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Peer-Review Record

Improvement of Damping Property and Its Effects on the Vibration Fatigue in Ti6Al4V Titanium Alloy Treated by Warm Laser Shock Peening

Metals 2019, 9(7), 746; https://doi.org/10.3390/met9070746
Reviewer 1: Anonymous
Reviewer 2: Anonymous
Reviewer 3: Anonymous
Reviewer 4: Anonymous
Metals 2019, 9(7), 746; https://doi.org/10.3390/met9070746
Received: 17 May 2019 / Revised: 20 June 2019 / Accepted: 25 June 2019 / Published: 3 July 2019

Round  1

Reviewer 1 Report

The paper deals with vibration fatigue of warm laser peened Ti alloys. The paper is well written and conceived. It is of interest for both academic and industrial readership. To make it suitable for publication, the authors shall address the following issues:

1)    The FE simulation of the frequency response must be better described. Is the applied pressure assumed to vary harmonically with time or stepwisely? What is the purpose of such FE analyses

2)    The experimental procedure of the vibration fatigue tests shall be better described. What does “the accelerated speed of vibration table was 10-fold acceleration of gravity” mean? What does “was tested by modal testing device every 50000 cycles until the specimens fractured” mean?

3)    Does damping produce heating of the specimen during fatigue tests?

4)    Are quantities plotted in Fig. 8 and 9 estimated from FEM? Are stresses and displacements maximum values or amplitudes?

Author Response

Question 1(Q1): The FE simulation of the frequency response must be better described. Is the applied pressure assumed to vary harmonically with time or stepwisely? What is the purpose of such FE analyses. 

Answer 1(A1): We are very grateful to the reviewers question. The excitation load applied in the simulation varies with time. Frequency response simulation can analyze the relationship between structural input load and output at different excitation frequencies. In this paper, the structural output (maximum displacement and maximum tensile stress) laws under different input loads (100, 200, 300 MPa) are obtained by frequency response simulation. The effects of untreated, RT-LP and WLP on the structural input-output relationship by changing the damping characteristics are compared. Related descriptions have been added in Section 2.4 of the paper.

Q2: The experimental procedure of the vibration fatigue tests shall be better described. What does “the accelerated speed of vibration table was 10-fold acceleration of gravity” mean? What does “was tested by modal testing device every 50000 cycles until the specimens fractured” mean?

A2: We are very grateful to the reviewers question. In the vibration fatigue experiment, the excitation force is controlled by the acceleration of the platform. The acceleration of the platform used in this experiment was 98 m2/s, which was about 10 times the acceleration of gravity. The relevant contents in the paper have been modified.

The vibration fatigue life of the structure was studied in the resonant state (the excitation frequency was near the natural frequency). Because the natural frequency of the structure generally decreases with the increasing loading time, this paper tested the structural natural frequency every 50,000 times, and then used it as the excitation frequency to continue the vibration experiment. Thus we can obtain the vibration fatigue life in resonance state. The relevant contents have been explained in Section 2.6 of the paper.

Q3: Does damping produce heating of the specimen during fatigue tests?

A3: We are very grateful to the reviewers question. In the process of vibration, the internal energy of material increases due to the damping, and then the material temperature rises. However, the thermal effect caused by damping  and its influence on vibration fatigue process have not been studied in this paper. The relevant work will be studied in the future.

Q4: Are quantities plotted in Fig. 8 and 9 estimated from FEM? Are stresses and displacements maximum values or amplitudes?

A4:We are very grateful to the reviewers question. The results in Fig. 8 and 9 are obtained by finite element simulation which represent the maximum displacement and the maximum tensile stress in the structural vibration process. The expressions in Fig. 8 and 9 have been modified.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript presents an experimental work on the influence of laser shot peening on the damping ratio of a Titanium alloy. Overall this is an interesting piece of research. Nevertheless, there are some aspects that need to be corrected/clarified prior to publication. Here are the most relevant ones:

·       In the presented work, the damping ratio is experimentally obtained, while it is not clear how the processed/unprocessed volume is taken into account. Moreover, the obtained damping ratios are employed for FEM simulations in different boundary conditions, while identical conditions to the experimental tests would be expected. It is not clear the outcome of the simulations. Moreover, results of experimental vibration fatigue tests are not provided and discussed.

