Experimental and Numerical Analysis of Conical Projectile Impact on Inconel 718 Plates
, Antonio Díaz-Álvarez 1, Richard Bernier 2, María Henar Miguélez 1 and José Antonio Loya 3Round 1
Reviewer 1 Report
Rows 53-55
The authors write: “The presented experimental ballistic curves for Inconel 718 can be considered especially useful for the design and optimisation of the containment of the aero-engine casing.”
However, the variables presented in the manuscript were only parameters of the projectile i.e. shape and angle of the nose, what suggests, that the article is rather an attempt of optimization of the projectile to punch an Inconel plate of the thickness of 1.6 mm and unknown hardness and heat treatment condition.
Hence, question is; what is the purpose of the article, because it does not result from the introduction.
Row 60
How the heat treatment of the Inconel was carried out and what is its hardness.
Row 76
What is the grade of the steel, how the heat treatment was carried out and what is its hardness.
Figure 11
In the signature of the figure 11 there are markings a, b, c, which are not visible in the figure.
Row 249
The authors drawn conclusion: “It is found that the ballistic limit and the failure mode of the target are strongly linked to the projectile nose shape”.
If this conclusion is true, the results shown in figure 9 should be supplemented with statistical analysis and differences between the ballistic limit values for different projectiles should be statistically significant, while in figure 9, authors did not show even uncertainty of results.
To justify the authors’ conclusion from row 249, the statistical analysis based on the standards listed below should be performed, otherwise someone could put forward a thesis that all those values (presented in fig. 9) are statistically the same.
ISO 2854: Statistical interpretation of data -- Techniques of estimation and tests relating to means and variances.
ISO 2602: Statistical interpretation of test results -- Estimation of the mean -- Confidence interval.
Author Response
The authors write: “The presented experimental ballistic curves for Inconel 718 can be considered especially useful for the design and optimisation of the containment of the aero-engine casing.”
However, the variables presented in the manuscript were only parameters of the projectile i.e. shape and angle of the nose, what suggests, that the article is rather an attempt of optimization of the projectile to punch an Inconel plate of the thickness of 1.6 mm and unknown hardness and heat treatment condition.
Hence, question is; what is the purpose of the article, because it does not result from the introduction.
The purpose of the paper is to characterize the mechanical behavior of Inconel 718 under impact conditions. The conical projectiles selected (commonly used in scientific literature for other materials), have not previously been used in Inconel 718. In author’s opinion, the ballistic response of the Inconel plates can be used as a guide when designed an impact structure.
Row 60
How the heat treatment of the Inconel was carried out and what is its hardness.
The treatment was carried out by the company that provided the material. The Inconel 718 used in the experiments was hardened by solution heat treatment and aged to reach a state similar to that typically faced by a tool during finishing operations of this superalloy. The hardness of the material was measured at different points, obtaining values from 44 to 45.5 HRc
Row 76
What is the grade of the steel, how the heat treatment was carried out and what is its hardness.
Projectiles were made of a maraging steel with a heat treatment (carried out by the company that provided the projectile) to reach a yield stress close to σy = 2GPa. The hardness of this material, measured at different points, varies around 52 HRc.
Figure 11
In the signature of the figure 11 there are markings a, b, c, which are not visible in the figure.
The authors would like to thank the reviewer for finding a typographical error.
Row 249
The authors drawn conclusion: “It is found that the ballistic limit and the failure mode of the target are strongly linked to the projectile nose shape”.
If this conclusion is true, the results shown in figure 9 should be supplemented with statistical analysis and differences between the ballistic limit values for different projectiles should be statistically significant, while in figure 9, authors did not show even uncertainty of results.
To justify the authors’ conclusion from row 249, the statistical analysis based on the standards listed below should be performed, otherwise someone could put forward a thesis that all those values (presented in fig. 9) are statistically the same.
ISO 2854: Statistical interpretation of data -- Techniques of estimation and tests relating to means and variances.
ISO 2602: Statistical interpretation of test results -- Estimation of the mean -- Confidence interval.
