2024 |
Védrine, L., Hagenmuller, P., Gélébart, L., Montagnat, M., & Bernard, A. (2024). Role Of Ice Mechanics On Snow Viscoplasticity. Geophysical Research Letters, 515(7).
Abstract: The Porous Structure Of Snow Becomes Denser With Time Under Gravity, Primarily Due To The Creep Of Its Ice Matrix With Viscoplasticity. Despite Investigation Of This Behavior At The Macroscopic Scale, The Driving Microscopic Mechanisms Are Still Not Well Understood. Thanks To High-Performance Computing And Dedicated Solvers, We Modeled Snow Elasto-Viscoplasticity With 3D Images Of Its Microstructure And Different Mechanical Models Of Ice. The Comparison Of Our Numerical Experiments To Oedometric Compression Tests Measured By Tomography Showed That Ice In Snow Rather Behaves As A Heterogeneous Set Of Ice Crystals Than As Homogeneous Polycrystalline Ice. Similarly To Dense Ice, The Basal Slip System Contributed At Most, In The Simulations, To The Total Snow Deformation. However, In The Model, The Deformation Accommodation Between Crystals Was Permitted By The Pore Space And Did Not Require Any Prismatic And Pyramidal Slips, Whereas The Latter Are Pre-Requisite For The Simulation Of Dense Ice. Knowledge Of Snow Settlement Is Essential For Many Applications, Such As Paleoclimatology And Avalanche Forecasting. Snow Densification Is Mainly Driven By Time Dependent And Irreversible Deformations. Simulating This Highly Nonlinear Behavior For Intricate Microstructures Is Time-Consuming, Leading To A Scarcity Of Studies And A Limited Understanding Of The Underlying Microscale Mechanisms. In This Study, We Took Advantage Of An Advanced Numerical Solver To Calculate The Behavior Of 3D Imaged Snow Samples And Compared It With In Situ Experiments. Our Analysis Has Shown That The Crystalline Structure Must Be Taken Into Account, But The Discrepancy Between Experiments And Simulations Suggests The Existence Of Other Mechanisms, Particularly Between Snow Grains. Interestingly, Deformation Mechanisms Other Than Those Required To Simulate Dense Ice Have Been Observed. Ice In Snow Cannot Be Considered As Homogeneous, Individual Crystals Are Shown To Impact Snow Creep The Models Shows That Basal Glide Of A Few Ice Zones Supports Most Of The Snow Deformation In The Simulations, The Contribution Of The Hard Slip Systems Is Negligible, And Deformation Accommodation Is Enabled By The Pore Space
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2023 |
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Ravanel, L., Guillet, G., Kaushik, S., Preunkert, S., Malet, E., Magnin, F., et al. (2023). Ice Aprons On Steep High-Alpine Slopes: Insights From The Mont-Blanc Massif, Western Alps. Journal Of Glaciology, .
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2022 |
Bernard, A., Hagenmuller, P., Montagnat, M., & Chambon, G. (2022). Disentangling Creep And Isothermal Metamorphism During Snow Settlement With X-Ray Tomography. Journal Of Glaciology, .
Abstract: Once Fallen, Snow Settles Due To The Combined Effects Of Metamorphism And Deformation Of The Ice Matrix Under Gravity. To Understand How These Coupled Processes Affect Snow Evolution, We Performed Oedometric Compression Tests And Continuously Monitored The Snow Microstructure.With X-Ray Tomography. Centimetric Samples With An Initial Density Between 200 And 300 Kgm(-3) Were Followed During An Initial Sintering Phase And Under Two Different Loads Of 2.1 And 4.7 Kpa At -8 Degrees C For Similar To 1 Week. The Microstructure Captured At A Voxel Size Of 8.5 Mu M Was Characterized By Density, Specific Surface Area (Ssa) And Two Metrics Related To Bond Network, Namely The Euler Characteristic And The Minimum Cut Surface. Load-Induced Creep Of The Ice Matrix Was Observed Only For Sufficiently Low Values Of Initial Density (<290 Kgm(-3) In Our Tests), And Was Shown To Be Associated To A Significant Increase Of The Number Of Bonds. Application Of The Load, However, Did Not Affect The Individual Bond Size Nor The Ssa, Which Appeared To Be Mainly Controlled By Isothermal Metamorphism. The Uniaxial Compression Did Not Induce Any Creation Of Anisotropy On The Microstructural Characteristics. Overall, Our Results Show That, For The Considered Conditions, The Deformation Of The Ice Matrix Mainly Leads To A Reduction Of The Pore Space And An Increase Of The Coordination Number, While Metamorphism Mainly Affects The Grain And Bond Sizes.
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2021 |
Georges, D., Saletti, D., Montagnat, M., Forquin, P., & Hagenmuller, P. (2021). Influence of Porosity on Ice Dynamic Tensile Behavior as Assessed by Spalling Tests. Journal Of Dynamic Behavior Of Materials, .
Abstract: The impact of ice on structures is a strong concern, in particular for aeronautical or space crafts that are strongly damaged by the impact of atmospheric ice, and more specifically by hailstones during hailstorms. During the impact, the hailstone is submitted to a complex loading including a strong dynamic tensile component that is responsible for its fragmentation and influences the mechanical loading transmitted to the impacted structure. However, up to now, very limited work were conducted on the tensile strength of ice under dynamic loading and the microstructure influence was out the scope of most studies. In particular the presence of porosity in ice as observed in hailstones is thought to significantly affect the ice mechanical response. The aim of this paper is to investigate the role of porosity on the tensile behavior of polycrystalline ice at high strain rates. To do so, spalling tests with a Hopkinson bar apparatus were conducted on microstructures characterized by porosities with two different pore size distributions. The dynamic tensile strength was computed by the use of the so-called Novikov formula and several indicators were used to assess the quality of each test. A whole set of high porosity samples was tested and additional tests were performed on low porosity ice, expanding the existing results in the literature. The fragmentation processes occuring during the spalling tests were observed by means of an ultra high speed camera and the influence of porosity on the main fracture planes was investigated by analysing post-spalling samples with an automatic ice texture analyser and X-ray tomography. Tensile strength is shown to increase with strain rate over the range 24 s(-1) to 120 s(-1) and to decrease with increasing porosity. The presence of large porosities in the high porosity samples appear to contribute preferentially to this strength decrease. Relevant observations concerning the detected cracks, the tortuosity of crack paths and the presence of porosities on the crack surfaces seem to validate the hypothesis of porosities playing a key role for crack initiation and propagation during ice fragmentation.
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Guillet, G., Preunkert, S., Ravanel, L., Montagnat, M., & Friedrich, R. (2021). Investigation of a cold-based ice apron on a high-mountain permafrost rock wall using ice texture analysis and micro-C-14 dating: a case study of the Triangle du Tacul ice apron (Mont Blanc massif, France). Journal Of Glaciology, 67(266), 1205–1212.
Abstract: The current paper studies the dynamics and age of the Triangle du Tacul (TDT) ice apron, a massive ice volume lying on a steep high-mountain rock wall in the French side of the Mont-Blanc massif at an altitude close to 3640 m a.s.l. Three 60 cm long ice cores were drilled to bedrock (i.e. the rock wall) in 2018 and 2019 at the TDT ice apron. Texture (microstructure and lattice-preferred orientation, LPO) analyses were performed on one core. The two remaining cores were used for radiocarbon dating of the particulate organic carbon fraction (three samples in total). Microstructure and LPO do not substantially vary with along the axis of the ice core. Throughout the core, irregularly shaped grains, associated with strain-induced grain boundary migration and strong single maximum LPO, were observed. Measurements indicate that at the TDT ice deforms under a low strain-rate simple shear regime, with a shear plane parallel to the surface slope of the ice apron. Dynamic recrystallization stands out as the major mechanism for grain growth. Micro-radiocarbon dating indicates that the TDT ice becomes older with depth perpendicular to the ice surface. We observed ice ages older than 600 year BP and at the base of the lowest 30 cm older than 3000 years.
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Montagnat, M., Bourcier, M., Philip, A., Bons, P., Bauer, C., Deconinck, P., et al. (2021). Texture characterization of some large hailstones with an automated technique. Journal Of Glaciology, 67(266), 1190–1204.
Abstract: Hailstone structures have been studied for over a century, but so far mainly by manual optical means. This paper presents new texture and microstructure data (i.e. crystal lattice orientations, grain sizes and shapes) measured with an Automatic Ice Texture Analyzer, which gives access to high spatial and angular resolutions. The hailstones show two main characteristics: (1) they are structured with several concentric layers composed of alternating fine equiaxed grains and coarse elongated and radially oriented grains, and (2) they show two texture types with c-axes oriented either parallel or perpendicular to the radial direction. Such textures are compared with the ones observed in lake S1 and S2 ices, respectively. The S1 texture type (with c-axes parallel to the columnar crystals that grew in the radial direction) may result from epitaxial growth from a polycrystalline embryo, while the S2 texture (c-axes in the plane perpendicular to the column direction) may result from the growth from an embryo made of a few crystals with mainly one crystallographic orientation. Our novel high-resolution maps and measurements of both microstructure and texture may help to shed new light on the long-term discussion on the growth mechanisms of large hailstones.
