Residual Stress Analysis of a 2219 Aluminum Alloy Ring Using the Indentation Strain-Gauge Method

Round 1

Reviewer 1 Report

Title: Unclear, poor English

Abstract: Missing numerical results, English language needs improvement. 

Introduction: Generally a good overview, however English language improvements needed.

Length scales should be discussed - different techniques are suitable for distinct length scales.

Methods: Insufficient experimental detail - very poor. English language improvement needed

Is this hole drilling?

Error bars needed for measurements - otherwise very difficult to assess.

Analytical model - again, insufficient details to make an assessment.

Finite element - insufficient detail and poor English language

Very difficult to assess results as the approach presented is very unclear.

 

 

Author Response

Dear Professor,

    We thank you very much for your helpful suggestion. We revised the manuscript carefully according to the comments. The revised version together with the responses have been submitted in the system. The main corrections in the manuscript and the responds to comments are as following:

1. Title: Unclear, poor English

Replay:

    We are very appreciative for what you suggest for us. The title “Homogenization of residual stress in aerospace large ring rolling process of 2219 aluminum alloy using expansion method” is replaced by “Study on residual stress homogenization of 2219 aluminum alloy ring by expansion method”. Your suggestion is very accurate. The original title cannot clearly express the research of paper.

2. Abstract: Missing numerical results, English language needs improvement.

Replay:

    Thank you for your good advice which is very appropriate. We have revised the new abstract and added numerical results. “the maximum residual maximum principal stress is +265MPa”, “ The expansion simulation results show that the reduction rates of residual stress are greater than 40% and the maximum residual stress is only 65MPa.” And the English language of abstract have been polished.

3. Introduction: Generally a good overview, however English language improvements needed.

Replay:

    Thank you very much for your valuable comments on the selection. In introduction part, we not only have improved the English language, but also we have replaced the old references with more recent journal papers. And the revised paper has been submitted to the system.

4. Length scales should be discussed - different techniques are suitable for distinct length scales.

Replay:

    Thank you very much for your patience, which has added specific conditions for our research. In this paper, the expansion method is proposed to homogenize the initial residual stress of rolling ring based on the principle of pre-stretching plate. The feasibility of the expansion method is analyzed by establishing a simplified theoretical model of ring. The simulation results of the integrated rolling and expanding ring model show that the initial residual stress is significantly reduced and homogenized. And the reduction rate of residual stress in X and Y direction is greater than 40% and the maximum residual stress is only 65MPa. So the residual stress homogenization method of expansion can be applied, and the homogenization effect is obvious. This research provides a technical basis for the development of expansion equipment. Actually, the hydraulic expansion method is used on smaller ring, while the mechanical expansion method is more widely used on larger ring due to the manufacturing difficulty of large hydraulic soft membranes.

5. Methods:

1) Insufficient experimental detail - very poor. English language improvement needed

Replay:

    We highly respect your consideration of this part. The details of the experiment can explain the study more clearly. Firstly, we have added the principle of the indentation strain gauge method, as following “As the residual stress at this point is released, the strain of the surrounding material changes. The three-channel strain gauge attached at this point measures the strain value, and the data is saved in the indentation stress instrument through the electrical signal. The software of the instrument calculates the residual stress value at this point through the elastic strain and the Young's modulus of the material. Applying this method to measure the residual stresses on curved surface of 9m-large ring, it’s important to make the rod of the pressure head which can produce the indentations vertical to the surface. The rod is positioned by a holder, and the three foots of the holder is used to regulate the location of the pressure head to make sure that the rod would be vertical to the surface.” Secondly, we have added the steps of the indentation strain gauge method, as following “In general, the indentation strain gauge method of residual stress measurement mainly has three steps. The first step is the preparation for experiment. The surface of material is polished with 100-mesh sandpaper to avoid the effect of surface roughness on the results. Turn on the indentation stress instrument, and run the software which is used to calculate and record the residual stress. The second strep is strain gauge attachment. Clean the measuring surface with acetone or alcohol, and then firmly attach the strain gauge to the material. Wire the strain gauges and the indentation stress instrument for signal connection. The third step is indentation and result treatment. Insert the microscope head into the holder for centering, which makes the indentation hitting point of the strain gauge coincide with the center point of the microscope. Then, insert the rod, choose the appropriate hitting pressure, and generally select the first gear for aluminum alloy. After that, press the "stress" button of the software to complete the zero setting. Finally, fire the hitting pressure and keep it stable for 5~10s to record the stress change.” Thirdly, we added the type of the strain gauge and the indentation stress instrument, as following “And this experiment adopts the BX120-3CA type three-channel resistance strain gauge and the KJS-3 type indentation stress instrument.”