·       As shown in figure 1, the treated area is restricted to the more sensitive location, close to the fixed support. Nevertheless, the authors should clarify the extension of the laser peening treated area/volume with respect to the complete sample volume, as the modal response is a function of the overall sample. If the modified volume is smaller than the sample complete volume, the obtained damping ratios must be corrected.

·       Authors must specify how many sample repetitions were performed to stablish the damping ratio for the unprocessed, LP and WLP plates.

·       In addition, it would be particularly interesting to test the repeatability of the fixing method and its influence on the modal response.

·       Authors must increase the frequency resolution in the experimental graphs of figure 7, and explain the mode frequency shift, if observed.

·       For the validation of simulation results, it would be expected to reproduce the conditions of the experimentally tested samples and compare the results, prior to modification of the boundary conditions (completely processed simulated area versus an experimentally processed restricted area). Authors should explain this.

·       Moreover, it is not clear if the pressure on the plates in simulations is to reproduce the effect of the laser process or for a different purpose.

·       The authors state that frequency response was registered each 50000 cycles during vibration testing, while the obtained results are not presented or commented. More importantly, fatigue results and number of repetitions are not provided in the draft.

·       The experimental system and attachment should be clearly described.

·       In Line 242 and following, authors state “After vibration fatigue testing, the average vibration fatigue life of 350-WLPed samples increases about 45.1 % and 148.7% compared to untreated and 244 RT-LPed samples respectively.” Is the fatigue life of the LP samples lower than that of the untreated samples? Authors should clarify and comment this aspect.

·       Please give the frequency of the pulses used for the treatment. Give also the beam quality in terms of BPP or M2 parameter.

·       Minor aspects:

o   Please correct the orientation of the dimension of the sketch in figure 1.

o   Please correct heading of subsection 3.2: Actual wording is: “Damping radio and residual stress”. Must b : “Damping ratio and residual stress”.

Author Response

Response to the comments of referees

Thank you for your helpful suggestions of editor and reviewers. According to these suggestions, we have revised this paper entitled “Improvement of damping property and its effects on the vibration fatigue in TC4 titanium alloy treated by warm laser shock peening”. Now, I reply to the comments one by one as follows.

Reviewer 2: 

Q1: In the presented work, the damping ratio is experimentally obtained, while it is not clear how the processed/unprocessed volume is taken into account. Moreover, the obtained damping ratios are employed for FEM simulations in different boundary conditions, while identical conditions to the experimental tests would be expected. It is not clear the outcome of the simulations. Moreover, results of experimental vibration fatigue tests are not provided and discussed.

A1: We are very grateful to the reviewers question. As shown in Fig. 5, RT-LP and WLP increase the internal friction of materials by increasing the friction between ɑ/β phase boundaries, but the above internal friction only works when the elastic/plastic deformation and phase boundaries movement is generated by vibration. In this study, the deformation and stress were mainly occurred in the stress concentration area at the fixed end during vibration tests, as shown in Fig. 10. Therefore, RT-LP and WLP were only applied to the stress concentration area at the fixed end of specimens in this study. The specific LPed position and area are shown in Fig. 1. Relevant descriptions have been added in Section 2.2 of the paper.

According to the experimental conditions, the boundary of the finite element model was set as the solid boundary. The material parameters of the simulation are shown in Table 1, and the damping ratio was set as shown in Fig. 6. The stress and displacement are defined as output during the frequency response simulation. Related descriptions have been added in Section 2.4 of the paper.

The purpose of vibration fatigue test is to obtain the vibration fatigue life and fracture morphology of untreated, RT-LPed and WLPed specimens. Relevant results have been discussed in this paper.

Q2: As shown in figure 1, the treated area is restricted to the more sensitive location, close to the fixed support. Nevertheless, the authors should clarify the extension of the laser peening treated area/volume with respect to the complete sample volume, as the modal response is a function of the overall sample. If the modified volume is smaller than the sample complete volume, the obtained damping ratios must be corrected.

A2: We are very grateful to the reviewers question. In this paper, the damping ratio obtained by modal testing method is the damping ratio of the whole sample (shown in Fig. 6), which includes material damping, air damping, component friction and so on. When the fixed method and environmental factors remain unchanged, the change of structural damping ratio is mainly caused by the change of material damping. RT-LP and WLP can increase material damping by changing the microstructure of local region. Therefore, the structural damping ratio of the whole sample can be used to indirectly reflect the material damping changes induced by RT-LP and WLP in this study. Related descriptions have been added in Section 2.3 of the paper.