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2020 |
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Montagnat, M., Chambon, G., Gaume, J., Hagenmuller, P., & Sandells, M. (2020). Editorial: About the Relevance of Snow Microstructure Study in Cryospheric Sciences. Frontiers In Earth Science, 8.
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Montagnat, M., Lowe, H., Calonne, N., Schneebeli, M., Matzl, M., & Jaggi, M. (2020). On the Birth of Structural and Crystallographic Fabric Signals in Polar Snow: A Case Study From the EastGRIP Snowpack. Frontiers In Earth Science, 8.
Abstract: The role of near-surface snow processes for the formation of climate signals through densification into deep polar firn is still barely understood. To this end we have analyzed a shallow snow pit (0-3 meters) from EastGRIP (Greenland) and derived high-resolution profiles of different types of mechanically relevant fabric tensors. The structural fabric, which characterizes the anisotropic geometry of ice matrix and pore space, was obtained by X-ray tomography. The crystallographic fabric, which characterizes the anisotropic distribution of thec-axis (or optical axis) orientations of snow crystals, was obtained from automatic analysis of thin sections. The structural fabric profile unambiguously reveals the seasonal cycles at EastGRIP, as a consequence of temperature gradient metamorphism, and in contrast to featureless signals of parameters like density or specific surface area. The crystallographic fabric profile unambiguously reveals a signal of cluster-type texture already at shallow depth. We make use of order of magnitude estimates for the formation time of both fabric signals and discuss potential coupling effects in the context of snow and firn densification.
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2019 |
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Bartels-Rausch, T., & Montagnat, M. (2019). The physics and chemistry of ice. Philosophical Transactions Of The Royal Society A-Mathematical Physical And Engineering Sciences, 377(2146).
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Journaux, B., Chauve, T., Montagnat, M., Tommasi, A., Barou, F., Mainprice, D., et al. (2019). Recrystallization processes, microstructure and crystallographic preferred orientation evolution in polycrystalline ice during high-temperature simple shear. Cryosphere, 13(5), 1495–1511.
Abstract: Torsion experiments were performed in polycrystalline ice at high temperature (0.97 T-m) to reproduce the simple shear kinematics that are believed to dominate in ice streams and at the base of fast-flowing glaciers. As clearly documented more than 30 years ago, under simple shear ice develops a two-maxima c axis crystallographic preferred orientation (CPO), which evolves rapidly into a single cluster CPO with a c axis perpendicular to the shear plane. Dynamic recrystallization mechanisms that occur in both laboratory conditions and naturally deformed ice are likely candidates to explain the observed CPO evolution. In this study, we use electron backscatter diffraction (EBSD) and automatic ice texture analyzer (AITA) to characterize the mechanisms accommodating deformation, the stress and strain heterogeneities that form under torsion of an initially isotropic polycrystalline ice sample at high temperature, and the role of dynamic recrystallization in accommodating these heterogeneities. These analyses highlight an interlocking microstructure, which results from heterogeneity-driven serrated grain boundary migration, and sub-grain boundaries composed of dislocations with a [c]-component Burgers vector, indicating that strong local stress heterogeneity develops, in particular, close to grain boundaries, even at high temperature and high finite shear strain. Based on these observations, we propose that nucleation by bulging, assisted by sub-grain boundary formation and followed by grain growth, is a very likely candidate to explain the progressive disappearance of the c axis CPO cluster at low angle to the shear plane and the stability of the one normal to it. We therefore strongly support the development of new polycrystal plasticity models limiting dislocation slip on non-basal slip systems and allowing for efficient accommodation of strain incompatibilities by an association of bulging and formation of sub-grain boundaries with a significant [c] component.
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L'Hote, G., Cazottes, S., Lachambre, J., Montagnat, M., Courtois, P., Weiss, J., et al. (2019). Dislocation dynamics during cyclic loading in copper single crystal. Materialia, 8.
Abstract: Crystalline plasticity can take place through numerous, small, uncorrelated dislocation motions (mild plasticity) or through collaborative events: dislocation avalanches (wild plasticity). Here, we study the correlation between dislocation patterning under cyclic loading and the nature of collective dislocation dynamics. The dislocation motion of a [110] oriented pure copper single crystal was dynamically followed using Acoustic Emission (AE) for different imposed stress amplitudes. The dislocation structure between each cyclic stress step was investigated using Electron BackScattered Diffraction (EBSD) and Rotational-Electron Channeling Contrast Imaging (R-ECCI) in a Scanning Electron Microscope (SEM). At low imposed stress, when the structure consists of dislocation cells, few dislocation avalanches are observed, while for a wall structure, at higher imposed stress, the contribution of avalanches is increased during the first cycles. For a given stress amplitude, the evolution of mild plasticity is synchronous with the plastic strain-rate, and rapidly vanishes after few cycles due to work hardening. The mean free path of the dislocations in this mild plasticity regime corresponds to the characteristic size of the dislocation structure (cell size, distance between walls). From one stress level to another, brutal rearrangements of the dislocation structure occur within a few numbers of cycles. Those rearrangements take place, at least partly, through dislocation avalanches. Upon reloading at a larger stress amplitude, dislocation avalanches can travel over distances much larger than the former dislocation mean free path. As the dislocation avalanches spread within the crystal, the memory of the previous dislocation structure is lost and a new dislocation structure emerges.
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Lachaud, C., Marsan, D., Montagnat, M., Weiss, J., Moreau, L., & Gimbert, F. (2019). Micro-Seismic Monitoring of a Shear Fault within a Floating Ice Plate. Journal Of Geophysical Research-Solid Earth, .
Abstract: The deformation of a circular fault in a thin floating ice plate imposed by a slow rotational displacement is investigated. Temporal changes in shear strength, as a proxy for the resistance of the fault as a whole, are monitored by the torque required to impose a constant displacement rate. Micro-seismic monitoring is used to study the relationship between fault average resistance (torque) and micro-ruptures. The size distribution of ruptures follows a power-law scaling characterized by an unusually high exponent (b similar or equal to 3), characteristic of a deformation driven by small ruptures. In strong contrast to the typical brittle dynamics of crustal faults, an 'apparently aseismic' deformation regime is observed in which small undetected seismic ruptures, below the detection level of the monitoring system, control the slip budget. Most (similar or equal to 71%) of the detected ruptures are organized in bursts with highly similar waveforms, suggesting that these ruptures are only a passive by-product of apparently aseismic slip events. The seismic signature of this deformation regime has strong similarities with crustal faulting in settings characterized by high temperature and with non-volcanic tremors.
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Saletti, D., Georges, D., Gouy, V., Montagnat, M., & Forquin, P. (2019). A study of the mechanical response of polycrystalline ice subjected to dynamic tension loading using the spalling test technique. International Journal Of Impact Engineering, 132.
Abstract: Polycrystalline ice has been extensively investigated during the last decades regarding its mechanical behaviour for quasi-static loadings. Conversely, only few studies can be found on its dynamic behaviour and scientists suffer from a lack of experimental observation to develop relevant modelling at high strain-rate ranges. Dynamic experiments have already been conducted in compression mode using Hopkinson bar set-up. Regarding tension, experimental observations and measurements are scarce. The literature gives only approximated strength values. The knowledge of the latter is essential to design structures that may experience ice impact. The present study aims at providing the first reproducible experimental data of the tensile strength of polycrystalline ice subjected to dynamic tensile loading. To do so, a spalling test technique has been used for the first time on ice to apply tensile loading at strain-rates from 41 s(-1) to 271 s(-1). The experimental results show that the tensile strength is sensitive to the applied strain-rate, evolving from 1.9 MPa to 16.3 MPa for the highest applied loading rate.
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2018 |
Li, J., Gonzalez, J., Leuschen, C., Harish, A., Gogineni, P., Montagnat, M., et al. (2018). Multi-channel and multi-polarization radar measurements around the NEEM site. Cryosphere, 12(8), 2689–2705.
Abstract: Ice properties inferred from multi-polarization measurements, such as birefringence and crystal orientation fabric (COF), can provide insight into ice strain, viscosity, and ice flow. In 2008, the Center for Remote Sensing of Ice Sheets (CReSIS) used a ground-based VHF (very high frequency) radar to take multi-channel and multi-polarization measurements around the NEEM (North Greenland Eemian Ice Drilling) site. The system operated with 30MHz bandwidth at a center frequency of 150 MHz. This paper describes the radar system, antenna configurations, data collection, and processing and analysis of this data set. Within the framework derived from uniaxial ice crystal model, we found that ice birefringence dominates the power variation patterns of co-polarization and cross-polarization measurements in the area of 100 km2 around the ice core site. The phase shift between ordinary and extraordinary waves increases nonlinearly with depth. The ice optic axis lies in planes that are close to the vertical plane and perpendicular or parallel to the ice divide depending on depth. The ice optic axis has an average tilt angle of about 11 : 6 degrees vertically, and its plane may rotate either clockwise or counterclockwise by about 10 degrees across the 100 km(2) area, and at a specific location the plane may rotate slightly counterclockwise as depth increases. Comparisons between the radar observations, simulations, and ice core fabric data are in very good agreement. We calculated the effective colatitude at different depths by using azimuth and colatitude measurements of the c axis of ice crystals. We obtained an average effective c axis tilt angle of 9 : 6 degrees from the vertical axis, very comparable to the average optic axis tilt angle estimated from radar polarization measurements. The comparisons give us confidence in applying this polarimetric radio echo sounding technique to infer profiles of ice fabric in locations where there are no ice core measurements.