The objective of the work is to obtain the ballistic curve (Vo-Vr) and the ballistic limit. As the reviewer point, a way to calculate the ballistic limit, called V50, is by means the STANAG 2920 standard which considers the probability of 50% for complete perforation.
However, the STANAG 2920 standard is carried out using grooved cannons with gunpowder; in which there is great variability. In this work, the tests have been carried out on an ungrooved cannon and the projectiles are guided and the impact very centred. As mentioned in the paper, no sabot was necessary because the inner diameter of the barrel is similar to that of the projectile. This methodology has been widely used by Prof. Alexis Rusinek and collaborators.
The study that the reviewer proposes can be considered for the future by comparing different materials. In the current study, the Vo-Vr curve is obtained for the calibration of numerical models subjected to the conical projectile impact.
The authors would thank the reviewers for the comments that have allowed for significantly improving the quality of the document.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The subject of the manuscript and results are very interesting and the text are well organized. However some minor corrections should be made to improve the quality of the manuscript. Slight corrections of English grammar are recommended, for example:
- line 60: .”… next table [13].” should be: “… following table [13].” or “… in the Table 1 [13].”
- line 74: “The gas-gun barrel used is approximately 13 mm so…” should be: “The used gas-gun barrel is approximately 13 mm so…”
- line 76: “The projectiles used are made…” should be: “The used projectiles are made…”
- line 91: “…and local failure mechanisms for the three types of projectiles considered.” should be: “…and 90 local failure mechanisms for the three types of projectiles considered.”
and similar mistakes throughout the text.
In addition, some editorial corrections are needed:
1. line 44: is this sentence correct?
2. line 59: Celsius degrees are used throughout the text, it would also be good to give the temperature in the same units.
3. line 67: area should be determined and presented in the square millimetres: mm2
4. line 70: “Schematic…” should be: “Scheme of…”
5. In the Figure 2 the Impact zone is described as “Impac zonet”
6. line 79: unnecessary pause: [14,15]-
7. line 112: “… is represented…” should be “…presented…”
8. line 194: the thickness of the Inconel 718 plates is given only in the Discussion, should be given in the Experimental section.
9. Text in the Figure 10 is poorly readable.
10. The Celsius degree symbol should be standardized throughout the text and in the figures. In the current version of the manuscript, 0 (zero) in the upper script is often used.
Author Response
The subject of the manuscript and results are very interesting and the text are well organized. However some minor corrections should be made to improve the quality of the manuscript. Slight corrections of English grammar are recommended, for example:
- line 60: .”… next table [13].” should be: “… following table [13].” or “… in the Table 1 [13].”
- line 74: “The gas-gun barrel used is approximately 13 mm so…” should be: “The used gas-gun barrel is approximately 13 mm so…”
- line 76: “The projectiles used are made…” should be: “The used projectiles are made…”
- line 91: “…and local failure mechanisms for the three types of projectiles considered.” should be: “…and 90 local failure mechanisms for the three types of projectiles considered.”
and similar mistakes throughout the text.
We thank the reviewer for these comments, which are totally pertinent. In this way, an extensive language editing has been carried out according to reviewer’s comment
In addition, some editorial corrections are needed:
1. line 44: is this sentence correct?
2. line 59: Celsius degrees are used throughout the text, it would also be good to give the temperature in the same units.
3. line 67: area should be determined and presented in the square millimetres: mm2
4. line 70: “Schematic…” should be: “Scheme of…”
5. In the Figure 2 the Impact zone is described as “Impac zonet”
6. line 79: unnecessary pause: [14,15]-
7. line 112: “… is represented…” should be “…presented…”
8. line 194: the thickness of the Inconel 718 plates is given only in the Discussion, should be given in the Experimental section.
9. Text in the Figure 10 is poorly readable.
10. The Celsius degree symbol should be standardized throughout the text and in the figures. In the current version of the manuscript, 0 (zero) in the upper script is often used.
