Viscoelastic Behaviour from Complementary Forced-Oscillation and Microcreep Tests

Abstract

There is an important complementarity between experimental methods for the study of high-temperature viscoelasticity in the time and frequency domains that has not always been fully exploited. Here, we show that the parallel processing of forced-oscillation data and microcreep records, involving the consistent use of either Andrade or extended Burgers creep function models, yields a robust composite modulus-dissipation dataset spanning a broader range of periods than either technique alone. In fitting this dataset, the alternative Andrade and extended Burgers models differ in their partitioning of strain between the anelastic and viscous contributions. The extended Burgers model is preferred because it involves a finite range of anelastic relaxation times and, accordingly, a well-defined anelastic relaxation strength. The new strategy offers the prospect of better constraining the transition between transient and steady-state creep or, equivalently, between anelastic and viscous behaviour.

A Theory of Inter‐Granular Transient Dislocation Creep: Implications for the Geophysical Studies on Mantle Rheology

“…Consequently, it is not possible to test the present model against the results reviewed in their paper. Micro‐creep studies in the dislocation creep regime would be useful to test the present model, although Jackson (2019) found it difficult to distinguish the Andrade‐type and the Burgers‐type behavior from the experimental data in either time‐domain and in the frequency domain conducted at a single condition.…”

“…Faul and Jackson (2015) reviewed experimental studies on transient creep with the emphasis on small strain deformation (micro‐creep experiments) (see also Jackson, 2019). Consequently, the results presented their paper are potentially relevant to the present work.…”

“…This is likely due to the effect of dislocation recovery to form low energy configuration such as sub-boundaries and/or to the effect of dynamic recrystallization by grain-boundary migration (Karato, 1988;Karato et al, 1980Karato et al, , 1982. Faul and Jackson (2015) reviewed experimental studies on transient creep with the emphasis on small strain deformation (micro-creep experiments) (see also Jackson, 2019). Consequently, the results presented their paper are potentially relevant to the present work.…”

Transient Creep in Olivine at Shallow Mantle Pressures: Implications for Time‐Dependent Rheology in Post‐Seismic Deformation

“…Although microphysical bases to both the Burgers and Andrade models are unclear, the former model is preferred because it predicts a finite initial strain rate (at t = 0) (Jackson, 2019;Karato, 2021). Karato (2021)…”

“…Short‐period cyclic microcreep experiments at high temperatures (1300−1500 K: e.g., Jackson et al., 2002) have revealed that the time‐dependency of the transient creep of olivine is well described by the Andrade creep function. Although microphysical bases to both the Burgers and Andrade models are unclear, the former model is preferred because it predicts a finite initial strain rate (at t = 0) (Jackson, 2019; Karato, 2021). Karato (2021) considered two slip systems in a polycrystalline aggregate in his model and showed that both transient and steady‐state creeps are approximately described by the power‐law equation with an effective pre‐exponential constant A ( =A t for transient creep; =A ss (< A t ) for steady‐state creep): $$$\dot{\varepsilon }=A\frac{{\sigma }^{n}}{{d}^{p}}{f}_{w}^{r}\cdot \mathrm{exp}\left(\frac{{-H}^{\ast }}{RT}\right)$$$ where σ is the applied stress, n is the stress exponent, d is grain size, p is the grain size exponent, f w is water fugacity, r is the water fugacity exponent, H * is the activation enthalpy, R is the gas constant, and T is temperature.…”