Temperature and strain controls on ice deformation mechanisms: insights from the microstructures of samples deformed to progressively higher strains at −10, −20 and −30&thinsp;°C

Fan, Sheng; Hager, Travis F.; Prior, David J.; Cross, Andrew J.; Goldsby, David L.; Qi, Chao; Negrini, Marianne; Wheeler, John

doi:https://doi.org/10.5194/tc-14-3875-2020

Articles | Volume 14, issue 11

https://doi.org/10.5194/tc-14-3875-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/tc-14-3875-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 14, issue 11

Research article

|

10 Nov 2020

Research article |

| 10 Nov 2020

Temperature and strain controls on ice deformation mechanisms: insights from the microstructures of samples deformed to progressively higher strains at −10, −20 and −30 °C

Sheng Fan, Travis F. Hager, David J. Prior, Andrew J. Cross, David L. Goldsby, Chao Qi, Marianne Negrini, and John Wheeler

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Final revised paper (published on 10 Nov 2020)
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Preprint (discussion started on 22 Jan 2020)
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Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review of paper by Fan and co-authors', Maurine Montagnat, 19 Feb 2020
- AC1: 'Response to Reviewer 1', Sheng Fan, 15 Jun 2020
RC2: 'Ms review', Olivier Castelnau, 02 Mar 2020
- AC2: 'Response to Reviewer 2', Sheng Fan, 15 Jun 2020

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (further review by editor and referees) (17 Jun 2020) by Evgeny A. Podolskiy

AR by Sheng Fan on behalf of the Authors (17 Jun 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (24 Jun 2020) by Evgeny A. Podolskiy

RR by Maurine Montagnat (22 Jul 2020)

RR by Olivier Castelnau (27 Jul 2020)

Suggestions for revision or reasons for rejection

The authors did a substantial improvement of the initial version of the paper, but still some work is needed before publication.

Page 19, lines 5-18. I don’t like the discussion on GBS which I find extremely restrictive (less than the first version of the paper but still). Apparently the authors want to prove that if there is a grain size sensitivity of the mechanical behaviour (weakening) then it must come from GBS. This is without remembering that plasticity essentially comes from dislocation slip, and that dislocations interact with other dislocations, with grain boundaries, with the internal stress field, can annihilate or climb or be nucleated, etc. leading to many possible size effects. One could for example rewrite line 9-10 “The grain size sensitivity is hidden in the flow stress data as grain size becomes controlled by the flow stress” by “The dislocation processes are hidden in the flow stress data as dislocation motion is controlled by the flow stress”. But there is unfortunately no mention of possible complex dislocation processes in the paper, that are well known to be size dependent (in a complex way, the literature is abundant !). Size effects due to strain-gradient plasticity could also be invoked (e.g. work by Geers, Forest, Fleck, etc). Line 14, the sentence “Without GBS another explanation is needed for the grain size sensitivity” require a more open discussion based on all other possible weakening mechanisms. Concerning that point, the response letter cannot be considered as satisfactory. Page 27, concerning the (inverse) Hall-Petch effect, the authors write: “Some recent work relates GBS associated with the inverse Hall-Petch relationship with amorphization of the grain boundaries (Guo et al., 2018) and a molecular dynamics modelling study of ice (Cao et al., 2018) generates an inverse Hall-Petch relationship that involves a combination of GBS, grain rotation, amorphization and recrystallization, phase transformation, and dislocation nucleation in both bicrystals and polycrystals. ». BUT: Guo’s paper is on nanocrystalline superhard materials (hardness similar than diamond), and Cao’s paper is a MD computational study on 40nm polycrystalline ice with flow stress around 600MPa ! Of course GBS can occurs in some materials but these two references on nm grains have nothing to do with the hundred-microns ice grains considered here. This is not to say that GBS is not active in ice, but the authors should be convincing by using a correct argumentation. That GBS occurs in some nanometric superhard material does not guarantee that it also occurs in ice.

