Influence Rule of Annular Notch Geometric Parameter on the Tubing Surface: A Case Study

Round 1

Reviewer 1 Report

The paper „Research on the Influence Rule of Annular Notch Geometric Parameter on the Tubing Surface” by Zhao et al. is not written according to the standards of scientific articles. I do not recommend the article for publication in Metals journal in its current form. In order to reconsider this article for publication, the following remarks should be taken into account:

- Due to the fact that the article does not have a classic, transparent layout, i.e. Introduction, Materials and methods, Results and discussion, the content provided is not clear for the reader.

- A mathematical model is a finite set of mathematical symbols and relations as well as strict rules for handling them. Thus, the sketches in Figure 2 are not mathematical models, they are only sketches of notch variants. Incidentally, the notch shapes should be sketched enlarged.

- The preparation of the FEM models is imprecisely described, and the mesh refinement at the bottom of the notch is too low to obtain precise simulation results.

- According to generally accepted rules, the research methodology should be precisely described in a scientific publication, so that the reader could potentially repeat the experiment. Meanwhile, the methodology of experimental research, which is to validate the simulation, is insufficiently described, it is not clear how and with what devices the authors conducted the experimental research.

- The basic mechanical properties of the material used should be presented in the table, as well as its chemical composition also in the table.

- The properties of the elements used in the FEM model should be described in more detail.

- Conclusions are too general. It is necessary to compare results obtained with results from references.

- Conclusions should contain plans for further research.

- Old references should be replaced by more recent journal paper references.

- The formatting does not fully comply with the guidelines imposed by the journal.

- Generally, the language needs revision.

Author Response

1. Due to the fact that the article does not have a classic, transparent layout, i.e. Introduction, Materials and methods, Results and discussion, the content provided is not clear for the reader.

Authors’ response:

Thanks a lot for the reviewer’s comments.

We apologize for this ignorance and we have checked and amended it in the manuscript.

 

2. A mathematical model is a finite set of mathematical symbols and relations as well as strict rules for handling them. Thus, the sketches in Figure 2 are not mathematical models, they are only sketches of notch variants. Incidentally, the notch shapes should be sketched enlarged.

Authors’ response:

Thanks a lot for the reviewer’s comments.

We have changed the name of Figure 2 in the text to "Schematic diagram of the finite element model of tube loading"; and enlarged the notched parts of the tube in Figure 2.

 

3. The preparation of the FEM models is imprecisely described, and the mesh refinement at the bottom of the notch is too low to obtain precise simulation results.

Authors’ response:

Thanks a lot for the reviewer’s comments.

We set the boundary conditions, meshed, and loaded the finite element models in Figure 3, Figure 4, Figure 5, and Figure 6 again, and especially when dividing the mesh, the mesh was refined at the root of the V-notch, near the V-notch, the grid is processed from coarse to fine, and other parts of the tube use coarser grids, which can improve the calculation efficiency and take into account the calculation accuracy. as follows:

Figure 3. Mises stress moiré diagram of V-notch tubing.

 

Figure 4. Mises stress moiré diagram of tubing with asymmetric V-notch towards the blanking end direction 45^o

 

Figure 5. Mises stress moiré diagram of tubing with asymmetric V-notch away from the blanking end direction 45^o.

 

Figure 6. Mises stress moiré diagram of tubing with U-notch.

 

4. According to generally accepted rules, the research methodology should be precisely described in a scientific publication, so that the reader could potentially repeat the experiment. Meanwhile, the methodology of experimental research, which is to validate the simulation, is insufficiently described, it is not clear how and with what devices the authors conducted the experimental research.

Authors’ response:

Thanks a lot for the reviewer’s comments.