Q3: Authors must specify how many sample repetitions were performed to stablish the damping ratio for the unprocessed, LP and WLP plates.

A3: We are very grateful to the reviewers question. In order to reduce the test errors of damping ratio, five samples were tested under each group of parameters, and the average value was taken as the damping ratio of the structure under this group of parameters.

Q4: In addition, it would be particularly interesting to test the repeatability of the fixing method and its influence on the modal response.

A4: We are very grateful to the reviewers question. In this paper, a four-holes structure was used to fix the sample, which effectively ensures the repeatability of the fixing method. At the same time, under the same processing parameters and fixing methods, the measurement errors of structural damping ratios of different samples are small, which indicates that the effect of repeated fixing on structural damping ratios is not significant.

Q5: Authors must increase the frequency resolution in the experimental graphs of figure 7, and explain the mode frequency shift, if observed.

A5: We are very grateful to the reviewers question. Figure 7 is mainly used to compare the displacement variation of untreated, RTLPed and WLPed samples near the structural natural frequency. Increasing the frequency resolution will not affect the analysis and conclusion of the research results in this paper.

Q6: For the validation of simulation results, it would be expected to reproduce the conditions of the experimentally tested samples and compare the results, prior to modification of the boundary conditions (completely processed simulated area versus an experimentally processed restricted area). Authors should explain this.

A6: We are very grateful to the reviewers question. The frequency response curves obtained by experiments and simulations are compared in this paper which is shown in Figure 4. The accuracy of finite element model and material parameters has been verified. At the same time, the correctness of the simulation conclusions is also verified by the theoretical analysis results.

Q7: Moreover, it is not clear if the pressure on the plates in simulations is to reproduce the effect of the laser process or for a different purpose.

A7: We are very grateful to the reviewers question. In this paper, applying different pressure on the plates is to study the effect of different loads on the maximum displacement/stress during the frequency response process.

Q8: The authors state that frequency response was registered each 50000 cycles during vibration testing, while the obtained results are not presented or commented. More importantly, fatigue results and number of repetitions are not provided in the draft.

A8: We are very grateful to the reviewers question. The vibration fatigue life of the structure was studied in the resonant state (the excitation frequency was near the natural frequency). Because the natural frequency of the structure generally decreases with the increasing loading time, this paper tested the structural natural frequency every 50,000 times, and then used it as the excitation frequency to continue the vibration experiment. Thus we can obtain the vibration fatigue life in resonance state. The relevant contents have been explained in Section 2.6 of the paper. In addition, the vibration fatigue life data of untreated, RT-LPed and WLPed specimens have been added in Section 3.4 of this paper.

Q9: The experimental system and attachment should be clearly described.

A9: We are very grateful to the reviewers question. In the second chapter of the paper, the names and technical parameters of the relevant experimental equipment have been added.

Q10: In Line 242 and following, authors state “After vibration fatigue testing, the average vibration fatigue life of 350-WLPed samples increases about 45.1 % and 148.7% compared to untreated and 244 RT-LPed samples respectively.” Is the fatigue life of the LP samples lower than that of the untreated samples? Authors should clarify and comment this aspect.   

A10: We are very grateful to the reviewers question. The original expression is incorrect. The fatigue life of RT-LPed samples is higher than that of untreated samples. The incorrect expression has been corrected and the vibration fatigue life data of untreated, RT-LPed and WLPed samples have been added.

Q11: Please give the frequency of the pulses used for the treatment. Give also the beam quality in terms of BPP or M2 parameter.

A11:We are very grateful to the reviewers question. The technical parameters and pulse frequency of the Nd:YAG laser have been added in Section 2.2 of the paper, as shown in Table 2 and 3.

Q12: Please correct the orientation of the dimension of the sketch in figure 1.

Q13: Please correct heading of subsection 3.2: Actual wording is: “Damping radio and residual stress”. Must b : “Damping ratio and residual stress”.

A12-13:We are very grateful to the reviewers question. The relevant contents of the paper have been revised according to the expert's opinions.

Author Response File: Author Response.pdf

Reviewer 3 Report

In general, the paper is correct but short.

I recommend improve the introduction. It must be appear similar process in order to show the context. Why is better the laser treatment than other thermal treatment?

I recommend introduce the applicability of this techniques.

I recommend introduce the novelty of the paper compared with other papers referenced.

I recommend to use Ti64, UNS R56400 or Ti6Al4V, it's a commonly notation.

The composition appear in a norm.