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2017 |
Calonne, N., Montagnat, M., Matzl, M., & Schneebeli, M. (2017). The layered evolution of fabric and microstructure of snow at Point Barnola, Central East Antarctica. Earth And Planetary Science Letters, 460, 293–301.
Abstract: Snow fabric, defined as the distribution of the c-axis orientations of the ice crystals in snow, is poorly known. So far, only one study exits that measured snow fabric based on a statistically representative technique. This recent study has revealed the impact of temperature gradient metamorphism on the evolution of fabric in natural snow, based on cold laboratory experiments. On polar ice sheets, snow properties are currently investigated regarding their strong variability in time and space, notably because of their potential influence on firn processes and consequently on ice core analysis. Here, we present measurements of fabric and microstructure of snow from Point Barnola, East Antarctica (close to Dome C). We analyzed a snow profile from 0 to 3 m depth, where temperature gradients occur. The main contributions of the paper are (1) a detailed characterization of snow in the upper meters of the ice sheet, especially by providing data on snow fabric, and (2) the study of a fundamental snow process, never observed up to now in a natural snowpack, namely the role of temperature gradient metamorphism on the evolution of the snow fabric. Snow samples were scanned by micro-tomography to measure continuous profiles of microstructural properties (density, specific surface area and pore thickness). Fabric analysis was performed using an automatic ice texture analyzer on 77 representative thin sections cut out from the samples. Different types of snow fabric could be identified and persist at depth. Snow fabric is significantly correlated with snow microstructure, pointing to the simultaneous influence of temperature gradient metamorphism on both properties. We propose a mechanism based on preferential grain growth to explain the fabric evolution under temperature gradients. Our work opens the question of how such a layered profile of fabric and microstructure evolves at depth and further influences the physical and mechanical properties of snow and firn. More generally, it opens the way to further studies on the influence of the snow fabric in snow processes related to anisotropic properties of ice such as grain growth, mechanical response, electromagnetic behavior. (C) 2016 The Author(s). Published by Elsevier B.V.
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Chauve, T., Montagnat, M., Barou, F., Hidas, K., Tommasi, A., & Mainprice, D. (2017). Investigation of nucleation processes during dynamic recrystallization of ice using cryo-EBSD. Philosophical Transactions Of The Royal Society A-Mathematical Physical And Engineering Sciences, 375(2086).
Abstract: Nucleation mechanisms occurring during dynamic recrystallization play a crucial role in the evolution of microstructures and textures during high temperature deformation. In polycrystalline ice, the strong viscoplastic anisotropy induces high strain heterogeneities between grains which control the recrystallization mechanisms. Here, we study the nucleation mechanisms occurring during creep tests performed on polycrystalline columnar ice at high temperature and stress (T=-5 degrees C; sigma = 0.5 MPa) by post-mortem analyses of deformation microstructures using cryogenic electron backscatter diffraction. The columnar geometry of the samples enables discrimination of the nuclei from the initial grains. Various nucleation mechanisms are deduced from the analysis of the nuclei relations with the dislocation sub-structures within grains and at grain boundaries. Tilt sub-grain boundaries and kink bands are the main structures responsible for development of polygonization and mosaic sub-structures. Nucleation by bulging at serrated grain boundaries is also an efficient nucleation mechanism near the grain boundaries where strain incompatibilities are high. Observation of nuclei with orientations not related to the 'parent' ones suggests the possibility of 'spontaneous' nucleation driven by the relaxation of the dislocation-related internal stress field. The complexity of the nucleation mechanisms observed here emphasizes the impact of stress and strain heterogeneities on dynamic recrystallization mechanisms. This article is part of the themed issue 'Microdynamics of ice'.
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Chauve, T., Montagnat, M., Lachaud, C., Georges, D., & Vacher, P. (2017). Strain field evolution at the ductile-to-brittle transition: a case study on ice. Solid Earth, 8(5).
Abstract: This paper presents, for the first time, the evolution of the local heterogeneous strain field around intra-granular cracking in polycrystalline ice, at the onset of tertiary creep. Owing to the high homologous temperature conditions and relatively low compressive stress applied, stress concentration at the crack tips is relaxed by plastic mechanisms associated with dynamic recrystallization. Strain field evolution followed by digital image correlation (DIC) directly shows the redistribution of strain during crack opening, but also the redistribution driven by crack tip plasticity mechanisms and recrystallization. Associated local changes in microstructure induce modifications of the local stress field evidenced by crack closure during deformation. At the ductile-to-brittle transition in ice, micro-cracking and dynamic recrystallization mechanisms can co-exist and interact, the later being efficient to relax stress concentration at the crack tips.
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Chauve, T., Montagnat, M., Piazolo, S., Journaux, B., Wheeler, J., Barou, F., et al. (2017). Non-basal dislocations should be accounted for in simulating ice mass flow. Earth And Planetary Science Letters, 473, 247–255.
Abstract: Prediction of ice mass flow and associated dynamics is pivotal at a time of climate change. Ice flow is dominantly accommodated by the motion of crystal defects – the dislocations. In the specific case of ice, their observation is not always accessible by means of the classical tools such as X-ray diffraction or transmission electron microscopy (TEM). Part of the dislocation population, the geometrically necessary dislocations (GNDs) can nevertheless be constrained using crystal orientation measurements via electron backscattering diffraction (EBSD) associated with appropriate analyses based on the Nye (1950) approach. The present study uses the Weighted Burgers Vectors, a reduced formulation of the Nye theory that enables the characterization of GNDs. Applied to ice, this method documents, for the first time, the presence of dislocations with non-basal [c] or < c + a > Burgers vectors. These [c] or (c + a) dislocations represent up to 35% of the GNDs observed in laboratory-deformed ice samples. Our findings offer a more complex and comprehensive picture of the key plasticity processes responsible for polycrystalline ice creep and provide better constraints on the constitutive mechanical laws implemented in ice sheet flow models used to predict the response of Earth ice masses to climate change. (C) 2017 Elsevier B.V. All rights reserved.
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Hidas, K., Tommasi, A., Mainprice, D., Chauve, T., Barou, F., & Montagnat, M. (2017). Microstructural evolution during thermal annealing of ice-I-h. Journal Of Structural Geology, 99, 31–44.
Abstract: We studied the evolution of the microstructure of ice-I-h during static recrystallization by stepwise annealing experiments. We alternated thermal annealing and electron backscatter diffraction (EBSD) analyses on polycrystalline columnar ice pre-deformed in uniaxial compression at temperature of -7 degrees C to macroscopic strains of 3.0-5.2. Annealing experiments were carried out at -5 degrees C and -2 degrees C up to a maximum of 3.25 days, typically in 5-6 steps. EBSD crystal orientation maps obtained after each annealing step permit the description of microstructural changes. Decrease in average intragranular misorientation at the sample scale and modification of the misorientation across subgrain boundaries provide evidence for recovery from the earliest stages of annealing. This initial evolution is similar for all studied samples irrespective of their initial strain or annealing temperature. After an incubation period >= 1.5 h, recovery is accompanied by recrystallization (nucleation and grain boundary migration). Grain growth proceeds at the expense of domains with high intragranular misorientations, consuming first the most misorientated parts of primary grains. Grain growth kinetics fits the parabolic growth law with grain growth exponents in the range of 2.4-4.0. Deformation-induced tilt boundaries and kink bands may slow down grain boundary migration. They are stable features during early stages of static recrystallization, only erased by normal growth, which starts after > 24 h of annealing. (C) 2017 Elsevier Ltd. All rights reserved.
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Moreau, L., Lachaud, C., Thery, R., Predoi, M. V., Marsan, D., Larose, E., et al. (2017). Monitoring ice thickness and elastic properties from the measurement of leaky guided waves: A laboratory experiment. Journal Of The Acoustical Society Of America, 142(5), 2873–2880.
Abstract: The decline of Arctic sea ice extent is one of the most spectacular signatures of global warming, and studies converge to show that this decline has been accelerating over the last four decades, with a rate that is not reproduced by climate models. To improve these models, relying on comprehensive and accurate field data is essential. While sea ice extent and concentration are accurately monitored from microwave imagery, an accurate measure of its thickness is still lacking. Moreover, measuring observables related to the mechanical behavior of the ice (such as Young's modulus, Poisson's ratio, etc.) could provide better insights in the understanding of sea ice decline, by completing current knowledge so far acquired mostly from radar and sonar data. This paper aims at demonstrating on the laboratory scale that these can all be estimated simultaneously by measuring seismic waves guided in the ice layer. The experiment consisted of leaving a water tank in a cold room in order to grow an ice layer at its surface. While its thickness was increasing, ultrasonic guided waves were generated with a piezoelectric source, and measurements were subsequently inverted to infer the thickness and mechanical properties of the ice with very good accuracy. (C) 2017 Acoustical Society of America.