We have supplemented the text with experimental research methods:

The high-speed rotating bending fatigue loading precision separation method of the eccentric wheel comprehensively utilizes the rapid initiation of micro-cracks and the controllable crack propagation technology, first artificially prefabricates annular gaps on the surface of the tube, and applies periodic cyclic bending fatigue to the radial direction of the tube through the high-speed rotation of the specially designed eccentric wheel. Load, the blanking die will load the tube radially during the rotation of the eccentric wheel, and each rotation is a loading cycle. Micro-cracks are rapidly initiated at the root of the notch, and the macro-cracks continuously expand to the center of the tube according to the specified direction and expansion rate in the section of the annular notch of the tube, and finally realize the efficient, precise and controllable separation of the tube. First, fix the tube with prefabricated notch, and then apply periodic radial load to the tube by adjusting the loading frequency of the motor, so that micro-cracks are formed at the root of the annular notch of the tube, and the cracks are promoted until the tube breaks, and the separation is completed.

 

5. The basic mechanical properties of the material used should be presented in the table, as well as its chemical composition also in the table.

Authors’ response:

Thanks a lot for the reviewer’s comments.

Table 1. Chemical Composition and Physical Properties of Materials

Material	C Content (%)	Cr Content (%)	Si Content (%)	Mn Content (%)	Melting point (℃)	Yield stress (Mpa)	Mass density(kg/m3)
304 stainless steel	0.07	18.53	0.74	1.50	1400	270	7850

 

6. The properties of the elements used in the FEM model should be described in more detail.

Authors’ response:

Thanks a lot for the reviewer’s comments.

We apologize for this ignorance and we have checked and amended it in the manuscript.

Moreover, the simulation object is 304 stainless steel, with elastic modulus of 2.1×10⁵Mpa, Poisson’s ratio of 0.3, and density of 7850 kg/m³. The failure criterion adopts the maximum principal stress criterion.

 

7. Conclusions are too general. It is necessary to compare results obtained with results from references.

Authors’ response:

Thanks a lot for the reviewer’s comments.

We have refined our conclusions as follows:

(1) According to the characteristics of the proposed precise separation technology of metal round tubing, annular V-notch, annular U-notch, asymmetric V-notch towards the blanking end direction 45^o, and asymmetric V-notch away from the blanking end direction 45^o are designed. Through numerical simulation calculation, the relevant experimental research is done on the crack propagation length of each kind of notch under the same experimental conditions. Through comprehensive analysis, it can be determined that the annular V-notch is the most suitable notch for this separation method. After analyzing the relationship between the crack initiation at the root tip of the V-notch and the stress field, as well as the stress state of the tubing under radial bending loading, the theoretical stress concentration factor expression of the annular V-notch is established: .

(2) Through the analysis of the influence of the three main geometric parameters of notch flare angle , notch root base angle radius , and notch depth  of the V-notch on tubing surface on the theoretical stress concentration factor, the influence rule is obtained. The smaller the notch flare angle , the greater the stress concentration effect of fracture. Therefore, the recommended flare angle for the tubing V-notch is 90°. With the increase of notch depth , the theoretical stress concentration factor first increases and then decreases. The notch depth  of the annular V-notch is preferably less than 3 mm. As the notch root base angle radius increases, the theoretical stress concentration factor decreases continuously. The suitable range of notch root base angle radius is 0.1mm-0.5mm. According to the influence law of the three main parameters, further research on the relationship between the geometric parameters of the annular V-notch and its value range is carried out. It is determined that the ideal value range of tubing annular V-notch geometric parameter is as follows: , , ,and .

(3) In the eccentric wheel high-speed rotational bending fatigue loading experiment, the tube materials are 45# steel tube, 304 stainless steel tube and T2Y copper tube respectively. The outer diameter of the tubing is 20mm, the wall thickness is 3mm, the flare angle  of the surface V-notch is 90^o, the root base angle radius  is 0.2mm, and the depth  is 0.5mm. Great precision separation effect is obtained, which verifies the rationality of annular V-notch geometric parameters on tubing surface. The follow-up research will combine the characteristics of the annular notch on tubing surface to study the crack initiation and propagation process during the precise separation process of the eccentric wheel high-speed rotating bending fatigue loading. Through the numerical simulation and experimental study on tubing separation, the tubing fatigue fracture separation mechanism and the crack propagation law will be further revealed.