Why this laser parameters are used? It must be clearly explained.

Why is used this technique to determine residual stress?

The scale bar of a same images don't appear.

How affect the microestructure?

How affect the process to the part? How is the surface after the treatment?

The surface must be characterized.

The methodology of fatigue test must be clearly explained.

The equipment used are missing.

Author Response

Response to the comments of referees

Thank you for your helpful suggestions of editor and reviewers. According to these suggestions, we have revised this paper entitled “Improvement of damping property and its effects on the vibration fatigue in TC4 titanium alloy treated by warm laser shock peening”. Now, I reply to the comments one by one as follows.

Reviewer 3: 

Q1: I recommend improve the introduction. It must be appear similar process in order to show the context. Why is better the laser treatment than other thermal treatment?

A1: We are very grateful to the reviewers question. At present, traditional heat treatment methods generally use a temperature higher than the phase transition point to modify the material. This generally results in high residual tensile stress on the surface, which is not conducive to the improvement of fatigue life. WLP uses the coupling effects of temperature and plastic deformation to achieve material modification, can form high amplitude compressive residual stress on the surface which can effectively improve the fatigue life of materials. According to the reviewers opinion, the relevant content has been added in the introduction.

Q2: I recommend introduce the applicability of this techniques. 

A2: We are very grateful to the reviewers question. At present, WLP is mainly applied to thin-walled metal parts, such as aeroengine blades, aircraft skin and so on. According to the expert opinion, the relevant contents have been added in the introduction.

Q3: I recommend introduce the novelty of the paper compared with other papers referenced.

A3: We are very grateful to the reviewers question. In this paper, the main innovative work compared with the existing literatures is to study the damping characteristics of WLPed titanium alloy and its influence on vibration fatigue life, which can be seen in the introduction.

Q4: I recommend to use Ti64, UNS R56400 or Ti6Al4V, it's a commonly notation. The composition appear in a norm.  

A4: We are very grateful to the reviewers question. The name "TC4 Titanium Alloy" has been used in many literatures [1-2], and the composition and properties of TC4 Titanium Alloy are described in Section 2.1 of this paper.

Q5: Why this laser parameters are used? It must be clearly explained.

A5: We are very grateful to the reviewers question. In order to prolong fatigue life, a lot of preliminary experiments have been carried out. The optimum laser parameters obtained are shown in Table 3. The same parameters have been used in many other papers [3].

Q6: Why is used this technique to determine residual stress?

A6: We are very grateful to the reviewers question. XRD measurement method is a non-destructive stress measurement method. It has the advantages of strong penetration depth and high measurement accuracy. Now it has become the most commonly used stress measurement method for LP and other deformation strengthening technologies [4-5].

Q7: How affect the microestructure? 

A7: We are very grateful to the reviewers question. RT-LP/WLP processing induces plastic deformation by super high shock wave pressure, changes the distribution of ɑ/β phases and the volume fraction of phase boundaries, and thus generates a series of alpha phase colonies and basketwave microstructures, as shown in Fig. 5. The results are analyzed in Section 3.1 of the paper.

Q8: How affect the process to the part? How is the surface after the treatment?The surface must be characterized.

A8: We are very grateful to the reviewers question. The surface morphology after WLP is shown in Fig. 1. According to the research content, the residual stress and microstructure on the samples surface were characterized and analyzed in this study.

Q9: The methodology of fatigue test must be clearly explained.

A9: We are very grateful to the reviewers question. The experimental method of vibration fatigue has been further explained in Section 2.6 of this paper.

Q10: The equipment used are missing. 

A10: We are very grateful to the reviewers question. Relevant parameters of vibration fatigue testing equipment have been added to the paper, as shown in Table 4.

References

[1] Li G R, Wang F F, Wang H M, et al. Microstructure and Mechanical Properties of TC4 Titanium Alloy Subjected to High Static Magnetic Field[J]. Materials Science Forum, 2017, 898:10.

[2] Li W, Gao N, Zhao H, et al. Crack initiation and early growth behavior of TC4 titanium alloy under high cycle fatigue and very high cycle fatigue[J]. Journal of Materials Research, 2018:1-11.

[3] Meng X, Zhou J, Huang S, et al. Residual Stress Relaxation and Fatigue Properties of TC4 Titanium Alloy Induced by Warm Laser Peening under High-Cycle Fatigue[J]. Rare Metal Materials & Engineering, 2015, 44(5):1185-1190.