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Richeton, T., Le, L. T., Chauve, T., Bernacki, M., Berbenni, S., & Montagnat, M. (2017). Modelling the transport of geometrically necessary dislocations on slip systems: application to single- and multi-crystals of ice. Modelling And Simulation In Materials Science And Engineering, 25(2).
Abstract: A model based on the elastic theory of continuously distributed dislocations, accounting for the transport of geometrically necessary dislocations (GND) on slip systems is developed. It allows keeping the crystallographic nature of glide by allocating velocities specific to slip systems to GND. At grain boundaries, the dislocation transport equation is resolved between a specific system in a grain and a specific system in the adjacent grain. It is used to simulate a compression creep test followed by unloading of a multiple slip deforming multi-crystal of ice during which kink band formation, grain boundary migration and localized grain nucleation are observed. The model predictions are compared to 2D strain fields obtained by digital image correlation and show a good agreement. Besides, the kink band position corresponds very well with an area of strong lattice misorientation predicted by the model and is also bounded by opposite densities of edge dislocations, in agreement with kink banding theory and characterization. Furthermore, the grain boundary migration is observed to happen from predicted low dislocation density area towards high dislocation ones-also in agreement with the theory. Lastly, the triple junctions where nucleation is observed are also characterized by high GND density and especially strong gradient of elastic energy density. These different features show the relevance of using a continuum theory of polarized dislocations per slip system to study the onset of relaxation mechanisms like kink banding, grain boundary migration and grain nucleation and possibly to propose nucleation and migration criteria.
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Sammonds, P., Montagnat, M., Bons, P., & Schneebeli, M. (2017). Ice microstructures and microdynamics. Philosophical Transactions Of The Royal Society A-Mathematical Physical And Engineering Sciences, 375(2086).
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Sammonds, P., Montagnat, M., Bons, P., & Schneebeli, M. (2017). Microdynamics of ice. Philosophical Transactions Of The Royal Society A-Mathematical Physical And Engineering Sciences, 375(2086).
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2016 |
Maurel, A., Mercier, J. F., & Montagnat, M. (2016). Critical investigation of calculation methods for the elastic velocities in anisotropic ice polycrystals. Cryosphere, 10(6), 3063–3070.
Abstract: Crystallographic texture (or fabric) evolution with depth along ice cores can be evaluated using borehole sonic logging measurements. These measurements provide the velocities of elastic waves that depend on the ice polycrystal anisotropy, and they can further be related to the ice texture. To do so, elastic velocities need to be inverted from a modeling approach that relate elastic velocities to ice texture. So far, two different approaches can be found. A classical model is based on the effective medium theory; the velocities are derived from elastic wave propagation in a homogeneous medium characterized by an average elasticity tensor. Alternatively, a velocity averaging approach was used in the glaciology community that averages the velocities from a given population of single crystals with different orientations. In this paper, we show that the velocity averaging method is erroneous in the present context. This is demonstrated for the case of waves propagating along the clustering direction of a highly textured polycrystal, characterized by crystallographic c axes oriented along a single maximum (cluster). In this case, two different shear wave velocities are obtained while a unique velocity is theoretically expected. While making use of this velocity averaging method, reference work by Bennett (1968) does not end with such an unphysical result. We show that this is due to the use of erroneous expressions for the shear wave velocities in a single crystal, as the starting point of the averaging process. Because of the weak elastic anisotropy of ice single crystal, the inversion of the measured velocities requires accurate modeling approaches. We demonstrate here that the inversion method based on the effective medium theory provides physically based results and should therefore be favored.
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2015 |
Chauve, T., Montagnat, M., & Vacher, P. (2015). Strain field evolution during dynamic recrystallization nucleation; A case study on ice. Acta Materialia, 101, 116–124.
Abstract: Nucleation mechanisms occurring during discontinuous dynamic recrystallization (DDRX) is investigated by Digital Image Correlation (DIC) during creep experiment on polycrystalline columnar ice. Thanks to the columnar microstructure, discrimination of the nucleus can be done without ambiguity comparing pre- and post- deformation texture. In-situ DIC analyses are performed around a triple junction were nucleation occurred to follow strain field evolution. Strain field evolution appears strongly linked to nucleation mechanisms, local grain boundary migration and sub-grain boundary formation such as tilt sub-grain boundaries and kink bands. Nucleation processes are correlated with strong strain heterogeneities well characterized by the principal strains evaluated by DIC. It was possible to follow nucleus growth through the evolution of strain localization along the new grain boundaries. Kink bands act as a buffer zone close to the triple junction and accommodate shear parallel to the c-axis. The local strain field appears to be efficiently redistributed by recrystallization processes which create a new microstructure more compatible with the local stresses. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Maurel, A., Lund, F., & Montagnat, M. (2015). Propagation of elastic waves through textured polycrystals: application to ice. Proceedings Of The Royal Society A-Mathematical Physical And Engineering Sciences, 471(2177).
Abstract: The propagation of elastic waves in polycrystals is revisited, with an emphasis on configurations relevant to the study of ice. Randomly oriented hexagonal single crystals are considered with specific, non-uniform, probability distributions for their major axis. Three typical textures or fabrics (i.e. preferred grain orientations) are studied in detail: one cluster fabric and two girdle fabrics, as found in ice recovered from deep ice cores. After computing the averaged elasticity tensor for the considered textures, wave propagation is studied using a wave equation with elastic constants c = < c > + delta c that are equal to an average plus deviations, presumed small, from that average. This allows for the use of the Voigt average in the wave equation, and velocities are obtained solving the appropriate Christoffel equation. The velocity for vertical propagation, as appropriate to interpret sonic logging measurements, is analysed in more details. Our formulae are shown to be accurate at the 0.5% level and they provide a rationale for previous empirical fits to wave propagation velocities with a quantitative agreement at the 0.07-0.7% level. We conclude that, within the formalism presented here, it is appropriate to use, with confidence, velocity measurements to characterize ice fabrics.
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Montagnat, M., Chauve, T., Barou, F., Tommasi, A., Beausir, B., & Fressengeas, C. (2015). Analysis of Dynamic Recrystallization of Ice from EBSD Orientation Mapping. Frontiers in Earth Science, 3, 81.
Abstract: We present high resolution observations of microstructure and texture evolution during dynamic
recrystallization (DRX) of ice polycrystals deformed in the laboratory at high temperature
(0.98Tm). Ice possesses a significant viscoplastic anisotropy that induces strong strain
heterogeneities, which result in an early occurrence of DRX mechanisms. It is therefore
a model material to explore these mechanisms. High resolution c-axis measurements at
sample scale by optical techniques and full crystallographic orientation measurements by cryo-
Electron Back Scattering Diffraction (EBSD) provide a solid database for analyzing the relative
impact of the macroscopic imposed stress versus the local and internal stress field on DRX
mechanisms. Analysis of misorientation gradients in the EBSD data highlights a heterogeneous
dislocation distribution, which is quantified by the Nye tensor estimation. Joint analyses of the
dislocation density maps and microstructural observations highlight spatial correlation between
high dislocation density sites and the onset of nucleation taking place by grain-boundary bulging,
subgrain rotation or by the formation of kink-bands.
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Piazolo, S., Montagnat, M., Grennerat, F., Moulinec, H., & Wheeler, J. (2015). Effect of local stress heterogeneities on dislocation fields: Examples from transient creep in polycrystalline ice. Acta Materialia, 90, 303–309.
Abstract: This work presents a coupled experimental and modeling approach to better understand the role of stress field heterogeneities on deformation behavior in material with a high viscoplastic anisotropy e.g. polycrystalline ice. Full-field elasto-viscoplastic modeling is used to predict the local stress and strain field during transient creep in a polycrystalline ice sample. Modeling input includes the experimental starting microstructure and a validated slip system dependent flow law. EBSD measurements on selected areas are used to estimate the local dislocation field utilizing the Weighted Burgers Vector (WBV) analysis. Areas of local stress concentration correlate with triple junctions and grain boundaries, originating from strain incompatibilities between differently oriented grains. In these areas of highly heterogeneous stress patterns, (a) kink bands are formed and (b) WBV analysis shows a non-negligible c-axis component of the WBV. The correlation between this defect structure and presence of kink bands suggests that kink band formation is an efficient accommodation deformation mode. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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2014 |
Montagnat, M., Azuma, N., Dahl-Jensen, D., Eichler, J., Fujita, S., Gillet-Chaulet, F., et al. (2014). Fabric along the NEEM ice core, Greenland, and its comparison with GRIP and NGRIP ice cores. Cryosphere, 8(4), 1129–1138.
Abstract: Fabric (distribution of crystallographic orientations) along the full NEEM ice core, Greenland was measured in the field by an automatic ice texture analyzer every 10 m, from 33m down to 2461m depth. The fabric evolves from a slightly anisotropic fabric at the top, toward a strong single maximum at about 2300 m, which is typical of a deformation pattern mostly driven by uniaxial compression and simple shearing. A sharp increase in the fabric strengthening rate is observed at the Holocene to Wisconsin (HW) climatic transition. From a simple model we estimate that this depth is located at a transition from a state dominated by vertical compression to a state dominated by vertical shear. Comparisons are made to two others ice cores drilled along the same ridge; the GRIP ice core, drilled at the summit of the ice sheet, and the NGRIP ice core, drilled 325 km to the NNW of the summit along the ridge, and 365 km upstream from NEEM. This comparison tends to demonstrate that the ice viscosity change with the HW climatic transition must be associated with the shear-dominated state to induce the abrupt fabric strengthening observed at NEEM. This comparison therefore reflects the increasing role of shear deformation on the coring site when moving NW along the ridge from GRIP to NGRIP and NEEM. The difference in fabric profiles be-tween NEEM and NGRIP also evidences a stronger lateral extension associated with a sharper ridge at NGRIP. Further along the core, centimeter scale abrupt texture (fabric and microstructure) variations are observed in the bottom part of the core. Their positions are in good agreement with the observed folding layers in Dahl-Jensen et al. (2013).