2) Is this hole drilling?

Replay:

    We are very appreciative for your valuable opinions. This is not a hole drilling. It is a tiny indentation point. And the pressure head is showing in Figure 1.

3) Error bars needed for measurements - otherwise very difficult to assess.

Replay:

    We are very grateful for your valuable advice. We added scattering of data in figure 2 the revised paper. Eight points along the circumferential direction of the ring are selected for residual stress measurement. And each measurement point has four measuring positions. The measured residual stress has only one value at each measurement location. Measuring position 1 is located at the top of the ring. The average stress is the stress of measuring position 2, measuring position 3 and measuring position 4, which are distributed on the outer cylindrical surface of the ring. The error of measurement result is mainly influenced by indentation stress instrument and environment. We added the accuracy of the instrument, as following “The sensitivity coefficient of the instrument is 1με and the stress accuracy of the instrument is ±20MPa”. And we added error bars of simulation data in figure 8 of the revised paper. It is necessary to indicate the error bars to leading a better understanding about the results dispersion.

6. Analytical model - again, insufficient details to make an assessment.

Replay:

    We appreciate your concern in this regard. The analytical model is used to analyze the feasibility of the expansion method. The simplified theoretical model of ring realizes the conversion of a ring to a plate, and the expanding force is equivalent to a tensile force in the circumferential direction and an extruding force in the radial direction. The conclusion of this theoretical analysis model is that when the coupling stress of residual stress and expanding force achieves σ_s > [σ_s], the residual stress of the rolling ring is released.

7. Finite element - insufficient detail and poor English language

Replay:

    Thank you very much for your patience in reading this article. We have explained the finite element part of the manuscript in detail. “In the rolling simulation, the material model of ring is set as an elasto-plastic behaviour of 2219 aluminum alloy, while all the rollers are defined as rigid bodies. And the mechanical properties of 2219 Al alloy are varied at different temperatures, as shown in Table 3. The mesh of the ring is tetrahedron, and the minimum mesh size is 0.8mm.” “The friction between the ring and the mold is Coulomb friction with a friction coefficient of 0.6. And the ambient temperature is 20°C during the process. The four parts of the mold are expanded in the radial direction of the ring with a feed of 1mm respectively to achieve the purpose of the ring expansion method.”

 

    We look forward to hearing from you regarding our submission. We would be glad to respond to any further questions and comments that you may have and thank you very much for your review.

 

Sincerely,

All authors.

Author Response File: Author Response.pdf

Reviewer 2 Report

Changes which must be made before publication:

Abstract

• Abstract should contain maximally 150 words.
• It is necessary to add research goals.

 

• Keywords should be ranked according to their importance.

 

Introduction

• Each reference should be written separately.
• For each reference it is necessary to state way of research and findings.
• If several references are stated together only the most important one should be given.
• Old references should be replaced by more recent journal paper reference from this topic.
• References should be written in accordance with guidelines.
• Number of references should be reduced.

.

Experimental

• Experimental system should be added in block scheme with input-output data as well as suitable explanation in the text given.
• The item "Results and discussions" should be separated in item "Results" and item "Discussion".
• TO figures 2 and 8 should be added scattering of data and test significanca.

 

 

 

Conclusion

• Conclusions are too general.
• It is necessary to state concrete findings in the given research.

It is necessary to compare results obtained with results from references

 

 

• The paper should be checked by a native English speaking expert.