[4] Zhou J, Jing L, Shu H, et al. Influence of Cryogenic Treatment Prior to Laser Peening on Mechanical Properties and Microstructural Characteristics of TC6 Titanium Alloy[J]. Materials Science & Engineering A, 2018, 718:S0921509318301254.

[5] Luo Q, Jones A H. High-precision determination of residual stress of polycrystalline coatings using optimised XRD-sin 2 ψ technique[J]. Surface & Coatings Technology, 2010, 205(5):1403-1408.

Author Response File: Author Response.pdf

Reviewer 4 Report

The paper entitled “Improvement of damping property and its effects on 2 the vibration fatigue in TC4 titanium alloy treated by 3 warm laser peening” by Meng et al deals with the study of the laser shock peening of a titanium alloy. The damping properties of the treated samples were measured, and the frequency response was simulated. The microstructure and fatigue properties of the samples were also analysed.

Results are in the scope of the Metals journal. These are interesting, but after reading the paper, I have some comments about it:

 

GENERAL COMMENTS:

             

1)    In general, this paper is interesting; however, the main problem of this paper is that is not clear why is relevant the damping properties analysis of the LSP samples. On the other hand, it is not clear how the simulation results are validated. Without validation the results are not reliable.

2)    The introduction should discuss in more detail the literature on laser shock peening (LSP). The review of the current literature on laser is oversimplified. On the other hand, the warm laser shock peening should be also reviewed and explained in more detail. Why is the research on the damping properties and frequency response interesting in this case? This question should be also answered in the introduction.

3)    In this work, the processing technique is called laser peening, while laser shock peening is the standard designation for this technique. Please, replace laser peening with laser shock peening along the text.

4)    Authors have used smooth curves to connect experimental points in Figs. 5 & 6. This smooth curves should be replaced by straight lines to connect the points as they are not depicting a real trend.

 

PARTICULAR COMMENTS:

 

1)    (Page 3) Please, add the position of the focal spot, focal length and pulse frequency. Was used a diode-pumped or a lamp-pumped Nd:YAG laser? Are one or several laser pulses used? Why were used the processing conditions given in Table 2? Are these the most suitable? Which were the criteria used to selected them? Please, add this explanation in the manuscript.

2)    (Pages 3-4) Please, provide more details regarding the simulation. Add the number of nodes, the type of elements used, was a mesh size convergence analysis performed?, material properties (and appropriated references for them) used in the simulations, validation analyses (comparison of experimental and simulation results), errors.

3)    (Pages 4-5) Where were the SEM images acquired? In the upper, middle or bottom part of the cross section of the treated sample?

4)    (Page 5) Please, provide a reference for equation (1). Also, add the units for the different magnitudes represented in this equation.

5)    (Page 7) Please, provide more details regarding the derivation of equations (2), (3) and (4).

Author Response

Response to the comments of referees

Thank you for your helpful suggestions of editor and reviewers. According to these suggestions, we have revised this paper entitled “Improvement of damping property and its effects on the vibration fatigue in TC4 titanium alloy treated by warm laser shock peening”. Now, I reply to the comments one by one as follows.

Reviewer 4:             

Q1: In general, this paper is interesting; however, the main problem of this paper is that is not clear why is relevant the damping properties analysis of the LSP samples. On the other hand, it is not clear how the simulation results are validated. Without validation the results are not reliable.

A1: We are very grateful to the reviewers question. It is concluded that the reason for the damping changes induced by RT-LP/WLP is that "RT-LP/WLP induces ɑ/β phase redistribution through plastic deformation, resulting in a series of alpha phase colonies and basketwave microstructures which effectively increase the number of phase boundaries. The increasing phase boundaries increase the internal friction of materials caused by phase boundary friction during vibration, and ultimately increase the structural damping".

The frequency response curves obtained by experiments and simulations are compared in this paper which is shown in Figure 4. The accuracy of finite element model and material parameters has been verified. At the same time, the correctness of the simulation conclusions is also verified by the theoretical analysis results.

Q2: The introduction should discuss in more detail the literature on laser shock peening (LSP). The review of the current literature on laser is oversimplified. On the other hand, the warm laser shock peening should be also reviewed and explained in more detail. Why is the research on the damping properties and frequency response interesting in this case? This question should be also answered in the introduction.

A2: We are very grateful to the reviewers question. According to the reviewers opinions, a literature review of LP and WLP has been added in the introduction, and the novelty of this study has been explained.