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Montagnat, M., Castelnau, O., Bons, P. D., Faria, S. H., Gagliardini, O., Gillet-Chaulet, F., et al. (2014). Multiscale modeling of ice deformation behavior. Journal Of Structural Geology, 61, 78–108.
Abstract: Understanding the flow of ice in glaciers and polar ice sheets is of increasing relevance in a time of potentially significant climate change. The flow of ice has hitherto received relatively little attention from the structural geological community. This paper aims to provide an overview of methods and results of ice deformation modeling from the single crystal to the polycrystal scale, and beyond to the scale of polar ice sheets. All through these scales, various models have been developed to understand, describe and predict the processes that operate during deformation of ice, with the aim to correctly represent ice rheology and self-induced anisotropy. Most of the modeling tools presented in this paper originate from the material science community, and are currently used and further developed for other materials and environments. We will show that this community has deeply integrated ice as a very useful “model” material to develop and validate approaches in conditions of a highly anisotropic behavior. This review, by no means exhaustive, aims at providing an overview of methods at different scales and levels of complexity. (C) 2013 Elsevier Ltd. All rights reserved.
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2013 |
Donges, J., Montagnat, M., Bastie, P., & Grennerat, F. (2013). 3D diffraction imaging and orientation mapping in deformed ice crystals. Nuclear Instruments & Methods In Physics Research Section B-Beam Interactions With Materials And Atoms, 300, 6–10.
Abstract: A method to acquire three dimensional diffraction data and orientation mapping with the 2D imaging setup of Hasylab beamline G3 is presented. The method has been successfully applied to undeformed large grains extracted from ice samples and extended to the 2D determination of lattice misorientation and lattice orientation distribution within deformed grains. (c) 2013 Elsevier B.V. All rights reserved.
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Gagliardini, O., Weiss, J., Duval, P., & Montagnat, M. (2013). On Duddu and Waisman (2012,2013) concerning continuum damage mechanics applied to crevassing and iceberg calving. Journal Of Glaciology, 59(216), 797–798.
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Gauthier, F., Montagnat, M., Weiss, J., Allard, M., & Hetu, B. (2013). Ice cascade growth and decay: a thermodynamic approach. Journal Of Glaciology, 59(215), 507–523.
Abstract: The ice volume evolution of a frozen waterfall (or ice cascade) was studied using a thermodynamic model. The model was developed from meteorological data collected in the vicinity of the waterfall and validated from ice volume measurements estimated from terrestrial lidar images. The ice cascade forms over a 45 m high rock wall located in northern Gaspesie, Quebec, Canada. Two stages of formation were identified. During the first stage, the growth is mainly controlled by air convection around the flowing and free-falling water. The ice cascade growth rate increases with decreasing air temperature below 0 degrees C and when the water flow reaches its lowest level. During the second stage, the ice cascade covers the entire rock-wall surface, water flow is isolated from the outside environment and ice volume increases asymptotically. Heat is evacuated from the water flow through the ice cover by conduction. The growth is controlled mainly by the conductive heat loss through the ice cover but also by the longwave radiation emitted at the ice surface during the night. In spring, melting of the ice cascade is dependent on the air convection over the ice surface but also on the sensible heat carried by the increasing water flow and the solar radiation received during the day.
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Riche, F., Montagnat, M., & Schneebeli, M. (2013). Evolution of crystal orientation in snow during temperature gradient metamorphism. Journal Of Glaciology, 59(213), 47–55.
Abstract: The physical properties of snow are tied to its microstructure. Especially for the slow, plastic deformation of snow and firn, the crystal orientation is an important factor in addition to the geometry of the ice matrix. While micro-computed tomography measures the snow microstructure precisely, it gives no information about the orientation of the ice crystals. In this study, we applied a temperature gradient of 50 K m(-1) to large blocks of undisturbed decomposed snow and sieved snow during 3 months. The mean temperature of the snow samples during the temperature gradient experiment was -20 degrees C. Two closely spaced snow samples were taken before the experiment, then every week during the first month and afterwards every month. From each sampling, one sample was analyzed by micro-computed tomography and the other was used for thin sections. The orientation of the c-axis was measured in the thin sections using an automatic ice texture analyzer. Initial density was 30% higher in the sieved snow sample. Density and specific surface area evolved alike, while the fabric showed a different evolution between the two samples. The undisturbed snow evolved from a weak single-maximum fabric towards a weak girdle fabric, while the sieved sample showed no evolution. The undisturbed snow sample converged toward the sieved sample fabric after 6 weeks, but continued its evolution thereafter. We suggest that the main factor causing this different behavior is the difference in density and in pore size.
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2012 |
Duval, P., Louchet, F., Weiss, J., & Montagnat, M. (2012). On the role of long-range internal stresses on grain nucleation during dynamic discontinuous recrystallization. Materials Science And Engineering A-Structural Materials Properties Microstructure And Processing, 546, 207–211.
Abstract: The role of long-range elastic interactions in discontinuous dynamic recrystallization is assessed using a simple analytical model, taking into account dislocation pileup relaxation during embryo formation. Long-range dislocation pileup rearrangements following absorption of leading dislocations by a dislocation-free embryo provides an additional driving force that results in a drastic decrease of both nucleation critical radius and saddle point energy. A very sharp transition between a saddle point behavior and spontaneous grain nucleation is evidenced. The role of long-range internal stresses on grain nucleation during dynamic discontinuous recrystallization of ice, metals and minerals is shortly discussed. (C) 2012 Elsevier B.V. All rights reserved.
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Grennerat, F., Montagnat, M., Castelnau, O., Vacher, P., Moulinec, H., Suquet, P., et al. (2012). Experimental characterization of the intragranular strain field in columnar ice during transient creep. Acta Materialia, 60(8), 3655–3666.
Abstract: A digital image correlation (DIC) technique has been adapted to polycrystalline ice specimens in order to characterize the development of strain heterogeneities at an intragranular scale during transient creep deformation (compression tests). Specimens exhibit a columnar microstructure so that plastic deformation is essentially two-dimensional, with few in-depth gradients, and therefore surface DIC analyses are representative of the whole specimen volume. Local misorientations at the intragranular scale were also extracted from microstructure analyses carried out with an automatic texture analyzer before and after deformation. Highly localized strain patterns are evidenced by the DIC technique. Local equivalent strain can reach values as much as an order of magnitude larger than the macroscopic average. The structure of the strain pattern does not evolve with strain in the transient creep regime. Almost no correlation between the measured local strain and the Schmid factor of the slip plane of the underlying grain is observed, highlighting the importance of the mechanical interactions between neighboring grains resulting from the very large viscoplastic anisotropy of ice crystals. Finally, the experimental microstructure was introduced in a full-field fast Fourier transform polycrystal model; simulated strain fields are a good match with experimental ones. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Montagnat, M. (2012). Déformation viscoplastique dans la glace ; du matériau modèle aux environnements naturels. Habilitation thesis, Université Grenoble Alpes, Grenoble.
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Montagnat, M., Buiron, D., Arnaud, L., Broquet, A., Schlitz, P., Jacob, R., et al. (2012). Measurements and numerical simulation of fabric evolution along the Tabs Dome ice core, Antarctica. Earth And Planetary Science Letters, 357, 168–178.
Abstract: We present measurements of fabrics and microstructures made along the Tabs Dome ice core, a core drilled in East Antarctica in the framework of the TALDICE project. Fabric and average grain size data are analyzed regarding changes in climatic conditions. In particular, the fabric strength increases sharply going downward from Holocene to Wisconsin ice. Following (Durand et al., 2007), this change is associated with a positive feedback between variations in ice viscosity, due to variations in dust content, and the impact of a shear stress component, increasing with depth. A ViscoPlastic Self-Consistent modeling approach is used to simulate the fabric evolution for a “perfect dome” configuration. The discrepancies between the measured and the simulated fabrics highlight the depth ranges where shear strongly affects the fabric strengthening. Finally, the grain size and fabric analyses show the occurrence of dynamic recrystallization mechanisms (continuous and discontinuous) along the core. (C) 2012 Elsevier B.V. All rights reserved.
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Piazolo, S., Borthwick, V., Griera, A., Montagnat, M., Jessell, M. W., Lebensohn, R., et al. (2012). Substructure Dynamics in crystalline materials: New insight from in-situ experiments, detailed EBSD analysis of experimental and natural samples and numerical modelling. In Recrystallization And Grain Growth Iv (Vol. 715-716, pp. 502–507).