We thank the reviewer for these comments, which are totally pertinent. In this way, an extensive language editing has been carried out according to reviewer’s comment
The authors would thank the reviewers for the comments that have allowed for significantly improving the quality of the document.
Author Response File: Author Response.pdf
Reviewer 3 Report
The paper deals with ballistics study on inconel 718 plates. This material is used in aero applications for parts that must sustain elevated temperatures. The authors provide a thorough study of the projectile impact on the material.
While the article is in general well thought out, there are some parts that need inmrpovement. I also suggest language editing, but as a reviwer whose native language is not English, I do not feel competent to point out grammar and style mistakes.
Comments to the authors are below:
Introduction:
It gives a good motivation for studies, bit I miss putting the information about "what has been done". In my opinion it is not concise, so I suggest rewritting the section to give readers a better background understanding.
Experimental campaign
Interesting use of the word campaign... Just Experimental will be enough. (This is one example of why I think this paper needs extensive English language editing services).
Use of degrees F is not in compliance with the metric system - please change all temperatures to K. (or C)
Is the composition of the material the one you used or from a datasheet? Are the 2 decimal places justified?
Figure 1 has letters that are very tiny and can be read on screen, but not when the paper is printed out, Redraw the figure to provide better visibility.
Figure 2: some spelling mistakes (impac zonet - I suppose should read impact zone)
ballistic curves: the fitting seems very good, can you maybe provide error for kappa?
Figure 8: at first glance, the line for Vr=Vo is the same as the "Simulations" line. I suggest to make the Vr=Vo line different than the simulations line to avoid this problem (for example, dashed or similar)
Discussion: I miss putting the results in context, and more words are needed to explain the comparison of numerical and simulation results.
I suggest editing the manuscript according to the points above.
Author Response
MANUSCRIPT METALS_ 502912 REVIEWER No. 3
The paper deals with ballistics study on inconel 718 plates. This material is used in aero applications for parts that must sustain elevated temperatures. The authors provide a thorough study of the projectile impact on the material.
While the article is in general well thought out, there are some parts that need inmrpovement. I also suggest language editing, but as a reviwer whose native language is not English, I do not feel competent to point out grammar and style mistakes.
Comments to the authors are below:
Introduction:
It gives a good motivation for studies, bit I miss putting the information about "what has been done". In my opinion it is not concise, so I suggest rewritting the section to give readers a better background understanding.
The authors appreciate the comment. The section was rewritten to improve English. The paper is novel because there are not many works focused on the impact on Inconel 718, so this section is not so extensive.
Experimental campaign
Interesting use of the word campaign... Just Experimental will be enough. (This is one example of why I think this paper needs extensive English language editing services).
We thank the reviewer for these comments, which are totally pertinent. In this way, an extensive language editing has been carried out according to reviewer’s comment
Use of degrees F is not in compliance with the metric system - please change all temperatures to K. (or C)
The authors appreciate the comment. All temperatures were changed to C.
Is the composition of the material the one you used or from a datasheet? Are the 2 decimal places justified?
The values of the composition of the Inconel are obtained from the book developed by R.C Reed.
Reed, R.C. The Superalloys: Fundamentals and Applications; Cambridge University Press: New York, 2006; ISBN 9780521859042.
Figure 1 has letters that are very tiny and can be read on screen, but not when the paper is printed out, Redraw the figure to provide better visibility.
We thank the reviewer for the comment. The letters have been changed.
Figure 2: some spelling mistakes (impac zonet - I suppose should read impact zone)
We thank the reviewer for the comment. This mistake has been changed
ballistic curves: the fitting seems very good, can you maybe provide error for kappa?
The error for kappa has been included in the text according to reviewer’s comment.
Figure 8: at first glance, the line for Vr=Vo is the same as the "Simulations" line. I suggest to make the Vr=Vo line different than the simulations line to avoid this problem (for example, dashed or similar)
We thank the reviewer for the comment
Discussion: I miss putting the results in context, and more words are needed to explain the comparison of numerical and simulation results.