 

 

Author Response

Dear Professor,

We thank you very much for your helpful suggestion. We revised the paper carefully according to the comments. The revised version together with the responses have been submitted in the system. The main corrections in the manuscript and the responds to comments are as following:

1. Abstract: Abstract should contain maximally 150 words. It is necessary to add research goals.

Replay:

We are very appreciative for what you suggest for me. In the revised paper, the abstract is that “Aerospace thin-walled rings are vulnerable to the machining distortion during the manufacturing process. Various research results show that the main factor causing machining deformation is the initial residual stress inside the blank. In this study, the residual stress of a 2219 aluminum alloy ultra-large rolling ring is measured by using the indentation strain gauge method, and results show the maximum residual maximum principal stress is +265MPa and stress distribution is uneven. To homogenize the initial residual stress of the ring, the expansion method is proposed based on the principle of pre-stretching plate, and the feasibility of the expansion method is analyzed by establishing a simplified theoretical model of ring. An integrated simulation model of rolling ring and expanding ring is established to investigate residual stress revolution. The expansion simulation results show that the reduction rates of residual stress are greater than 40% and the maximum residual stress is decreased to 65MPa.” And the research goal is that “To achieve the initial residual stress homogenization for ultra-large ring, the expansion method is proposed.”

2. Keywords should be ranked according to their importance.

Replay:

Thank you very much for your valuable advice. Keywords are ranked according to their importance, which can highlight the important direction of the research. The keywords are written as “expansion method; residual stress homogenization; rolling ring; 2219 aluminum alloy ring” in the revised paper.

3. Introduction: Each reference should be written separately. For each reference it is necessary to state way of research and findings. If several references are stated together only the most important one should be given. Old references should be replaced by more recent journal paper reference from this topic. References should be written in accordance with guidelines. Number of references should be reduced.

Replay:

Thank you for your good advice which is very appropriate. In the revised paper, each reference have been written separately, and each reference is introduced by stating the way of research and findings. There are no references that are stated together. What's more, the old references are replaced by recent journal papers. And these references are written in accordance with guidelines. The number of references is 28, rather than 35.

4. Experimental:

1) Experimental system should be added in block scheme with input-output data as well as suitable explanation in the text given.

Replay:

We appreciate your concern in this regard. We have added the block scheme of experimental system which is shown in figure 1 in the part 2.3 of the revised paper. Through this picture, the measurement experiment can be better understood. Thank you again for your valuable suggestions.

2) The item "Results and discussions" should be separated in item "Results" and item "Discussion".

Replay:

Thank you very much for your reminding. In the revised paper, the item “Results and discussions” has been separated in item “Results” and item “Discussion”. The item “Results” mainly explains the results of residual stress of rolling ring and the results of residual stress homogenization after expansion, while the item “Discussion” mainly analyzes the residual stress distribution of ultra-large rolling ring and the residual stress of rolling ring and expansion ring.

3) To figures 2 and 8 should be added scattering of data and test significanca.

Replay:

Thank you very much for your helpful suggestion. We added scattering of data in figure 2 and figure 8 of the revised paper. It is necessary to indicate the error bars to leading a better understanding about the results dispersion. In experiment, the measured residual stress has only one data at each measurement location. Eight points along the circumferential direction of the ring are selected for residual stress measurement. And each measurement point has four measuring positions. Measuring position 1 is located at the top of the ring. Three measuring positions are distributed on the outer cylindrical surface of the ring. By adding the scattering of data, the experimental data can be better understood.

In addition, the error of measurement result is mainly influenced by indentation stress instrument and environment. And we added details about the experiment results in the revised paper, as following “And this experiment adopts the BX120-3CA type three-channel resistance strain gauge and the KJS-3 type indentation stress instrument. The sensitivity coefficient of the instrument is 1με and the stress accuracy of the instrument is ±20MPa.”

5. Conclusion: Conclusions are too general. It is necessary to state concrete findings in the given research. It is necessary to compare results obtained with results from references. The paper should be checked by a native English speaking expert.

Replay:

