Abstract
We have made creep experiments on columnar grained ice and characterised the microstructure and intragranular misorientations over a range of length scales. A FFT full-field model was used to predict the deformation behaviour, using the experimentally characterised microstructure as the starting material. This is the first time this combination of techniques has been used to study the deformation of ice. The microstructure was characterised at the cm scale using an optical technique, the automatic ice texture analyser AITA and at the micron scale using electron backscattered diffraction EBSD. The crystallographic texture and intragranular misorientations were fully characterised by EBSD (3 angles). The deformed microstructure frequently showed straight subgrain boundaries often originating at triple points. These were identified as kink bands, and for the first time we have measured the precise misorientation of the kink bands and deduced the nature of the dislocations responsible for them. These dislocations have a basal edge nature and align in contiguous prismatic planes enabling deformation along the c-axis. In addition, non-uniform grain boundaries and regions of recrystallization were seen. We present coupling between fine scale characterization of intragranular misorientations, from experiments, and prediction of internal stresses that cause it. The model predicts the morphology of the observed local misorientations within the grains, however it over predicts the misorientation values. This is because the annealing and recrystallization mechanisms are not taken into account in the model. Ice is excellent as a model material for measuring, predicting and understanding deformation behaviour for polycrystalline materials. Specifically for ice this knowledge is needed to improve models of ice sheet dynamics that are important for climatic signal interpretation.
Highlights
To improve climatic signal interpretation, and predictions, accurate modelling of ice dynamics is essential
To interpret the climatic signal correctly, dating of the ice core strongly relies on ice flow models, available ice-age markers, and ice texture characterization as a marker of ice flow discontinuities (Buiron et al, 2011; Greenland Ice core Project (GRIP) Members, 1993; Parrenin et al, 2001)
Dynamic recrystallization mechanisms are very efficient in ice (Duval, 1979; Jacka and Li, 1994; Kipfstuhl et al, 2006; Montagnat et al, 2009)
Summary
To improve climatic signal interpretation, and predictions, accurate modelling of ice dynamics is essential. Dynamic recrystallization mechanisms are very efficient in ice (Duval, 1979; Jacka and Li, 1994; Kipfstuhl et al, 2006; Montagnat et al, 2009) They are known to accommodate deformation processes as observed along ice cores taken from ice sheets (Alley et al, 1986a,b; de la Chapelle et al, 1998; Duval and Castelnau, 1995; Montagnat and Duval, 2000) and to influence the texture evolution and the flow of ice. Metals, rocks and ice, all polycrystalline aggregates, show remarkable similarities in their deformation and recrystallization behaviour (see for instance Frost and Ashby, 1982; Goodman et al, 1981; Humphreys and Hatherly, 1996; Kocks et al, 1998; Schulson and Duval, 2009). Rocks and ice, all polycrystalline aggregates, show remarkable similarities in their deformation and recrystallization behaviour (see for instance Frost and Ashby, 1982; Goodman et al, 1981; Humphreys and Hatherly, 1996; Kocks et al, 1998; Schulson and Duval, 2009) In this respect, both ice core data and ice deformation laboratory experiments provide very good systems to study the deformation heterogeneity development and dynamic recrystallization mechanisms for highly anisotropic materials. This has already been validated for ice (Lebensohn et al, 2009), here, for the first time, we extend the methodology by using direct input from experimental measurements
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