Research on the Dynamic Damage Properties and Determination of the Holmquist–Johnson–Cook Model Parameters for Sandstone
Round 1
Reviewer 1 Report
Dynamic behavior of rock is interesting and old topic; However, the following comments should be considered before the manuscript can be considered further.
General comments:
In the conventional SHPB test, a rectangular incident wave is generated by a direct impact of the striker to the free end of the incident bar. This incident wave features a very sharp arising part as well as great oscillations; and it takes longer time for the sample to reach dynamic stress equilibrium. For brittle solids like rocks with small failure strain (as seen in figure 4 a &b), the sample may fail immediately from its end when it is impacted by the incident bar. To solve this problem, authors are suggested to use pulse shaping technique to generate a non-dispersive ramp pulse (copper disc might be good option). Authors should redo the SHPB tests
If it is possible, I would be great to couple the high-speed camera with SHPB to observe crack propagation.
Base on the fig 2 the time-varying stresses on both sides of the samples do not perfectly match with each other.
Please add strain rate -time curve .
Please explain how many sample authors did test in each strain rate (fig 4)? At least 3 samples should be tested in each strain rate.
Repeated impact tests should be completely explained in the methodology part. What is strain rate of repeated test. Does strain rate have effect on the result of repeated impact test?
It would be great if authors calculate the elastic modulus of sample after repeated impact test. As seen in fig 8 with increase in the number of impacts gradually decreases the elastic modulus. The reduction in the elastic modulus is a function of the number of active flaws within a solid. Please discuss more about it. maybe authors can use some equation like this
Ef= E*(1-D)
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The high rate mechanical properties of rocks have been studied using the Kolsky bar since the late 1960s, but until about 11 years ago the number of publications worldwide on this topic remained less than 10 per year. In the last four years, interest suddenly increased so that now there are more than 100 articles published each year on the high rate properties of rocks. But as far as I know, this is the first to report the effect on dynamic strength of dynamically damaging rock. So this paper is to be welcomed. I recommend it for publication so long as the authors attend to the points listed below.
First, as sandstone is a quasi-brittle material, the strains their Kolsky bar can apply before specimen failure are small. So there are issues of the accuracy of the technique, particularly for parameters such as the modulus.
Second (following on from above), they quote data and coefficients in their constitutive equations to too high a level of precision than is justified.
Minor corrections:
Lines 21 & 27. Coefficients of equation too precise.
Line 38. Replace ‘problem4’ by ‘problem[4]’
Line 40 Replace ‘dynamics5’ by ‘dynamics[5]’
Line 43. Replace ‘properties6,7’ by ‘properties[6,7]’
Line 45. Replace ‘Hauser11’ by ‘Hauser[11]’
Line 48. Replace ‘partial energy’ by ‘only some of the energy’
Equation (16). Coefficients of equation too precise.
Tables 3, 4, 5, 6, 7, 8, 9. Numbers too precise.
Line 467. Replace ‘77 GP’ by ’77 GPa’
Figure 19 is missing.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Accept