Page 16 line 16 : similarly, strange to put reference to Elati et al. here to show that GBS happens in some fine grain structure materials. This reference is on a High Entropy Alloy, which may differ significantly from ice deformation (if not please justify). There are other materials in which GBS is active without having to go to fine grains, such as Salt (see papers by Bornert, Dimanov and Bourcier).

Page 8 line 10 : as already indicated in my first review, the distribution shown in figure 4 can really not be described as a “bimodal” one ! Same line 17 (bimodal grain size). Please modify.

Page 15 line 4 : I don’t know whether this is a standard treatment in the glaciology or mineral physics community, but the identification of an activation energy for the “flow stress” (or tertiary creep in “constant load experiments”) is not accurate, as the sample microstructures vary between specimens.

Page 2 line 25 : “displacement rate” instead of “displacement”

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ED: Reconsider after major revisions (further review by editor and referees) (28 Jul 2020) by Evgeny A. Podolskiy

AR by Sheng Fan on behalf of the Authors (22 Aug 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (25 Aug 2020) by Evgeny A. Podolskiy

RR by Maurine Montagnat (03 Sep 2020)

RR by Olivier Castelnau (15 Sep 2020)

Suggestions for revision or reasons for rejection

This is my third review of this paper. The paper has been improved compared to the previous (second) version, grain boundary sliding (gbs) is now presented more as a possible way to explain observations than to be THE good candidate. The discussion has been somehow enlarged.

I am still not totally convinced by the discussion, but to go forwards I suggest to proceed with the publication of the paper after commenting the points below :

** item 1 of page 20 about gbs : The role of gbs is still not clear to me as I’ve already explain in my previous reviews, as well as the (poor) evidence of gbs occurence. I also really wonder how GBS can modify the boundary misorientation. This is not discussed in the paper although it should be central to understand how gbs is believed to modify the microstructures. I check some of the cited literature (Jiang et al 2000, Goldsby and Kohlstedt 1997, 2001, Bestmann and Prior 2003, Cross and others 2017b) in which this is not explained either. By the way, the results obtained in previous published paper seems to be improved in this new paper. For example, my understanding of Cross et al 2017b is that these authors “propose” gbs as an active mechanisms, i.e. as one possible solution (bottom of before-last page). In the manuscript, it is written (page 20 line 18) : “Cross et al 2017b found evidence for specific orientation being randomized by gbs”. To me, there is a clear difference between a “proposition” and an “evidence”.

** section 4.2, last three lines : as indicated in my last review, there are other candidates than the 3 indicated here. For example, according to Orowan’s equation, an increase in the density of mobile dislocations during strain (eg. by the activation or multiplication of dislocations sources) can also lead to significant weakening. The authors could explain why they believe that dislocation processes don’t come in play here.

And also :

** page 6 line 25, “Misorientation angle distributions are illustrated as ” is written twice.

** page 8 line 15, notation D_SMR=\bar sqrt(D**2) is misleading. It seems to be the square of the square root, i.e. D ??

** page 8 line 17 : there is still mention to a “bimodal” grains size distribution which is not visible in any of the presented data… Please see my previous review.

** page 8 line 19 : “grain size converge as the strain increases” … converges towards which value ?? please indicate.

** page 21 line 24 : “analytical numerical models” is weird… either analytical, or numerical ?

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ED: Publish subject to minor revisions (review by editor) (18 Sep 2020) by Evgeny A. Podolskiy

AR by Sheng Fan on behalf of the Authors (23 Sep 2020) Author's response Manuscript

ED: Publish as is (02 Oct 2020) by Evgeny A. Podolskiy

AR by Sheng Fan on behalf of the Authors (02 Oct 2020) Manuscript

Short summary

We performed uniaxial compression experiments on synthetic ice samples. We report ice microstructural evolution at –20 and –30 °C that has never been reported before. Microstructural data show the opening angle of c-axis cones decreases with increasing strain or with decreasing temperature, suggesting a more active grain rotation. CPO intensity weakens with temperature because CPO of small grains is weaker, and it can be explained by grain boundary sliding or nucleation with random orientations.