Q3: In this work, the processing technique is called laser peening, while laser shock peening is the standard designation for this technique. Please, replace laser peening with laser shock peening along the text.

A3: We are very grateful to the reviewers question. The technical names in the paper have been revised.

Q4: Authors have used smooth curves to connect experimental points in Figs. 5 & 6. This smooth curves should be replaced by straight lines to connect the points as they are not depicting a real trend.

A4: We are very grateful to the reviewers question. Figs 5 and 6 have been revised in accordance with the reviewers opinion.

Q5: (Page 3) Please, add the position of the focal spot, focal length and pulse frequency. Was used a diode-pumped or a lamp-pumped Nd:YAG laser? Are one or several laser pulses used? Why were used the processing conditions given in Table 2? Are these the most suitable? Which were the criteria used to selected them? Please, add this explanation in the manuscript. 

A5: We are very grateful to the reviewers question. Focus position and pulse frequency have been added to the paper. In this paper, a lamp-pumped Nd:YAG laser with multiple laser pulses is used which technical parameters can be seen in Fig.2. The overlap rate between adjacent pulses is 50% and each sample was treated once.

In order to prolong fatigue life, a lot of preliminary experiments have been carried out. The optimum laser parameters obtained are shown in Table 3. The same parameters have been used in some other papers [1].。

Q6: (Pages 3-4) Please, provide more details regarding the simulation. Add the number of nodes, the type of elements used, was a mesh size convergence analysis performed? material properties (and appropriated references for them) used in the simulations, validation analyses (comparison of experimental and simulation results), errors.

A6: We are very grateful to the reviewers question. The information of element type, number of elements and boundary type has been added in this paper. The material parameters in the simulation process are set as shown in Table 1. In addition, The frequency response curves obtained by experiments and simulations are compared in this paper which is shown in Figure 4. The accuracy of finite element model and material parameters has been verified. At the same time, the correctness of the simulation conclusions is also verified by the theoretical analysis results.

Q7: (Pages 4-5) Where were the SEM images acquired? In the upper, middle or bottom part of the cross section of the treated sample?

A7: We are very grateful to the reviewers question. Scanning electron microscopy (SEM) images were obtained in the crack growth zone of fatigue fracture cross-section which is in the subsurface layer (about 500 microns away from the top surface) of the specimens. Relevant contents have been added in Section 3.4 of this paper.

Q8: (Page 5) Please, provide a reference for equation (1). Also, add the units for the different magnitudes represented in this equation.

A8: We are very grateful to the reviewers question. References and units of the different magnitudes have been added according to expert opinions.

Q9: (Page 7) Please, provide more details regarding the derivation of equations (2), (3) and (4). 

A9: We are very grateful to the reviewers question. Details have been added to the derivation process based on reviewers opinions.

References

[1] Meng X, Zhou J, Huang S, et al. Residual Stress Relaxation and Fatigue Properties of TC4 Titanium Alloy Induced by Warm Laser Peening under High-Cycle Fatigue[J]. Rare Metal Materials & Engineering, 2015, 44(5):1185-1190.

Author Response File: Author Response.pdf

Round  2

Reviewer 2 Report

Authors answered to most questions posed by this reviewer and corrected the manuscript accordingly. Nevertheless, there are still some missing aspects:

·       As shown in figure 1, the treated area is restricted to the more sensitive location, close to the fixed support. Nevertheless, the authors should clarify the extension of the laser peening treated area/volume with respect to the complete sample volume, as the modal response is a function of the overall sample. If the modified volume is smaller than the sample complete volume, the obtained damping ratios must be corrected.

·       For the validation of simulation results, it would be expected to reproduce the conditions of the experimentally tested samples and compare the results, prior to modification of the boundary conditions (completely processed simulated area versus an experimentally processed restricted area). Authors should explain this.

·       Please give the beam quality of the laser used in the experiments, in terms of BPP or M2 parameter.

Author Response

Response to the comments of referees

Thank you for your helpful suggestions of editor and reviewers. According to these suggestions, we have revised this paper entitled Improvement of damping property and its effects on the vibration fatigue in Ti6Al4V titanium alloy treated by warm laser shock peening”. Now, I reply to the comments one by one as follows.

Reviewer 2:

Question 1(Q1): As shown in figure 1, the treated area is restricted to the more sensitive location, close to the fixed support. Nevertheless, the authors should clarify the extension of the laser peening treated area/volume with respect to the complete sample volume, as the modal response is a function of the overall sample. If the modified volume is smaller than the sample complete volume, the obtained damping ratios must be corrected.