Abstract: The understanding of the dynamics of substructures during deformation and annealing is fundamental in our ability to predict microstructural and physical properties such as rheological behaviour of crystalline materials. Here, we present an overview of new insights into substructure dynamics through a combination of in-situ heating experiments, detailed Electron Backscatter Diffraction (EBSD) analysis and numerical modelling. Our main findings are summarised as follows: A) In-situ annealing of substructure-rich, near isotropic minerals such as NaCl show distinct temperature dependent behaviour. B) A numerical approach in which a lower energy state is achieved by local adjustment i.e. rotation of crystalline materials enables us to reproduce the experimentally observed, temperature dependent substructure dynamics observed in A). C) Microstructures observed in a material with a highly anisotropic viscoplastic behaviour, i.e. ice, point to direct stress translations across grain boundaries, closely related grain boundary asperities and subgrain boundary tips, arrays of quasi-parallel subgrain boundaries frequently crossing whole grains; some of which are developed as kink-bands. D) Development of a numerical simulation system which is able to predict deformation induced substructure development and recrystallization in crystalline material, including highly anisotropic material such as ice. Comparison between model and experiments enables the researcher to refine the interpretation of microstructures observed in C). Through the combination of in-situ experiments and numerical modelling it is now possible to develop an in-depth understanding of subgrain scale processes as well as establish numerical models which reproduce the experimental observations. These can be utilised to predict microstructural development and rheological behaviour of a large variety of crystalline materials.
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Suquet, P., Moulinec, H., Castelnau, O., Montagnat, M., Lahellec, N., Grennerat, F., et al. (2012). Multi-scale modeling of the mechanical behavior of polycrystalline ice under transient creep (Vol. 3).
Abstract: Ice is a challenging material for understanding the overall behavior of polycrystalline materials and more specifically the coupling between elastic and viscous effects during transient creep. At the single crystal level, ice is an hexagonal material with a rather weak elastic anisotropy but with a strong viscoplastic anisotropy. The strain-stress curve of ice single crystals shows a softening behavior depending on the strain-rate. The strong viscous anisotropy of ice gives rise to the progressive development of intergranular and intragranular strain heterogeneities and to stress concentrations which play an important role in the understanding of the creep behavior of ice polycrystals. The single crystal constitutive relations of Castelnau et al [1] are slightly modified here for a better evolution of the reference resolved shear stress on the slip systems and to account for kinematic hardening at the single crystal level. These constitutive relations are then used in a full-field simulation performed by an elasto-viscoplastic FFT-based method. The material parameters of the model are determined by comparison with experimental data available for single crystals as well as for polycrystals. (C) 2012 Published by Elsevier B.V. Selection and/or peer review under responsibility of Dr. Oana Cazacu.
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2011 |
Buiron, D., Chappellaz, J., Stenni, B., Frezzotti, M., Baumgartner, M., Capron, E., et al. (2011). TALDICE-1 age scale of the Talos Dome deep ice core, East Antarctica. Clim. Past., 7(1), 1–16.
Abstract: A new deep ice core drilling program, TALDICE, has been successfully handled by a European team at Talos Dome, in the Ross Sea sector of East Antarctica, down to 1620m depth. Using stratigraphic markers and a new inverse method, we produce the first official chronology of the ice core, called TALDICE-1. We show that it notably improves an a priori chronology resulting from a one-dimensional ice flow model. It is in agreement with a posteriori controls of the resulting accumulation rate and thinning function along the core. An absolute uncertainty of only 300 yr is obtained over the course of the last deglaciation. This uncertainty remains lower than 600 yr over Marine Isotope Stage 3, back to 50 kyr BP. The phasing of the TALDICE ice core climate record with respect to the central East Antarctic plateau and Greenland records can thus be determined with a precision allowing for a discussion of the mechanisms at work at sub-millennial time scales.
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Grennerat, F., Montagnat, M., Castelnau, O., Vacher, P., & Duval, P. (2011). Intragranular strain field in columnar ice during transient creep regime and relation with the local microstucture. In European Physical Journal Conferences (Vol. 6). Bremand F.
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Montagnat, M., Blackford, J. R., Piazolo, S., Arnaud, L., & Lebensohn, R. A. (2011). Measurements and full-field predictions of deformation heterogeneities in ice. Earth And Planetary Science Letters, 305(1-2), 153–160.
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. (C) 2011 Elsevier B.V. All rights reserved.
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Roessiger, J., Bons, P. D., Griera, A., Jessell, M. W., Evans, L., Montagnat, M., et al. (2011). Competition between grain growth and grain-size reduction in polar ice. Journal Of Glaciology, 57(205), 942–948.
Abstract: Static (or 'normal') grain growth, i.e. grain boundary migration driven solely by grain boundary energy, is considered to be an important process in polar ice. Many ice-core studies report a continual increase in average grain size with depth in the upper hundreds of metres of ice sheets, while at deeper levels grain size appears to reach a steady state as a consequence of a balance between grain growth and grain-size reduction by dynamic recrystallization. The growth factor k in the normal grain growth law is important for any process where grain growth plays a role, and it is normally assumed to be a temperature-dependent material property. Here we show, using numerical simulations with the program Elle, that the factor k also incorporates the effect of the microstructure on grain growth. For example, a change in grain-size distribution from normal to log-normal in a thin section is found to correspond to an increase in k by a factor of 3.5.
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Stenni, B., Buiron, D., Frezzotti, M., Albani, S., Barbante, C., Bard, E., et al. (2011). Expression of the bipolar see-saw in Antarctic climate records during the last deglaciation. Nat. Geosci., 4(1), 46–49.
Abstract: Ice-core records of climate from Greenland and Antarctica show asynchronous temperature variations on millennial timescales during the last glacial period(1). The warming during the transition from glacial to interglacial conditions was markedly different between the hemispheres, a pattern attributed to the thermal bipolar see-saw(2). However, a record from the Ross Sea sector of East Antarctica has been suggested to be synchronous with Northern Hemisphere climate change(3). Here we present a temperature record from the Talos Dome ice core, also located in the Ross Sea sector. We compare our record with ice-core analyses from Greenland, based on methane synchronization(4), and find clearly asynchronous temperature changes during the deglaciation. We also find distinct differences in Antarctic records, pointing to differences in the climate evolution of the Indo-Pacific and Atlantic sectors of Antarctica. In the Atlantic sector, we find that the rate of warming slowed between 16,000 and 14,500 years ago, parallel with the deceleration of the rise in atmospheric carbon dioxide concentrations and with a slight cooling over Greenland. In addition, our chronology supports the hypothesis that the cooling of the Antarctic Cold Reversal is synchronous with the Bolling-Allerod warming in the northern hemisphere 14,700 years ago(5).
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Weiss, J., Montagnat, M., Cinquin-Lapierre, B., Labory, P. A., Moreau, L., Damilano, F., et al. (2011). Waterfall ice: mechanical stability of vertical structures. Journal Of Glaciology, 57(203), 407–415.
Abstract: We present a study of the mechanical (in)stability of the ephemeral waterfall ice structures that form from the freezing of liquid water seeping on steep rock. Three vertical structures were studied, two near Glacier d'Argentiere, France, and one in the Valsavarenche valley, northern Italy. The generation of internal stresses in the ice structure in relation to air- and ice-temperature conditions is analyzed from pressure sensor records. Their role in the mechanical instability of the structures is discussed from a photographic survey of these structures. The main result is that dramatic air cooling (several degrees C h(-1) over several hours) and low temperatures (<-10 degrees C), generating tensile stresses and brittleness, can trigger a spontaneous or climber-induced mechanical collapse, leading to unfavorable climbing conditions. Ice internal pressure fluctuations are also associated with episodes of marked diurnal air-temperature cycle, with mild days (few degrees C above 0 degrees C) and cool nights (few degrees C below 0 degrees C), through the occurrence of water <-> ice phase transitions within the structure. These ice internal stress fluctuations seem, however, to have a local influence, are associated with warm (near 0 degrees C), wet and therefore particularly soft ice and do not trigger a collapse of the structure.
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2010 |
Duval, P., Montagnat, M., Grennerat, F., Weiss, J., Meyssonnier, J., & Philip, A. (2010). Creep and plasticity of glacier ice: a material science perspective. Journal Of Glaciology, 56(200), 1059–1068.
Abstract: Major advances in understanding the plasticity of ice have been made during the past 60 years with the development of studies of the flow of glaciers and, recently, with the analysis of deep ice cores in Antarctica and Greenland. Recent experimental investigations clearly show that the plastic deformation of the ice single crystal and polycrystal is produced by intermittent dislocation bursts triggered by long-range interaction of dislocations. Such dislocation avalanches are associated with the formation of dislocation patterns in the form of slip lines and slip bands, which exhibit long-range correlations and scale invariance. Long-range dislocation interactions appear to play an essential role in primary creep of polycrystals and dynamic recrystallization. The large plastic anisotropy of the ice crystal is at the origin of large strain and stress heterogeneities within grains. The use of full-field approaches is now a compulsory proceeding to model the intracrystalline heterogeneities that develop in polycrystals. Ice is now highly regarded among the materials science community. It is considered a model material for understanding deformation processes of crystalline materials and polycrystal modeling.
