Characterization and Analysis of Micromechanical Properties on DNTF and CL-20 Explosive Crystals
Round 1
Reviewer 1 Report
This paper reports a somewhat observational (but new) set of data on indentation behavior of and properties of two energetic materials.
When reporting values for the first time, the benefit to the community is the first reports help establish a baseline of information. The challenge is that the accuracy can be hard to determine, but it's incumbent on the authors to ensure stringent reporting.
In that vein a few points need to be addressed.
1. The authors suggest there are micro cracks and defects (fig 2) based on jumps in load depth curves. Indenting molecular organics can show cracks that way, existing cracks (pores) can do that, but you can also get cracks that don't show up in load - depth curves except in a subtle manner (see Burch et al in JMR, https://doi.org/10.1557/jmr.2019.345). You need to reword some of this to clarify if the cracks are being caused by the indenter, or existing flaws are sensed by the indenter.
For the indentation community figure 4 and 5 are not particularly useful. They should be moved to supplemental figures.
2. The depth dependent modulus concerns me. While there are reports of decreased modulus with increasing depth in energetics (doi.org/10.1002/crat.201500301) other reports in this journal on similar materials demonstrated that with proper testing there was no clear decrease in modulus with increased sample size ( doi:10.3390/cryst10020126 ). So while figure 7 I buy, figure 6 concerns me and needs a better explanation or more proof the modulus isn't constant by sample volume.
3. Eq 7 is developed for only one particular crack geometry (running from indent corners in a half penny geometry). This isn't the geometry noted in figure 10. So while there may be some rough scaling, the calculation of fracture toughness here isn't appropriate, and table 2 is concerning to me.
Overall this paper has good information that the field can use. As a first report on a type of material I would hope the authors could be more precise and establish the standard by which others testing these materials are held to, with some modifications that can occur here.
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The paper can be published in this form.
Author Response
Thanks for your review and suggestions.
Reviewer 3 Report
My comments from the beginning:
abstract: please disabbreviate DNTF and CL-20 at first appearance
"Cl-20" - should be "CL-20", and it other places as well
"The results show that the hardness for DNTF and CL-20 was 0.57GPa and 12 0.84GPa, and the elastic modulus are 10.34GPa and 20.30GPa, respectively" - please, specify the errors
Introduction - "Material mechanics performance plays a crucial role on the response 24 behavior of crystals under external mechanical load (such as the impact, friction, impact, etc.), which could result in the formation of "hot spots", and also relate to impact sensitivity." - i recommend to stregthen this statement by giving the most recent overviews on this problem, e.g., https://doi.org/10.1016/j.cej.2021.129804
At the end of the literature overview on indentation and relevant topics, the authors should discuss the recent paper on it https://doi.org/10.1039/D2CP00832G In fact, there are some similarities with the present study results, i.e., for rigidity of CL-20 surface, and for mobility of compounds that have the lower melting point (as in this study is DNTF)
Besides, since the authors discuss the application of SPM to energetic materials, i suggest to give the proper background to the topic, to discuss in ht eintroduction also the review of this area: https://doi.org/10.1016/j.enmf.2022.05.004
Figures 8,9 have incorrect captions. I recommend to present the molecular structures of the discussed compounds at the beginning of paper instead. This discussion of the chemical structure should be supplemented by giving the literature references on their synthesis and properties.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