Thank you very much for your patience, which has added specific conditions for our research. In the revised paper, the conclusion is written as that “Large rolling ring is a class of common part in the field of aerospace, but deformation has always been a difficult problem. Numerous studies show that the machining deformation is mainly caused by the residual stress, especially the initial residual stress of blank. In this study, 2219 aluminum alloy rolling ring as the research object, the expansion method for residual stress homogenization is proposed. The main conclusions are as follows: 1. The rolling ring process is investigated. The movement and working principle of rollers in the rolling ring process are analyzed. The rolling ring process parameters are proposed for 2219 aluminum alloy rings with a diameter of nearly 10m and a diameter of 0.2m respectively. 2. The indentation strain gauge method is applied to measure the residual stress of an ultra-large ring. At the top of the ring, the residual maximum principal stress is tensile stress, and the maximum residual maximum principal stress is +265MPa. The maximum tensile and compressive stresses on the outer surface are respectively +172MPa and -80MPa. 3. Based on the principle of pre-stretching plate, the simplified theoretical model of ring homogenization is established. And the analysis result shows that when the coupling stress of residual stress and expanding force achieves σ_s > [σ_s], the residual stress of the rolling ring is released. 4. The integrated simulation model of rolling ring and expanding ring is established, and the influence of expansion on residual stress is analyzed. A large amount of residual stress is induced in the rolling ring process. By expansion process, the residual stress of the rolling ring is homogenized. The results of expanding ring process show that the reduction rates of the maximum stress in X and Y direction are both greater than 40%.”

In addition, the results are compared with the results of Wei et al. in paragraph 2 of part 2.3, following as “In the X direction, the maximum residual compressive stress decrease by 40.63%, and the maximum residual tensile stress decrease by 50.38%. In Y direction, the maximum residual compressive stress decrease by 47.46%, while the maximum tensile stress decrease by 51.24%. Compared with the research by Wei et al. [27], the residual stress reduction of TC4 ring is less than 25% by the expansion method.”

 

We look forward to hearing from you regarding our submission. We would be glad to respond to any further questions and comments that you may have and thank you very much for your review.

 

Sincerely,

All authors.

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript is written just as a technical report and many scientific arguments and techinic detals are missing. It is necessary to complet some details to lead a better understanding.

For experimental residual  stress analysis, it is extremely important to indicate the used protocole with the specific operating paremeters. It is also important to discuss the experimental precision and assocaited errors about residual stress results. In figure 2, it is necessary to indicate the error bars to leading a better undersdanding about the experimental dispersion comparing to real materials' variation. It is also important to indicate the corresponding direction for obtained residual stress in figure 2. How about the anisotropy of residual stress distribution dues to rolling ?

In modelization part 3.1, the elastic properties of material has been considered. But the expansion method and the associated residual stress evolution deals with strong plastic deformation and elasto-plastic equilibrium. In this case, the use of the only elastic behaviour is not sufficient and not pertinent. The used elasto-plastic behaviour should be precised.

The Ring Rolling Process is realized at 150°C (according to table 3), how can manage the thermal residual stress evolution after plastic deformation ? what are the used thermal dilatation coefficient ? 

It is necessary to give a minimum information about the expansion process parameters, the used physical characteristics in modelization.

It is important to show the residual stress evolution after expansion in the similar zones  comparing to the results presented in figure 2.

It is necessary to indicate the corresponding zones and locations for results presented in figure 8 before expantion comaring to figure 2.

It is important to explain how the residual stresses have been obtained in depth of samples after expasion by experiment (in figure 8) ?

It is interersting to citer some results from previous studies in comparaison with results obtained in this study. It is also extremely important to give some explanation tracks about the residual stress evolution during and after hot rolling, during and after expasion process, and discuss the associated mechanisms. 

Author Response

Dear Professor,

We thank you very much for your helpful suggestion. We revised the paper carefully according to the comments. The revised version together with the responses have been submitted in the system. The main corrections in the manuscript and the responds to comments are as following:

1. The manuscript is written just as a technical report, and many scientific arguments and technical details are missing. It is necessary to complete some details to lead a better understanding.

Replay:

Thank you for your good advice which is very appropriate. In the revised paper, we added many details about the experiment of residual stress measurement in paragraph 2~4 of part 2.3, the simulation of rolling ring process in in paragraph 2 of part 3.2, the simulation of expansion process in part 3.2, the results in part 4 and the discussion in part5.

2. For experimental residual stress analysis, it is extremely important to indicate the used protocol with the specific operating parameters. It is also important to discuss the experimental precision and associated errors about residual stress results. In figure 2, it is necessary to indicate the error bars to leading a better understanding about the experimental dispersion comparing to real materials' variation. It is also important to indicate the corresponding direction for obtained residual stress in figure 2. How about the anisotropy of residual stress distribution dues to rolling?