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Ma, Y., Gagliardini, O., Ritz, C., Gillet-Chaulet, F., Durand, G., & Montagnat, M. (2010). Enhancement factors for grounded ice and ice shelves inferred from an anisotropic ice-flow model. J. Glaciol., 56(199), 805–812.
Abstract: Polar ice is known to be one of the most anisotropic natural materials. For a given fabric the polycrystal viscous response is strongly dependent on the actual state of stress and strain rate. Within an ice sheet, grounded-ice parts and ice shelves have completely different stress regimes, so one should expect completely different impacts of ice anisotropy on the flow. The aim of this work is to quantify, through the concept of enhancement factors, the influence of ice anisotropy on the flow of grounded ice and ice shelves. For this purpose, a full-Stokes anisotropic marine ice-sheet flowline model is used to compare isotropic and anisotropic diagnostic velocity fields on a fixed geometry. From these full-Stokes results, we propose a definition of enhancement factors for grounded ice and ice shelves, coherent with the asymptotic models used for these regions. We then estimate realistic values for the enhancement factors induced by ice anisotropy for grounded ice and ice shelves.
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Montagnat, M., Weiss, J., Cinquin-Lapierre, B., Labory, P. A., Moreau, L., Damilano, F., et al. (2010). Waterfall ice: formation, structure and evolution. J. Glaciol., 56(196), 225–234.
Abstract: For the first time, to our knowledge, a scientific study of the formation and evolution of waterfall ice, the ephemeral ice structures that form from the freezing of liquid water seeping on steep rock, was performed. We surveyed and analysed three waterfall ice structures near Glacier d'Argentiere, Mont Blanc massif, France, between winter 2007 and spring 2009. We reconstruct the global evolution of two vertical ice structures using automatic digital cameras, while the internal ice microstructure was analysed using ice coring and sampling. Macro- and microstructural observations are considered, along with temperature conditions recorded at a nearby meteorological station and directly within the ice structure. They reveal that vertical structures initially grow rapidly from the aggregation of stalactites with microstructures indicative of temperature conditions during their crystallization. After this initial stage, the volume of the ice structure reaches an asymptotic value, as water continues to flow inside the structure, isolated from the outside cold ice; the outer surface remains dry. At the end of the season, the collapse of the free-standing structure does not occur by progressive melting, but is initiated by a horizontal crack propagation at the top. The initiation of this crack seems to be triggered by a drastic temperature decrease.
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2009 |
Lebensohn, R. A., Montagnat, M., Mansuy, P., Duval, P., Meysonnier, J., & Philip, A. (2009). Modeling viscoplastic behavior and heterogeneous intracrystalline deformation of columnar ice polycrystals. Acta Mater., 57(5), 1405–1415.
Abstract: A Full-field formulation based on fast Fourier transforms (FFT) has been adapted and used to predict the micromechanical fields that develop in two-dimensional columnar Ih ice polycrystals deforming in compression by dislocation creep. The predicted intragranular mechanical fields are in qualitative good agreement with experimental observations, in particular those involving the formation of shear and kink bands. These localized bands are associated with the large internal stresses that develop during, creep in such anisotropic material, and their location, intensity, morphology and extension are found to depend strongly on the crystallographic orientation of the grains and on their interaction with neighboring crystals. The predictions of the model are also discussed in relation to the deformation of columnar sea and lake ice, its well as with the mechanical behavior of granular ice of glaciers and polar ice sheets. Published by Elsevier Ltd. on behalf of Acta Materialia Inc.
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2008 |
Castelnau, O., Duval, P., Montagnat, M., & Brenner, R. (2008). Elastoviscoplastic micromechanical modeling of the transient creep of ice. J. Geophys. Res.-Solid Earth, 113(B11), 14 pp.
Abstract: A salient feature of the rheology of isotropic polycrystalline ices is the decrease of the strain rate by more than 2 orders of magnitude during transient creep tests to reach a secondary creep regime at a strain which is systematically of similar to 1%. We use a recent (so-called "affine'') version of the self-consistent mean-field theory to model the elastoviscoplastic behavior of ice. The model aims at bridging scales between the rheology of single grain and the one of polycrystals by evaluating the intergranular interactions. It takes into account the long-term memory effects, which manifests itself by the fact that local stress and strain rate in grains depend on the whole mechanical history of the polycrystal. It is shown that the strong hardening amplitude during the transient creep is entirely explained by the stress redistribution within the specimen, from an almost uniform stress distribution upon instantaneous loading (purely elastic response) to strong interphase and intraphase heterogeneities in the stationary regime (purely viscoplastic response). The experimental hardening kinetic is much too slow to be explained by the same process; it is attributed to the hardening of hard glide slip systems (prismatic slip) in the transient regime. Moreover, the model very well reproduces the permanent creep rate of several highly anisotropic specimens of the Greenland Ice Core Project ice core (pronounced crystallographic textures), when accounting for a single-grain rheology that well matches the experimental one. Our results are consistent with recent findings concerning dislocation dynamics in ice.
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Piazolo, S., Montagnat, M., & Blackford, J. R. (2008). Sub-structure characterization of experimentally and naturally deformed ice using cryo-EBSD. J. Microsc.-Oxf., 230(3), 509–519.
Abstract: In this work, we present first results of high-resolution EBSD for ice with a spatial resolution down to 0.25 μm. The study highlights the potential of EBSD to significantly increase our understanding of deformation and annealing processes associated with the build-up of internal stresses due to strain incompatibility between grains. Two polycrystalline samples were analyzed: a natural sample of polar ice from the Vostok ice core (Antarctica) and an experimentally deformed sample of laboratory grown columnar ice. In summary, we observe the following: (1) inhomogeneous deformation through the grains is translated into lattice distortions that are concentrated mainly at grain boundaries and triple junctions (natural and experimental sample), (2) these distortions may be continuous (natural and experimental sample) or may form distinct tilt boundaries and sub-grains of 10-50 μm size (experimental sample). These form mainly by rearrangement of basal edge dislocations into low-energy configurations (i.e. tilt boundaries) in various prism planes. Continuous lattice distortions originate from screw or mixed edge and screw dislocations lying in the basal plane.
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2007 |
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Chevy, J., Montagnat, M., Duval, P., Fivel, M., & Weiss, J. (2007). Dislocation patterning and deformation processes in ice single crystals deformed by torsion. Royal Soc Chemistry.
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Taupin, V., Varadhan, S., Chevy, J., Fressengeas, C., Beaudoin, A. J., Montagnat, M., et al. (2007). Effects of size on the dynamics of dislocations in ice single crystals. Phys. Rev. Lett., 99(15), 4 pp.
Abstract: Single crystals of ice subjected to primary creep in torsion exhibit a softening behavior: the plastic strain rate increases with time. In a cylindrical sample, the size of the radius affects this response. The smaller the radius of the sample becomes while keeping constant the average shear stress across a section, the softer the response. The size-dependent behavior is interpreted by using a field dislocation theory, in terms of the coupled dynamics of excess screw dislocations gliding in basal planes and statistical dislocations developed through cross slip occurring in prismatic planes. The differences in the results caused by sample height effects and variations in the initial dislocation microstructure are discussed.
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Weiss, J., & Montagnat, M. (2007). Long-range spatial correlations and scaling in dislocation and slip patterns. Philos. Mag., 87(8-9), 1161–1174.
Abstract: Although the intermittent and heterogeneous nature of plastic flow has been known for several decades, only recently have observations performed on the surface of deformed samples by atomic force microscopy (AFM) or scanning white-light interferometry, or in the bulk by X-ray topography, revealed the scale invariant character of dislocation and slip patterns emerging from collective dislocation interactions. This scale invariance implies that the spatial fluctuations of dislocation density and/or slip never vanish as one coarsens the observation scale. An immediate consequence is that a priori obvious concepts such as “slip bands” or dislocation density can be ill-defined. These detailed characterizations of the plastic flow heterogeneity also challenge the modelling of plasticity.
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2005 |
Gillet-Chaulet, F., Gagliardini, O., Meyssonnier, J., Montagnat, M., & Castelnau, O. (2005). A user-friendly anisotropic flow law for ice-sheet modelling. J. Glaciol., 51(172), 3–14.
Abstract: For accurate ice-sheet flow modelling, the anisotropic behaviour of ice must be taken fully into account. However, physically based micro-macro (mu-M) models for the behaviour of an anisotropic ice polycrystal are too complex to be implemented easily in large-scale ice-sheet flow models. An easy and efficient method to remedy this is presented. Polar ice is assumed to behave as a linearly viscous orthotropic material whose general flow law (GOLF) depends on six parameters, and its orthotropic fabric is described by an 'orientation distribution function' (ODF) depending on two parameters. A method to pass from the ODF to a discrete description of the fabric, and vice versa, is presented. Considering any available mu-M model, the parameters of the GOLF that fit the response obtained by running this mu-M model are calculated for any set of ODF parameters. It is thus possible to tabulate the GOLF over a grid in the space of the ODF parameters. This step is performed once and for all. Ice-sheet flow models need the general form of the GOLF to be implemented in the available code (once), then, during each individual run, to retrieve the GOLF parameters from the table by interpolation. As an application example, the GOLF is tabulated using three different mu-M models and used to derive the rheological properties of ice along the Greenland Icecore Project (GRIP) ice core.
