temperature interval marking the glass transition from an unequivocally defined glass transition temperature (Tg) to a higher temperature (T) where the melt is fully relaxed (Richet, 1984;Dingwell and Webb, 1989;Dingwell (1995); Bottinga and Richet, 1996). The usual simplification is that silicate melt heat capacity (Cp melt ) is independent of temperature allowing Cp(T) to be replaced by a constant representing the change in configurational heat capacity (Cp c ) associated with the glass to melt transition (i.e.…”

Section: Introductionmentioning

confidence: 99%