The following sentences have been included in the text according to reviewer’s comment
Numerical predictions follow the trend of experimental data. It is observed that at higher velocities, the damage is more localized, although numerically there are small differences. However, at low velocities, the model correctly predicts bending. Regarding the maximum deflection values, it is difficult to obtain that value due to the petalling effect.
I suggest editing the manuscript according to the points above.
The authors would thank the reviewers for the comments that have allowed for significantly improving the quality of the document.
Author Response File: Author Response.pdf
Reviewer 4 Report
The paper presents experimental and numerical analysis of 3 different projectile shapes on 718 Inconel plates. There is a good correlation between the numerical and experimental results. The conclusions are supported by the results.
The authors should expand the Abstract to include some quantifiable data.
Explain the reason for choosing the nose angle of 40 and 72 (previous work or commonly used in existing literature).
Some technical details about the velocity sensors should be provided. For example, sensitivity, accuracy etc.
Some minor comments:
Page 1; line 40: ..........has not been sufficiently...........
Page 3; lines 74-75: Please paraphrase.
Page 3; line 95: ..........in Figure 4. The.........
Page 4; lines 112-113: Please paraphrase.
Page 5; line 122: ..........shape agree with......
Page 5; line 136: ..........(zone A) and the........
Page 6; line 166: ..........expression for this...........
Page 8; line 198: ..........observation agree with......
Page 9; line 219: ..........X axis. The.......
Page 9; line 221: ..........agree with the results......
Page 11; line 254: ..........On the other.......
Author Response
MANUSCRIPT METALS_ 502912 REVIEWER No. 4
The paper presents experimental and numerical analysis of 3 different projectile shapes on 718 Inconel plates. There is a good correlation between the numerical and experimental results. The conclusions are supported by the results.
The authors should expand the Abstract to include some quantifiable data.
According to reviewer’s comment, the Abstract has been expanded including some quantifiable data.
This paper analyses the impact behaviour of Inconel 718 through experimental and numerical approach. Different conical projectiles were tested in order to obtain the ballistic curves and failure mechanisms. A 3D numerical model corresponding to the experimental tests was developed using the Johnson-Cook constitutive model. The experimental data (residual velocities, global and local perforation mechanisms) were successfully predicted with the numerical simulations. The influence of the projectile's nose angle was found to be important when designing ballistic protections. The projectile with the narrowest angle, 400, developed a ballistic limit approximately 10 m/s lower than the projectile with a 720 nose. The use of double nose projectile for the same nose angle, 720, led to a ballistic limit 12 m/s lower than that obtained for the single nose.
Explain the reason for choosing the nose angle of 40 and 72 (previous work or commonly used in existing literature).
These nose angles of projectile were previously used by Professor A. Rusinek and collaborators in other materials (steels). In author’s opinion, to use same projectile geometries could allow future comparisons with other materials.
Some technical details about the velocity sensors should be provided. For example, sensitivity, accuracy etc.
We thank the reviewer for this comment, which is totally pertinent. In this way, the authors have added the following text according to the reviewer’s comments:
“The velocity sensors have an accuracy of 1 m/s approx.”
Some minor comments:
Page 1; line 40: ..........has not been sufficiently...........
Page 3; lines 74-75: Please paraphrase.
Page 3; line 95: ..........in Figure 4. The.........
Page 4; lines 112-113: Please paraphrase.
Page 5; line 122: ..........shape agree with......
Page 5; line 136: ..........(zone A) and the........
Page 6; line 166: ..........expression for this...........
Page 8; line 198: ..........observation agree with......
Page 9; line 219: ..........X axis. The.......
Page 9; line 221: ..........agree with the results......
Page 11; line 254: ..........On the other.......
We thank the reviewer for these comments, which are totally pertinent. In this way, an extensive language editing has been carried out according to reviewer’s comment
The authors would thank the reviewers for the comments that have allowed for significantly improving the quality of the document.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
I accept the present form of the manuscript and the explanations of the authors.
Reviewer 3 Report
The authors have taken into consideration all raised points, and now the manuscript is, in my opinion, suitable for publication.