 

8. 8. Conclusions should contain plans for further research.

Authors’ response:

Thanks a lot for the reviewer’s comments.

We have supplemented our plans for follow-up studies in point (3) of our conclusions:

(3) In the eccentric wheel high-speed rotational bending fatigue loading experiment, the tube materials are 45# steel tube, 304 stainless steel tube and T2Y copper tube respectively. The outer diameter of the tubing is 20mm, the wall thickness is 3mm, the flare angle  of the surface V-notch is 90^o, the root base angle radius  is 0.2mm, and the depth  is 0.5mm. Great precision separation effect is obtained, which verifies the rationality of annular V-notch geometric parameters on tubing surface. The follow-up research will combine the characteristics of the annular notch on tubing surface to study the crack initiation and propagation process during the precise separation process of the eccentric wheel high-speed rotating bending fatigue loading. Through the numerical simulation and experimental study on tubing separation, the tubing fatigue fracture separation mechanism and the crack propagation law will be further revealed.

 

9. Old references should be replaced by more recent journal paper references.

Authors’ response:

Thanks a lot for the reviewer’s comments.

References related to the research content in this journal have been added to the "Reference" as follows:

1     Liu, Y.; Ikeda, S.; Liu, Y.; Kang, L.; Ge, H. Experimental Investigation of Fracture Performances of SBHS500, SM570 and SM490 Steel Specimens with Notches. Metals. 2022, 12(4),672. https://doi.org/10.3390/met12040672

2     Chmelko, V.; Harakal, M.; Zlabek, P.; Margetin, M.; Durka, R. Simulation of Stress Concentrations in Notches. Metals. 2022, 12(1),43. https://doi.org/10.3390/met12010043

4     Li, J.; Yu, R.; Xu, G.; Chen, C.; Ha, Y.; Song, L.; Zhang, H. Research on Hot Deformation Behavior of F92 Steel Based on Stress Correction. Metals. 2022,12, 698. https://doi.org/10.3390/met12050698 

5     Bai, W.; Chen, W.; Zeng, C.; Wu, G.; Chai, X. Thermo-hydraulic performance investigation of heat pipe used annular heat exchanger with densely longitudinal fins. Appl. Therm. Eng. 2022, 211, 118451. https://doi.org/10.1016/j.applthermaleng.2022.118451.

12    Hojati, A.; Akhavan-Behabadi, M.; Hanafizadeh, P.; Ahmadpour, M. Effect of geometrical parameters on entropy generation during R134a boiling flow inside unique internally grooved tubes: Experimental approach. INT J THERM SCI. 2021, 163, 106845.

https://doi.org/10.1016/j.ijthermalsci.2021.106845.

 

10. The formatting does not fully comply with the guidelines imposed by the journal.

Authors’ response:

Thanks a lot for the reviewer’s comments.

We have perfected the format

 

11Generally, the language needs revision.

Authors’ response:

Thanks a lot for the reviewer’s comments.

Language has been polished.

Author Response File: Author Response.pdf

Reviewer 2 Report

To be accepted it is necessary to make the different minor corrections:

The typographic layout needs to be corrected.

It is necessary to correct the size of the symbol characters, making them the same size as the text (except for sub-index, etc.).

The quality of the figures (FEM meshes) should be improved.

Author Response

1. The typographic layout needs to be corrected.

Authors’ response:

Thanks a lot for the reviewer’s comments.

We apologize for this ignorance and we have checked and amended it in the manuscript.

 

2. It is necessary to correct the size of the symbol characters, making them the same size as the text (except for sub-index, etc.).

Authors’ response:

Thanks a lot for the reviewer’s comments.

We apologize for this ignorance and we have checked and amended it in the manuscript.

 

3. The quality of the figures (FEM meshes) should be improved.

Authors’ response:

Thanks a lot for the reviewer’s comments.

We apologize for this ignorance and we have checked and amended it in the manuscript.