Replay:

We highly respect your consideration of this part. In the revised version, we have added details about the experiment, as following “And this experiment adopts the BX120-3CA type three-channel resistance strain gauge and the KJS-3 type indentation stress instrument. The sensitivity coefficient of the instrument is 1με and the stress accuracy of the instrument is ±20MPa.” In the residual stress experiment, Young's modulus and Poisson's ratio are necessary, and these parameters are listed in Table 1 of the revised manuscript. We added the error bars of the experiment results in figure 3. Eight points along the circumferential direction of the ring are selected for residual stress measurement. And each measurement point has four measuring positions. The measured residual stress has only one value at each measurement location. Measuring position 1 is located at the top of the ring. The average stress is the stress of measuring position 2, measuring position 3 and measuring position 4, which are distributed on the outer cylindrical surface of the ring. The error of measurement result is mainly influenced by indentation stress instrument and environment. The stress in Figure 3 is the maximum principal stress, not the direction stress. The uneven distribution of residual stress in the ring is affected by the nonuniform force load, thermal load and phase transition of the material.

3. In modelization part 3.1, the elastic properties of material has been considered. But the expansion method and the associated residual stress evolution deals with strong plastic deformation and elasto-plastic equilibrium. In this case, the use of the only elastic behaviour is not sufficient and not pertinent. The used elasto-plastic behaviour should be precise.

Replay:

Thank you very much for your valuable comments on the selection. In the actual rolling and expansion process, the ring is always in a state where elastic and plastic deformation exist. And the material model of ring is set as an elasto-plastic behaviour of 2219 aluminum alloy, while all the rollers are defined as rigid bodies in the simulation. In addition, the mechanical properties of 2219 Al alloy are varied at different temperatures, as shown in Table 3 of the revised paper.

4. The Ring Rolling Process is realized at 150°C (according to table 3), how can manage the thermal residual stress evolution after plastic deformation ? what are the used thermal dilatation coefficient ?

Replay:

We are very grateful for your valuable advice. In the actual rolling and expansion process, the ring is always in a state where elastic and plastic deformation exist. And the thermal residual stress is induced by the different radiating speeds of the ring. Thermal dilatation coefficient is 22.3×10^-6/℃, as shown in Table 1 of the revised paper. In addition, the mechanical properties of 2219 Al alloy are varied at different temperatures, as shown in Table 3 of the revised paper.

5. It is necessary to give a minimum information about the expansion process parameters, the used physical characteristics in modelization.

Replay:

We are very appreciative for your valuable opinions. In the revised paper, we have described the expansion process in detail. “The material properties of the expansion ring are defined as those of the ring rolling process, an elasto-plastic behaviour of 2219 aluminum alloy.” and “The mold is set as a rigid body, which means that it is not affected by temperature and working load. The friction between the ring and the mold is Coulomb friction with a friction coefficient of 0.6. And the ambient temperature is 20°C during the process. The four parts of the mold are expanded in the radial direction of the ring with a feed of 1mm respectively to achieve the purpose of the ring expansion method.”

6. It is important to show the residual stress evolution after expansion in the similar zones comparing to the results presented in figure 2.

Replay:

We are very appreciative for what you suggest for us. In the experiment, the indentation strain gauge method is applied to measure the residual stress of the rolling ring. But the KJS-3 type indentation stress instrument can only measure the residual stress on the surface of material, and currently there is no device that can measure the residual stress at a deeper thickness. Compared with the residual stress on the surface of the ring, the residual stress distribution of the whole ring is more worthy of study. Because the residual stress distribution of the whole ring has a more significant effect on mechanical properties and dimensional stability. So the residual stress along the radial direction is compared, as shown in Figure 8 of the revised paper.

7. It is necessary to indicate the corresponding zones and locations for results presented in figure 8 before expansion comparing to figure 2.

Replay:

We appreciate your concern in this regard. In the residual stress measurement, 8 points along the circumferential direction of the ring are selected for residual stress measurement, as shown in Figure 2(b) of the revised paper. And each measurement point has four measuring positions. Measuring position 1 is located at the top of the ring. Three measuring positions are distributed on the outer cylindrical surface of the ring, which are measuring position 2, measuring position 3 and measuring position 4 respectively. The simulated residual stress before and after expansion process is obtained as the following: The ring is layered with 2mm thickness for each layer along the radial thickness direction. The thickness of 0-2mm from the outer cylindrical surface to the inner cylindrical surface is the first layer. On each layer, four points are selected as measuring points in the circumferential direction. The average value of the residual stress at the four points represents the stress distribution of the layer. And for figure 8, the residual stress in the X and Y directions after the expansion of the ring is compared with that before the expansion at the same points.