Answer 1(A1): We are very grateful to the reviewers question. In this paper, the modified volume is smaller than the sample complete volume. Based on the reviewers opinion, the structural damping ratios in Fig.6 have been analyzed further. On the basis of Eq.3, the difference of material damping ratio in LPed and untreated samples (Δηmaterial) was obtained as shown in Fig.7. It indicates that the damping ratio generated by internal friction in 350℃-WLPed sample is much greater than that in RT-LPed and untreated samples. Related contents have been added in Section 3.2 of the paper.

Q2:For the validation of simulation results, it would be expected to reproduce the conditions of the experimentally tested samples and compare the results, prior to modification of the boundary conditions (completely processed simulated area versus an experimentally processed restricted area). Authors should explain this.

A2:We are very grateful to the reviewers question. The modal testing device as shown in Fig.2 was used to obtain the natural frequency and structural damping ratio of samples (as shown in Fig.4a and Fig.6) which are consistent with simulation conditions and results. However, the input load is controlled by manual tapping during modal tests, so it is difficult to obtain a certain load value and get a accurate distance and vibration stress data. Therefore, it is hard to verify the simulation results of displacement and vibration stress in frequency response under a certain load value. In order to illustrate the rationality and the correctness of the simulation results, the displacement during frequency response process was theoretically deduced and the conclusions consistent with the simulation results were obtained. In the future, the experimental device will be further improved and the relevant results will be verified.

Q3:Please give the beam quality of the laser used in the experiments, in terms of BPP or M2 parameter.

A3:We are very grateful to the reviewers question. The BPP of this laser is less than 20 mm·mrad which has been added in Table.2 of the paper.

Reviewer 3 Report

The paper has been improved.

Only two minor recommendations:

- In Figure 11, I think its necessary change the red color for other one that import more contrast

- The term Ti6Al4V or Ti64 are most commonly used than TC4. I recomend change the term in order maximice the impact.

Author Response

Response to the comments of referees

Thank you for your helpful suggestions of editor and reviewers. According to these suggestions, we have revised this paper entitled Improvement of damping property and its effects on the vibration fatigue in Ti6Al4V titanium alloy treated by warm laser shock peening”. Now, I reply to the comments one by one as follows.

Reviewer 3:

Question 1(Q1): In Figure 11, I think its necessary change the red color for other one that import more contrast.

Answer 1(A1): We are very grateful to the reviewers question. The red color in Fig.11 has been replaced to green color in the paper.

Q2:The term Ti6Al4V or Ti64 are most commonly used than TC4. I recomend change the term in order maximice the impact.

A2: We are very grateful to the reviewers question. The name "TC4 titanium alloy" has been replaced by Ti6Al4V titanium alloy in the paper.

Reviewer 4 Report

 In its present state, the paper entitled “Improvement of damping property and its effects on the vibration fatigue in TC4 titanium alloy treated by warm laser shock peening” is acceptable for publication. Authors have addressed most of the concerns of the reviewer; however, I suggest to change some points prior to the final publication of this paper:

Please, replace “Operation      material” with “Laser source” in Table 2. Please, add also the TEM mode for      this laser, and the focus spot position with regard to the surface (was      the laser beam focused on the top of the metal?).

Author Response

Response to the comments of referees

Thank you for your helpful suggestions of editor and reviewers. According to these suggestions, we have revised this paper entitled Improvement of damping property and its effects on the vibration fatigue in Ti6Al4V titanium alloy treated by warm laser shock peening”. Now, I reply to the comments one by one as follows.

Reviewer 4:

Question 1(Q1): Please, replace “Operation material” with “Laser source” in Table 2. Please, add also the TEM mode for this laser, and the focus spot position with regard to the surface (was the laser beam focused on the top of the metal?).

Answer 1(A1): We are very grateful to the reviewers question. The Operation material has been replaced by Laser source in Table 2. Moreover, the TEM mode of the laser is TEM 00 which has been added in Table 2. Finally, The focus spot position with regard to the surface has been added in Fig.2.

Round  3

Reviewer 2 Report

Authors answered to all the questions posed by this reviewer, and corrected the manuscript accordingly. Therefore, in my opinion it can be accepted for publication.

Metals, EISSN 2075-4701, Published by MDPI AG
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