Author Response File: Author Response.pdf

Reviewer 3 Report

Metals-1684938

 

This paper presents an theoretical and experimental investigation regarding the influence of notch geometry on the stress concentration effect of tubular specimens. The technical purpose is the mechanical separation into two pieces of the tube by exploiting the initiation and propagation of a fatigue crack in the low cycle regime. The Authors describe the technical problem, derive an analytical expression for the stress concentration effect, perform finite element numerical simulations for  determining the influence of the notch geometrical parameters on the linear elastic stress concentration factor.

While I understand the important practical application of the presented study, in my opinion the paper fails to meet the minimum requirements for being considered for publication in metals:

• There is not significant scientific advancements because the study is essentially an analysis of the stress concentration effects in notches by varying the geometrical parameters (notch opening angle, notch depth, notch tip radius)
• The paper contains badly constructed sentences or inappropriate expressions like “notch flare angle”, “three-way stress state”. It is sufficient to refer to standard textbooks in solid mechanics and mechanics of material to find the correct English terms

 

For the previous reasons I regret to state that in my opinion the paper is not suitable for publication in Metals and should be rejected.

Author Response

1. There is not significant scientific advancements because the study is essentially an analysis of the stress concentration effects in notches by varying the geometrical parameters (notch opening angle, notch depth, notch tip radius).

Authors’ response:

Thanks a lot for the reviewer’s comments.

The first process of actual tubing production process is blank separation. The separation process directly affects tubing utilization, part processing quality, production efficiency and production costs. Among many mechanical parts, metal tubing is widely used, such as extrusions, metal chains, bearings, internal splines and standard parts. Almost all parts related to short tubing involve separation process with a large number of parts. Today’s development concepts of green manufacturing and efficient precision forming urgently need a new tubing high-efficiency precision separation method to provide technical support. The exploration of efficient, precise and material-saving metal tubing separation methods has important engineering application value.

In order to adapt to this development trend and requirement, the high-efficiency precision separation method for tubing under eccentric wheel high-speed rotational bending fatigue loading is proposed, which aims to solve the problems of waste materials, low efficiency and poor section quality in the existing tubing separation methods, and provide an effective way to achieve high efficiency and precision of tubing separation. This high-efficiency precision separation method comprehensively utilizes the rapid initiation of microcracks and the controllable crack propagation technology. The tubing surface is artificially prefabricated with annular notches. Through the high-speed rotation of the designed eccentric wheel, the periodic cyclic bending load is applied to the tubing radial direction. Under the stress concentration effect of annular notch and the dynamic load of bending fatigue, microcracks rapidly develop at the root of annular notch. In addition, the macrocracks continuously expand to the tubing center according to the specified direction and growth rate in the section of the annular notch. Ultimately, efficient, precise and controllable separation of tubing is achieved.

The stress concentration effect of tubing notch analyzed in this paper is the first important problem to be solved by the tubing precise separation method. The influence law of tubing notch geometrical parameters can lay the foundation for the subsequent exploration of the expansion process of tubing cracks, thus promoting in-depth research on the precision separation method of eccentric wheel high-speed rotational bending fatigue loading proposed in this paper.

 

2. The paper contains badly constructed sentences or inappropriate expressions like “notch flare angle”, “three-way stress state”. It is sufficient to refer to standard textbooks in solid mechanics and mechanics of material to find the correct English terms

Authors’ response:

Thanks a lot for the reviewer’s comments.

Language has been polished.

 

Author Response File: Author Response.pdf

Reviewer 4 Report

The work presents tests of pipes made of various materials, with various types of notches, which were subjected to rotary fatigue bending. Numerical calculations were also carried out.