8. It is important to explain how the residual stresses have been obtained in depth of samples after expansion by experiment (in figure 8)?

Replay:

We are very grateful for your valuable advice. In the revised paper, we have explained the method of obtaining the residual stress. “The ring is layered with 2mm thickness for each layer along the radial thickness direction. The thickness of 0-2mm from the outer cylindrical surface to the inner cylindrical surface is the first layer. On each layer, four points are selected as measuring points in the circumferential direction. The average value of the residual stress at the four points represents the stress distribution of the layer.”

9. It is interesting to citer some results from previous studies in comparison with results obtained in this study. It is also extremely important to give some explanation tracks about the residual stress evolution during and after hot rolling, during and after expansion process, and discuss the associated mechanisms.

Replay:

Thank you very much for your reminding. The effect of expansion on the residual stress has been compared in the part of 5.2 of the revised paper. “The expansion process achieves the homogenization and reduction of residual stress. In the X direction, the maximum residual compressive stress decrease by 40.63%, and the maximum residual tensile stress decrease by 50.38%. In Y direction, the maximum residual compressive stress decrease by 47.46%, while the maximum tensile stress decrease by 51.24%. Compared with the research by Wei et al. [27], the residual stress reduction of TC4 ring is less than 25% by the expansion method.” Besides, the process of residual stress homogenization has been discussed in the part of 5.2 of the revised manuscript.

 

We look forward to hearing from you regarding our submission. We would be glad to respond to any further questions and comments that you may have and thank you very much for your review.

 

Sincerely,

All authors.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Title: Study is superfluous - perhaps

"Residual stress analysis of a 2219 aluminium alloy ring using the indentation strain gauge method"

Abstract has improved - but the following sentence is unclear " An integrated simulation model of rolling ring and expanding ring is established to investigate residual stress revolution."

Introduction has improved but further English language corrections required - suggest making use of a text editing service.

No discussion of length scales added to the text.

Improved explanation of indentation method - however English language requires improvement. Why wasn't hole drilling used? It seems a more precise and easier technique to apply to this sample.

Intrinsically all measurement methods produce error and it is important to include these errors in all measurements presented, including position 1 - without this the result is essentially meaningless. This must then be combined together with repeat measurements to obtain the final error bar.

For example from the original profile one would interpret some compressive stresses at points 3 and 4. The error bars (which I suggest would be bigger if the errors on each point were included) show that this may not be the case - the entire ring may be in tension. I am very worried about the precision and reliability of these results after seeing this plot.

The discussion on the FEA has improved, but is still far from suitable. There are many parameters missing - what volume elements were used? What variables? How was the mesh assessed? - Without these I do not feel I can trust the results.

How do the experimental results relate to the model? They seem distinct and with very limited relationships to me.

Overall the authors have improved the manuscript but it is far away from being suitable for acceptance.

 

Author Response

Dear Professor,

We thank you very much for your helpful suggestion. We revised the paper carefully according to the comments. The revised version together with the responses have been submitted in the system. The main corrections in the manuscript and the responds to comments are as following:

1. Title: Study is superfluous – perhaps "Residual stress analysis of a 2219 aluminium alloy ring using the indentation strain gauge method"

Replay:

Thank you very much for your valuable advice. The title “Residual stress analysis of a 2219 aluminum alloy ring using the indentation strain gauge method” is more appropriate for this paper.

2. Abstract has improved - but the following sentence is unclear " An integrated simulation model of rolling ring and expanding ring is established to investigate residual stress revolution."

Replay:

Thank you for your good advice which is very appropriate. In the revised paper, we rephrased the unclear sentence, as following “A simulation model which can fully inherit the results of the previous process to achieve continuous simulation of rolling and expanding process is established to investigate residual stress revolution.”

3. Introduction has improved but further English language corrections required - suggest making use of a text editing service.

Replay:

Thank you very much for your helpful suggestion. In the revised paper, we polished the English language.