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2004 |
Hamelin, B., Bastie, P., Duval, P., Chevy, J., & Montagnat, M. (2004). Lattice distortion and basal slip bands in deformed ice crystals revealed by hard X-ray diffraction. J. Phys. IV, 118, 27–33.
Abstract: Hard X-ray diffraction experiments were performed on ice single crystals deformed in pure torsion. The torsion strain appears to be totally accommodated by geometrically necessary basal screw dislocations. Dislocation slip is concentrated on macroscopic basal slip bands, which are clearly seen on the prismatic diffraction lines. The slip band spacing is decreasing with the increase of the finite torsion strain. The deformation appears to result from the increase of the number of slip bands and not from the accumulation of dislocations within these bands. The elastic interaction between dislocations located in neighbouring slip bands is weak since they all have the same sign and move in the same direction.
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Martinez-Esnaola, J. M., Montagnat, M., Duval, P., & Sevillano, J. G. (2004). Geometrically necessary dislocations in a c-axis oriented cylindrical bar of basal-slipping hexagonal crystals deformed in torsion. Scr. Mater., 50(2), 273–278.
Abstract: A crystallographic analysis of the size-dependent geometrically necessary dislocations (GND) stored in a cylindrical hexagonal single crystal deformed by torsion with its c-axis aligned with the torsion axis has been made. The only activation of basal slip and strain rate dependence of critical resolved shear stresses have been assumed. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Montagnat, M., & Duval, P. (2004). Dislocations in ice and deformation mechanisms: from single crystals to polar ice (Vol. 229). Trans Tech Publications Ltd.
Abstract: We present the main features of the plasticity of ice Ih: both monocrystalline and polycrystalline. The nature and dynamics of dislocations are analyzed, with emphasis being placed on the mechanical behavior of single crystals. The strong plastic anisotropy of the ice crystal is at the origin of the formation of strong strain heterogeneities within the polycrystal. Under the low-stress conditions of polar ice sheets, basal slip associated with the formation of orientation gradients is the main deformation mode. Lattice distortion promotes the formation of boundaries and continuous recrystallization.
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Montagnat, M., & Duval, P. (2004). The viscoplastic behaviour of ice in polar ice sheets: experimental results and modelling. C. R. Phys., 5(7), 699–708.
Abstract: The slow motion of polar ice sheets is governed by the viscous deformation of anisotropic ices. Physical mechanisms controlling the deformation of ice crystal and polycrystal are reviewed. For the low stress conditions prevailing in ice sheets, the stress exponent of the flow law is lower than 2 and the deformation is dominated by the glide of dislocations on the basal plane. The mismatch of slip at grain boundaries induces large strain inhomogeneities partially relieved in ice sheets by grain growth and recrystallisation. The hard X-ray diffraction technique can be used to describe the orientation gradients within grains. The structure of ice along deep ice cores in Antarctica and Greenland exhibits significant changes in the shape, size and orientation of grains. A large variation of ice viscosity with depth is therefore expected. Polycrystal deformation models accounting for the changing theological properties of polar ice are discussed. These models must predict and take into account the intracrystalline field heterogeneity. (C) 2004 Academie des sciences. Published by Elsevier SAS. All rights reserved.
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Montagnat, M., Duval, P., Chevy, J., Hamelin, B., & Bastie, P. (2004). Gradients de déformation et dislocations geométriquement nécessaires dans des monocristaux de glace déformés en torsion. In Colloque National MECAMAT. Aussois.
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2003 |
Montagnat, M., Duval, P., Bastie, P., & Hamelin, B. (2003). Strain gradients and geometrically necessary dislocations in deformed ice single crystals. Scr. Mater., 49(5), 411–415.
Abstract: Hard X-ray diffraction experiments were performed on ice single crystals deformed in torsion. This work shows the relationship between the density of geometrically necessary dislocations and strain gradients. The torsion strain appears to be totally accommodated by geometrically necessary basal screw dislocations. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
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Montagnat, M., Duval, P., Bastie, P., Hamelin, B., & Lipenkov, V. Y. (2003). Lattice distortion in ice crystals from the Vostok core (Antarctica) revealed by hard X-ray diffraction; implication in the deformation of ice at low stresses. Earth Planet. Sci. Lett., 214(1-2), 369–378.
Abstract: Hard X-ray diffraction experiments have been carried out on ice monocrystals taken from the 3623 m long Vostok core (Antarctica). Strain gradients associated with the storage of geometrically necessary dislocations appear to be a general feature of the deformation microstructure of ice. The observed lattice distortion is related to the bending of the basal plane and the torsion of the lattice around the c-axis. The lattice distortion is shown to be compatible with the basal dislocations generally observed in ice crystals, Supporting the assumption of deformation modes governed by basal slip and accommodated by recrystallization processes. The dependence of the ice viscosity on grain size in ice sheets appears to be compatible with these accommodation modes. (C) 2003 Elsevier B.V. All rights reserved.
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2002 |
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Duval, P., & Montagnat, M. (2002). Comment on "Superplastic deformation of ice: experimental observations'' by D. L. Goldsby and D. L. Kohlstedt. J. Geophys. Res.-Solid Earth, 107(B4), 2 pp.
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2001 |
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Montagnat, M. (2001). Contribution à l'étude du comportement viscoplastique des glaces des calottes polaires : modes de déformation et simulation du développement des texturesThèse de l'Université Joseph-Fourier, Grenoble 1. Ph.D. thesis, , .
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Montagnat, M., Duval, P., Bastie, P., Hamelin, B., Brissaud, O., de Angelis, M. T., et al. (2001). High crystalline quality of large single crystals of subglacial ice above Lake Vostok (Antarctica) revealed by hard X-ray diffraction. Comptes Rendus Acad. Sci. Ser II-A, 333(8), 419–425.
Abstract: X-ray diffraction experiments were carried out on large ice crystals from accreted ice above Lake Vostok, a subglacial lake lying beneath the East Antarctic ice sheet. Results indicate a surprisingly very low lattice distortion. This crystalline quality does not seem to be affected by impurities. Abnormal grain growth should occur and could explain both the large grain size and the low lattice distortion. Accreted ice is therefore supposed to be non-plastically deforming. These results should be taken into account for further studies of the permeability of accreted ice to drilling fluid present in the borehole. (C) 2001 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.
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2000 |
Duval, P., Arnaud, L., Brissaud, O., Montagnat, M., & de la Chapelle, S. (2000). Deformation and recrystallization processes of ice from polar ice sheets (Vol. 30). Int Glaciological Soc.
Abstract: Information on deformation modes, fabric development and recrystallization processes was obtained by study of deep ice cores from polar ice sheets. It is shown that intracrystalline slip is the main deformation mechanism in polar ice sheets. Grain-boundary sliding does not appear to be a significant deformation mode. Special emphasis was laid on the occurrence of “laboratory” tertiary creep in ice sheets. The creep behavior is directly related to recrystallization processes. Grain-boundary migration associated with grain growth and rotation recrystallization accommodates dislocation slip and counteracts strain hardening. The fabric pattern is similar to that induced only by slip, even if rotation recrystallization slows down fabric development. Fabrics which develop during tertiary creep, and are associated with migration recrystallization, are typical recrystallization fabrics. They are associated with the fast boundary migration regime as observed in temperate glaciers. A decrease of the stress exponent is expected from 3, when migration recrystallization occurs, to a value <2 when normal grain growth occurs.
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Montagnat, M., & Duval, P. (2000). Rate controlling processes in the creep of polar ice, influence of grain boundary migration associated with recrystallization. Earth Planet. Sci. Lett., 183(1-2), 179–186.
Abstract: Information on the deformation modes and recrystallization processes in polar ice sheets was obtained thanks to the analysis of the ice structure along two deep ice cores from Greenland and Antarctica. It is shown that the deformation of polar ice at low stresses is produced by intracrystalline slip accommodated by grain boundary migration (gbm). A deformation model based on an equilibrium between work-hardening and recovery processes has been developed. The decrease in dislocation density is due to both gbm associated with grain growth and the formation of boundaries by recrystallization. The value of the dislocation density along the Byrd and GRIP ice cores obtained thanks to the model is about 1x10(11) m(-2). This value is in agreement with data from synchrotron X-ray diffraction on samples taken along the core. This deformation model can account for the deformation of polar ice at low stresses. It is shown that the flow law with a stress exponent lower than 2 can be related to the efficiency of gbm as a recovery process. (C) 2000 Elsevier Science B.V. All rights reserved.
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Montagnat, M., & Duval, P. (2000). Relation between deformed grain orientations, nucleation and texture development in ice. In N. Hansen, X. Huang, D. J. Jenssen, L. Labeyrie, E. M. Lauridsen, T. Leffers, et al. (Eds.), 21st Riso International Symposium on Materials Science: Recrystallization – Fundamental Aspects and Relations to Deformation Microstructure (pp. 459–465). Ed.
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1998 |
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Fiévet, C., Montagnat, M., & Chévrier, P. (1998). Arc energy balance in the arc chute of a low voltage circuit breaker. In XIIIth Symposium on Physics of Switching Arc (Vol. Ii, pp. 333–336). Czek Republic.
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