Comments on the paper

1. Fig. 7 - in the caption, please specify the unit of the given dimensions.
2. Page 3, lines 9t – it should be MPa and the same in table 1. Check out all the work.
3. Three types of material are presented in the work. It would be good to give the material properties and chemical composition of the materials tested.
4. Figs. 3 - 6 - the von Mises stress values are given. Please mark a unit next to the stress values.
5. In which notches occurred the fastest, and in which crack initiation occurred the latest during sharp notch testing?
6. Fig. 19 - no scale in the photos. The same Fig. 9 - photo.
7. In Fig. 2 we have the markings h, ro, alpha, while in the text on pages 2 and 3 these markings are missing next to the numbers. Then it will be easier to define what dimensions are in the figures 2 and 9.
8. It would also be worthwhile to quote the following papers: 1) Rozumek D., Marciniak Z., Fatigue properties of notched specimens made of FeP04 steel. Materials Science, Vol. 47, No. 4, 2012, pp. 462-469, 2) Rozumek D., Faszynka S., Influence of the notch radius on fatigue crack propagation in beam specimens of 2017A-T4 alloy. Materials Science, Vol. 53, No. 3, 2017, pp. 417-423.

Author Response

Manuscript ID: metals-1684938
Title: Research on the Influence Rule of Annular Notch Geometric Parameter on the Tubing Surface
Journal: Metals

 

Dear editors,

On behalf of my co-authors, we would like to give the author’s great thanks to you and the anonymous reviewers for the valuable suggestions, which have been carefully taken into account during the revision of our manuscript metals-1684938. Please find enclosed a description of the changes made to this paper, which is in response to the reviewers’ comments.

We would like to express our great appreciation to you and the reviewers for comments on our paper, and we are looking forward to hearing from you.

 

Sincerely,

Ren-Feng Zhao

Editorial decision: major revisions

 

 

Reviewer #4:

1. Fig. 7 - in the caption, please specify the unit of the given dimensions.

Authors’ response:

Thanks a lot for the reviewer’s comments.

We apologize for this ignorance and we have checked and amended it in the manuscript.

Figure 7. Schematic diagram of specimen structure. (a) V-notch specimen; (b) U-notch specimen; (c) Asymmetric V-notch specimen towards the blanking end direction 45°; (d) Asymmetric V-notch specimen away from the blanking end direction 45°.

 

2.Page 3, lines 9t – it should be MPa and the same in table 1. Check out all the work.

Authors’ response:

Thanks a lot for the reviewer’s comments.

The "Mpa" in Table 1 in the text has been changed to "MPa", and the whole text has been checked, and no other similar errors have been found.

 

3.Three types of material are presented in the work. It would be good to give the material properties and chemical composition of the materials tested.

Authors’ response:

Thanks a lot for the reviewer’s comments.

We apologize for this ignorance and we have checked and amended it in the manuscript.

Table 2. Chemical Composition and Physical Properties of Materials.

Material	Si Content (%)	Ni Content (%)	Cr Content (%)	Cu Content (%)	Elastic Modulus (MPa)	Yield stress (MPa)	Mass density (kg/m3)
45# steel tube	0.35	0.30	0.25	0.25	2.1E+05	335	7850
T2Y copper tube	/	0.005	/	99.95	1.37E+05	80	8900

 

4.Figs. 3 - 6 - the von Mises stress values are given. Please mark a unit next to the stress values.

Authors’ response:

Thanks a lot for the reviewer’s comments.

We apologize for this ignorance and we have checked and amended it in the manuscript.

 

Figure 3. Mises stress moiré diagram of V-notch tubing.

 

Figure 4. Mises stress moiré diagram of tubing with asymmetric V-notch towards the blanking end direction 45^o.

 

Figure 5. Mises stress moiré diagram of tubing with asymmetric V-notch away from the blanking end direction 45^o.

Figure 6. Mises stress moiré diagram of tubing with U-notch.

 

5.In which notches occurred the fastest, and in which crack initiation occurred the latest during sharp notch testing?

Authors’ response:

Thanks a lot for the reviewer’s comments.

From the experimental results, the annular V-notch and the 45^o notch toward the blanking end are the most likely to initiate cracks, and the crack initiation of both is obvious, and the initiation length is not much different; in contrast, the U-notch crack initiation The slowest, the notch that is the least prone to crack initiation among the four types of notch types.

 

6.Fig. 19 - no scale in the photos. The same Fig. 9 - photo.