4. No discussion of length scales added to the text.

Replay:

We are very appreciative for your valuable opinions. We added the discussion of length scales to the revised version in paragraph 4 of part 5.2, as following “This research provides a technical basis for the development of expansion equipment. Actually, the hydraulic expansion method is used on smaller ring, while the mechanical expansion method is more widely used on larger ring due to the manufacturing difficulty of large hydraulic soft membranes. The expansion equipment can be designed as a replaceable working head of the mold in actual production to adapt to different sizes of rolling rings.”

5. Improved explanation of indentation method - however English language requires improvement. Why wasn't hole drilling used? It seems a more precise and easier technique to apply to this sample.

Replay:

Thank you very much for your valuable comments on the selection. In the revised paper, we carefully polished the English language.

The hole drilling method is a very good residual stress measurement method. And it can be used to measure residual stress at smaller depths. The residual stress is measured by drilling a hole, where the residual stress is relieved and the strain is generated. The residual mark of the indentation strain gauge method is a tiny indentation point, while the residual mark of the hole drilling method is a hole. Compared with the indentation method, the drilling method causes great damage to the ring, which is detrimental to subsequent processing. In addition, it is required that the drill is perpendicular to the measured surface at all times. Compared with the indentation method, the measurement time of the drilling method is longer. The measurement conditions of the ultra-large ring restrict the longer operation, especially the measurement of the outer surface of the ring. Therefore, the indentation strain gauge method is used to measure the residual stress.

6. Intrinsically all measurement methods produce error and it is important to include these errors in all measurements presented, including position 1 - without this the result is essentially meaningless. This must then be combined together with repeat measurements to obtain the final error bar.

Replay:

We highly respect your consideration of this part. We added errors of data in figure 3 of the revised paper. Eight points along the circumferential direction of the ring are selected for residual stress measurement, and each measurement point has four measuring positions, as showing in figure 1. The measured residual stress has only one value at each measurement location. We added the error limit to each point by considering the measurement error, which is the instrument measurement error ±20MPa, as showing in figure 2.

Figure 1. Measurement location of ring

Figure 2. Measurement location of ring

7. For example from the original profile one would interpret some compressive stresses at points 3 and 4. The error bars (which I suggest would be bigger if the errors on each point were included) show that this may not be the case - the entire ring may be in tension. I am very worried about the precision and reliability of these results after seeing this plot.

Replay:

We are very grateful for your valuable advice. The residual stress on the surface of the rolling ring is measured by the indentation strain gauge method, and the measured stress is residual maximum principal stress. The experimental result is stress value at a very small depth on the surface of the ring. Along the radial depth, residual compressive stress will appear. Both tensile stress and compressive stresses exist in the ring and they are in a balanced state. Besides, the simulation results show that the residual maximum principal stress on the surface of the ring is also the tensile stress, as shown in Figure 1. We explained this stress distribution in paragraph 2 of part 5.1 of the revised paper, as following “The residual tensile stresses at other points are mainly caused by rolling springback.”

(a)

(b)

Figure 1. Simulation results of ring rolling process: (a) Residual maximum principal stress result; (b) Residual stress in X direction.

Huang et al. [1] measured the initial residual stress by using the crack-compliance method. Figure 2 shows the initial residual stress distribution profile along thickness direction in the blank. And the residual stress on surface along pre-stretched direction is also tensile stress.

Figure 2. Initial residual stresses profile of 7050-T7451 plate.

8. The discussion on the FEA has improved, but is still far from suitable. There are many parameters missing - what volume elements were used? What variables? How was the mesh assessed? - Without these I do not feel I can trust the results.

Replay:

We are very appreciative for what you suggest for us. The mesh tool of SIMUFACT software is used for meshing to ensure better compatibility. The mesh of the ring is tetrahedron with 10/4 nodes, and the element type is Tetrahedral 157. The minimum element length is set as 0.8mm, and the meshing mode is set to adaptive division. The number of elements is 461892. So the meshed model is shown in Figure 3. This meshed ring can be applied if it maintains complete edges and corners and has at least one grid on each 1mm thickness along radial direction after meshing.

Figure 3. Meshed ring model.