Authors’ response:

Thanks a lot for the reviewer’s comments.

Figure 9 in the text is only to illustrate the gap on the outer surface of the tube, which has nothing to do with the specific size of the tube, so there is no need to put a ruler; the experimental tube blank of 304 stainless steel with a ruler has been supplemented in Figure 19 in the text.

 

Figure 19. Sectional view of tubing precision separation obtained from the experiment: (a) 45# steel tube; (b) 304 stainless steel tube; (c) T2Y copper tube; (d) 304 stainless steel with ruler.

 

7.In Fig. 2 we have the markings h, ro, alpha, while in the text on pages 2 and 3 these markings are missing next to the numbers. Then it will be easier to define what dimensions are in the figures 2 and 9.

Authors’ response:

Thanks a lot for the reviewer’s comments.

We apologize for this ignorance and we have checked and amended it in the manuscript.

 

8.It would also be worthwhile to quote the following papers: 1) Rozumek D., Marciniak Z., Fatigue properties of notched specimens made of FeP04 steel. Materials Science, Vol. 47, No. 4, 2012, pp. 462-469, 2) Rozumek D., Faszynka S., Influence of the notch radius on fatigue crack propagation in beam specimens of 2017A-T4 alloy. Materials Science, Vol. 53, No. 3, 2017, pp. 417-423.

Authors’ response:

Thanks a lot for the reviewer’s comments.

The authors have added the relevant articles to the references as follows:

13    Rozumek, D.; Marciniak, Z. Fatigue properties of notched specimens made of FeP04 steel. Mater. Sci. 2012, 47(4), 462-469.

14    Rozumek, D.; Faszynka, S. Influence of the notch radius on fatigue crack propagation in beam specimens of 2017A-T4 alloy. Mater. Sci. 2017, 53(3), 417-423.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors took into account the comments of the reviewers and put a lot of work into improving and supplementing the manuscript. In the current form, I recommend the article for publication in the Metals journal.

Author Response

1. The authors took into account the comments of the reviewers and put a lot of work into improving and supplementing the manuscript. In the current form, I recommend the article for publication in the Metals journal.

Authors’ response:

Thanks a lot for the reviewer’s comments.

Reviewer 3 Report

I thank the Authors for the answers provided to my previous review. I read them carefully, but unfortunately I did not found significant improvements. As the Authors themselves state "The stress concentration effect of tubing notch analyzed in this paper is the first important problem to be solved...". The point is that the analysis of the stress concentration at the V-notch of the tube is not enough from a scientific point of view for considering the paper for publication in Metals. Therefore, I regret to confirm that the paper is not suitable for publication in its present form and should be rejected.

Author Response

1. I thank the Authors for the answers provided to my previous review. I read them carefully, but unfortunately I did not found significant improvements. As the Authors themselves state "The stress concentration effect of tubing notch analyzed in this paper is the first important problem to be solved...". The point is that the analysis of the stress concentration at the V-notch of the tube is not enough from a scientific point of view for considering the paper for publication in Metals. Therefore, I regret to confirm that the paper is not suitable for publication in its present form and should be rejected.

Authors’ response:

Thanks a lot for the reviewer’s comments.

1. The author has fully considered the opinions of the reviewers, and has carefully revised and supplemented the paper for every question and revision request raised by the reviewers, and explained the questions raised. However, the reviewers have Still disagree with the publication of the paper in the journal Metals, which the authors regret.
2. The reviewer mentioned that "The point is that the analysis of the stress concentration at the V-notch of the tube is not enough from a scientific point of view for considering the paper for publication in Metals.", the author has this view take a different attitude.

(1) The author believes that the study of the influence law of the geometric parameters of the annular notch on the surface of the tube is not only a very important scientific issue, but also necessary to study;

(2) The author believes that the reviewer may have biased against the research, or did not understand the significance and value of the research.

Reviewer 4 Report

The Authors took into account the comments of the Reviewer. Based on the above mentioned, I recommend publishing the article in the journal Metals.

Author Response

thank you very much for your suggetions.