9. How do the experimental results relate to the model? They seem distinct and with very limited relationships to me.

Replay:

We appreciate your concern in this regard. For the large rolling ring with a diameter of nearly 10m, the experimental results show that the residual stress distribution is uneven, and the residual maximum principal stress reaches +265MPa. It is necessary to homogenize the residual stress of the rolling ring. In the simulation part, the integrated simulation model of ring rolling and expanding is established, which is used to simulate the residual stress evolution of rolling ring. The results of expanding ring process show that the reduction rates of the maximum stress in X and Y direction are both greater than 40%, and the maximum residual stress is only 65MPa. By expansion process, the residual stress of the rolling ring is homogenized. This study can be a good practical reference in the residual stress and machining deformation control of large ring.

 

We look forward to hearing from you regarding our submission. We would be glad to respond to any further questions and comments that you may have and thank you very much for your review.

 

Sincerely,

All authors.

 

References

• Huang, X.; Sun, J.; Li, J. Finite element simulation and experimental investigation on the residual stress-related monolithic component deformation. J. Adv. Manuf. Technol 2015, 77, 1035–1041. doi: 10.1007/s00170-014-6533-9

Author Response File: Author Response.pdf

Reviewer 3 Report

in the revised version of the maniscript, author has made necessary correctins including all ramarks from reviewers. I suggest to accept as it.

Author Response

Dear Professor,

We thank you very much for your helpful suggestion. Your comments are very helpful for our manuscript. We would be glad to respond to any further questions and comments that you may have.

Thank you again for your review and patience.

 

Sincerely,

All authors.

Round 3

Reviewer 1 Report

New sentence in the abstract does not offer any improved clarity. I still do not know what you are trying to say.

The authors appear to have missed the point I was making about length scales. Why are you measuring stress at the mm? Should it be at the um? The discussion added is unclear and makes use of poor English language.

Measurement error is generally not a constant value - it should depend upon the results obtained.

The FEA analysis has improved.

The English language remains below the standard required for publication.

 

Author Response

Dear Professor,

We thank you very much for your helpful suggestion. We revised the paper carefully according to the comments. The revised version together with the responses have been submitted in the system. The main corrections in the manuscript and the responds to comments are as following:

1. New sentence in the abstract does not offer any improved clarity. I still do not know what you are trying to say.

Replay:

We highly respect your consideration of this part. In the revised paper, we rephrased the unclear sentence, as following “A FE model is established to investigate residual stress evolution during the rolling ring and the expanding ring process.”

2. The authors appear to have missed the point I was making about length scales. Why are you measuring stress at the mm? Should it be at the um? The discussion added is unclear and makes use of poor English language.

Replay:

We are very grateful for your valuable advice. In the revised paper, the residual stresses of simulation results in X and Y direction are showing in Figure 9. And the residual stresses are measured at each layer with 2mm thickness. The minimum element length is set as 0.8mm, which ensures that there is at least one complete element on each layer. The measurement stresses of each layer are more accurate. By this method, the residual stress distribution of the whole ring is better evaluated. And the problem that the residual stress at deeper depths cannot be measured by experiment is solved. If the thickness is set as , the minimum element length is smaller. Simulation efficiency is greatly reduced, and it is very likely that the calculation result is divergent. In this study, the residual stress distribution of the whole ring is more needed, not just at the .

3. Measurement error is generally not a constant value - it should depend upon the results obtained.

Replay:

We are very appreciative for what you suggest for us. Eight points along the circumferential direction of the ring are selected for residual stress measurement, and each measurement point has four measuring positions. Actually, we only measured one residual stress value at each measuring position, as shown in Figure 1. And the instrument measurement error ±20MPa is added, which ensures the evaluation of the experimental results. Too many indentation points of the measurement experiment will damage the large ring and affect the quality of subsequent processing. Thank you again for your guidance on the experiment. We will pay more attention to the scientificity and reproducibility of the experiment in the next study.

Figure 1. Measurement results of residual maximum principal stress of large rolling ring

4. The FEA analysis has improved.

Replay:

We thank you very much for your helpful suggestion. Your comment is very helpful for our paper.

5. The English language remains below the standard required for publication.

Replay:

We appreciate your concern in this regard. In the revised paper, we carefully polished the English language.

 

Thank you again for your patience. And we look forward to hearing from you regarding our submission. We would be glad to respond to any further questions and comments that you may have and thank you very much for your review.

 

Sincerely,

All authors.

 

Author Response File: Author Response.pdf